AVIAN RESPONSE TO THINNING AND BURNING
PRESCRIPTIONS IN THE WILLIAM B. BANKHEAD NATIONAL
FOREST, ALABAMA
by
EMILY N. SUMMERS
A THESIS
Submitted in partial fulfillment of the requirements
for the degree of Master of Science
in the Department of Biological and Environmental Sciences
in the School of Graduate Studies
Alabama A&M University
Normal, Alabama 35762
November 2014
Submitted by EMILY N. SUMMERS in partial fulfillment of the requirements
for the degree of MASTER OF SCIENCE in PLANT AND SOIL SCIENCE.
Accepted on behalf of the Faculty of the Graduate School by the Thesis
Committee:
_________________________________
_________________________________
_________________________________ Major advisor
_________________________________
_________________________________Dean of the Graduate School
_________________________________Date
ii
Copyright by
EMILY N. SUMMERS
2014
iii
AVIAN RESPONSE TO THINNING AND BURNING PRESCRIPTIONS IN THE
WILLIAM B. BANKHEAD NATIONAL FOREST, ALABAMA
Summers, Emily, M.S., Alabama A&M University, 2014. 186 pp.
Thesis Advisor: Yong Wang, PhD.
Environmental disturbance, natural or anthropogenic, has the ability to influence
individual avian species and entire communities by changing the availability of suitable
habitat. My study considered how two silviculture tools, thinning and prescribed
burning, affected habitat conditions and the associated avian community. This study was
located in the William B. Bankhead National Forest, and partnered, in collaboration with
the USDA Forest Service which initiated a Forest Health and Restoration Project to
promote healthy forest growth and ecosystem resilience via thinning and fire disturbance
to achieve projected future desired conditions throughout the forest. The Black-andwhite Warbler (Mniotilta varia) did not tolerate burning and showed declines in
abundance, notably following a recent March burn. Congruent with the avian response,
many microhabitat characteristics that correlated with the abundance of specific species
or guilds, such as the basal area, basal area of snags, woody cover, canopy, and forest
understory displayed in a treatment or year effect. Multivariate techniques showed strong
relationships between microhabitat variables and bird community, at both individual bird
species or guild level. Occupancy models explained variation among species of
conservational concern’s occupancy and detectibility in the William B. Bankhead
National Forest, yielding useful information about individual species habitat selection,
such as the Wood Thrush’s affinity to choose sites with a high basal area of hardwood.
This research found that complex habitats created temporally through active forest
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management supported a host of avian species associated with early successional habitats
while still retaining many avian species that prefer mature forests.
KEY WORDS: Cumberland Plateau, silviculture, community, habitat selection,
occupancy modeling
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TABLE OF CONTENTS
CERTIFICATE OF APPROVAL………………………………………………………………….…ii
ABSTRACT AND KEYWORDS……………………………………………...……………….……iv
LIST OF TABLES ............................................................................................................. xi
LIST OF FIGURES ......................................................................................................... xiii
LIST OF ABBREVATIONS .............................................................................................xv
ACKNOWLEDGEMENTS ............................................................................................ xvii
CHAPTER 1- INTRODUCTION, LITERATURE REVIEW, STUDY SITE, AND
EXPERIMENTAL DESIGN ...............................................................................................1
Introduction ..............................................................................................................1
Statement of the Problem .........................................................................................3
Importance of Avifauna ...............................................................................4
Objectives ................................................................................................................7
Research Predictions ................................................................................................7
Literature Review.....................................................................................................9
Silviculture .................................................................................................10
Harvest .......................................................................................................11
Prescribed Burning.....................................................................................14
Thinning and Burning Combined…...….……………………...….…………………...16
Detection and Occupancy ..........................................................................18
Purpose of Study………………………………………………………………………………21
Study Site ...............................................................................................................21
Experimental Design ..............................................................................................24
CHAPTER 2- RESPONSE OF MICROHABITAT CHARACTERISTICS TO FOREST
STAND TREATMENT .....................................................................................................26
Introduction ............................................................................................................26
Methodology ..........................................................................................................27
Habitat Sampling .......................................................................................27
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Data Analysis .............................................................................................29
Results ....................................................................................................................31
Principal Component Analysis ..................................................................32
Response of Microhabitat Variables to Treatment ....................................35
Pretreatment, Immediate, and 6-7 Years Post-Treatment Responses of
Microhabitat Variables...............................................................................39
Discussion……………………………………….…….………………………………………..49
CHAPTER 3- AVIAN RESPONSE OF MICROHABITAT CHARACTERISTICS TO
FOREST STAND TREATMENT .....................................................................................57
Introduction ............................................................................................................57
Methodology ..........................................................................................................58
Bird Sampling ............................................................................................58
Guild Arrangement ....................................................................................59
Data Analysis .............................................................................................61
Results ....................................................................................................................63
Canonical Correspondence Analysis .........................................................63
Individual Species Response......................................................................69
Avian Community Response .....................................................................84
Morisita’s- Horn Similarity Index .............................................................92
Discussion ..............................................................................................................96
CHAPTER 4- UNDERSTANDING AVIAN-HABITAT RELATIONSHIPS THROUGH
SITE OCCUPANCY MODELING OF SPECIES OF CONCERN IN THE BNF ........113
Introduction ..........................................................................................................113
Study Site .............................................................................................................114
Methodology ........................................................................................................117
Focal Species ...........................................................................................120
Worm-eating Warbler ..............................................................................120
Prarie Warbler ..........................................................................................120
Wood Thrush ...........................................................................................121
Brown-headed Nuthatch ..........................................................................122
Results ..................................................................................................................123
Wood Thrush ...........................................................................................123
Worm-eating Warbler ..............................................................................123
Brown-headed Nuthatch ..........................................................................124
Prairie Warbler .........................................................................................125
Discussion ............................................................................................................129
CHAPTER 5- FINAL CONCLUSIONS AND MANAGEMENT
RECOMMENDATIONS .................................................................................................132
REFERENCES ................................................................................................................136
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APPENDICES .................................................................................................................149
APPENDIX A- Descriptive Tables .....................................................................149
APPENDIX B- Microhabitat and Species Response Tables ...............................156
VITA
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LIST OF TABLES
Table
Page
1.
Component loadings, eigenvalues, and percent variance accounted for based on
varimax rotated principle component analysis of microhabitat variables collected
at stand-level 6-8 years following silviculture treatments in Bankhead National
Forest, AL (n=108). .............................................................................................. 34
2.
Component loadings, eigenvalues, and percent variance accounted for based on
varimax rotated principle component analysis of microhabitat variables collected
at stand-level 6-8 years following silviculture treatments in Bankhead National
Forest, AL (n=36). ................................................................................................ 35
3.
Mean + standard error and results of analysis of variance (ANOVA) (dfs for
treatment effect tests were 8 and error df 80, and dfs for block effect tests were 3
and error df 15) of microhabitat variables ............................................................ 38
4.
Morisita’s-Horn similarity index for the breeding bird community six years
following silviculture treatment in Bankhead National Forest, AL, 2012-2013. . 93
5.
Morisita’s-Horn similarity index for the breeding bird community seven years
following silviculture treatment in Bankhead National Forest, AL, 2012-2013. . 93
6.
Morisita’s-Horn similarity index for the breeding bird community before, one
year post and intermediately following silviculture treatment in Bankhead
National Forest, AL, 2004-2013. .......................................................................... 94
7.
Guild membership of species detected in 36 treated research stands on William B.
Bankhead National forest, 2012-2013. ................................................................. 95
8.
Rankings of models using Akaike’s Information Criterion (AIC) in program
PRESENCE to explain occupancy (ψ) and detection probability (p) of the Wood
Thrush in the Willliam B. Bankhead Nationsl Forest. ........................................ 126
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9.
Rankings of models using Akaike’s Information Criterion (AIC) in program
PRESENCE to explain occupancy (ψ) and detection probability (p) of the Brownheaded Nuthatch in the Willliam B. Bankhead Nationsl Forest. ........................ 126
10.
Rankings of models using Akaike’s Information Criterion (AIC) in program
PRESENCE to explain occupancy (ψ) and detection probability (p) of the WormEating Warbler in the Willliam B. Bankhead Nationsl Forest............................ 127
11.
Rankings of models using Akaike’s Information Criterion (AIC) in program
PRESENCE to explain occupancy (ψ) and detection probability (p) of the Brownheaded Nuthatch in the Willliam B. Bankhead Nationsl Forest. ........................ 128
12.
Summary of results following single-season parameterization of occupancy(ψ)
and detection probability (p) of select avian species of conservation concern in the
William B. Bankhead National Forest………………………………………….128
A.1.
Birds previously encountered in BNF research stands and their associated guilds
............................................................................................................................. 149
A.2.
Habitat characteristics of sixteen vegetation variables used to assess habitat
associations of the avian community on 36 stands in the William B. Bankhead
Forest................................................................................................................... 151
A.3.
Habitat site-specific covariates used in site occupancy models for four focal bird
species in the William B. Bankhead Forest. ....................................................... 152
A.4.
Survey-specific covariates used in site occupancy models for four focal bird
species in the William B. Bankhead Forest. ....................................................... 152
B.1.
Mean + standard error and results from Multivariate Analysis of Variance
(MANOVA) of microhabitat and forest structure variables of six silvicultural
treatments (n =4 for each treatment) in the Bankhead National Forest………...156
B.2.
Mean + standard error and results from Multivariate Analysis of Variance
(MANOVA) of bird species response to six silvicultural treatments (n =3 for each
treatment) in the Bankhead National Forest……………………………………158
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B.3.
Mean + standard error and results from Multivariate Analysis of Variance
(MANOVA) of bird community variables to six silvicultural treatments (n =3 for
each treatment) in the Bankhead National Forest………………………………162
B.4.
Raw data from 2013 bird survey data collected on 36 research stands in the
Bankhead National Forest and used in CCA analysis……………………….....164
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LIST OF FIGURES
Figure
Page
1.
Location of research stands in William B. Bankhead National Forest, AL……..23
2.
Thinning and burning prescriptions schedule, implemented by year. .................. 25
3.
Treatment/year interaction of woody cover percent following silvicultural
treatments in the Bankhead National Forest, AL. ................................................. 39
4.
Treatment/year interaction of litter cover percent following silvicultural
treatments in the Bankhead National Forest, AL. ................................................. 39
5.
Treatment/year interaction of herbaceous cover following silvicultural treatments
in the Bankhead National Forest, AL.. ................................................................. 42
6.
Treatment/year interaction of present canopy coverfollowing silvicultural
treatments in the Bankhead National Forest, AL .................................................. 43
7.
Treatment/year interaction of presence of understory following silvicultural
treatments in the Bankhead National Forest, AL .................................................. 44
8.
Treatment/year interaction of presence of midstory following silvicultural
treatments in the Bankhead National Forest, AL. ................................................. 44
9.
Treatment/year interaction of stand tree density following silvicultural treatments
in the Bankhead National Forest, AL. .................................................................. 45
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10.
Treatment/year interaction of tree species richness following silvicultural
treatments in the Bankhead National Forest, AL, Pretreatment, 1-yr post, and 6-7
post-treatment. ...................................................................................................... 45
11.
Treatment/year interaction of basal area following silvicultural treatments in the
Bankhead National Forest, AL ............................................................................. 46
12.
Treatment/year interaction of basal area of pines following silvicultural treatments
in the Bankhead National Forest, AL. .................................................................. 47
13.
Treatment/year interaction of basal area of snags following silvicultural
treatments in the Bankhead National Forest, AL .................................................. 48
14.
Stand ordination plot……………………………………………………………..65
15.
First and second canonical correspondence axes for microhabitat characteristics
and avian species abundance 6-8 years after silviculture treatments, Bankhead
National Forest, AL, 2013…………………………………………………….…66
16.
First and second canonical correspondence axes for microhabitat characteristics
and habitat association guild abundance 6-8 years after silviculture treatments,
Bankhead National Forest, AL, 2013. .................................................................. 67
17.
First and second canonical correspondence axes for microhabitat characteristics
and nesting guild abundance 6-8 years after silviculture treatments, Bankhead
National Forest, AL, 2013.. .................................................................................. 68
18.
First and second canonical correspondence axes for microhabitat characteristics
and foraging guild abundance 6-8 years after silviculture treatments, Bankhead
National Forest, AL, 2013. ................................................................................... 69
19.
Treatment/year interaction of Acadian Flycatcher mean density following
silvicultural treatments in the Bankhead National Forest, AL. ............................. 70
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20.
Treatment/year interaction of Carolina Chickadee mean density following
silvicultural treatments in the Bankhead National Forest, AL. ............................. 71
21.
Treatment/year interaction of Eastern Towhee mean density following
silvicultural treatments in the Bankhead National Forest, AL. ............................. 73
22.
Treatment/year interaction of White-eyed Vireo mean density following
silvicultural treatments in the Bankhead National Forest, AL. ............................. 73
23.
Treatment/year interaction of Red-bellied Woodpecker mean density following
silvicultural treatments in the Bankhead National Forest, AL. ............................. 74
24.
Treatment/year interaction of Red-headed Woodpecker mean density following
silvicultural treatments in the Bankhead National Forest, AL. ............................. 75
25.
Treatment/year interaction of Prairie Warbler mean desnity following
silvicultural treatments in the Bankhead National Forest, AL. ............................. 76
26.
Treatment interaction of Black-and-white Warbler mean density following
silvicultural treatments in the Bankhead National Forest, AL………………...…77
27.
Treatment interaction of Eastern Wood-pewee mean density following
silvicultural treatments in the Bankhead National Forest, AL. ............................. 78
28.
Treatment interaction of Summer Tanager mean density following silvicultural
treatments in the Bankhead National Forest, AL .................................................. 79
29.
Treatment interaction of Pileated Woodpecker mean density following
silvicultural treatments in the Bankhead National Forest, AL.............................. 80
30.
Treatment interaction of Yellow-breasted Chat mean density following
silvicultural treatments in the Bankhead National Forest, AL.............................. 81
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31.
Treatment interaction of Brown-headed Nuthatch mean density following
silvicultural treatments in the Bankhead National Forest, AL.............................. 82
32.
Treatment interaction of Brown-headed Cowbird mean density following
silvicultural treatments in the Bankhead National Forest, AL.............................. 83
33.
Treatment/year interaction of tree nesting guild mean density following
silvicultural treatments in the Bankhead National Forest, AL.............................. 86
34.
Treatment/year interaction of cavity nesting guild mean density following
silvicultural treatments in the Bankhead National Forest, AL.............................. 86
35.
Treatment/year interaction of tree neotropical migrant mean density following
silvicultural treatments in the Bankhead National Forest, AL.............................. 88
36.
Treatment/year interaction of tree resident species mean density following
silvicultural treatments in the Bankhead National Forest, AL.............................. 89
37.
Treatment/year interaction of interior/edge habitat guild mean density following
silvicultural treatments in the Bankhead National Forest, AL.............................. 90
38.
Treatment/year interaction of open/edge habitat guild mean density following
silvicultural treatments in the Bankhead National Forest, AL.............................. 91
39.
Location of survey sites used in site occupancy models developed in William B.
Bankhead National Forest, AL ........................................................................... 116
40.
Habitat sampling datasheet. ................................................................................ 153
41.
Transect/distance sampling datasheet. ................................................................ 154
42.
Habitat sampling datasheet. ................................................................................ 155
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LIST OF ABBREVATIONS
NFMA - National Forest Management Act
BNF - William B. Bankhead National Forest
ENFA - Ecological Niche Factor Analysis
BA - Basal Area
FS - United States Department of Agriculture’s Forest Service
SRS - Southern Research Station
AAMU - Alabama A&M University
PCA - Principle Component Analysis
ANOVA - Analysis of Variance
MANOVA - Multivariate Analysis of Variance
LSD - Least Squared Differences
SPSS - Statistical Package for the Social Sciences
DBH - Diameter at breast height
GIS - Geographic Information System
MSA - Mean Square Adequacy
KMO - Kaiser-Meyer-Olkin
C - Control
IB- Infrequent Burn only (9 year burn interval)
FB - Frequent Burn only (3 year burn interval)
HT - Heavy Thin
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LT - Light Thin
HT xFB - Heavy Thin with Frequent Burn (3 year burn interval)
LT xFB - Light Thin with Frequent Burn (3 year burn interval)
HTxIB - Heavy Thin with Infrequent Burn (9 year burn interval)
LT xIB - Light Thin with Infrequent Burn (9year burn interval)
CCA - Canonical correspondence analysis
VIF - Variable Inflation Factor
SE - Standard Error
AIC - Akaike’s Information Criterion
ΔAIC - Delta Akaike’s Information Criterion
xvi
ACKNOWLEDGEMENTS
I thank my academic adviser, Dr. Wang, for all the support and advice he has
offered throughout my educational journey. I also thank my additional committee
members, Dr. William Stone, Dr. Callie Jo Schweitzer, and Dr. Dawn Lemke for all their
suggestions and professional assistance in my research endeavors. Many other graduate
students, field technicians, and staff also aided in the many tasks it took to achieve this
goal and they are all appreciated.
xvii
CHAPTER 1
INTRODUCTION, LITERATURE REVIEW, STUDY SITE, AND
EXPERIMENTAL DESIGN
Introduction
Recent discoveries of songbird population declines in numerous forests of the
Eastern United States have shifted attention to researching the various impacts of
silviculture practices on the conservation of avian communities (Lanham et al., 2002).
Historically, management primarily focused on game birds due to their economic and
recreational values, but today, non-game birds have been proven to hold high value due
to their vast ecological services and recreational value (Sekercioglu, 2006). Forest
management practices coupled with bird conservation efforts could improve ecological
integrity of forest ecosystems. Bird community structure can be used as an indicator of
forest health because many species are specialists or obligates and are therefore sensitive
to changes in vegetation and habitat characteristics on both a micro-site and landscape
level (Gillies & St. Clair, 2008). Furthermore, the avian density and diversity in a given
area can serve to demarcate the ecological wellness of the ecosystem.
Alabama has the second largest acreage of private landholdings in the nation, and
its economy depends on the forest timber industry (Alabama Forestry Commission 2009).
With much of the land under private ownership, it is increasingly important for both
1
private forested lands, and specifically, national forests to be managed in a way that
provide suitable habitats for wildlife, especially migrating birds. In 2000, new mandates
were added to the National Forest Management Act (NFMA) of 1976. They
recommended that management be conducive to long-term ecological sustainability and
provide viable habitat to increase the likelihood that species within the range of the plan
are represented in the landscape (Buehler, 2005). Forest managers have the capability to
alter habitats using various silviculture techniques such as thinning and prescribed
burning. These techniques are designed to mimic natural disturbance regimes and
manipulate canopy and understory characteristics. Studies show higher avian species
densities, richness, and diversity in managed forests than in unmanaged and undisturbed
mature forests (Annand & Thompson, 1997; Baker & Lacki 1997; Greenberg et al.,
2007). Furthermore, some avian species require their habitats to be created by fire or
follow major disturbances for nest placement and foraging (Klaus et al., 2005).
Bird responses to silviculture techniques vary among species, and the frequency
of the disturbances and the time since disturbance can also create variation in bird
responses. Disturbances elicit changes in microclimate, habitat structures, food
resources, nesting availability, and nest parasitism, consequently impacting the breeding
success and probability of occurrence in the environment impacted by the disturbance
(Weins, 1989).
Occupancy modeling has gained popularity, especially with advances in computer
technology and the creation of programs with usability and compatibility. Species/habitat
relationships can be further explored using these predictive techniques and compared to
statistical techniques, commonly used with analyzing on the ground research. Four
2
species were modeled in this study: Wood Thrush (Hylocichla mustelina), Brown-headed
Nuthatch (Sitta pusilla), Prairie Warbler (Setophaga discolor), and Worm-eating Warbler
(Helmitheros vermivorus). These species were chosen based on their conservation status
in the William B. Bankhead National Forest (BNF), biological life histories, and
consideration of varying responses to silviculture disturbances.
Statement of the Problem
Early successional and forest- dependent bird species have experienced rapid
population declines over the last 50 years in eastern parts of North America (Donavan &
Flather, 2002). Historically the landscape of the southeastern portions of the United
States has changed considerably due to land conversion. Land conversions for
agriculture and urban development, extensive timber harvesting, and exclusion of fire in
hardwood forests, have all resulted in a loss of suitable habitats for wildlife. This has
specifically contributed to increased vulnerability and population declines of songbirds
that migrate and breed in the region of the southeastern U.S. (Owen, 2002). The
exclusion of proper forest management prevents the disturbance regime’s ability to create
and sustain early successional habitats which are needed by many vulnerable forest bird
species (Askins, 2001; Trani et al., 2001).
Studies examining the long-term effects of thinning and burning on passerine
species are limited in the Southeast, and rarely include multiple treatment types and
pretreatment data. This study gives us the opportunity to monitor short-term response of
birds to thinning, burning, a combination of both, and a control, as well as the
intermediate response of the birds 6-7 years post-treatment. It may take several years to
3
observe any treatment effect due to an altered habitat, so continuous monitoring is
important to capture the continuum or gradient (Chambers & Germaine, 2003). Certain
species will respond immediately to disturbance while other species will only exhibit a
temporal response (Augenfield et al., 2008; Twedt & Somershoe, 2009). Because the
response differs both spatially and temporally, it is important to continuously monitor
bird response to capture the response of possible vulnerable species.
Importance of Avifauna
Many bird species inhabiting the forest serve as ecosystem services providers.
BNF provides some large, non-fragmented areas along with diverse forest community
types and habitats and hosts up to 211 breeding, overwintering, and migrating bird
species. Birds contribute to all four classified ecosystem service types: provisioning,
regulating, supporting, and cultural services (Whelan et al., 2008). Birds serve as
predators, prey, pollinators, scavengers, seed dispersers, seed predators, and “ecosystem
engineers” (Sekercioglu, 2006). One dynamic cultural aspect of birds is that bird
watching has become one of the most popular outdoor recreational activities. In the
United States, 45 million bird watchers spend $32 billion in retail stores, generating $85
billion in overall economic impact, and supporting over 860,000 jobs (LaRouche, 2001).
In the state of Alabama, bird watching is a $626 million dollar industry rivaling hunting
in terms of its economic impact (Alapark, 2013). Birds also contribute to other cultural
services via activities such as art, photography, and religious customs.
Most important ecologically, are the provisioning and supporting services birds
provide. First, herbivorous insect populations can be regulated by insect eating species;
4
thus, increasing crop yield. Although more research is needed, to examine the
relationship between birds and pest control, some examples have shown significant
reductions in pest population numbers. During the breeding season birds shift from a
granivorous diet to a diet of mostly insects, and this reduces densities of Lepidoptera
larvae on forest understory vegetation (Holmes, 1990). Studies in the United States show
birds control many insect pest species of forests; thus, estimating the cost to replace bird
biological control with pesticides or genetic engineering to be at least $7.34 per acre
(Moskowitz & Talberth, 1998). For example, the chimney swift spends most of its time
consuming insects, with a conservative estimate of consumption for a breeding pair of
swifts to be 5,000 to 6,000 insects daily (Woods, 1940). Woodpeckers are capable of
regulating populations of the devastating bark beetle through strong numerical and
functional responses (Fayt et al., 2005). Infested trees loss value as timber, regardless of
tree survival, and the economic impact of pest from loss of timber yields and measures
taken to prevent infestations may cost a billion dollars per year (Whelan et al., 2008). In
the eastern United States, including the southeast, the gypsy moth (Lymantria dispar) has
actively destructed 30 million hectares of forests since 1970 (New York State Department
of Environmental Conservation, 2014). The larvae consumes the tree leaves in early
spring, reducing vigor and allowing susceptibility to disease and additional pests and
ultimately killing the tree; some tree species impacted include oak, pine, maple, ash, and
apple ( New York State Department of Environmental Conservation, 2014). Chickadees,
robins, blue jays, nuthatches, and cuckoos all predate the gypsy moth larvae and are able
to alleviate the negative ecological consequences of gypsy moth forest destruction, and
certainly able to make a positive impact in young oak sapling like those regenerating in
5
the BNF restoration study sites (McManus et al., 1989). While working in the Missouri
oak forest, researchers found that excluding birds from white oak samplings (Quercus
alba) significantly increased the density of leaf-damaging insects, leading to leaf damage
and resulting in decreased production of new biomass in the next growing season
(Whelan et al., 2008).
Raptors are known to significantly stabilize their prey populations, leading to less
crop pests and disease spreading rodents in human landscapes, but much more research is
needed to conclude their impact on agricultural ecosystems (Sekercioglu, 2006). The
vulture’s role as a scavenger helps sustain energy flow elevated in the food web, salvage
carcasses, and minimize the spread of diseases (Sekercioglu, 2006). Vultures’ role as
scavengers is the most underappreciated services within the avian order, but is most
likely to have the most impact on public and wildlife health if declines in vulture
populations occur (Sekercioglu, 2006).
Woodpeckers can be also be classified as ecosystem engineers, directly changing
the physical state of tree material by providing burrows and cavities for several other
species to inhabit and providing nutritious sap for other organisms to forge (Sekercioglu,
2006). The pileated woodpecker serves as a keystone species in the Bankhead National
Forest functioning as a link of persistence of many other species and influencing the
ecosystem positively compared to its abundance (Duncan, 2003). The importance and
magnitude of avian ecological services is unmistakable, but a vast amount of research it
needed to determine the economic impact of birds and the services they provide and
possible consequences of population declines.
6
Objectives
My study considered how two silviculture tools, thinning and prescribed burning,
affected the avian community and vegetation features of a mixed pine-hardwood forest in
north-central Alabama. The ecological mechanisms, which led to the temporal and
treatment specific species responses and composition changes associated with
intermediate disturbances of thinning and prescribed burning, were evaluated. My
objectives were to (1) examine differences in microhabitat variables and the avian
community among treatment regimes, (2) determine relationships between microhabitat
and avian community structure, (3) explore possible variations in temporal responses to
disturbance by individual bird species and community as a whole, and (4) develop
occupancy models for select vulnerable species in the BNF.
Research Predictions
Diverse microhabitats will be created in relation to the treatment regimes
along a gradient of treatment intensity. Hypothesis 1: (a) Thinning will have the
largest impact on vegetation structure complexity and available suitable habitat for birds;
(b) vegetation structure will be more complex in stands thinned and burned versus those
only thinned or burned alone (Wilson, Masters, & Bukenhofer, 1995); and (c) burning
will affect the herbaceous layer, regeneration, and understory.
Relationships will be discovered between the microhabitat and avian
community structure and individual species occurrence. Hypothesis 2: (a) Species
diversity will vary throughout treatment type and will be correlated with habitat
heterogeneity; (b) avian species diversity will be greatest in those stands thinned due to
7
increases in understory heterogeneity (Weins, 1989); (c) canopy nesting and foraging
species will decline in heavy thinned stands due to decreased overstory and midstory
habitat complexity; (d) sub-canopy nesting and foraging birds and those that prefer early
successional habitat, will increase due to the increase of understory complexity; (e)
since decreased leaf litter is not observed on burned stands (Wick, 2008; C. Schweitzer,
personal communication, March 10, 2014) ground nesting and foraging birds will be
unaffected in burned stands.
The avian community and various individual species will show a temporal
response to silviculture disturbance. Hypothesis 3: (a) Avian species will respond
differently throughout time to the thinning and burning prescriptions due to changes in
the microhabitat through time; (b) on thinned stands, some species that originally were
displaced after initial treatments will return 7-8 years post disturbance (Twedt &
Somershoe, 2009); (c) on thinned stands, some species that emigrated into the study
stands may have immigrated 7-8 years post initial treatment due to the closure of canopy
(d) early-successional species should continuously be represent in the stands with
frequent fire prescription (three year rotations).
Avian species distribution in the Bankhead National Forest will be influenced
by the spatial arrangement and heterogeneity of the forest composition and sitespecific habitat variation. Hypothesis 4: (a) Vulnerable species will be represented
congruent with the amount of preferred available habitat located within the forest related
to the fine scale habitat features; (b) landscape level structure and spatial components
such as topography and distance from streams will determine where target species
arrogate in the forest and therefore impact avian communities; (c) occupancy of the
8
Brown-headed Nuthatch (Sitta pusilla) will be related to conifer basal area (BA) and will
be highest in those sites managed with prescribed fire; (d) Prairie Warbler (Setophaga
discolor) occupancy will be influenced by presence of a high shrub component coupled
with percent overstory; (e) the Worm-eating Warbler (Helmitheros vermivorus) will
occupy mature sites with forested slopes and complex understory components; (f)
occupancy of the Wood Thrush (Hylocichla mustelina) will depend on presence of
mature hardwood forests and forest floor elements such as leaf litter.
Literature Review
Forest management techniques and tools have changed and adapted to meet
various objectives and goals on both private and public lands. On national forests,
management objectives include providing multiple uses within the forests, such as
providing wildlife habitat and recreation and maintaining ecological sustainability. This
emphasis on managing for healthy forest ecosystems has heightened interest in
identifying causal relationships between wildlife and habitat associations. Understanding
these relationships is essential to understand declines in bird populations in the eastern
United States.
Silviculturists have the ability to manipulate the environment to mimic or induce
the natural disturbance regime, therefore influencing the successional patterns of the
stand and composition matrix of the landscape. Forest disturbance influence the
biological, chemical, and physical properties of the environment. Scientists have been
researching the effects on the environment post silviculture prescriptions for decades, and
many found the resulting state of the environment and its inhabitants depends greatly on
9
the intensity and technique of the prescription, the geographic location of the study site,
and the specific site characteristics (Greenberg et al., 2007; Haulton, 2008; Rush et al.,
2012).
The impacts of silviculture treatments on the diversity and composition of avian
communities was researched. Past and current research in this area showed responses to
various treatments (even/uneven aged harvest, free thinning, and prescribed burning) by
bird communities varied based on the bird species, intensity of treatment, time since
treatment, and spatial matrix of the landscape. Different species or groups of species
require diverse habitat characteristics based on their biological life characteristics
including forging, nesting, and breeding, and because of this they respond differently to
disturbance. Birds are a diverse group of organisms with complex biological dynamics
and habitat associations, and this makes them excellent forest management indictors.
Many bird species depend on disturbances such as fire or openings created via timber
harvesting, because these disturbances result in viable habitats in which these species can
thrive and breed (Klaus et al., 2005)
Silviculture
Silviculture is an active management process applied at the stand level in which
forest health can be controlled through harvest, regeneration, and/or tending to meet
diverse forest needs and values (Matthews, 1991). The studies on the effects of timber
harvest on breeding bird populations have reported varying results; some detailed, with
species that benefit from disturbance, others noted detrimental effects to habitat
conditions created post-harvest, and some studies reported species showing no direct
10
response at all (Sallabanks et al., 2000). Silviculture prescriptions that target creating
new stands, i.e. regeneration treatments, provides habitat for early successional species,
many generalists species, and interior species post-breeding (Baker & Lacki, 1997).
Intermediate level treatments are those that are designed to enhance growth, quality,
vigor, and composition of a stand after establishment but before final harvest; they can
also be particularly beneficial to bird by providing diverse habitats that are designed to be
dynamic in nature (Smith et al., 1997). These intermediate level disturbances can be
especially valuable to a myriad of bird species that require different habitat structures
depending on their species or life stage.
Harvest
Bird response to active forest management differs along spatial and temporal
gradients. In bottomland hardwood habitat, lower levels of tree retention (0-20%)
resulted in lower species richness and a lower similarity value between pre- and posttreatment bird communities (Harrison et al., 2005). Birds in tree and shrub nesting or
foraging guilds benefit from higher BA residual trees, whereas ground dwellers are less
affected by BA of trees retained (Tittler et al., 2001). With time thinning created habitat
for ground nesting and ground foraging species, but many of these species preferred
open-habitat or were habitat generalists, while interior forest dwelling species diversity
was actually higher before thinning (Harrison et al., 2005; Tittler et al., 2001).
Silvicultural systems defined as a planned series of treatments for tending
harvesting and re-establishing a stand, alter the structure of the stand by creating
openings or gaps in which avian guilds and individual species respond (Mitchell et al.,
11
2008). Uneven aged management has been touted by some to be conductive to creating
desirable habitat for some birds in specific ecosystems, such as those studied in Maine
(Campbell et al., 2007). Habitat suitability for most bird species depends largely on size
of openings and habitat complexity. Group selection cuts maintained mature forest
species over the long term, 20 years, but those species requiring early-successional
habitat only benefited temporarily during early succession regeneration of shrub and
scrub (Campbell et al., 2007). Some mature forest species such as the Worm-eating
Warbler and Hooded Warbler (Setophaga citrine) also use early successional habitat, but
prefer small forest gaps created by small scale disturbance (Annand & Thompson 1997;
Gram et al., 2003; Campbell et al., 2007). Group selection alone may not create large
enough gaps for many early successional species (Rodewald &Vitz, 2005), so it is
important for forest management to include a variety of harvest prescriptions creating
multiple sizes of openings to guarantee high habitat and thus species diversity across the
entire forest landscape (Lent & Capen, 1995).
Thinning reduces competition for resources (light, nutrients, water) by removing
the undesired competitive species from the overstory and/or midstory; thus, opening up
the canopy and allowing desired species to thrive, ultimately changing the stand
composition to a desired condition (Franklin et al. 2007). Free thinning removals trees to
control stand density, and it allows managers to use a combination of thinning criteria
without strict regard to crown position. Free thinning does require expertise in tree
selection and retention management (Smith, 1997). Retention of few trees mimics largescale disturbance, while retention of a greater number of trees tends to mimic small-scale
disturbance (Harrison et al., 2005). Large scale natural disturbances are those that are
12
stand level disturbances that result in a large area being impacted; examples include
wildfires, wind throw, or severe insect infestations (Klaus et al., 2009). Small scale
disturbances are those that are not stand level disturbances, but within stand disturbances
impacting single trees and creating little stand variability; examples include single tree
fall and localized insect infestations (Klaus et al., 2009). Historically, fire disturbance in
the southern Appalachians consisted of small scale, frequent fires in comparison to the
large scale fires in other geographic regions of the U.S. (Sousa, 1984). Present-day fire
disturbance in the southern Appalachians has been influenced by humans; indigenous
people and early settlers may have increased fire frequency while in the last century fire
suppression polices have sharply decreased fire frequencies in many vegetation types,
including mixed-hardwood stands (Sousa, 1984).
Both natural and anthropogenic disturbance regimes impact forest communities
and also animal community dynamics, with large scale disturbance favoring colonizing
species and small scale disturbances favoring competitive species (Miller, 1982). Many
studies conclude thinning as an intermediate-scale disturbance, has significant positive
effects on many neotropical migrants and early-successional species, given the large
amount of understory re-growth within the first couple years after harvest (Augenfeld et
al., 2008; Haulton, 2008). Indigo Bunting (Passerina cyanea), Pine Warbler (Setophaga
pinus), and Brown-headed Cowbirds (Molothrus ater) increased in abundance in a Texas
study after a loblolly pine plantation was thinned, while White-eyed Vireos (Vireo
griseus), Worm-eating Warblers, and Hooded Warblers were negatively affected by the
thinning (Chritton 1988). Following thinning, many studies find overall species richness
to increase, but have no direct effect on total bird densities (Montana et al., 2006).
13
Previously the bird community was studied on a portion selected for this study and results
showed tree nesting species to increase the most on thinned stands (Wick, 2008).
Prescribed Burning
Beginning in the 1930’s, fire has been isolated from southeastern United States
hardwood forests possibly leading to fuel buildup, encroachment of undesirable plant
species, exclusion of fire dependent species, and ecological instability (Greenberg et al.,
2007). Today, fire is being introduced back into systems to encourage wildlife
conservation, regeneration of desirable species, and to control the fuel source aggregation
that may enhance the possibility of wildfires (Greenberg et al., 2007). The short and long
term effects on breeding bird populations following prescribed burning episodes are
poorly known in the southern Appalachian physiographic region of the United States.
Ongoing research in stands subject to prescribed fire and other active management is
receiving heightened attention in terms of changes in the bird communities. Fire
suppression was one factor that contributed to extirpation of several bird species in
sections of the southern Appalachians that benefit from fires due to the specific habitats
fire creates including these: the Bachman’s Sparrow (Peucaea aestivalis), Northern
Bobwhite (Colinus virginianus), Red-cockaded Woodpecker (Picoides borealis), and
Golden-winged Warbler (Vermivora chrystoptera) (Rush et al., 2012).
The resulting habitat created by prescribed fires is dependent on the fire location,
duration, and intensity dependent. In oak savannahs bird density and species richness
were higher on frequently burned sites than on fire suppressed sites (Davis et al., 2000).
In coastal scrub and pine scrub habitats stands treated with fire experienced decreases in
14
bird density and species richness (Greenberg et al., 1995). A recent Georgia study in
mixed pine-oak stands and oak stands subjected to fire ranging in severity and time since
burn, showed high intensity fires to be most impactful to those species benefiting from
prescribed burns (Rush et al., 2012). Among the species benefiting from high intensity
fires are the Eastern Towhee (Pipilo erythrophthalmus) and the Indigo Bunting, while the
Hooded Warbler was highest in those stands receiving the lowest intensity fires. Many
species showed no response to fire; few birds benefited from the fire in their study and no
changes in habitat characteristics such as canopy cover, basal area of snags, and shrub
stem densities were noted (Rush et al., 2012). An Ohio study in a mixed-oak forest,
showed similar bird densities in burned and unburned sites when low intensity fires were
implemented resulting in low tree mortality (Artman et al., 2001). Research has shown
fire impacted ground and low shrub nesters and forgers most in the short term by altering
the forest floor’s habitat characteristics. Following fire treatments, Hooded Warblers
shifted their breeding territories and Wood Thrushes moved their nests from xeric and
intermediate sites to mesic sites (Artman et al., 2001; Artman & Downhower, 2003).
Altered nesting behavior and shifted nest placement (higher off the ground to alleviate
the effects of low-intensity fires) resulting in similar nest survival rates in burned and
unburned sites were also reported (Artman & Downhower, 2003). The resulting
environment following a fire treatment can provide food for ground forgers and cavity
nesters, due to a reduction in leaf litter and greater exposure of resources, as well as an
increase in the number of snags that are created (Dickson et al., 1995). Most prescribed
fires reduced shrubs and small trees in the understory, but high intensity fires have the
potential to kill larger trees and shrubs, increasing the light source and encouraging the
15
growth of succulent vegetation ultimately increasing insect densities and fruiting
vegetation (Greenberg et al., 2007). In the initial assessment of the bird communities in
mixed oak-pine stands on the southern Cumberland Plateau subjected to one dormant
season fire, bird diversity increased, but tree nesting species showed the highest decrease
on the burned stands one year post-treatment (Wick, 2008). It is likely that repeated fire
treatments will affect the bird community differently than short-term response due to
temporal changes in vegetation structure (Greenberg et al., 2007), making it important to
survey both the bird community and vegetation for several years following treatment
(Raphael et al., 1987).
Thinning and Prescribed Burning Combined
Studies with a combination of thinning and burning are limited, especially in the
southern Appalachian region when considering the bird community responses. The
southern Appalachian physiographic region is comprised of both mountainous landscapes
in the northern portion and an extensive highly eroded Plateau in the south (Yarnell,
1998). Local disturbances such as fire, windstorms, ice storms, snow storms, and soil
movement have produced a mosaic of vegetation across the landscape (Yarnell, 1998).
Historically and present-day human activity such as use of fire, timber harvesting, house
building, hunting, farming, and war has also shaped the landscape (Yarnell, 1998). Only
a few studies have assessed the bird community after thinning and burning prescriptions
with the continuation of this study being one of the few (Greenberg et al., 2007;
Kilpatrick, Lanham, &Waltrop, 2010; Wilson et al., 1995; Wick, 2008). Avian density,
or abundance, was the highest in stands that had been both thinned and burned, differing
16
from the initial post response of avian abundance in this study (Wilson et al, 1995).
Wick’s result showed avian density to be negatively impacted most by those thinned and
burned stands compared to those thin only stands (Wick, 2008). Mechanical reduction of
the understory and high severity fire burning prescriptions in a North Carolina hardwood
study showed highest species richness compared to treatments receiving only a burn or
only a thin, or no treatment at all (control) (Greenberg et al., 2007). In the upper
Piedmont of South Carolina compromised of mixed pine/hardwood sites, a positive
responses to thinning and burned treatments included: shrub nesters, cavity nesters,
ground foragers, and migratory species. This was five years following a prescribed fire
and at least ten years following thinning (Kilpatrick et al., 2010). Furthermore, the
Worm-eating Warbler showed decreased abundance in those stands thinned and burned,
while the Indigo Bunting and Eastern Bluebird (Sialia sialis) was most abundant in the
burned and thinning sites with a 1-2 year delay in their response, while the Eastern-wood
Peewee (Contopus virens) responded positively immediately following disturbance and
prescribed fire (Greenberg et al., 2007; Saab & Powell, 2008). Thinning and burning
combined can provide the habitat needed by early successional species while also
supporting many mature forest species one year after treatment, but it is important to
closely monitor the stands to access changes in the bird community through time. In the
short term, ground nesting and foraging species are expected to be negatively impacted
the most, but should return to the treated stands once the forest ground habitat
characteristics are restored to pretreatment conditions.
17
Detection and Occupancy
Occupancy models have the ability to predict occurrence of a particular species or
group of species using covariates as predictors of occupancy. Occupancy (ψ) can be
defined as the probability of a species occupying a site a, and detection probability (p) is
the probability that a species will be detected at site a at a given time, t (Mackenzie et al.,
2002). Comparison studies have shown that failing to incorporate detection probabilities
into species distribution models leads to bias results, especially for species more difficult
to detect (Kery et al., 2010; Rota et al., 2011). Species distribution modeling and wildlife
habitat suitability modeling has been widely used to capture relationships between
species occurrences and landscape and environmental variables to predict the potential of
distribution of a particular species (Dettmers &Bart, 1999; Brotons et al., 2004). Most
species distribution models rely on presence-only data, and over large scale regions this
may suffice to predict occupancy, but it is increasingly important to utilize presenceabsence data when examining smaller scale landscapes and when inferring about less
detected, rare species (Brotons et al., 2004). When tested statistically, generalized linear
models, generalized additive models, classification and regression tree analysis, and
artificial neural networking analysis, built upon presence/absence data performed
significantly better than Ecological Niche Factor Analysis (ENFA), Bioclim and Domain,
those models built upon presence only data (Brotons et al., 2004). The challenge with
modeling species distributions is that detection is imperfect, and many techniques do not
have the ability to account for this bias, leading to erroneous results and conclusions (Gu
& Swihart, 2000; MacKenzie, 2012). Observer detection can be impacted by several
abiotic or biotic factors; furthermore, detection is species specific since many birds’ life
18
history strategies, behaviors, and appearances impact whether or not the species will be
heard or seen (McCallum, 2005). Environmental factors such a time of day, temperature,
wind, and sky conditions may also affect whether an individual will be detected in a
given survey (McCallum, 2005). It is accepted that the detection probability
methodology provided researchers opportunities to adjust for imperfect detection, as
abundance estimates are adjusted in the data analysis (Thompson, 2002). Site-occupancy
modeling was developed to address the issue of detection probability. A model that
incorporated detection into model estimates was created, leading to more robust
occupancy estimation, especially for estimating occupancy for less commonly detected
species. More recently, ecologists have created even more complex models and
incorporated detection probabilities into occupancy modeling, rendering more robust
species occurrence probabilities (MacKenzie et al., 2002; Royle et al., 2005; Kery et al.,
2010; Hansen, Millspaugh, & Rumble, 2011; Smith et al., 2012).
Landscape characteristics also have an impact on avian distributions and
occupancy. In the past four decades, several migratory bird populations have declined in
the eastern US due to forest fragmentation and loss of viable and suitable habitat due to
anthropogenic environmental disturbances (or the lack of natural disturbances) making it
increasingly important to understand relationships between species declines and various
impacts of disturbance (Askins et al., 1990; Donovan & Flather, 2002). Understanding
wildlife-habitat relationships requires a consideration of a spatial component, since
ecological processes are scale dependent and interactions seemingly occurring on a small
scale could be part of a larger scale phenomenon (Loehle et al., 2006; Mitchell et al.,
2008). Many coarse-scale landscape studies agreed that avian diversity and most guilds
19
are related positively with the heterogeneity of forest age classes and forest composition
types (Mitchell et al., 2006). In some landscapes, harvesting can create an edge effect,
causing more prevalent nesting parasitism by the brown headed cowbird (Hoover, 1995).
This can cause an increased in competition among the edge species resulting in loss of
fitness of vulnerable migrant bird species (Wilcove & Robinson, 1990). However, in
largely forested landscapes studies have shown to have limited edge effects (Rudnicky &
Hunter, 1993), low numbers of nest predation and parasitism (Moorman et al., 2002), and
overall little effect on nest success (Gram et al., 2003). Bird community structure was
explained more clearly by availability of habitat rather than landscape configuration in
finely contrasting landscapes such as forests composed of varying age classes and forest
types (McGarigal & McComb 1995; Drolet et al. 1999; Penhollow & Stauffer, 2000).
Topography and moisture gradients can reflect upon the microhabitat vegetation
structure, and can be a critical factor in determining preferred habitat for a focal bird
species (Dettmers & Bart, 1999). Both fine scale and coarse scale landscape
characteristics can help explain wildlife-habitat relationships, but is important to choose
appropriately synonymous variables to answer the research questions.
Purpose of Study
This study was undertaken in conjunction with the two branches of the United
States Department of Agriculture’s Forest Service (FS), the William B. Bankhead
National Forest (BNF), the Southern Research Station (SRS), and Alabama A&M
University (AAMU). The mission of the overarching forest restoration study
implemented by these entities is to monitor short- term and long- term effects of various
silviclutural techniques on the BNF’s ecosystem integrity and ability to restore forest
20
composition to upland hardwoods. With this goal, wildlife habitat and viability and
forest health are compensatory to the restoration goals. Few long term studies consider
both the effects of thinning and burning treatments on avian communities. This study
examined nine different treatments (silviculture prescriptions) including a combination of
thinning and burning regimes. In addition to an extensive monitoring program to follow
bird species abundance and sustainability over the long term, this research included
occupancy modeling within the BNF to capture the relationships between bird
community structure, site specific vegetation variables, and landscape- scale variables.
Study Site
The study site was located in the northern third portion of the William B.
Bankhead National Forest (BNF) in Winston and Lawrence counties, located in northeast
Alabama (Figure 1). The BNF is a 72,800 ha transitional forest within the southern
Cumberland Plateau sub-region. It is classified as a strongly dissected plateau, gentle
slopes with good drainage, and soils dominated by Hartsells, Linker, Nectar, Wynnville,
Albertville, and Enders types (Smalley, 1979). The forest’s current condition can be
attributed to its disturbance history. Forest conversion to agriculture land began in the
1800’s, with heavy timber harvest and wildfires occurring in the 1900’s. In the 1930’s
large portions of the forest was planted with loblolly pine (Pinus taeda). The forest was
recently the subject of southern pine beetle (Dendroctonus frontalis) infestations,
resulting in high loblolly pine mortality, increased salvage logging, and a shift in desired
future conditions of the forest. All these past disturbances contribute to the diversity,
composition, and overall condition of the forest. The BNF initiated a Forest Health and
21
Restoration Project (Gaines & Creed, 2003) to promote healthy forest growth and
ecosystem resilience via thinning and prescribed fire to achieve projected future desired
conditions including the initiation of management to move the northern portion of the
forest towards upland hardwood dominance. Thinning favored the retention of hardwood
species and was implemented before the fire prescriptions. Prescribed burns on the
northern portion of the BNF were conducted in the dormant season when temperatures
were relatively low and humidity was high (January-March). Conducting dormant season
fires under all the correct weather conditions, keeps the prescribed fires from getting out
of control, while also allowing professional personnel to safely contain the prescribed
fires. The fires were characterized as low-intensity understory fires reaching heights no
higher than two meters, limiting the fire to the litter layer and understory. Burns were
allowed to burn continuously until all leaf litter and fuels were consumed and until the
fire ceased.
22
Figure 1. Location of research stands in William B. Bankhead National Forest, AL
23
Experimental Design
The large scale and logistical difficulties of this study resulted in a research
design of a randomized complete block layout with the initial treatments implemented
through three years (block 1 in 2005-2006, block 2 and 3 in 2006-2007, and block 4 in
2008) (Table 2). The two treatment factors were three thin levels [no thin, and 17 m2 ha1
residual basal area (light thin, LT)], and 11 m2 ha-1 residual basal area (heavy thin, HT)]
and three burn treatments [no burn, nine-year burn interval (infrequent burn, IB), and
three-year burn interval (frequent burn, FB)]. Each treatment was replicated four times
and blocked by year of implementation, resulting in a total of 36 research stands.
Treatments were assigned randomly to delineated study stands within each block.
Research stands were located on upland pine-hardwood sites, composed of a
minimum of sixty percent 20-30 year old loblolly pine or Virginia pine mixed with
predominately oak species. Stand sizes ranged, but the average stand size was 12 ha with
similar tree ages and densities.
My study continued a project of Jill Wick (Graduate student, MS 2008, Alabama
A&M University, Normal, AL). Wick collected pretreatment data in 2005 and 2 years
post-treatment (2006 and 2007) on 6 of the 9 treatment stands for blocks 1, 2, and 3 (18
stands total), excluding treatments involved in the infrequent burns (treatments 2, 8, and
9; Figure 2) since the complete implementation of these treatments and block 4 did not
fall within her time of thesis study at AAMU. Post-treatment data for the remaining
treatments and stands were collected during the summer of 2013 to include all nine
treatments in blocks 1-3. In my study, data were collected on all 36 research stands
including all nine treatments for all four blocks.
24
Since the initial treatments implementations were staggered through three years
(block 1 in 2005-2006, block 2 and 3 in 2006-2007, and block 4 in 2008), by May 2013,
those stands in blocks 1-3 with three year burn interval (frequent burn) prescription had
been burned 3 times, while the same prescription on block 4 were only burned twice. For
the thinned stands, either light thin or heavy thin, my study captured the time period of 7
year post initial logging for block 1, 6 years post initial logging for block 2 and 3, and 5
years post initial logging for block 4. Stands with infrequent burns (9 year return
interval) had received only one burn to date, in all blocks, by the May 2013 field season.
Treatment
Prescription
Code
Block 1
Block 2
Block 3
Block 4
1
No thin, No burn (control)
C
2006
2007
2007
2008
2
No thin, 9 year burn return interval
FB
2005
2006
2006
2007
3
No thin, 3 year burn return interval
IB
2005
2006
2006
2007
4
Heavy thin, No burn
HT
2005
2006
2006
2007
5
Light thin, No burn
LT
2005
2006
2006
2007
6
Heavy thin, 3 year burn interval
HTxFB
2005
2006
2006
2007/08
7
Light thin, 3 year burn interval
LTxFB
2005
2006
2006
2007/08
8
Heavy thin, 9 year burn interval
HTxIB
2005/06
2006/07
2006/07
2007/08
9
Light thin, 9 year burn interval
LTxIB
2005/06
2006/07
2006/07
2007/08
Treatment Block
Burn 2
Burn 3
Burn 4/2
Interval
3
3
3 and 9
Block 1
2009
2012
2015
Block 2
2010
2013
2016
Block 3
2010
2013
2016
Block 4
2011
2014
2017
Figure 2.Thinning and burning prescriptions schedule, implemented by year.
25
CHAPTER 2
RESPONSE OF MICROHABITAT CHARACTERISTICS TO
FOREST STAND TREATMENT
Introduction
Forest management practices can alter species composition and microhabitat
condition and structure. The magnitude of change may depend on the silviculture
prescription. Large scale disturbances have a greater impact on these characteristics,
while small scale changes may not influence the microhabitat, forest structure, and
species composition as greatly. The thinning and burning prescriptions implemented in
this study are intermediate silvilculture techniques. Free thinning targets and removes
trees in the lower crown class increasing limiting resources (water and light) for
remaining trees in the stand, and therefore “freeing” dominant and co-dominate tree
species (Smith et al.,1997). The goal is to control the tree density in the stand and
redistribute the available growing space for residual trees. Unlike other silviculture
methods silvilculturists’ goal is not to regenerate a new crop tree or create permanent
canopy gaps, but to increase overall ecological health of the stand by allowing natural
regeneration and harboring space for residuals to thrive (Hemery & Savill, 2004). After a
major disturbance, forest floor herbs, seed banks, advanced regeneration and roots
respond quickly to the increased availability of nutrients and light (Thompson &
26
DeGraaf, 2001). This period of stand initiation is when animal and plant diversity is the
highest due to the mix of herbs, grasses, shrubs, and trees; this period of stand initiation
continues as long as the canopy stays open enough for seedlings to establish and maintain
ground vegetation (Thompson & DeGraaf, 2001). The oak-fire hypothesis advocates that
periodic fires disturbance is required to regenerate oak and conserve and maintain oak
forests (Abrams, 1992). Despite the ample amount of research in eastern U.S. forests,
successful oak regeneration to the ultimate recruitment into the canopy has not been fully
understood, with much more research regarding physiology of the key desired species
and competitor species required, along with questions related to scale of management and
on the ground fire handling skills (Arthur et al., 2012). This part of the study quantified
the microhabitat characteristics of 36 research stands that underwent silviculture
treatments beginning in 2005, with some stands having a reoccurring burn every three
years. I explored the relationships between habitat variables and the treatment regimes
by testing the null hypothesis that there was no difference in variable values among the
36 research stands.
Methodology
Habitat Sampling
At the end of the breeding season in 2013, habitat surveys were performed (JulyAugust) for all 36 research stands. A modified version of the James and Shugardt (1970)
sampling method was used to sample forest vegetation. Wick (2008) and Sutton (2013)
methodology (previous researchers at these sites) was followed to ensure consistency of
27
data collection for comparing results among years. Both Wick (2008) and Sutton (2013)
methodologies were chosen because both shared the same sampling protocol and ensured
a more timely data collection to meet the needs of not only this project but another cocurrent research project. Within each stand, three habitat plots were established for preand post-treatment data collection. Following Wick (2008), a central point was
delineated using ArcGIS in stands not previously surveyed and three plots were located
by random compass bearing and distance (30-50 m) from this point. In the 18 stands,
previously sampled by Wick (2008), a central point was established by co-current
research partners. At each sampling plot two 20 m perpendicular transects were
established and placed north-south and east-west from the center of the habitat plot.
Along these transects the presence or absence of the following parameters were assessed
at 0.5 m intervals along each transect: litter, bare ground, herbaceous cover, and woody
cover. This methodology was a systematic point sampling technique, where a 2 m PVC
pipe was placed at each 0.5 m interval along the transect and the presence or absence was
recorded or tallied, with a percentage then calculated for each microhabitat variable.
Litter depth (to nearest mm) were measured along each transect every 2 m using a metric
delineated ruler placed level with the top layer of the soil surface. At 5 m intervals,
percent canopy cover (using a hand-held convex spherical densitometer, Model-A, Forest
Densiometers, Rapid City, SD, to nearest percent) and the presence of each vertical forest
layer was recorded. Vertical forest layers were visually assessed and assigned a value of
1-4, with the following designations: 1) ground cover (< 2 m); 2) understory (> 2 m - < 4
m); 3) mid-story (> 4 m - < 6 m); and 4) overstory (> 6 m) (FIA, 1998). A percentage of
each layer was determined from calculating from a tally taken at 5 m intervals including
28
whether or not that layer was present. This data taken much like a running tally taken at
each interval to acquire a total percent of each layer present in each treatment stand.
Additional forest characteristics, such as tree species composition, trees per ha, and stem
diameters at breast height (measured with a diameter tape at 1.37 meters above ground
line, or diameter at breast height, dbh) were provided by the USDA FS Southern
Research Station via Dr. Callie Schweitzer (Research Forester, USDA Forest Service,
Huntsville, AL). Data was collected using permanent vegetation plots (0.08 ha circular
plots systematically arranged in each stand). Within these FS plots the species and dbh of
all trees greater than 14.2 cm dbh were recorded to the nearest fourth of a cm using a
diameter tape.
Data Analysis
Forest composition was explained for the pre and post-treatment conditions using
both 0.01 ha plot data (those including 3.81 cm and greater dbh trees) and 0.08 ha plot
data (those including all 14.2 cm and greater dbh trees) and was provided by the USDA
FS Southern Research Station via Callie Schweitzer. Simple percentages of dominant
tree species and changes in forest composition were calculated using simple
mathematical functions in Excel. For PCA, all original variables were visually and
statistically checked for normality, based Shapiro Wilk tests, and presence of outliers
using SPSS v.20. Log and square root transformations were used when needed to
achieve normality assumptions. Principle component analysis (PCA), a factor dimension
reduction method, was used to group microhabitat variables. Principle component
analysis is an eigenanalysis-based ordination technique that uses eigenvalues to explain
29
variation within a dataset. Much like regression, PCA creates linear combinations of the
original variables to produce the axes, or principal components. Generally most of the
meaningful variation can be explained in the first two axes, making it easy to visualize
relationships among original variables when plotted graphically. Initial PCA analysis
was run to examine the correlation matrix and mean square adequacy values (MSA).
Variables with low MSA (< 0.5) were removed one at a time to ensure sufficient
multicollinearity in the PCA analysis. The correlation matrix was used because all data
collected included different measurement scales. All components with final eigenvalues
greater than one were retained. Two PCAs were run, one at a plot level (n=108) and
another at a stand level (n=36) to explore possible variation in the results due to sample
size. Varimax rotation was used to maximize the loadings to one or a few components
and minimize loadings on the other components for each variable, which resulted in the
simpler loading matrix, making axes interpretation easier. All nine treatments were
assessed using data for the sixth and seventh year following initial harvests and
undergoing repeated burns on some of the research stands with a one-way analysis of
variance (ANOVA). A post hoc Least Squared Differences (LSD) test followed when
the ANOVA was significant. This allowed for the location for the sources of the
differences for the principal components and all habitat variables. A multivariate
analysis of variance (MANOVA) with repeated measures was run to examine the
temporal changes in the microhabitat variables by the treatment type and treatment by
year interaction, with year as the within-subject factor and treatment as the betweensubjects factor. The MANOVA was performed for the data collected from blocks 1-3
including six treatments (three treatments with infrequency burns were excluded) in each
30
block since vegetation data of pretreatment and immediate post-treatment was only
collected in these stands. The post hoc LSD test was used to examine differentiation
among treatments and year. Additionally, if there was a treatment/year interaction a
mixed model was run on those variables and a LSD test followed to detect differences
among treatments the years of that displayed a treatment effect. Additionally, a one-way
ANOVA was run to test the effects different burning regimes (no burn, infrequent burn,
and frequent burn) on microhabitat. Variables were log or square root transformed where
needed to meet normality assumptions for the ANOVA test. PCA and all ANOVAs and
MANOVAs were run using IBM SPSS v.20.
Results
The research stands in the BNF were upland sites with mixed oak-pine
composition. Extensive planting of loblolly pine (Pinus taeda) in the 1970’s resulted in
an age cohort of 25-50 year old loblolly pines throughout the stands with a notable
amount of hardwood species (Quercus, Acer, Carya) in the midstory and overstory.
When examining the 0.08 ha plots pre-treatment (those including all 14.2 cm and greater
dbh trees), the dominant tree species was Pinus taeda compromising 75% of the average
total basal area pre-treatment. Pinus virginiana made up 13%, while Quercus alba,
Quercus prinus, and Quercus coccinea were the dominant hardwood species, but only
contributing 4.5% to the total basal area in the research stands. Liriodendron tulipifera
also made up 3.8% of total basal area. Six to seven years post-treatment, Pinus taeda still
remained the dominant tree species and contributed 67% of the total basal area across
stands. Again, Pinus virginiana made up 14% and Liriodendron tulipifera 3%, while
31
Quercus spp. made up 9.4% of the total basal area across research stands. Also accessed
pre- and post- treatment were those 0.01 ha plots (those including 3.81 cm and greater
dbh trees) to note any changes in the smaller diameter trees following silviculture
treatment. Pre-treatment Pinus taeda compromised 47% of the basal area across research
stands, followed by Pinus virginiana (16%), Quercus spp. (12%), Acer rubrum (9%), and
Liriodendron tulipifera (6%). Six to seven years following initial treatment and repeated
prescribed fires slight changes were found. Pinus taeda still comprised the highest
percentage of the total basal area (48%) across research stands, but slight changes were
noted in the following: Pinus virginiana (13%), Quercus spp. (19%), Acer rubrum (10%),
and Liriodendron tulipifera (5%).
Principal Component Analysis
At the plot level, all original 18 variables were used in the PCA. All variables
with MSA values <.5 were taken out the analysis one at a time to ensure sufficient
multicollinearity. A total of 14 variables had relatively high multivariate correlation
(Kaiser-Meyer-Olkin [KMO] Measure of Sampling Adequacy=0.739) and were used for
the PCA analysis. Those removed from the analysis were presence of ground cover, tree
species richness, and percent coarse woody debris. The remaining 14 variables were
reduced to three components with eigenvalues greater than 1 (Table 2). The three
components retained approximately 66% of the original variation in the microhabitat
dataset (Bartlett’s Test of Sphericity χ2= 1284.90, df=91, p=0.000). The first component
was related to mean tree density and basal area, the second represented forest understory
and floor characteristics, and the third represented forest structure and canopy.
32
At the stand level, the sample size was reduced to 36 by calculating an average for
each stand for all 18 original variables. The same methodology used for the plot level
PCA was applied, to show magnitude of sample size effects. Fourteen variables retained
were based on MSA values. Variables removed from the analysis included: tree species
richness, presence of ground cover, and percent coarse woody debris. These remaining
habitat variables again showed high correlation (Kaiser-Meyer-Olkin [KMO] Measure of
Sampling Adequacy=0.711). Retaining all components with eigenvalues greater than one
again resulted in three principal components, accounting for approximately 72% of the
original variation (Bartlett’s Test of Sphericity χ2= 455.871, df=91, p=0.000). The three
components extracted in general showed similar patterns (loadings) as those from plot
based PCA.
33
Table 1. Component loadings, eigenvalues, and percent variance accounted for based on varimax rotated
principle component analysis of microhabitat variables collected at stand-level 6-8 years following
silviculture treatments in Bankhead National Forest, AL (n=108).
Habitat Variable
Component 1
Component 2
Component 3
Stand Tree Density
0.927
0.173
0.185
BA
0.92
0.21
0.21
BA Pine
0.899
0.174
0.177
Woody Cover
-0.751
0.336
0.074
BA Snag
0.546
-0.178
0.436
Litter Cover
-0.028
0.936
0.166
Bare Ground
-0.024
-0.91
-0.209
Litter Depth
0.173
0.706
0.113
Rock
0.438
-0.459
-0.064
Overstory
0.278
0.279
-0.103
Herbaceous Cover
-0.04
-0.084
-0.816
Canopy
0.121
0.025
0.745
Understory
-0.114
0.415
0.709
Midstory
0.333
0.17
0.628
Eigenvalue
3.817
2.95
2.524
% Variance
27.524
21.069
18.026
% Cumulative
27.261
48.33
66.356
34
Table 1. Component loadings, eigenvalues, and percent variance accounted for based on varimax rotated
principle component analysis of microhabitat variables collected at stand-level 6-8 years following
silviculture treatments in Bankhead National Forest, AL (n=36).
Habitat Variable
Component 1
Component 2
Component 3
Stand Tree Density
0.917
0.215
0.165
BA
0.897
0.24
0.206
BA Pine
0.885
0.201
0.173
Woody Cover
-0.883
0.267
-0.008
BA Snag
0.665
-0.135
0.185
Rock
0.519
-0.495
-0.071
Overstory
0.378
0.322
-0.003
Litter Cover
-0.05
0.929
0.253
Bare Ground
0.017
-0.903
-0.295
Litter Depth
0.283
0.691
0.038
Herbaceous Cover
-0.09
-0.023
-0.873
Understory
-0.153
0.392
0.787
Canopy
0.25
0.107
0.766
Midstory
0.388
0.183
0.706
Eigenvalue
4.39
2.937
2.757
% Variance
31.356
20.98
19.691
% Cumulative
31.356
52.336
72.027
Response of Microhabitat Variables to Treatment
Results of a one-way ANOVA comparing differences among treatments for
microhabitat variables showed that 6-8 years following initial treatment many habitat
variables are still displaying differences among treatments. Both canopy (F = 3.35, df =
35
8,80 p = 0.010; Table 3) and herbaceous cover (F = 2.90, df = 8, 80 p = 0.02; Table 3)
showed a significant difference among treatments. Canopy and herbaceous cover were
inversely correlated, and treatments having less canopy cover yielded more herbaceous
cover. Heavily thinned and frequently burned, LTxFB, HTxIB, LTxIB stands had lower
canopy cover and a higher percentage of herbaceous cover, compared to C, FB, IB, HT,
or LT stands. Understory differed among treatments (F = 5.7, df = 8, 80 p <0.001; Table
3) with more understory in C, IB, HT,LT, and HTxIB, and LTxIB stands compared to
FB, HTxFB, and LTxFB stands. Midstory data also displayed differences among
treatments (F = 3.81, df = 8, 80 p = 0.005; Table 3) with C stands having more midstory
than HT, LT, HTxFB, LTxFB, and HTxIB and LTxIB stands. Woody cover percentage
showed a significant differences among treatments (F = 8.92, df = 8, 80 p <0.001; Table
3) with a clear gradient from highest woody cover percentage in HT,LT, HTxIB, and
LTxIB stands followed by HTxFB and LTxFB stands. Lowest percentage of woody
cover was in C, IB, and FB stands. Herbaceous cover varied among treatment regimes,
with lowest percent of herbaceous cover in C compared to those stands that were burned,
which had significantly higher percentages of herbaceous cover including grasses and
thorny shrubs. Thinned stands had higher percentages of herbaceous cover than C stands,
but not as much as stands that received both thinning and burns. Basal area total (F =
50.37, df = 8, 80 p <0.001; Table 3) and BA of pines (F = 29.57, df = 8, 80 p <0.001;
Table 3) both showed a strong significant difference among treatments. For total BA, C,
FB, and IB had highest BA followed by LT then HT. Treatments LTxFB and LTxIB had
similar BA, and so did HTxFB and HTxIB stands which also had lowest BA of all
treatments, as expected. Basal area of pine followed a similar trend to that of total BA.
36
Mean tree density also differed significantly (F = 40.31, df = 8, 80 p <0.001; Table 3) and
showed similar differences among treatments as BA due to the thinning. Principle
component 1 (F = 26.78, df = 8, 80 p<0.001; Table 3) and PC 2 (F = 4.92, df = 8, 80
p=0.001; Table 3) differed among silvilcultural treatments 6-8 years post-harvest.
Variables associated with tree density and BA (PC 1) were associated with those stands
neither burned or thinned or burned only, whereas those stands thinned or thinned and
burned showed decreases in this habitat component. Variables associated with the forest
floor, litter and bare ground also differed between treatments 6-8 years post-harvest.
Control stands and thin only had higher values for litter cover and litter depth with and
negative correlation with presence of bare ground. Pos hoc test noted clear difference in
this component between controls and thin/burn stands on a three year burn return interval.
For component two, the most similar stands were those not receiving frequent burns.
Variables associated with vertical forest structure: percent understory cover, percent
midstory cover, and canopy cover (PC 3) did not differ (F = 0.68, df = 8, 80 p=0.71;
Table 3) between treatments 6-8 years post-harvest. This component, which was
indicative of the forest structure, also had a negative correlation with herbaceous cover,
thus more vertical canopy structure resulted in less forest floor herbaceous cover.
Minimum block effects were displayed for microhabitat variables 6-8 years
following initial treatment. The only habitat variable that experienced a block effect, or
difference in mean values between blocks in 2013 was percent of herbaceous cover (F =
3.56, df = 3, 15 p=0.03; Table 3).
37
38
96.1+2.0b
0.1+0.1
27.0+0.0
8.9+2.1a
5.1+0.5
98.1+1.2a
21.5+0.96b
24.75+1.93
0.6+0.6ab
22.00+1.68a
41.6+8.0ab
2.2+0.0d
2.14+0.01a
4.11+0.47
0.81+0.06ab
1.7+0.0a
CWD %
Ground Cover %
Herbaceous %
Litter Depth(cm)
Litter %
Midstory %
Overstory %
Rock %
Understory %
Woody %
BA: Total
BA: Pines
BA: HW
BA: Snags
Stand Tree
1.2+0.2abc
1.0+0.4ad
0.15+0.52
PC 1
PC 2
PC 3
0.61+0.52
0.5+0.4abd
0.9+0.2ab
6.20+0.85
1.7+0.1a
0.64+0.09abc
3.65+0.55
2.11+0.06a
2.2+0.4d
48.6+5.8abd
20.50+1.85a
0.0+0.0a
21.00+2.94
14.25+1.38ab
99.6+0.0a
5.6+0.7
19.5+5.1ab
27.0+0.0
0.3+0.2
96.0+3.3b
0.21+0.2a
IB
0.06+0.52
-0.4+0.4bcd
1.6+0.2ac
6.40+0.78
1.8+0.0d
0.57+0.05bcd
3.74+0.43
2.15+0.03a
2.2+0.2d
32.6+8.5ab
9.75+3.75b
1.5+0.9b
26.75+0.25
14.5+4.09ab
80.7+11.1ab
4.7+0.4
35.2+6.6bcd
27.0+0.0
0.5+0.4
93.7+2.0a
11.4+8.3a
FB
-0.75+0.52
0.7+0.4ad
-0.9+0.2degh
6.55+1.09
1.3+0.0bc
0.31+0.11bcd
3.47+0.79
1.72+0.0bd
1.8+0.0a
77.5+4.8cd
20.00+4.34a
0.0+0.0a
21.00+1.08
12.75+3.43a
96.6+1.2a
3.5+0.8
20.4+7.4ab
27.0+0.0
1.0+0.5
92.4+3.4a
2.4+1.1a
HT
LT
0.18+0.52
0.7+0.4ad
-0.8+0.2degh
6.05+0.64
1.3+0.0bc
0.19+0.11cd
3.67+0.60
1.82+0.04bcd
1.9+0.3b
84.4+2.0cd
21.5+2.18a
0.0+0.0a
22.50+0.87
11.25+2.39a
99.4+0.5a
4.6+0.8
15.5+8.8ab
27.0+0.0
0.3+0.20
91.5+2.7a
0.4+0.4a
Treatments
-0.56+0.52
-0.9+0.4cd
0.6+0.2defgh
5.75+0.98
1.2+0.0bc
0.46+0.07bcd
3.10+0.56
1.70+0.02bd
1.8+0.3ae
66.2+7.2bcd
9.00+4.24b
0.9+0.3ab
20.75+2.53
5.25+4.92ac
56.8+24.9b
4.0+1.2
41.4+8.7cd
27.0+0.0
0.0+0.0b
77.3+9.2c
42.18+24.7b
HTxFB
0.06+0.52
-1.2+0.4c
-0.2+0.2fh
4.90+0.66
1.4+0.0bc
0.25+0.08cd
2.45+0.78
1.88+0.02cd
1.9+0.1bc
66.0+8.8bcd
5.50+0.96b
0.3+0.2a
22.00+2.8
5.50+1.44ac
78.6+12.2ab
4.4+0.9
37.2+11.1cd
27.0+0.0
0.2+0.2
76.77+7.05c
21.19+12.1ab
LTxFB
-0.04+0.52
0.1+0.4abd
-1.0+0.2deg
6.00+0.96
1.2+0.0ae
0.34+0.07bcd
2.72+0.85
1.73+0.04bd
1.8+0.0ae
80.5+6.1cd
20.25+2.02a
0.0+0.0a
23.75+1.80
7.25+2.66a
99.7+0.3a
4.4+0.6
38.4+11.8cd
26.8+0.3
0.2+0.2
89.3+5.2a
0.0+0.0a
HTxIB
0.30+0.52
-0.4+0.4bcd
-0.3+0.2defh
6.00+0.84
1.4+0.0bc
0.37+0.22bcd
3.24+0.68
1.89+0.0cd
1.9+0.0bc
80.3+4.6cd
17.8+0.96a
0.1+0.1a
22.50+1.71
6.50+1.56a
99.8+0.1a
0.68
4.92
26.78
0.40
40.31
3.12
0.57
29.57
50.37
8.92
5.70
2.36
1.05
3.81
2.70
0.67
2.90
4.5+0.4
2.08
39.6+6.4 cd
1.59
3.35
2.55
26.5+0.3
0.0+0.0b
81.9+6.4a
0.1+0.1a
LTxIB
F(T)2
0.71
0.001
<0.001
0.910
<0.001
0.01
0.79
<0.001
<0.001
<0.001
<0.001
0.05
0.43
0.005
0.03
0.71
0.02
0.08
0.18
0.01
0.04
P(T)
1.57
2.94
1.65
2.75
0.66
1.39
2.39
2.04`
1.12
1.58
1.54
1.90
1.18
1.50
2.73
0.09
3.56
1.70
1.90
1.13
2.09
0.22
0.53
0.20
0.65
0.58
0.27
0.94
0.14
0.36
0.22
0.23
0.15
0.34
.239
0.07
0.50
0.03
0.20
0.15
0.36
0.13
F(B)3 P(B)
Abbreviated labels are denoted as C = control, IB = infrequent burn only (9 year burn interval), FB= frequent burn only (3 year burn interval) HT = heavy thin, LT = light thin, HT xFB = heavy thin with frequent
burn (3 year burn interval), LT xFB = light thin with frequent (3 year burn interval), HTxIB= heavy thin with infrequent burn (9 year burn interval), and LT xIB= light thin with infrequent burn (9year burn interval)
2.
Dfs for treatment effect tests were 8 and error df was 80
3.
Dfs for block effect tests were 3
1.
5.80+0.36
TreeSp.Richness
Density
1.3+0.8a
2
Canopy %
C
Bare Ground %
Variable
1
Table 3. Mean + standard error and results of analysis of variance (ANOVA) (dfs for treatment effect tests were 8 and error df 80, and dfs for block effect tests were 3 and error df 15) of microhabitat variables
6-8 years following silvicultural treatment in the William B. Bankhead National Forest, 2013.
Pretreatment, Immediate, and 6-7 Years Post-Treatment Responses of Microhabitat
Variables
The comparison of microhabitat variable variation in relation to treatment and
year effects showed that almost all variables showed variation among treatments and
years. Percent of woody cover showed block, treatment, year, and treatment/year
interactions (Pblock=0.02 Ptreat<0.001, Pyear<0.001, Ptreat*yr<0.001; Table B.1, Figure 3).
Six to seven years following treatment, there was a treatment/year interaction for percent
woody cover. The highest percentages of woody cover were present in HT and LT
followed by HTxFB and LTxFB stands and lowest percent of woody cover in FB and C
stands.
Figure 3. Treatment/year interaction of woody cover percent following silvicultural treatments in the
Bankhead National Forest, AL, Pretreatment, 1-yr post, and 6-7-yr post-treatment. Abbreviated labels are
denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily thinned LT= lightly thinned,
HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly thinned with frequent burn (3
year interval).
39
Litter cover showed treatment, year, and treatment/year effects (Ptreat=0.02, Pyear=0.02,
Ptreat*yr=0.05; Table B.1, Figure 4) with less litter 6-7 years post-treatment and after
completion of three burns. A treatment/year interaction was noted one year following
initial treatment implementation, with HTxFB stands having a lower percentage of litter
than all other treatments. Light thinned and frequent burned stands also had a lower
percent of litter compared to the C stands.
Figure 4. Treatment/year interaction of basal area of snags following silvicultural treatments in the
Bankhead National Forest, AL, Pretreatment, 1-yr post, and 6-7-yr post-treatment. Abbreviated labels are
denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily thinned LT= lightly thinned,
HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly thinned with frequent burn (3
year interval).
Herbaceous cover had a treatment/year interaction (Ptreat*yr=0.001; Table B.1, Figure 5).
Six-seven years post initial treatment FB, HTxFB, and LTxFB stands had the highest
percent of herbaceous cover compared to C, HT, or LT stands. Herbaceous cover had
also decreased in those stands only thinned.
40
Figure 5. Treatment/year interaction of herbaceous cover percent following silvicultural treatments in the
Bankhead National Forest, AL, Pretreatment, 1-yr post, 6-7yr post-treatment. Abbreviated labels are
denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily thinned LT= lightly thinned,
HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly thinned with frequent burn (3
year interval).
Canopy cover displayed treatment, year, and treatment/year interactions (Ptreat<0.001,
Pyear<0.001, Ptreat*yr=0.001; Table B.1, Figure 6), with lowest percent of canopy closure
one year following silviculture treatment and becoming similar to pretreatment levels 6-7
years post- treatment. Percent canopy cover was significantly lower in HTxFB, LTxFB,
HT, and LT stands than in FB or C stands one year following initial treatment. Six to
seven years following initial treatment, only HTxFB and LTxFB stands differed from C
and FB stands. Thin only stands had percent canopy cover comparable to the burn only
and control stands.
41
Figure 6. Treatment/year interaction of percent canopy cover following silvicultural treatments in the
Bankhead National Forest, AL, Pretreatment, 1-yr post, 6-7 yr post-treatment. Abbreviated labels are
denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily thinned LT= lightly thinned,
HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly thinned with frequent burn (3
year interval).
The percent of understory occupied by woody vegetation showed treatment, year, and
treatment/year interactions (Ptreat=0.01, Pyear<0.001, Ptreat*yr<0.001; Table B.1, Figure 7).
One year following treatment, HT, LT, HTxFB, and LTxFB stands had significantly
lower percentages of understory compared to the FB, and C stands. Six to seven years
following initial treatment, HT, LT, and C stands had higher percentages of understory,
while FB, HTxFB, and LTxFB had less percent understory. This due to fire prescriptions
being implemented in many of those stands in the year of data collection.
42
Figure 7. Treatment/year interaction of presence of understory following silvicultural treatments in the
Bankhead National Forest, AL, Pretreatment, 1-yr post, 6-7 yr post-treatment. Abbreviated labels are
denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily thinned LT= lightly thinned,
HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly thinned with frequent burn (3
year interval).
Percent of midstory occupied by woody vegetation also showed year and treatment/year
interactions one year following initial treatments (Pyear=0.002, Ptreat*yr=0.02; Table B.1,
Figure 8). One year following treatment, percent midstory was similar in all stands,
except FB stands which had significantly more percent midstory present. Six-seven years
following treatment, HTxFB and LTxFB were the only stands having less percent
midstory than the C stands; however they did not significantly differ from FB, HT, or LT
stands.
43
Figure 8. Treatment/year interaction of presence of midstory following silvicultural treatments in the
Bankhead National Forest, AL, Pretreatment, 1-yr post, 6-7 yr post-treatment. Abbreviated labels are
denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily thinned LT= lightly thinned,
HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly thinned with frequent burn (3
year interval).
Tree species richness displayed year and treatment/year interactions (Pyear<0.001,
Ptreat*yr<0.001; Table B.1, Figure 10) with species richness decreasing one year following
treatment, but returning to pretreatment levels 6-7 years post initial treatment. Stand tree
density displayed treatment, year, and treatment/year effects (Ptreat<0.001, Pyear<0.001,
Ptreat*yr<0.001; Table B.1, Figure 9). One year following treatment, stand tree density
was higher in FB stands than in C stands, and fewest trees were present in HT, LT,
HTxFB, and LTxFB stands. Six-seven years following treatment also shows the same
trend for the treatment/year interaction.
44
Figure 9. Treatment/year interaction of stand tree density following silvicultural treatments in the Bankhead
National Forest, AL, Pretreatment, 1-yr post, 6-7 yr post-treatment. Abbreviated labels are denoted as C =
control, FB =frequent burn only (3 year interval), HT= heavily thinned LT= lightly thinned, HTxFB=
heavily thinned with frequent burn (3 year interval) LTxFB= lightly thinned with frequent burn (3 year
interval).
Figure 10. Treatment/year interaction of tree species richness following silvicultural treatments in the
Bankhead National Forest, AL, Pretreatment, 1-yr post, 6-7 yr post-treatment. Abbreviated labels are
denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily thinned LT= lightly thinned,
HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly thinned with frequent burn (3
year interval).
45
Total BA showed treatment, year, and treatment/year effects (Ptreat=0.001, Pyear<0.001,
Ptreat*yr<0.001; Table B.1, Figure 11) and as expected after treatment implementation BA
decreased in all harvested stands, and all harvested stands had lower BAs than control or
burn only stands. Basal area remained different among research stands 6-7 year
following initial treatment, with C and FB stands having significantly higher BA than
harvested stands. Light thin and LTxFB had similar BA and more BA than HT and
HTxFB stands, which had comparable total BA.
Figure 11. Treatment/year interaction of total basal area following silvicultural treatments in the Bankhead
National Forest, AL, Pretreatment, 1-yr post, 6-7 yr post-treatment. Abbreviated labels are denoted as C =
control, FB =frequent burn only (3 year interval), HT= heavily thinned LT= lightly thinned, HTxFB=
heavily thinned with frequent burn (3 year interval) LTxFB= lightly thinned with frequent burn (3 year
interval).
Basal area of pines also showed treatment, year, and treatment/year (Ptreat=0.001,
Pyear=0.004, Ptreat*yr=0.03; Table B.1, Figure 12). Basal area of hardwood species showed
46
a year effect (Pyear=.001; Table B.1) with a decrease in hardwood species occurring one
year following treatment, but 6-7 years following initial treatment hardwood BA was
comparable to that of pretreatment.
Figure 12. Treatment/year interaction of basal area of pines following silvicultural treatments in the
Bankhead National Forest, AL, Pretreatment, 1-yr post, 6-7 yr post-treatment. Abbreviated labels are
denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily thinned LT= lightly thinned,
HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly thinned with frequent burn (3
year interval).
Basal area of snags displayed year and treatment/year effects (Pyear=0.004, Ptreat*yr<0.001;
Table B.1, Figure 13). Pretreatment, snag density differed among stands, with LT and
HTxFB stands having more snags than other stands. Control stands had significantly
more snags than all other stands 6-7 years following treatment, while HT and LT stands
47
had less snags than C or FB stands. Thinned and burned stands had more snags than HT
and LT, but less snags than C stands.
Figure 13. Treatment/year interaction of basal area of snags following silvicultural treatments in the
Bankhead National Forest, AL, Pretreatment, 1-yr post, 6-7 yr post-treatment. Abbreviated labels are
denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily thinned LT= lightly thinned,
HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly thinned with frequent burn (3
year interval).
Presence of rock displayed year and treatment effects (Ptreat=0.04, Pyear=0.02; Table B.1)
with rock being present most often 6-7 years following treatment in the stands that
recently received a burn. Bare ground showed both a treatment and year effect
(Ptreat=0.03, Pyear= 0.02; Table B.1) with higher percentages of bare ground being
intermediately following initial treatments. Heavily thinned and burned stands had a
higher percentage of bare ground than any other treatment with the exception of LTxFB
stands. Coarse woody debris also displayed only a year effect (Pyear<0.001; Table B.1),
48
with a decrease in coarse woody debris 6-7 years post-treatment. Ground cover displayed
a year effect (Pyear<0.001; Table B.1) with values differing in all years and highest levels
of ground cover present 6-7 years post initial treatment. Litter depth displayed block and
treatment effects (Pblock=.001, Ptreat=.002; Table B.1). Block two had a lower litter depth
than block one or block three, while blocks one and three were similar. Overall, control
stands had higher litter depth levels than any of the other treatments. All the other
treatments had similar measurements of litter depth.
Discussion
PCA analysis of habitat characteristics 6-8 years post-harvest of initial
disturbance in the BNF resulted in groups of variables into principal components,
reducing the number of variables and the complexity involved to interpret relationships
among habitat variables. My analysis of two separate component analysis revealed that
sample size effected extraction of components and total variance explained by the PCA.
The analysis with a high sample size, based on plot level (n=108) resulted in a more
realistic explanation of principal component grouping of the original variables, but was
unable to explain a high percent of the variance in the dataset. The analysis with a lower
sample size (n=36) at a stand level explained more of the variation within the dataset, but
some variables grouped in component one made less biological sense than that with the
higher sample size, such as presence of rock correlating positively with BA and stand tree
density. This relationship may not be considered significant since the correlation was
ranked so low (0.5). Percent of overstory also grouped with component one, with a very
slight (0.3) correlation among BA, tree density and the percent of overstory, again
49
ranking low enough to disregard the validity of the result. In this study, it is clear that
sample size has an effect on the results of a PCA, as related to the amount of variance
explained, but the habitat variables are grouped very similarly regardless of sample size
resulting in similar principal component extraction. It is clear that the study design,
consisting of four replications of nine treatments, was valid and proficient at capturing
stand variation at the study level.
Six-seven years following initial treatments and repeated frequent burns
microhabitat variables measured show changes in mean response; however, following 6-7
years of treatment, not all habitat variables differed among treatments. For example,
litter depth, presence of bare ground, coarse woody debris, ground cover, and litter no
longer differ among treatments. Forest structure of the overstory, BA of hardwood tree
species, and tree species richness also show no differences between treatments. Percent
canopy cover was significantly different among treatments, with stands thinned and
frequently burned having lower percent canopy cover (Table 3). Those stands thinned
only or thinned and burned on nine year return intervals had the highest percentage of
woody cover (Table 3). The control and burn only stands had the lowest percentage of
woody cover. An increase in woody vegetation and stump sprouts are responses shown
after fire, and responses are further increased when thinning is added (Kilpatrick et al.,
2010). Herbaceous cover was highest in those stands under a frequent fire return interval
followed by stands receiving less frequent burns (Table 3). Controls had the least
percentage of herbaceous cover, and herbaceous cover increased with an increase in stand
disturbance, previously found by Zak (2008) and also collaborating with a similar fire
studies located on mixed pine-oak sites within the Cumberland Plateau (Arthur et al.,
50
1998; Coleman & Rieske, 2006; Kilpatrick et al., 2010; Zak, 2008). After five years, in
an oak forest in southern Ohio researchers found that the herbaceous layer species
composition and diversity increased in burned stands compared to unburned stands, but
the composition changes were small in magnitude and the herbaceous layer was not
altered enough to show long term composition changes (Hutchinson et al., 2005). The
study concluded that single fires can only cause minor changes in light availability and
results in ephemeral response (Hutchinson et al., 2005). Several studies have found
herbaceous species diversity and density was significantly increased when the fires were
more intense or additional silviculture methods were used in conjunction with fire, such
as a thinning which creates larger canopy openings (Ducey et al., 1996; Elliot et al.,
1996; Brose & Van Lear, 1998; Zak, 2008). As expected, total BA, BA of pines, and tree
density was still lowest on the heavily thinned stands and highest on the control stands
and those only burned (Table 3). Basal area of snags was also highest in control stands
and those stands only burned (Table 3). Percent understory was consistently lowest in
those stands frequently burned, and the greatest percent understory found in those that
were unburned or burned infrequently (Table 3). Percent midstory was impacted most by
those stands both thinned and burned, with percent midstory very low on these stands
(Table 3), with the same response shown in Kilpatrick et al. (2010). Midstory occupancy
was highest in control and burn only stands, followed by those stands only thinned.
Principal component one showed a correlation among BA, BA of snags, tree
species abundance, and overstory, and negative correlation with woody cover. Control
and burn only stands were significantly different from those stands thinned or thinned
and burned. These results demonstrate that 6-7 years flowing initial treatment clear
51
differences among control and disturbed sites still exist in variables related to BA such as
the negative relationship with the presence woody cover. This relationship was also
reported by Waltrop et al. (2008) who showed that after four years woody cover was
highest in treated stands (burned; mechanically thinned; mechanically thinned and
burned) as sprouts from trees and shrubs became established (Waltrop et al., 2008).
Component two, related to litter depth, cover and presence of bare ground differed among
control stands and those stands once thinned and frequently burned. Component three
was related to forest understory and midstory structure. Canopy cover was inversely
related to herbaceous cover- as percent canopy cover increased percent of herbaceous
cover present decreased. Clearly these disturbances are impacted forest succession and
forest structure, but there was no significant difference among treatments related to this
relationship 6-7 years following initial treatments.
Infrequent burns without any thinning mimic small -scale changes (Greenberg et
al., 2007; Rush et al., 2012), under which tree mortality is not high enough to alter the
overstory canopy and BA characteristics. Therefore, the research stands infrequently
burned have similar habitat characteristics as those of control stands. The other research
stands, with the exception of FB stands, no longer significantly differ from the control.
The burned stands have a reduction of leaf litter only in the short term; burns occurred in
the year of data collection for two research blocks. When examining all nine treatments
6-7 years post-treatment, difference among treatments were no longer reported for litter
depth. Forest succession within the stands has allowed the re-growth of the understory
and shrub layer, which in turn has since contributed to the percent litter cover and litter
52
depth. Another low intensity fire study showed similar results and concluded that only
two years post burn, litter exceeded pre-burn levels (Artman et al., 2001).
Over time, it is clear that the research stands have changed considerably
compared to pretreatment and one year post treatment conditions. A decrease 6-7 years
following initial treatments was found for coarse woody debris, more than likely due to
the repeated fires on many of the stands. Fuels are consumed during a prescribed fire,
and coarse woody debris is diminished in diameter, so many logs no longer meet the
minimum dbh requirements after a burn. Percent canopy decreased immediately
following thinning treatments, but 6-7 years after initial treatment canopy returned to
pretreatment levels in thinned only stands. Thinning in combination with frequent
prescribed burning created an environment that impacted the midstory and regeneration
over time. A reduction in non-target and competing midstory and understory stems are
imperative to the successful regeneration of oak species, since oak has an intermediate
tolerance to shade and therefore advanced oak regeneration will not survive or thrive
under a dense canopy (Loftis, 1990; Crow, 1988). Our findings showed percent
occupancy of midstory to be the highest in control stands and lower in stands receiving
frequent burns. Other studies supported our findings that prescribed fire reduces the
midstory density (Barnes & Van Lear, 1998; Kilpatrick et al., 2010). In a prescribed fire
study on the Daniel Boone National Forest in Kentucky, the midstory was not impacted
by low-intensity, back-burning surface fires (Coleman & Rieske, 2006). Many stands
had received only one prescribed burn (on the nine year return interval) had grown
enough to restrict direct sunlight to the forest floor and showed increased density of
woody vegetation in the understory, thus are now in the stage of understory reinitiation.
53
Combined use of fire and thinning or partial harvesting, increases light to the forest floor
potentially promoting oak advance reproduction and limiting dominance of shadeintolerant species (Brose et al., 2008). In the Virginia Piedmont, conducting fires several
years after a harvest (up to 50% residual basal area) was shown to increase oak vigor in
relation to other strong competitors such as yellow-poplar and red maple (Brose & Van
Lear, 1998). Brose (2010) also found that a single prescribed fire alone does very little
to improve upon the vigor and competitive status of oak regeneration, and Hutchinson
(2012) found that multiple burns following a canopy disturbance encouraged oak and
hickory advance regeneration.
Snag density displayed a year effect and treatment/year interaction (Table 4). The
data showed a decrease in snag density one year after treatment, due to harvesting
damage and fire-induced mortality of small stems. Snag density did not increase over
time, with control and burn only stands maintaining the highest number of snags (also
reported by Wick, 2008). Control stands had significantly more snags than all other
stands 6-7 years following treatment, while HT and LT stands had less snags than C or
FB stands, due to possible knock over and degradation over the course of the study. Over
time snags in stands receiving burns may also decay and fall over (Greenberg et al.,
2007). Simon et al. (2002) found that five years following burning, snag densities were
~50 times as great in burn stands than harvested stands, but that difference significantly
reduced as snag densities on burned stands decreased over time (Simon et al., 2002).
Prescribed burning affects the microhabitat characteristics, especially in the short
term and in the years of a burn. Many variables associated with the forest floor
characteristics such as presence of litter, bare ground, coarse woody debris, and rock
54
displayed year effects; additionally presence of bare ground and litter displayed a
treatment effect. One-way ANOVA results showed, presence of rock, litter, herbaceous
cover, and bare ground to differ among burning regimes, further indicating a treatment
effect. Forest structure variables such as presence of understory and midstory also
showed changes among burned stands. Presence of bare ground and rock were noted
more often in the year of prescribed burns, indicating that the fire exposed the forest floor
and rocks are overturned making them more likely to be encountered during the habitat
surveys. The relationship between bare ground and lower percentage of leaf litter was a
short term response of the burns and other studies confirm this finding (Artman et al.,
2001; Coleman & Reiske, 2006). On the Daniel Boone National forest in Kentucky, leaf
litter cover decreased by 85% on burned stands compared to unburned stands, but by the
second year following the burn these differences were no longer apparent (Coleman &
Reiske, 2006). Herbaceous cover can only be explained statistically when performing a
one-way ANOVA, looking at differences among burn regimes. Herbaceous cover
increases on burned stands in the year of a burn, however infrequent burns do not
contribute to the maintenance of herbaceous cover through time. Bare ground essentially
became easier to discern in the year of a burn, and exposed the forest floor, creating
habitat that allows herbaceous cover and grasses to sprout. This is only a short term
microhabitat response to the fire that was not discernible in the data in the second or third
year following a prescribed burn. Understory changes dramatically in the short term in
response to prescribed burning. Understory is depleted during the year of a burn, which
is the goal of forest management. Within a year following a burn, understory returns.
Midstory was highest in stands receiving no burns, and lower in stands receiving three
55
year burns, indicating the frequent prescribed burns impacted the midstory layer of
vegetation in this study on the BNF. In conclusion, light and heavy thinning and
prescribed burning can have an immense impact on forest vegetation and microhabitat
characteristics. A magnitude of treatment intensities were studied and results showed
that forest vegetation and microhabitat responses were synonymous with the level of
intensity applied in the treatment. For example, thinning combined with prescribed
burning yielded the greatest changes to the microhabitat while infrequent burning alone
did little to change the microhabitat over time.
56
CHAPTER 3
INDIVIDUAL AVAIN SPECIES AND COMMUNITY RESPONSE TO
FOREST STAND TREATMENT
Introduction
Recent discoveries of songbird population declines in numerous forests of the
Eastern United States has shifted attention to research the various impacts of silviculture
practices on conservation of avian communities (Lanham et al., 2002). Stand
manipulation can impact microhabitat characteristics and in turn affect the breeding
habitat for summer bird breeding communities. Recent studies have concluded that
habitat loss and degradation has led to declines in Neotropical migrants and many earlysuccessional species, justifying priority conservation status to be given to Neotropical
migrants (Augenfield et al., 2008; Lanham et al., 2002; Twedt & Somershoe, 2008). Any
form of tree removal, other than for means of land development, encourages early
successional growth, but bird response differs from method to method. In this study, the
effects of thinning, dormant season burns, and a combination of the two treatment factors
were explored. Very few studies in the Eastern U.S. have looked at the method of
thinning and prescribed fire specifically, and even fewer have researched the combination
of the two methods (Wick, 2008; Wilson et al., 1995). Therefore, it was important to
quantify if early successional habitat has been created in this study to provide habitat for
57
species of conservation concern. Many studies fail to report intermediate temporal
responses, and only examine immediate response (1-2 years post-harvest) although
maximum response to treatment for many bird species and guilds are shown to be 5-8
years post-harvest (Twedt & Somershoe, 2008).
Breeding bird individual and avian guild response to thinning and burning
regimes within BNF were studied. Also, examined was the temporal differences of
current results to those found by Wick (2008), with the null hypothesis being that
community characteristics, species response, and guild response does not differ among
treatment regimes or time since disturbance.
Methodology
Bird Sampling
The bird community was quantified using the line-transect and distance sampling
method (Buckland et al., 2001). Since this study was a continuation of that by Wick
(2008). The line transects established in 2005 on previously used 18 research stands
were used in this study. Transects were also established in the remaining stands of blocks
1-3 in 2012, and the entire block 4 in 2013. Transects within each stand were 50 m from
the edge of the stand and 100 m apart from each other. This resulted in 27 stands being
surveyed for bird community in 2012, and full 36 stands being surveyed in 2013.
All stands were surveyed a total of three times during the peak of breeding season
(early May-late June) in each year [2004,2005, 2006 (from Jill Wick’s study), 2012 and
2013. Surveys were started at sunrise and ended no later than 11:00 Central Standard
58
Time (CST), with no sampling taking place when rain or high wind speed. Stands were
visited on a block basis to ensure that all 9 treatments were sampled within a similar time
frame before moving to the next block. The order of block and stand visits were
generated by the randomization function in Excel, thus visitations to stands were
randomly assigned, though due to spatial and time constraints some stands were grouped
based on location. For each survey the observer slowly walked along the transect and
recorded birds seen or heard within 50 m on either side of the transect (Wick, 2008).
When a bird was detected the following data were collected: species, sex, age (juvenile or
adult), behavior, and location perpendicular to the transect. Incidental flyovers were
recorded, but not used for statistical analysis.
Guild Arrangement
Guilds will be classified by foraging behavior (A, aerial; F, foliage; G, ground, B,
bark) (Ehrlich et al., 1986), nest location (G, ground; S, shrub; T, tree; C, cavity) (Ehrlich
et al., 1986), migratory status (N, Neotropical migrant; T, temperate migrant; R, resident)
(Sauer et al., 1996; Imhof, 1976), and habitat association (O/E, open-edge; I/E, interioredge; I, interior) (Blake & Karr, 1987; Freemark & Collins, 1992).
1) Foraging guilds
a. Aerial (A): forage on flying insects while the bird is in flight
b. Foliage (F): forage mostly on insects or fruits situated on vegetation
c. Ground (G): forage from low vegetation, soil, and leaf litter
d. Bark (B): forage for insects underneath tree bark
2) Nest location guilds
59
a. Ground (G)
b. Shrub (S)
c. Tree (T)
d. Cavity (C)
3) Migrant guilds
a. Neotropical (N): species that migrate to Central or South America in the
fall
b. Temperate (T): species that spend at least part of their winter in the
southern part of the United States and/or northern Caribbean Islands
c. Resident (R)
4) Habitat Associations
a. Open-edge (O/E): early- successional, edge-, and field-dwelling species
b. Interior-edge (I/E): species that prefer forest interiors but are believed to
be less disrupted by forest disturbance, as well as forest edge inhabitants
c. Interior (I): species that require mature forests with closed canopies
Fine scale habitat relationships and landscape-scale habitat relationships are most
likely unique for each individual species of bird (Mitchell et al., 2008), but perhaps less
variable among groups of ecologically similar species. Grouping of species into guilds is
necessary in land management, since it is not achievable to manage for all species
individually (Mitchell et al., 2006). While it is important to remember guilds can answer
important questions, it is also important to pay attention to habitat associations of
individual species, especially those associated with forest interior habitat (Szaro, 1986).
60
Data Analysis
Species richness, evenness, and Shannon Weiner diversity will be calculated to
access the avian community in each of the research stand s (Krebs, 1999). A relative bird
abundance index following Wick (2008) was calculated by dividing the number of bird
detections by the transect length for each individual stand. Among the three surveys
performed, the survey with the highest number of detections of a particular species was
selected to use as the base to calculate relative abundance of each species. Since each
stand varied in area, a standardization of bird abundance had to be calculated. This was
achieved by dividing the number of birds (of each species) encountered by 900, the
average amount of meters of transect length in a given stand. Therefore, the abundance
or density measurement is reported as the number of birds per 900 meters. The terms
abundance and density are used interchangeably, but refer to the same measure of
population change. In different bird studies these two terms are often used
interchangeably when discussing the relationships between predictors of population
change (Koleček & Reif, 2011).
Statistical analysis MANOVA to determine changes in the bird community
among treatment type and stands. Depending on the results of the MANOVA analysis, a
post hoc LSD test was performed for multiple comparisons. Individual species response
of common summer breeders was assessed along with defined avian guild responses.
Bird community characteristics such as evenness, diversity, and richness were also
analyzed. Intermediate responses was explored, along with pretreatment and immediate
responses on 18 of the research stands previously studied (Wick, 2008). To evaluate bird
species similarity among the research stands, I calculated Morisita’s-Horn similarity
61
index. This index is considered the best overall measure of similarity for ecological
niche use. The index ranges from 0 to 1, with 0 indicating the combination of sites have
no species in common, while 1 represents a complete overlap in species between the two
sites (Magurran, 1988). Morisita’s index avoids complexities derived from effects of
sample size and diversity because result is not based upon sample size and diversity,
making it the best to use when any transformations are used or one wants to alleviate
biases derived from effects of sample size and varying diversities (Wolda, 1981).
Canonical correspondence analysis (CCA) was used to determine relationships between
treatment types and relationships among habitat variables and species associations.
Variables with high correlation (P correlation >0.7) were eliminated to avoid over-fitting
the model. Only species with greater than five detections were analyzed to avoid bias. A
forward selecting Monte Carlo permutation test (499 iterations) was performed to
determine significance of bird-habitat relationships under the reduced model. CANOCO
v. 4 was used to perform all statistical analysis related to the CCA. All statistical tests
were considered significant at 0.05 alpha level. A MANOVA with repeated measures
was performed to detect any interaction between treatments and year on the avian
community measurements (species and guild abundance, species richness, ShannonWeiner diversity, and species evenness) and also individual species response of most
frequently encountered birds. Individual species response of common summer breeders
was assessed along with defined avian guild responses. Intermediate responses was
explored, along with pretreatment and immediate responses on 18 of the research stands
previously studied (Wick, 2008). Due to a staggering of the experimental design, only a
glimpse into relationships in year eight could be asserted since only one replicate was
62
used during statistical analysis. All other years and treatments had three replicates, so
when looking at the eighth year following treatment, one must be careful interpreting
results due to low sample size. All statistical analyses were run using SPSS v. 20 with
results being reported as mean with standard error, and statistical tests will be declared
significant at an alpha level of 0.05.
Results
In 2012, there were 1886 total individual detections comprised of 48 passerine
species among three surveys on 27 of the research stands of blocks 1-3. In 2013, there
were 2870 individual detections comprised of 50 passerine species among three surveys
on 36 of the research stands of blocks 1-4. Diversity certainly increased 6-8 years
following treatment compared to pretreatment (35 spp.) and initial post-treatment (40
spp.). Between 2012 and 2013, two new species were detected, the Blue-winged Warbler
and the Yellow-throated Warbler. Several species were detected 6-8 years post initial
treatment that were never detected pretreatment or initially following treatment, these
include: Red-bellied Woodpecker, Eastern Towhee, Blue-winged Warbler, Yellowthroated Warbler, Red-headed Woodpecker, Ruby-throated Hummingbird, and Northern
Flicker.
Canonical Correspondence Analysis
Four CCA’s were performed to determine relationships between environmental
habitat data and avian species abundance. Data was derived from the 2013 bird surveys
(Appendix B, Table 21) and habitat surveys conducted in the 2013 season. The first used
63
all birds as the input species data and environmental variables were reduced to ensure a
more simplified graphically explanation of species-environment relationships. Highly
correlated variables were identified and removed using the variable inflation factor (VIF)
in the log output (Montgomery & Peck, 1982). Variables with a VIF >20 were removed
from the analysis, resulting in 11 variables used in the CCA. The next three analyses
used guild abundance as the species input data. The following guilds were accessed:
nesting, foraging, and habitat associations. For the CCA with all bird species included,
species-habitat correlations were high (r>.85). In the first three axis, species abundance
and microhabitat explained approximately 34% (total inertia=0.878) of variance. The
first axes accounted for 16.7 % of variance (eigenvalue=0.147) in species abundance and
37.8 % of the species-habitat correlation. The second axis accounted for 9.6%
(eigenvalue=0.084) of species abundance and 21.4% of the species-habitat correlation.
Most variation is captured in the first two axes, with eigenvalues lower for the third and
fourth axes. The CCA for nesting guild abundance explained approximately 51% of the
total variation in nesting guild abundance and the environment. Again, axes one and two
explained most of the variation. Axis one explained 28% (eigenvalue= 0.035) of the
variation and axis two explained 16% (eigenvalue=0.02). The CCA for habitat
association guild abundance explained about 55% (total inertia=0.056) of the variation of
guild abundance. The first axis accounted for 42% (eigenvalue=0.023) of the variation
while the second contributed 14% (eigenvalue=0.008) of the variation. In this analysis
the third axis contributed more variation (30%) than the second, (eigenvalue=0.017). The
CCA for foraging guild abundance did not explain variation in foraging guild abundance
as well as the other analysis, with only 35% variation (total inertia=0.051) in foraging
64
guild abundance explained. The first (eigenvalue=0.011) and fourth axis (0.019)
explained most of the variation in this dataset, but strong associations were not
discovered in the output.
Figure 14. Stand ordination plot (C=control, B=burn, T=thin only, TB=thin and burn).
65
Figure 15. First and second canonical correspondence axes for microhabitat characteristics and avian
species abundance 6-8 years after silviculture treatments, Bankhead National Forest, AL, 2013.
Microhabitat codes: US=understory, MS=midstory, OS=overstory, Litter_c =litter cover, Litter_D=litter
depth, Woody_co= woody vegetation cover, Herb_co=herbaceous vegetation cover, Canopy=canopy,
BA=basal area, BA_snag=basal area of snags Avian species codes: ACFL=Acadian flycatcher, BAWW=
black-and-white warbler, BGGN=blue-gray natcatcher, BHVI=blue-headed vireo, BHCO=brown-headed
cowbird, BHNU=brown-headed nuthatch, BLJA=blue jay, BTGW=black-throated green warbler
BWWA=blue-winged warbler, CACH=Carolina chickadee, CAWR=Carolina wren, DOWO=downy
woodpecker, EATO=eastern towhee, EAWP=eastern wood-peewee, GCFL=great-crested flycatcher,
HOWA=hooded warbler, INBU=indigo bunting, KEWA=Kentucky warbler, MODO=mourning dove,
NOCA=northern cardinal, NOPA=northern parula, OVEN=ovenbird, PIWA=pine warbler, PIWO=pileated
woodpecker, PRAW=prairie warbler, RBWO=red-bellied woodpecker, REVI=red-eyed vireo,
RHWO=red-headed woodpecker, SCTA=scarlet tanager, SUTA=summer tanager, TUTI=tufted titmouse,
WEWA=worm-eating warbler, WEVI=white-eyed vireo, WOTH=wood thrush, YBCH=yellow-breasted
chat, YTVI=yellow-throated vireo.
66
Figure 16. First and second canonical correspondence axes for microhabitat characteristics and habitat
association guild abundance 6-8 years after silviculture treatments, Bankhead National Forest, AL, 2013.
Microhabitat codes: US=understory, MS=midstory, OS=overstory, Litter_c =litter cover, Litter_D=litter
depth, Woody_co= woody vegetation cover, Herb_co=herbaceous vegetation cover, CWD=coarse woody
debris, Canopy=canopy, BA=basal area, BA_snag=basal area of snags Guild Codes: HO/E=open/edge
species, HInterio=interior species, HI/E=Interior/edge species.
67
Figure 17. First and second canonical correspondence axes for microhabitat characteristics and nesting
guild abundance 6-8 years after silviculture treatments, Bankhead National Forest, AL, 2013. Microhabitat
codes: US=understory, MS=midstory, OS=overstory, Litter_c =litter cover, Litter_D=litter depth,
Woody_co= woody vegetation cover, Herb_co=herbaceous vegetation cover, CWD=coarse woody debris,
Canopy=canopy, BA=basal area, BA_snag=basal area of snags Guild codes: NCavity=cavity nesters,
NGround-ground nesters, NParasit=parasite nesters, NShrub=shrub nesters, Ntree=tree nesters.
68
Figure 18. First and second canonical correspondence axes for microhabitat characteristics and foraging
guild abundance 6-8 years after silviculture treatments, Bankhead National Forest, AL, 2013. Microhabitat
codes: US=understory, MS=midstory, OS=overstory, Litter_c =litter cover, Litter_D=litter depth,
Woody_co= woody vegetation cover, Herb_co=herbaceous vegetation cover, Canopy=canopy, BA=basal
area, BA_snag=basal area of snags Guild codes: FArial=aerial foragers, FBark=bark foragers,
FFoliage=foliage foragers, FGround=ground foragers.
Individual Species Response
Examination included how frequently encountered individual bird species
responded to silviculture treatments and their temporal response 6-7 years following
initial treatment. The terms density and abundance are used interchangeably throughout
the text, but refer to the same measure of the population estimate for that particular
species. This measure is calculated as the mean number of individual birds/900 meters of
transects. A MANOVA with repeated measures, year the within subjects, repeated
measure, and block and treatment the between subjects factors resulted in many species
69
showing individual effects, or a combination of effects in response to silviculture
treatment in the BNF. Five species displayed a block effect, twelve species showed
treatment effects (positive or negative) in response to silviculture treatment, 23 species
showed a year effect, and eight species showed a treatment/year interaction. A treatment
effect, year effect and treatment/year interaction (Ptreat=0.004, Pyear<0.001, Ptreat*yr=0.008;
Table B.2, Figure 19) was examined in the Acadian Flycatcher. The treatment/year
interaction was in the pretreatment, with highest numbers present in LTxFB. Lower
densities were seen in B, HT, LT, and HTxFB stands.
Figure 19. Treatment/year interaction of Acadian Flycatcher mean density following silvicultural
treatments in the Bankhead National Forest, AL, Pretreatment, 1-yr post, 6-yr post, and 7-yr posttreatment. Abbreviated labels are denoted as C = control, FB =frequent burn only (3 year interval), HT=
heavily thinned LT= lightly thinned, HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB=
lightly thinned with frequent burn (3 year interval).
70
The Carolina Chickadee had year and treatment/year effects (Pyr<0.001, Ptreat*yr=0.036;
Table B.2, Figure 20). Seven years following treatment, the Carolina Chickadee
responded positively and abundances were highest in FB, HTxFB, and LTxFB stands.
Figure 20. Treatment/year interaction of Carolina Chickadee mean density following silvicultural
treatments in the Bankhead National Forest, AL, Pretreatment, 1-yr post, 6-yr post, and 7-yr post-treatment.
Abbreviated labels are denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily
thinned LT= lightly thinned, HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly
thinned with frequent burn (3 year interval).
The Eastern Towhee displayed a treatment effect, year effect, and treatment/year
interaction (Ptreat=0.01, Pyear<0.001, Ptreat*yr=0.03; Table B.2, Figure 21). The
treatment/year interaction was shown six years following initial treatment, with the
Eastern Towhee was most abundant in HTxFB and LTxFB stands, and lowest in C and B
71
stands. No differences were shown between HT and LT and C and B or HTxFB and
LTxFB.
Figure 21. Treatment/year interaction of Eastern Towhee mean density following silvicultural treatments in
the Bankhead National Forest, AL, Pretreatment, 1-yr post, 6-yr post, and7-yr post-treatment. Abbreviated
labels are denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily thinned LT=
lightly thinned, HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly thinned with
frequent burn (3 year interval).
The White-eyed Vireo displayed a year and treatment/year interaction (Pyear<0.001,
Ptreat*yr=0.02; Table B.2, Figure 22), with high densities found 6-7 years post-treatments
and very few detections pretreatment and one year post. The treatment/year interaction
was shown in the seventh year following initial treatment with higher abundances in LT,
HT, and HTxFB stands compared to C, FB, and LTxFB stands.
72
Figure 22. Treatment/year interaction of White-eyed Vireo mean density following silvicultural treatments
in the Bankhead National Forest, AL, Pretreatment, 1-yr post, 6-yr post, and 7-yr post-treatment.
Abbreviated labels are denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily
thinned LT= lightly thinned, HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly
thinned with frequent burn (3 year interval).
The Red-bellied Woodpecker (Melanerpes carolinus) displayed block, treatment, year,
and treatment/year interaction effects (Pblock=0.05, Ptreat=0.001, Pyr<0.001,
Ptreat*yr==0.005; Table B.2, Figure 23). The treatment/year interaction was displayed six
years post-treatment, and highest densities were found LTxFB stands compared to all
other treatments. Heavily thinned and HTxFB stands had similar densities to those of FB
and LT stands, but were still higher in abundance than C stands. Frequently burned and
LT stands were comparable to C stands.
73
Figure 23. Treatment/year interaction of Red-bellied Woodpecker mean density following silvicultural
treatments in the Bankhead National Forest, AL, Pretreatment, 1-yr post, 6-yr post, and 7-yr post-treatment.
Abbreviated labels are denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily
thinned LT= lightly thinned, HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly
thinned with frequent burn (3 year interval).
The Red-headed Woodpecker (Melanerpes erythrocephalus) displayed both a year effect
and a treatment/year interaction (Pyr=0.004, Ptreat*yr=0.01; Table B.2, Figure 24) with
highest abundances in years six and seven in HTxFB and LTxFB stands. Both the Redbellied Woodpeckers and the Red-headed woodpeckers were not present in any of the
research stands pre-treatment or one year post-treatment.
74
Figure 24. Treatment/year interaction of Red-headed Woodpecker mean density following silvicultural
treatments in the Bankhead National Forest, AL, Pretreatment, 1-yr post, 6-yr post, and 7-yr post-treatment.
Abbreviated labels are denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily
thinned LT= lightly thinned, HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly
thinned with frequent burn (3 year interval).
The Prairie Warbler had block, treatment, year, and treatment/year interaction
(Pblock=0.02, Ptreat=0.003, Pyear<0.001, Ptreat*yr==0.001; Table B.2, Figure 25). The
treatment/year interaction was displayed six years post-treatment and showed abundances
to be highest in LTxFB stands, followed by HT, LT, and HTxFB stands. Control and FB
stands had significantly lower densities than all other treated stands. Treatment effects
were similar in the seventh year; however, LT stands no longer differed in abundances
from the control stands or other treated stands.
75
Figure 25. Treatment/year interaction of Prairie Warbler mean density following silvicultural treatments in
the Bankhead National Forest, AL, Pretreatment, 1-yr post, 6-yr post, and 7-yr post-treatment. Abbreviated
labels are denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily thinned LT=
lightly thinned, HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly thinned with
frequent burn (3 year interval).
The Black-and-white Warbler had a treatment effect (Ptreat=0.008; Table B.2, Figure 26)
with higher densities found in heavily thinned stands, but lower densities seen in stands
receiving burns (HTxFB, FB, LTxFB). There were no differences in Black-and-white
Warbler abundance among control stands and lightly thinned stands over the course of
the study.
76
Figure 26. Treatment interaction of Black-and-white Warbler abundance following silvicultural treatments
in the Bankhead National Forest, AL, Pretreatment, 1-yr post, 6-yr post, and 7-yr post-treatment.
Abbreviated labels are denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily
thinned LT= lightly thinned, HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly
thinned with frequent burn (3 year interval).
There was no difference among C, HT, and LT. The Eastern Wood- pewee showed both
a treatment and year effect (Ptreat=0.04, Pyear=0.04; Table B.2, Figure 27). Highest
densities were found in stands receiving any disturbance, and HTxFB and LTxFB stands
had significantly higher abundances than C and FB stands, but similar abundances to HT
and LT stands. Eastern Wood-pewees were not present pretreatment, and years six and
seven do not statistically differ in abundance.
77
Figure 27. Treatment interaction of Eastern Wood-Pewee abundance following silvicultural treatments in
the Bankhead National Forest, AL, Pretreatment, 1-yr post, 6-yr post, and 7-yr post-treatment. Abbreviated
labels are denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily thinned LT=
lightly thinned, HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly thinned with
frequent burn (3 year interval).
The Summer Tanager displayed a treatment effect (Ptreat=0.001; Table B.2, Figure 28)
with highest densities found in LTxFB compared to all other treatments. There were no
significant differences in results of abundance of the Summer Tanager shown in the
stands that underwent thinning, in the stands undergone thinning and prescribed burning,
or in the stands only undergoing prescribed burning.
78
Figure 28. Treatment interaction of Summer Tanager abundance following silvicultural treatments in the
Bankhead National Forest, AL, Pretreatment, 1-yr post, 6-yr post, and 7-yr post-treatment. Abbreviated
labels are denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily thinned LT=
lightly thinned, HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly thinned with
frequent burn (3 year interval).
The Pileated Woodpecker (Dryocopus pileatus) showed a treatment effect (Ptreat=0.03;
Table B.2; Figure 29) with higher densities in LTxFB than in C, FB, HT, or LT stands.
No significant difference in Pileated Woodpecker abundance was shown between the
LTxFB stands and the HTxFB stands.
79
Figure 29. Treatment interaction of Pileated Woodpecker abundance following silvicultural treatments in
the Bankhead National Forest, AL, Pretreatment, 1-yr post, 6-yr post, and 7-yr post-treatment. Abbreviated
labels are denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily thinned LT=
lightly thinned, HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly thinned with
frequent burn (3 year interval).
The Red-eyed Vireo had a year effect (Pyr<0.001; Table B.2) with highest densities being
in the pretreatment and lowest densities six years post-treatments. The Yellow-breasted
Chat (Icteria virens) had both a treatment and year effect (Ptreat=0.008, Pyear<0.001; Table
B.2; Figure 30). Higher densities were found in HTxFB and LTxFB stands, while the
lowest densities were found in C stands. HT and LT stands were also had significantly
higher densities than C stands, but not FB stands. A temporal response was apparent,
with highest densities found six years post-treatment. This species was not found
pretreatment.
80
Figure 30. Treatment interaction of Yellow-breasted Chat abundance following silvicultural treatments in
the Bankhead National Forest, AL, Pretreatment, 1-yr post, 6-yr post, and 7-yr post-treatment. Abbreviated
labels are denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily thinned LT=
lightly thinned, HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly thinned with
frequent burn (3 year interval).
The Brown-headed Nuthatch displayed both a treatment and year effect (Ptreat<0.001,
Pyr=0.005; Table B.2; Figure 31), with highest densities in HTxFB and LTxFB stands
compared to all other stands. Temporally, the highest densities were found six years
post-treatment compared to pre and one year post-treatments. No differentiation was
found between six and seven years post initial treatment.
81
Figure 31. Treatment interaction of Brown-headed Nuthatch abundance following silvicultural treatments
in the Bankhead National Forest, AL, Pretreatment, 1-yr post, 6-yr post, and 7-yr post-treatment.
Abbreviated labels are denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily
thinned LT= lightly thinned, HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly
thinned with frequent burn (3 year interval).
The Brown-headed Cowbird also showed a treatment and year effect (Ptreat=0.001,
Pyr=0.02; Table B.2; Figure 32) with highest abundance of this species occurring in
LTxFB stands. Heavily thinned and HTxFB stands also had higher densities than C and
FB stands. Densities were higher one year post initial treatment, compared to all other
years. Densities were similar in years six and seven.
82
Figure 32. Treatment interaction of Brown-headed Cowbird abundance following silvicultural treatments in
the Bankhead National Forest, AL, Pretreatment, 1-yr post, 6-yr post, and 7-yr post-treatment. Abbreviated
labels are denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily thinned LT=
lightly thinned, HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly thinned with
frequent burn (3 year interval).
The Great-crested Flycatcher (Myiarchus crinitus) only displayed a year effect
(Pyr=0.005; Table B.2) with densities highest pretreatment compared to all other years.
The Hooded Warbler also only showed a year effect (Pyr=0.03; Table B.2) with
pretreatment abundances being higher than one year post silvilculture treatment.
Numbers of Hooded Warblers have increased since treatment, but decrease in the year of
burns (year seven). The Northern Cardinal (Cardinalis cardinalis) displayed only a year
effect (Pyr=0.009; Table B.2) with higher abundances found in 6-7 years post- treatment
compared to one year post-treatment. The Pine Warbler (Pyr=0.02; Table B.2) displayed
year effect as well, with higher abundances of this species found pretreatment. The Pine
83
Warbler displayed differences among year six and pretreatment, with pretreatment having
higher abundances. The Yellow-billed Cuckoo (Coccyzus americanus) showed a year
effect (Pyr<0.001; Table B.2) with abundances lower 6-7 years post-treatment than before
treatment implementation. The Northern Parula (Setophaga americana) showed a year
effect (Pyr=0.004; Table B.2), with higher densities seven years post-harvest than
pretreatment or one year post. Six years post-treatments shared similar densities with the
other years. The Eastern Phoebe (Sayornis phoebe) had a year effect (Pyr=0.008; Table
B.2) with highest densities 6-7 years following treatments. The Downy Woodpecker
(Picoides villosus) showed a year effect (Pyr<0.001; Table B.2) with higher densities 6-7
years post-treatment than pretreatment or one year post-treatment. A few species
displayed a block effect only, Black-throated Green Warbler (Setophaga virens)
(Pblock=0.03; Table 18), Tufted Ttitmouse (Baeolophus bicolor) (Pblock=0.03; Table B.2),
and Kentucky Warbler (Geothlypis formosa) (Pblock=0.02; Table B.2).
Avian Community Response
Among the community variables, Shannon-Weiner diversity indices displayed
block, treatment, and year effects (Pblock=0.009, Ptreat=0.004, Pyear<0.001; Table B.3) in
response to silviculture treatment. Diversity was highest in LT stands and lowest in C,
and diversity increased in all treated stands compared to controls. Both thinned and
HTxFB stands also had higher diversity than FB stands. Six years post-treatment
diversity was the highest. Species richness (Ptreat=0.04, Pyear<0.001; Table B.3) displayed
both treatment and year effects, and showed a significant difference one year following
initial treatments. No statistical differences were found among all stands between
84
pretreatment and 6-7 years post-treatment for species richness. Richness increased in all
treated stands compared to controls. Frequently burned stands were similar to all other
treatments and the control stands. Relative bird abundance had block, treatment, and year
effects (Pblock=0.03, Ptreat=0.03, Pyear<0.001; Table B.3). Abundance was highest six
years following treatment, and was higher in all treated stands compared to control
stands. The shrub nesting guild displayed both a treatment and year effect (Ptreat=0.002,
Pyear=0.04; Table B.3) with shrub nester abundance being highest in HT, LT, HTxFB, and
LTxFB stands. Abundance of shrub nesters was lowest in C and FB stands. No
statistical differences were found among HT, LT, HTxFB, or LTxFB stands.
Temporally, shrub nester density was highest six years post-harvest compared to one year
post-treatment.
Cavity nesters displayed both treatment and treatment/year effects (Ptreat=0.03,
Ptreat*yr=0.03; Table B.3, Figure 34). Pretreatment and intermediate responses were
similar. Tree nesters showed only a treatment/year interaction (Ptreat*yr=0.03; Table B.3,
Figure 33). Six years following treatment, cavity nesters were most abundant in LTxFB
stands, compared to all other treatments. Lightly thinned stands had more cavity nesters
than C stands, but were similar in abundance to FB, HT, and HTxFB stands.
85
Figure 13. Treatment/year interaction of tree nesting guild mean density following silvicultural treatments
in the Bankhead National Forest, AL, Pretreatment, 1-yr post, 6-yr post, and 7-yr post-treatment.
Abbreviated labels are denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily
thinned LT= lightly thinned, HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly
thinned with frequent burn (3 year interval).
Figure 2. Treatment/year interaction of cavity nesting guild abundance following silvicultural treatments in
the Bankhead National Forest, AL, Pretreatment, 1-yr post, 6-yr post, and 7-yr post-treatment. Abbreviated
labels are denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily thinned LT=
lightly thinned, HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly thinned with
frequent burn (3 year interval).
86
Arial foraging guild abundance displayed a treatment effect (Ptreat=0.01; Table B.3).
Highest densities were found in LTxFB stands, and lowest densities were shown to be in
HT, C, and FB stands. No differences were found between C, LT, FB, and HTxFB
stands. Foliage foraging abundance showed treatment and year effects (Ptreat=0.004,
Pyear=0.02 Table B.3). Stands with higher densities of foliage foragers included the FB,
C, and LT stands. Strong differences were not seen among treatments, but C and FB
stands did statically differ from HT, HTxFB and LTxFB stands (with lower densities of
foliage foragers). Ground foragers displayed both a treatment and year effects in
response to silviculture treatments (Ptreat=0.004, Pyear<0.001; Table B.3). Ground forager
densities were higher in HTxFB and LTxFB stands compared to C, FB, HT, and LT
stands. Temporally, no differences occurred between pretreatment and 6-7 years posttreatment. Densities of ground foragers show slight increase in year of burns.
Neotropical migrants displayed both a treatment and year effect to silvilcuture treatments
(Pblock= 0.002, Ptreat=0.000, Pyear0.000 and Ptreat*yr=0.003; Table B.3, Figure 35). Six year
following treatment, neotropical migrants had lowest abundances in C and FB stands.
Abundance increased in HT and LT stands, but HTxFB and LTxFB stands had the
highest abundances. Seven years following initial treatments, only FB stands had lower
abundances than any other treatments, but all other treatments were similar in abundance.
87
Figure 35. Treatment/year interaction of tree neotropical migrant abundance following silvicultural
treatments in the Bankhead National Forest, AL, Pretreatment, 1-yr post, 6-yr post, and 7-yr post-treatment.
Abbreviated labels are denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily
thinned LT= lightly thinned, HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly
thinned with frequent burn (3 year interval).
Residents showed both a treatment effect and a treatment/year interaction (Ptreat=0.003,
Ptreat*yr=0.05; Table B.3, Figure 36). Six years following initial treatment, resident density
differences were seen between C, FB, and LTxFB stands, with lower densities in stands
receiving no disturbance, and slightly higher in HT, LT, HTxFB, and LTxFB stands.
Seven years following treatment, a treatment/year interaction was also noted with highest
densities in LTxFB and HTFB compared to C and LT stands.
88
Figure 36. Treatment/year interaction of tree resident species abundance following silvicultural treatments
in the Bankhead National Forest, AL, Pretreatment, 1-yr post, 6-yr post, and 7-yr post-treatment.
Abbreviated labels are denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily
thinned LT= lightly thinned, HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly
thinned with frequent burn (3 year interval).
Interior/edge habitat specialists displayed treatment, year, and treatment/year interactions
(Ptreat=0.02, Pyear=0.01, Ptreat*yr=0.02; Table B.3, Figure 37). Six years post-treatment,
interior/edge species densities were found to be different among all treated stands and
LTxFB stands, with LTxFB stands supporting more interior/edge species than controls or
other treatments. Similarities were noted among the other treatments: HT, LT, and
HTxFB. Seven years following treatment, C and HT stands did not differ from any other
stands, but HTxFB and LTxFB stands had significantly more interior/edge species than
FB or LT stands.
89
Figure 37. Treatment/year interaction of interior/edge habitat guild abundance following silvicultural
treatments in the Bankhead National Forest, AL, Pretreatment,1-yr post, 6-yr post, and 7-yr post-treatment.
Abbreviated labels are denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily
thinned LT= lightly thinned, HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly
thinned with frequent burn (3 year interval).
Open/edge species showed treatment, year, and treatment/year interactions (Ptreat<0.001,
Pyear=0.001, Ptreat*yr=0.006; Table B.3, Figure 38) as well. Six years following treatments
LT, HTxFB and LTxFB had highest abundances compared to C and FB stands. Seven
years following initial treatment, HT, LT, HTxFB and LTxFB stands had higher
densities than C and FB stands. The highest densities of open/edge species were found in
HTxFB, LTxFB, HT, and LT stands, while the lowest densities were in C and FB stands.
There was a strong temporal response for this group, likely because forest succession
over time encouraged occupancy of these scrub-shrub dependent species. Pretreatment
numbers were fairly low for this group (4.67) with higher densities discovered 6-7 years
following treatment (11.38 and 13.82).
90
Figure 38. Treatment/year interaction of open/edge habitat guild abundance following silvicultural
treatments in the Bankhead National Forest, AL, Pretreatment,1-yr post, 6-yr post, and 7-yr post-treatment.
Abbreviated labels are denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily
thinned LT= lightly thinned, HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly
thinned with frequent burn (3 year interval).
Several guilds only displayed a year effect. Species evenness showed a year effect
(Pyear=0.05; Table 19) with evenness increasing following silviculture treatment. A clear
difference among pretreatment and 7 years post was displayed, but no differences among
the other years. Ground (Pyear=0.05; Table B.3) and parasite (Pyear<0.001; Table B.3)
nesting guilds also show a year effect. Parasite nester brown-headed cowbird densities
were highest one year following treatment, and 6-7 years post-harvest densities no longer
show a difference among the pretreatment numbers. Ground nesters density decreased
immediately following treatment, but 6-7 years post-harvest showed no significant
difference with pretreatment densities. Interior species also displayed a year effect
91
(Pyear=0.006; Table B.3) with densities decreasing immediately following treatment, but
showing no difference in densities 6-7 years post-treatment compared to pretreatment.
Morisita’s- Horn Similarity Index
Six years following harvest and initial burns, Morisita’s-Horn index of similarity
showed the bird community to be most similar between stands infrequently burned (0.81)
and control stands (1.00). Control stands were least similar to those stands subjected to
heavy thinning and infrequent burns (0.63) and light thin with infrequent burns (0.67).
Seven years following harvest, control stands are most similar to the infrequently burned
stands (0.88) but least similar to those stands that were under heavy thinning and frequent
burning (0.52). After seven years, pretreatment controls and those stands thinned and
burned still have the least similarities in the bird community, followed by those burn only
stands. Thinned stands are still dissimilar as well (0.69), but to a less degree than the
thinned and burned stands (0.67-0.58). When comparing pretreatment, immediate
response, and intermediate responses of the bird community, those stands both thinned
and burned are much different in species composition than control stands, thinned stands,
and burn only stands. Control stands have remained quite similar throughout the years
(0.9-0.8). Control stand species composition is the most similar among the burn only
stands one year after initial treatment (0.87), but is less similar after repeated fires, 6-7
years following initial treatments (0.71). The bird community is least similar among all
the treated stands between the pretreatment and intermediate time frames, proving that
temporality greatly impacts the avian community.
92
Table 4. Morisita’s-Horn similarity index for the breeding bird community six years following silviculture
treatment in Bankhead National Forest, AL, 2012-2013.
C
IB
FB
HT
LT
HTxFB
LT xFB
HT xFB
LT xFB
C
-
0.808
0.742
0.786
0.758
0.704
0.678
0.632
0.657
IB
0.808
-
0.795
0.838
0.816
0.786
0.788
0.707
0.732
FB
0.742
0.795
-
0.788
0.761
0.714
0.774
0.645
0.744
HT
0.786
0.838
0.788
-
0.9
0.889
0.889
0.85
0.881
LT
0.758
0.816
0.761
0.9
-
0.92
0.904
0.89
0.903
HTxFB
0.704
0.786
0.714
0.889
0.92
-
0.916
0.914
0.89
LTxFB
0.678
0.788
0.774
0.889
0.904
0.916
-
0.905
0.891
HTxIB
0.632
0.707
0.645
0.85
0.89
0.914
0.905
-
0.897
LTxIB
0.657
0.732
0.744
0.881
0.903
0.89
0.891
0.897
-
a
Abbreviated labels are denoted as C = control, IB = infrequent burn only (9 year burn interval), FB=
frequent burn only (3 year burn interval) HT = heavy thin, LT = light thin, HT xFB = heavy thin with
frequent burn (3 year burn interval), LT xFB = light thin with frequent (3 year burn interval), HTxIB=
heavy thin with infrequent burn (9 year burn interval), and LT xIB= light thin with infrequent burn (9year
burn interval)
Table 5. Morisita’s-Horn similarity index for the breeding bird community seven years following
silviculture treatment in Bankhead National Forest, AL, 2012-2013.
C
IB
FB
HT
LT
HTxFB
LTxFB
HTxIB
LTxIB
C
-
0.833
0.715
0.682
0.694
0.581
0.622
0.674
0.617
IB
0.833
-
0.714
0.667
0.72
0.595
0.611
0.696
0.624
FB
0.715
0.714
-
0.666
0.622
0.65
0.779
0.662
0.632
HT
0.682
0.667
0.666
-
0.862
0.806
0.778
0.9
0.873
LT
0.694
0.72
0.622
0.862
-
0.804
0.735
0.893
0.852
HTxFB
0.581
0.595
0.65
0.806
0.804
-
0.846
0.842
0.817
LTxFB
0.622
0.611
0.779
0.778
0.735
0.846
-
0.795
0.762
HTxIB
0.674
0.696
0.662
0.9
0.893
0.842
0.795
-
0.925
LTxIB
0.617
0.624
0.632
0.873
0.852
0.817
0.762
0.925
-
a
Abbreviated labels are denoted as C = control, IB = infrequent burn only (9 year burn interval), FB=
frequent burn only (3 year burn interval) HT = heavy thin, LT = light thin, HT xFB = heavy thin with
frequent burn (3 year burn interval), LT xFB = light thin with frequent (3 year burn interval), HTxIB=
heavy thin with infrequent burn (9 year burn interval), and LT xIB= light thin with infrequent burn (9year
burn interval)
93
94
0.716
0.729
0.679
IntB
IntT
IntT/B
0.687
0.791
0.712
0.766
0.81
0.808
0.848
0.85
0.862
0.89
-
0.881
PB
0.69
0.783
0.744
0.833
0.846
0.853
0.873
0.923
0.932
-
0.89
0.917
PT
0.696
0.722
0.783
0.83
0.865
0.818
0.878
0.888
-
0.932
0.635
0.707
0.726
0.855
0.7993
0.776
0.867
-
0.888
0.923
0.85
0.903
0.922
0.862
1C
PT/B
0.709
0.754
0.817
0.746
0.846
0.819
-
0.867
0.878
0.873
0.848
0.872
1B
0.858
0.856
0.766
0.733
0.881
-
0.819
0.776
0.818
0.853
0.808
0.792
1T
0.771
0.734
0.776
0.717
-
0.881
0.846
0.7993
0.865
0.846
0.81
0.783
1T/B
0.639
0.725
0.715
-
0.717
0.733
0.746
0.855
0.83
0.833
0.766
0.805
IntC
0.743
0.682
-
0.715
0.776
0.766
0.817
0.726
0.783
0.744
0.712
0.716
IntB
0.849
-
0.682
0.725
0.734
0.856
0.754
0.707
0.722
0.783
0.791
0.729
IntT
Abbreviated labels are denoted as PC = pretreatment control, PB = pretreatment with burn only, PT=
pretreatment thin only, 1C= one year post control, 1B= one year post burn only, 1T= one year post thin
only, 1T/B= one year post thin and burn combined, IntC= intermediate control, IntB= intermediate burn
only, IntT= intermediate thin only, IntT/B= intermediate thin and burn combined
a
0.805
0.872
1B
IntC
0.903
1C
0.783
0.922
PT/B
1T/B
0.917
PT
0.792
0.881
PB
1T
-
PC
PC
Table 6. Morisita’s-Horn similarity index for the breeding bird community before, one year post and
intermediately following silviculture treatment in Bankhead National Forest, AL, 2004-2013.
-
0.849
0.743
0.639
0.771
0.858
0.709
0.635
0.696
0.69
0.687
0.679
IntT/B
Table 7. Guild membership of species detected in 36 treated research stands on William B. Bankhead
National forest, 2012-2013.
Species
Code
Common Name
Scientific Name
ACFL
AMGO
BAWW
BTGW
BGGN
BHVI
BLJA
BWWA
BHCO
BHNU
CACH
CARW
CHWW
DOWO
EABL
EAKI
EAPH
EATO
EAWP
EWPW
GRCA
GCFL
HAWO
HOWA
INBU
KEWA
LOWA
MODO
NOCA
NOFL
NOPA
OVEN
PIWA
PIWO
PRWA
RBWO
REVI
RHWO
Acadian flycatcher
American goldfinch
Black-and-white warbler
Black-throated green warbler
Blue-gray gnatcatcher
Blue-headed vireo
Blue jay
Blue-winged warbler
Brown-headed cowbird
Brown-headed nuthatch
Carolina chickadee
Carolina wren
Chuck-will’s-widow
Downy woodpecker
Eastern bluebird
Eastern kingbird
Eastern phoebe
Eastern towhee
Eastern wood- peewee
Eastern whip-poor-will
Gray catbird
Great crested flycatcher
Hairy woodpecker
Hooded warbler
Indigo bunting
Kentucky warbler
Louisiana waterthrush
Mourning dove
Northern cardinal
Northern flicker
Northern parula
Ovenbird
Pine warbler
Pileated woodpecker
Prairie warbler
Red-bellied woodpecker
Red-eyed vireo
Red-headed woodpecker
RTHU
SCTA
SUTA
SWWA
TUTI
WITU
WBNU
WEVI
WEAW
WOTH
YBCH
YBCU
YTVI
YTWA
Ruby-throated hummingbird
Scarlet tanager
Summer tanager
Swainson’s warbler
Tufted titmouse
Wild turkey
White-breasted nuthatch
White-eyed vireo
Worm-eating warbler
Wood thrush
Yellow-breasted chat
Yellow-billed cuckoo
Yellow-throated vireo
Yellow-throated warbler
Empidonax virescens
Spinus tristis
Mniotilta varia
Setophaga virens
Polioptila caerulea
Vireo solitarius
Cyanocitta cristata
Vermivora cyanoptera
Molothrrus ater
Sitta pusilla
Poecile carolinensis
Tryothorus ludovicianus
Caprimulgus carolinensis
Picoides villosus
Sialia sialis
Tyrannus tyrannus
Sayornis phoebe
Pipilo erythrophthalmus
Contopus virens
Caprimulgus vociferus
Dumetella carolinensis
Myiarchus crinitus
Picoides villosus
Setophaga citrina
Passerina cyanea
Geothlypis formosa
Seiurus motacilla
Lenaida macroura
Cardinalis cardinalis
Colaptes auratus
Setophaga americana
Seiurus aurocapillus
Setophaga pinus
Dryocopus pileatus
Setophaga discolor
Melanerpes carolinus
Vireo olivaceus
Melanerpes
erythrocephalus
Archilochus colubris
Piranga olivacea
Piranga ruba
Limnothlypis swainsonii
Baeolophus bicolor
Meleagris gallopavo
Sitta carolinensis
Vireo griseus
Helmitheros vermivorus
Hylocichla mustelina
Icteria virens
Coccyzus americanus
Vireo flavifrons
Setophaga dominica
Nesting
Guild
Migration
Guild
Habitat
Guild
Forage
Guild
a
T
S
G
T
T
T
T
G
P
C
C
C
G
C
C
T
C
G
T
G
S
C
C
S
S
G
G
T
S
C
T
G
T
C
S
C
S
C
N
R
T
N
T
N
R
N
R
R
R
R
N
R
R
N
R
N
R
N
T
R
N
N
N
N
R
R
R
R
N
N
R
T
N
R
N
R
I
O/E
I
I
I/E
I/E
I/E
O/E
O/E
I
I/E
O/E
O/E
I/E
O/E
O/E
I/E
I/E
I/E
O/E
O/E
I/E
I
I
O/E
I/E
I/E
O/E
I/E
O/E
I/E
I
I/E
I
O/E
I/E
I/E
O/E
A
F
B
F
F
F
F
F
G
B
F
G
A
B
G
A
A
G
A
A
G
A
B
F
F
G
G
G
G
G
F
G
B
B
F
B
F
A
T
T
T
S
C
G
C
S
G
T
S
T
T
T
N
N
R
N
N
R
T
N
N
N
N
N
N
N
O/E
I
I/E
I/E
I/E
O/E
I
O/E
I
I/E
O/E
I/E
I/E
I/E
N
F
F
G
F
G
B
F
F
G
F
F
F
B
a. Classification: forage guild (A, aerial; F, foliage; G, ground, B, bark) (Ehrlich et al., 1986), nest location
(G, ground; S, shrub; T, tree; C, cavity) (Ehrlich et al., 1986), migratory destination (N, Neotropical
migrant; T, temperate migrant; R, resident) (Sauer et al.,1996, Imhof, 1976), and habitat association (O/E,
open-edge; I/E, interior-edge; I, interior) (Blake & Karr, 1987, Freemark & Collins, 1992).
95
Discussion
Many of the variables associated with the bird community changed in response to
silviculture treatment. After 6-7 years, changes in habitat characteristics contributed to
changes found in the bird community, whereas; immediately following treatments,
treatment effects impacting the bird community were not yet found to differ (Wick,
2008). For example, in a meta-analysis study researchers reported that studies with ≥4
years of data found ground foragers and cavity nesters to positively respond to burning
and thinning/burning throughout time (Kalies et al., 2010). The importance of surveying
over time following disturbance was manifested in the results that more clearly show how
the forest and avian communities are responding.
Diversity increased in stands that had been disturbed and was highest six years
post-treatment. A slight decrease in the seventh year was more than likely due to burning
prescriptions implemented in that year. Guilds such as the shrub nesters, cavity nesters,
ground foragers, aerial foragers, neotropical migrants, residents, interior/edge species,
and open/edge species all show treatment or treatment/year interactions, indicating that
they are experiencing a temporal response to the silviculture treatments. All of the guilds
increased in abundance in response to the disturbance regimes and densities were lower
in the control and burn only stands. Positive responses by these guilds indicate that the
disturbances have created habitat characteristics within the stands that these guilds can
utilize and successfully inhabit. Kilpatrick et al. (2010), found in their study on the upper
piedmont of South Carolina that nest abundance of shrub nesters, cavity nesters, ground
foragers, and migratory species were higher in thin/burn and burn stands than in stands
receiving no treatment (Kilpatrick et al., 2010). Ground foragers generally benefit
96
immediately following prescribed burning, because a specialized foraging habitat is
created, consisting of an open forest floor exposing insects and seeds (Blake, 2005).
However, this microhabitat is short lived when the leaf litter returns the following year
and bare ground essentially disappears, making ground foraging species to return to
pretreatment levels unless fires are prescribed more frequently (Dickson, 1995). Aerial
foragers’ positive response to treatments that included a prescribed fire was also shown in
other studies and can be attributed to the open understory that is created and provides
amble foraging habitat for this guild (Campbell et al., 2007; Greenberg et al., 2007;
Kalies et al., 2010). Cavity nesters responded positively to treatments, especially those
under light thinning and frequent burnings, although no increase in snag density was
found. The highest BA of snags was in control and burn only stands. Snag BA has been
shown to decrease immediately following treatment, and for cavity nesting birds to show
declines, however; in this study increases in cavity nesters and cavity nesters showed a
positive response to treatment regimes. Other studies suggested that other non-cavity
nesting species (ex. Hermit Thrush (Catharus guttatus)) may also benefit from snag
presence, given that snags provide cover, food, or singing perches (LeCoure et al., 2001;
Schulte & Niemi, 1998; Simon et al., 2002). Shrub nesters were most abundant six years
following treatment when the shrub component was most complex in three blocks of
research stands that had not been recently burned. However, shrub nesting abundances
decreased in the seventh year when burns were implemented in two blocks, and a
decrease of the shrub layer was apparent. Shrub nesters positive response to treatment
was not immediate; it took 1-2 years following a burn for habitat to be created and shrub
nesting species to be attracted to these stands. Another study in the southeastern US
97
supports this claim as well noting that the increase in stump sprouts, herbaceous cover,
and woody cover through time in response to the fire and thins, positively influence the
abundance of shrub nesting species (Kilpatrick et al., 2010). Residents also benefit from
the disturbance regimes, with lower densities in control and burn only stands.
Interior/edge species guild responded most positively to light thinning in stands with
burns. Light thins allowed interior birds to be represented in those stands, but created
enough edge that those species can also thrive. Strong conclusions cannot be extracted
from this guild since this guild contains the most species and species that do not share
common nesting or foraging behaviors. Open/edge species experienced a treatment/year
interaction, indicating change in forest microhabitat characteristics driven by the
treatments. A habitat created through time encouraged occupancy of these species that
depend on open conditions and complex edge components. This response is most
pronounced after 6-7 years, due to repeated burning implemented in the stands. Burning
alone may not create a diverse enough habitat to attract these guilds. Studies have shown
fire intensity to largely affects the avian response. Low intensity fires alone may not be
able to change stand characteristics, and therefore not influence the avian community
response (Greenberg et al., 2007). Low intensity burn prescriptions mimic small scale
changes in the forest structure, and therefore small changes in the overall avian
community. Burning in combination with thinning influences the avian community
additionally, since canopy gaps are created and regeneration of herbaceous and woody
cover is enhanced. Thus; disturbances have varying effects on the vegetation and
therefore impacting the avian community (Greenberg et al., 2007; Simon et al., 2002;
Perry & Thill, 2013).
98
Many of the avian community variables displayed a year effect. Species
evenness, richness, and abundance decreased in the year following treatment most likely
due to the abrupt change in the environment. Ground nesters, along with interior species,
experience an immediate decline following initial treatments, but these guilds recovered
6-7 years post-treatment. Each of these guilds’ abundances are comparable to
pretreatment values indicating that overall the birds do recover relatively shortly after
treatment implication.
Individual bird response following silviculture treatment is complex and holds a
strong temporal component due to changes in the forest structure though stand
development impacting breeding bird habitat (Greenberg et al., 2007). The Acadian
Flycatcher is a species of concern which did display a treatment by year interaction in the
pretreatment. Another study showed this species to decline in harvested stands following
silviculture treatment, especially those removing higher quantities of BA; its need for a
mature closed canopy is apparent (Rodewald & Smith, 1998). In our study site Acadian
Flycatchers were detected frequently in burn only sites, indicating that burning probably
does not negatively impact this species but actually provides optimal foraging habitat.
Aquilani et al. (2000) also showed densities of Acadian Flycatchers to increase slightly in
non-harvested burned sites (Aquilani et al., 2000). Other aerial foraging species such as
the Great-crested Flycatcher and Red-headed Woodpecker had a positive response to
thinning and burning with the highest densities occurred in LTxFB stands 6-7 years post
initial treatment. Repeated burns created the open habitat conditions in which these
species can forage; it has been documented that visibility and abundance of insects
increased following prescribed burns (Greenberg et al., 2007; Campbell et al., 2007).
99
Their foraging behavior is aerial hawking, described as perching on a branch overlooking
an opening and waiting for insects to pass by, at which time the bird attacks the prey
aerially. The Eastern Wood-pewee is the only flycatcher that showed a treatment effect,
with a positive response in all disturbed sites immediately following treatment and into
the sixth and seventh years following treatment. Other studies confirm this immediate
response to various harvest methods and burning prescriptions (Wilson et al., 1995;
Rodewald & Smith, 1998; Artman et al., 2001; Greenberg et al., 2007).
Ground nesting species are generally the group of species of most concern by the
ornithological community when considering the negative impacts of prescribed burning.
The timing of the burning and nesting times did not overlap in this study since the burns
took place in the dormant, late winter season; thus, breeding birds were not directly
impacted by the actual fire itself. However, the resulting temporary habitat conditions
following a fire may impact certain species by creating a less desirable nesting location
(Artman et al., 2001). Species recovery is based on the severity of the fire, vegetation
regrowth following a fire, and local habitat conditions. Habitat availability may be
maintained in localized areas where the fire was not able to reach or was less intense
(Artman et al., 2001). The Black-and-white Warbler was rarely detected in any stand that
received a burn. Black-and-white Warblers were found in thinned stands, but it did not
tolerate burning. Related studies indicate Black-and-white Warblers decrease in
abundance temporarily from burning prescriptions due to short term decreases in the
understory and litter depth (Greenberg et al., 2007). However, another study showed the
Black-and-white Warbler to have no response to fire treatment or time following fire
(Rush et al., 2012). The Ovenbird did not display a direct treatment effect, but the year
100
effect confirmed that there was a decline in the seventh year, indicating that the fire
prescriptions implemented in that year may have negatively impacted this species. Other
studies showed that the Ovenbird responses negatively to harvesting and do best in
control stands (Baker & Lacki, 1997; Rodewald & Smith, 1998). Other harvesting and
prescribed burning studies (Wilson et al., 1995; Artman et al., 2001; Blake, 2005; Rush et
al., 2012) showed the Ovenbird to have a negative response to subsequent prescribed
burns. Since only a year effect was displayed, it is hard to say with any confidence that
the ovenbird was negatively or positively impacted by silvilculture treatment in this
study. Neither the Kentucky Warbler (Geothlypis formosa) nor the Worm-eating Warbler
displayed a treatment or temporal response, indicating some degree of fire tolerance by
these species. Reported study results vary for these species. Some studies showed
Worm-eating Warblers more abundant in disturbed stands (Aquilani et al., 2000;
Augenfield et al., 2008). Others concluded they showed a negative response to harvests
and burning, at least in the short term (Rodewald & Smith, 1998; Artman et al., 2001).
This study showed Worm-eating Warblers do decline one year following treatment but
recover 6-7 years post-treatment, and repeated fires do not seem to have an adverse effect
on them. The slow moving and slow burning behavior combined with the spatial extent
of the dormant season burns, prescribed in this study, for unburned-isolated areas within
any given stand that could in turn be used as a suitable nesting site for many of these
ground nesting species (Hanners & Patton, 1998). The Worm-eating Warbler is known
to nest only on forested slopes, and those are the areas most likely isolated from thinning
and/or burning in this study. Because Kentucky Warblers require small gaps in the forest
canopy for successful habitation, they have been found to occur in stands not subjected to
101
active tree harvesting that does not create small gaps (Augenfield et at., 2008; Perry &
Thill, 2013). The Eastern Towhee and Blue-winged Warbler (Vermivora cyanoptera) are
also considered ground nesting species, but they are different in most other ground
nesting species that require interior or non-disturbed sites because they use early
successional habitats. They nest on the ground or very close to the ground, often situated
in a low lying shrub and have been shown to positively correlate to the abundance of
short shrubs in its breeding habitat and negatively correlate with overstory BA and
canopy cover (Yahner, 1986). The Eastern Towhee was found to nest in high densities of
regenerating red maple (Acer rubrum), blackberry thickets (Rubus allegheniensis), and
greenbrier (Similax spp.) (Gates & Dixon, 1981), and these species had the highest
densities in thinned and burned stands (Zak, 2008; personal observation). Thinned and
frequently burned sites have the highest densities of Eastern Towhees because burning
created a thick understory component that these species need for nesting success
(Kilpatrick et al., 2010). The low sample size of Blue-winged Warbler (n=9) inhibited
performance of statistical testing. Making any inferences involving this species was
limited. The Blue-winged Warbler was only detected on HTxFB and LTxFB stands,
those that will receive burns in the year 2014, or those that have received two burns to
date, the last burn implemented two years prior to my bird survey. This indicated that
repeated prescribed burns gradually create the habitat needed for habitat specialists. The
negative response some of the ground nesting species experienced can be attributed to the
changes in the forest floor in the year of a burn, since there was a short term reduction in
leaf litter and low understory used for nesting material and cover (Blake, 2005). Without
nesting cover provided by the dense understory, predatory response increased as well
102
discouraging nesting selection within these recently burned stands (Rich, 2012; Blake,
2005). Low intensity burning in the dormant season does alleviate negative impacts with
some ground species returning to burned stands one year following a prescribed burn.
The patchiness characteristics created by the low intensity, slow burning fires could have
allowed ground nesting species such as the Worm-eating Warbler to still be able to nest
within burned sites (Wick, 2008; personal observation).
Several woodpecker species show a positive response to treatment. The Pileated
Woodpecker densities were highest in the light thinned stands burned frequently. The
Red-headed Woodpecker showed similar response with all detections also being on
burned only stands or stands thinned and burned. The Red-headed Woodpecker and Redbellied Woodpecker were not detected in any of the research stands pretreatment.
Through heavy thinning and repeated burns, suitable habitat characteristic such as open
canopy has been created for these species. Several down dead trees are commonly
present in burned and thinned and burned stands, creating ample foraging opportunities
for these woodpecker species (personal observation).
Secondary cavity nesters show varying treatment and temporal responses. The
Carolina Chickadee responded positively in the seventh year when prescribed burns were
implemented, indicating that they responded positively in the short term in response to
fire. The Eastern Phoebe showed only a year response, indicating that through time
possible snag creation benefited this species by providing nesting structure, however;
neither the Carolina Wren (Tryothorus ludovicianus) nor the Tufted Titmouse showed a
treatment or year effect. No clear pattern of distribution for the Tufted Titmouse was
apparent throughout study sites in Kilpatrick et al.’s study either. Secondary cavity
103
nesters, such as the Carolina Chickadee and Brown-headed Nuthatch, did have higher
nest abundances in thin/burn sites (Kilpatrick et al., 2010).
Early successional, disturbance dependent species which were once not
represented in the stands in the pretreatment, have become some of the most detected
species 6-7 years following treatment. This shift in the bird community can be attributed
to the habitat conditions resulting from the silviculture treatments. The Indigo Bunting
responded positively to thinning and burning treatments, with highest densities in those
stands receiving both thins and frequent burns. Other studies show that Indigo Buntings
were more most abundant in stands that were clear cut, stands that had undergone a
combination of both understory cutting and selective harvest in the forest overstory, or
stands mechanically thinned and burned. This collaborated with our findings that Indigo
Buntings preferred intense silvicultural methods that created early successional habitats
(Greenberg et al., 2007; Perry & Thill, 2013; Rodewald & Smith, 1998). The Prairie
Warbler, a Partners in Flight Conservation Watchlist species had increased densities
immediately following treatment, and continue to increase in treated sites, collaborating
with other studies showing an affinity for disturbed forests with a large portion of
overstory trees removed, promoting understory growth (Gram et al., 2003; Kilpatrick et
al., 2010; Wick, 2008). Both the Prairie Warbler and White-eyed Vireo showed a strong
treatment/year interaction indicating that through time these species are responding
positively to the treatment regimes. The Yellow-breasted Chat also showed treatment
and year effects. With increasing disturbance all these species’ densities increase. Peaks
in density of Prairie Warbler, Yellow-breasted Chat, and White-eyed Vireo are often seen
4-8 years following harvests and/or additional disturbance, as we see in my study 6-8
104
years following initial treatments in the BNF (Perry & Thill, 2013; Rodewald & Smith,
1998). A constant supply of disturbance is needed to support and maintain populations of
highly disturbance dependent species such as the Prairie Warbler, Yellow-breasted Chat,
and White-eyed Vireo. Other studies collaborate with our findings that early
successional species benefit most from high intensity treatments that in time create
suitable habitats contributing to their breeding success (Kilpatrick et al., 2010; Perry &
Thill, 2013).
Species in the tree nesting guild showed various responses to thinning and
burning regimes. A couple tree nesters have shown a positive treatment or year effect
including the Summer Tanager and Northern Parula. The Summer Tanager had highest
densities in the lightly thinned frequently burned stands, collaborating with another recent
study showing this species to respond positively enough to be an indicator species on
burned stands in an oak dominated stand (Blake, 2005). The Northern Parula showed the
highest densities in year seven in the year of a burn, and after a replication of three burns,
indicating that immediate effects of fire positively affect this tree nesting species. The
Northern Parula has also responded positively to mechanical thinning and burning in
another study (Greenberg et al., 2007) and was most abundant in extensively harvested
(>40% of canopy removed) stands in a Louisiana study (Norris et al., 2009). The Blackthroated Green Warbler displayed a block effect, likely due to its affinity to inhabit and
nest near water in Virginia pine or hemlock stands, which are selectively located in some
of our stands dependent on treatment block. It is important to note that a tree nesting
species of conservation concern, the Wood Thrush did not display any negative responses
to either thinning or burning; this neutral response to thinning and burning was also found
105
in a study in Georgia (Powell et al., 2000). On the other hand, some species have shown
declines in abundance since treatment implementation, including the Yellow-billed
Cuckoo and Pine Warbler. The Yellow- billed Cuckoo exhibited a year effect, possible
in response to thinning. Densities were highest in the pretreatment compared to all other
years since harvest. Norris et al. also showed this species to drop in density when
harvests exceeded individual selection (Norris et al., 2009). The Pine Warbler showed a
negative year effect, but has returned to pretreatment levels by seven years post-harvest.
The Red-eyed Vireo displayed a year effect, with highest densities in the pretreatment
compared to all other years following treatment. Red-eyed Vireo is a closed canopy tree
nester, with highest densities also found in mature, non-harvested stands in other studies
(Baker & Lacki, 1997). These species are not of conservation concern and were common
throughout the study site, so any negative impacts from these select research stands were
likely not impacting the populations in the BNF.
Several species that did not show a treatment effect or did not have a high enough
sample size to perform an MANOVA test such as: Northern Flicker (Colaptes auratus),
Northern Cardinal, Gray Catbird (Dumetella carolinensis), Eastern Bluebird, and
Mourning Dove (Lenaida macrooura) but were detected more frequently during the year
of a prescribed fire. This suggested the temporary bare ground habitat following
prescribed burning provided ground foraging habitat in the short term. The Northern
Cardinal is also more abundant 6-7 years post-treatment than pretreatment, most likely
because this species is a shrub nester and more habitat has been created in treated stands
that they may utilize during breeding season. Eastern Wild Turkey (Meleagris
gallopavo) was also seen using burned areas, as seen in several other prescribed fire
106
studies (Blake, 2005; Greenberg et al., 2007; Saab & Powell, 2008). Note that many of
these species are ground foraging species, and the ground foraging guild experienced a
positive treatment effect. In the years following a prescribed fire, complex understory
components created habitat for several shrub nesting species. The Hooded Warbler is a
species preferring shaded habitats, and chose small forest gaps where shrubby habitat has
been created to nest and forage during the breeding season. The thinned stands have
provided this habitat, however a decrease in abundance of this species through time could
be due to the burning. The Hooded Warbler was equally dispersed among control and
thin only stands, but abundance decreased on thin/burn stands and burn only stands even
though no treatment effect could be determined statistically. Other studies show small
gaps created by tree fall or uneven-aged selection method positively affects the species
(Annand &Thompson 1997; Moorman et al., 2002). Pretreatment abundances were
nearly double that of 6-7 years post, possibly indicating control stands that consistently
have small canopy openings, provided by fallen trees, serve as the most suitable habitats.
Greenberg et al. showed Hooded Warbler numbers also decrease on mechanically thinned
and burned stands, due to the temporary reduction of the understory (Greenberg et al.,
2007). In the year of burns, it was apparent that the Hooded Warblers negatively
responded due to fire, but a direct treatment effect or treatment/year interaction was not
shown in this study. Another study indicated the Hooded Warbler can withstand low
intensity fires, categorized as the fires in this study (Blake, 2005; Wick, 2008). It is most
likely that this species cannot tolerate both thinning and burning disturbances combined
or frequent burns, at least in our study site; however, those stands receiving only one burn
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since treatment implementation, on the nine year return interval, supported Hooded
Warblers.
The only parasite nesting species present in my study was the brown headed
cowbird and it showed both a treatment and year effect. Due to its high affinity for edge
habitat, it is always considered a species of concern that may negatively impact other bird
species’ nesting success, especially in recently disturbed sites. This study showed an
increase in this species on disturbed sites following a strong gradient from control sites
having the lowest densities and highly thinned, frequently burned sites having the highest
densities of the nest parasite. The year effect did show that this species only responds
immediately, and densities return to pretreatment levels 6-7 years post-treatment. The
Brown-headed Cowbird is always a concern, but more so in highly fragmented forests.
The BNF is a contiguous forest where negative impacts and edge effects and parasite
nesters are considered minimum by past studies (Rudnicky & Hunter, 1993; Wilcove &
Robinson, 1990).
It is important to note that all resident species can exhibit sporadic population
changes from year to year, likely due to food resource availability and weather conditions
(droughts, floods, or tornados) and what may appear to be an influential treatment or year
effect could be due to various factors other than a response to the treatments (Marone,
1992). Examples of these resident species showing yearly fluctuations include in this
study include: Carolina Chickadee, Northern Cardinal, Pine Warbler, Eastern Phoebe,
and Downy Woodpecker. Also, there were limitations in the avian survey methodology,
so making inferences about avian species and community response to silvicultural
treatments must be closely examined and acknowledged. Multiple-observer biases could
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have been present. Three observers collected data over the course of this nine year, and
study and skill levels may have varied among researchers. Observer bias and observerexpectancy is common in avian studies and several resources conclude that biases are
inevitable; however, we tried to avoid observer biases by prepping our interns and
conducting pre- season surveys together with the previous observer (Balph &Balph,
1984; Simons, Alldredge, Pollock, & Wettroth, 2007). Double-observer approaches have
been tested in point count surveys, with contradictory results regarding improved
accuracy of species detection and abundance estimation (Nichols et al., 2000; Alldredge
et al., 2008). Although distance estimation was not used to make inferences about
populations or estimate density, this methodology has been shown to perform poorly in
hypothesis testing and showed large positive bias in density or abundance estimates
(Alldredge et al., 2008). Less detected species or species with similar vocalizations were
those that could have suffered from observer biasing in this study. The three vireos
detected in this study have very similar songs and rarely call, making it more difficult to
differentiate between them in the field for non-experienced ornithologists, resulting in
erroneous data. Several of the less detected species: Blue-winged Warbler, Wood
Thrush, Eastern Phoebe, Eastern Bluebird, have very unique songs, making it less likely
that there would be false-positives or false-negatives. Hypothesis testing was only
performed on the more common species, so no strong inferences could be made for the
less detected species in the study.
The canonical correspondence analysis was able to depict multivariate
relationships between avian abundance and the environment more clearly than running
simple ANOVAs and regressions. The graphical display from all avian species showed
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species that nest on the ground such as the Black-and-white Warbler and Worm-eating
Warbler were correlated to the presence of a complex understory with high litter depth.
The Hooded Warbler was also highly correlated with understory and litter depth as well,
likely because this species nests in low shrubs and females forage in low shrubs during
the breeding season. The Scarlet Tanager (Piranga olivacea), Wood Thrush, Red-eyed
Vireo, and Worm-eating Warbler were closely correlated to a more closed canopy
indicating their preference for a more interior forest, therefore found more in the control
stands. Species such as the Indigo Bunting, Red-headed Woodpecker, and Brown-headed
Nuthatch were all positively correlated to the presence of herbaceous cover and lower
canopy closure. Those stands with significant amounts of herbaceous cover were the
ones frequently burned and once thinned. Abundances of species preferring conditions
created by fire were found highest in those stands once thinned and frequently burned
(every three years). The Northern Cardinal and Pine Warbler were located in the center
of the ordination plot, indicating they are the more generalist species represented in the
study stands. Species such as the Ovenbird, Black-throated Green Warbler (Setophaga
virens), Summer Tanager, Carolina Wren, Pileated Woodpecker, and Downy
Woodpecker were related to stands with higher BAs and presence of snags. These
species typically had higher abundances in stands with only prescribed burning. Two
early-successional species found in high abundances in thinned or thin/burn stands were
the Prairie Warbler and Yellow-breasted Chat. They were correlated with presence of
woody cover and areas with less BA. The CCA for the habitat association guild showed
interior species to be plotted closer to components associated with litter, litter depth and
presence of midstory. One would think these species would be highly dependent on
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canopy closure and BA, but since these harvests were conducted 6-8 years ago succession
has created a structure in the thinned and thinned and burned stands that resemble a more
closed canopy due to regeneration. Interior/edge species were those more closely related
to the presence of overstory. This showed us that even after silviculture disturbance
forest interior birds are still able to utilize treated stands, whether it is for nesting or
foraging. Open/edge species were associated with the presence of herbaceous and woody
cover and less canopy and overstory. This showed that early-successional species are
still thriving in the areas that were once thinned and in stands both thinned and burned
even 6-8 years post-harvest. Nesting guild abundance ordination showed both cavity and
tree nesting species to be related to amount of canopy and BA of snags. Shrub nesting
species were associated with midstory vertical structure and areas with less BA; while
ground nesting species showed a direct correlation with litter depth and litter cover. The
nest parasite Brown- headed Cowbird did not show a clear correlation with any of the
habitat variables, probably due to low sample size. The foraging guilds did not show
high correlation with any of the variables. Arial and ground foragers were too far out in
the plot to make strong inferences, but the bark and aerial foragers were moderately
correlated with BA, BA of snags, and herbaceous cover. Foliage forages showed a strong
correlation with presence of high canopy cover and a midstory component. Ground
foragers showed a moderate correlation with litter depth and woody cover. Most bark
foragers did better in those areas not thinned or only burned, due to the quantity of
loblolly pines left standing in those stands. Foraging resources are likely more
homogeneously spread throughout the stands 6-8 years following treatment versus
immediately following thinning. Ground foragers were more likely to be found in burned
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stands. Keep in mind, foraging and nesting guild abundance may not be the best
descriptor of habitat selection in disturbed sites, due to the interchangeability of bird use.
For example, some species that typically nest in the interior were found to be foraging
within early-successional habitats, and this has been found in other studies (Schulte &
Niemi, 1998). Furthermore, each species has an unique set of environmental factors that
influence reproduction and survival, and characteristics chosen to define the guild, such
as nesting or foraging, may not be of equal importance for all species (Jaksic, 1981).
Control stands shared the most similarities between the bird communities of burn
only stands on a nine year interval likely because the amount of disturbance in those
stands is the least influential to the bird community. Since the burns only occurred every
nine years, the stand characteristics between controls and infrequently burned stands
remain analogous. Seven years following treatment, controls were again most similar to
nine year burn only stands, since they have not yet undergone a second burning
prescription. However, stands with 3-year burns underwent a burn before the breeding
season of 2013, and resulted in the bird community to be least similar between controls
and stands heavily thinned and burned. Intermediately, pretreatment control and burn
only stands shared less similarities in the bird community because these stands had
undergone disturbance every three years, immediately affected the bird occupancy in
those stands. Thinned only stands were still dissimilar, but had not undergone additional
disturbance since 2005/2006. Therefore, the bird community had not experienced abrupt
changes in the environment.
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CHAPTER 4
UNDERSTANDING AVIAN-HABITAT RELATIONSHIPS
THROUGH SITE OCCUPANCY MODELING OF SPECIES OF
CONCERN IN THE BNF
Introduction
Understanding wildlife-habitat relationships requires a consideration of a spatial
component, since ecological processes are scale dependent and interactions seemingly
occurring on a small scale could be part of a larger phenomenon (Loehle et al., 2006;
Mitchell et al., 2008). Detection probability must be considered and incorporated into the
modeling process to achieve a robust estimate of occupancy (MacKenzie et al., 2002). In
this study, the objective of species distribution modeling was to determine habitat-based
distributions of specific avian species of concern declared by Partners in Fight (Rich,
2004) and determine suitable habitat for these species, particularly in the BNF.
Development of occupancy models could add additional evidence of habitat selection
based on microhabitat covariates not only on the studies research sites, but throughout the
landscape of the BNF. The species selected were those vulnerable to forest management
practices and silviculture techniques such as thinning or fire prescriptions (ex. Wormeating Warbler) according to literature (Rodewald & Smith, 1998; Artman et al., 2001).
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Those who require periodic disturbance for creating early successional habitat achieved
through active forest management and are considered vulnerable were also assessed (ex.
Prairie Warbler) (Gram et al., 2003; Perry & Thill, 2013; Rodewald & Smith, 1998;
Wick, 2008). Management indicator species, showing declining trends in population size
throughout their ranges, including the BNF, such as the Brown-headed Nuthatch and the
Wood Thrush were also modeled (US Forest Service, 2014). Active forest management
in the BNF will change forest composition, and models could give forest managers
insight to how species of conservation concern will likely respond to large-scale forest
manipulation over the long term.
Study Site
The study site was located in the William B. Bankhead National Forest (BNF) in
Winston and Lawrence counties, located in northeast Alabama (Figure 39). The BNF is a
72,800 ha transitional forest within the southern Cumberland Plateau sub-region. It is
classified as a strongly dissected plateau, gentle slopes with good drainage, and soils
dominated by Hartsells, Linker, Nectar, Wynnville, Albertville, and Enders types
(Smalley, 1979). The forest’s current condition can be attributed to its disturbance
history. Forest conversion to agriculture land began in the 1800’s, with heavy timber
harvest and wildfires occurring in the 1900’s. In the 1930’s the forest was heavy planted
with loblolly pine (Pinus taeda) (Gaines & Creed, 2003). The forest has more recently
been the subject of southern pine beetle (Dendroctonus frontalis) infestations leaving
thousands of acres of dead standing pine (Gaines & Creed, 2003). All these past
disturbances contribute to the diversity, composition, and overall condition of the forest.
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The BNF initiated a Forest Health and Restoration Project (Gaines & Creed, 2003) to
promote healthy forest growth and ecosystem resilience via thinning and fire disturbance
to achieve projected future desired conditions and return the forest to a mixed oak-pine
upland ecosystem. Thinning favored the retention of hardwood species and was
implemented before the fire prescriptions. Prescribed burns on the northern portion of
the BNF are conducted in the dormant season (January-March) with low-intensity
understory fires. In the more southern portion of the forest, restoration goals were to
encourage growth of not only oak/hickory forest, but also create the once naturally
occurring shortleaf/bluestem woodlands- again using intermediately thinning of loblolly
pine and periodical prescribed burns to promote the growth of shade intolerant native
grasses, forbs, and shrubs (Gaines & Creed, 2003). Artificial reforestation of longleaf
pine was also used to replace forests lost by southern bark beetle infestations.
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Figure 39. Location of survey sites used in site occupancy models developed in William B. Bankhead
National Forest, AL.
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Methodology
The USDA Forest Service, Region 8, conducted bird point count data in
2005,2006, 2011, and 2012 (Breeding Season surveys), and these data were utilized for
the occupancy modeling. These bird counts were 10-minute fixed radius point counts.
Surveys began at sunrise and ended no later than 11:00 Central Standard Time (CST).
Field surveyors were all experienced in bird point count surveying, to avoid biasing
surveying accuracy. Vegetation data collected at each survey point, also collected by
BNF personnel, was combined with GIS landscape variables (elevation, climate, and
topography) to ascertain if patterns of habitat selection exist within these target species.
Site-occupancy modeling methodology which uses coupled hierarchical logistic
regression was used to model for both occupancy and detection. The software used was
PRESENCE v.5.8, and it has the capacity to model for both occupancy and detection.
PRESENCE software demonstrates the linear relationships between selected independent
covariates and dependents occupancy and detection using a logit link and maximum
likelihood approach. A priori or candidate models and covariates used in the models
were selected based on an information- theoretic approach derived from literature and
information known about the study site and the target species (Burnham & Anderson,
2002). Site covariates included habitat variables that most likely had a high ability to
predict occupancy and varied for each species dependent upon the focal species’s
breeding habitat preference and biology (Dettmers & Bart, 1999).
The models used were a single-season, single- species parameterization. Models
were built using 2005 and 2006 survey data, while models were tested using the survey
data from the years 2011 and 2012. Analysis began with the simplest null model keeping
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both occupancy and detection constant: psi(.), p(.). A two-stage modeling approach was
then used where detection is first modeled, holding occupancy constant. Next,
occupancy was modeled with site covariates combined with the best performing detection
models, using survey specific covariates produced in the first stage. To ensure no
multicollinearity among habitat variables, all candidate habitat covariates were screened
in SPSS v.20 using the multicollinearity function. If the variable inflation value (VIF)
was >5 then independence could not be assumed. All continuous covariates were
standardized using the z-transformation, and categorical variables were dummy coded to
improve performance of the software (MacKenzie, 2012). Ordinal categorical variables
were left as was, since the program can determine difference between 0 and 1, 1 and 2,
etc with increases in value. Model performance was weighed using the Akaike’s
Information Criterion (AIC) value associated with the model. Models with lower AIC
values were considered more parsimonious in nature, and therefore the models that could
likely explain patterns within the dataset. The delta AIC (ΔAIC) is the difference in the
best fitting model and subsequent models, and was used to rank models. Models with
ΔAIC <2 were considered to have an appropriate fit, while models with ΔAIC values 2-7
were considered less likely to explain occupancy but may influence occupancy, and those
with ΔAIC values>10 were thought to show no support in the state of occupancy.
Analytic statistical analysis using parametric bootstrapping and the Pearson’s chi- square
test was used to access goodness- of- fit of the models. Parametric bootstrapping
calculates a variance inflation factor, c-hat (MacKenzie & Bailey, 2004), and if the model
has a c-hat value close to 1 (within one-tenth of a decimal place) it is considered to be an
adequate descriptor of the data (Burnham & Anderson, 2002). If c-hat was lower than
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0.80 or higher than 1.5, the c-hat was adjusted. If the value was lower than 1, the c-hat
value was changed to 1, and if c-hat > 1 then a tool within the program is used to change
the appropriate value and make proper parameter adjustment counts in each model. This
accounted for model uncertainty and possible overdispersion of the dataset. Five hundred
parametric bootstraps were performed on each of the global models for each species to
access fit and supply the inflation factor, c-hat. When c-hat values were adjusted, the
AIC must also be adjusted, known as the quasi-AIC scores. The QAIC penalizes a model
for overdispersion of data by inflating the standard error values and also condensing the
AIC values among competing models (QAIC). Global models were used to access model
fit, because it is thought that if the data fits the global model, then it will also support the
more simplistic models resulting as derivatives of the global model (Burnham &
Anderson, 2002; Cooch & White, 2001). Most supported models, those with ΔAIC or
ΔQAIC values less <4 were used in modeling averaging. Model averaging takes the
average of the occupancy and detection estimates, along with standard error values from
the most supported models, giving the most likely estimates based on the most supported
models. Validity of the model was tested using test data. Test data used in this study was
2011 and 2012 survey data, and an observation was made on how well the model fitted
that “test” data. New occupancy coefficients were extracted from the test data, while
incorporating the same covariates as in each of the model-averaged occupancy models.
Model-averaging was only applied to the occupancy models, because model averaging
cannot be performed on detection probabilities in the program PRESENCE. Spearman
rank correlations were then derived by evaluating the correlation between the frequency
of observed and expected observation in each probability bin (Johnson et al., 2006).
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Number of actual observations from the test data were counted for each of the probability
bins, and it was expected that adequate models would show a high positive correlation
between observed and expected frequencies (Hansen et al., 2011; Johnson et al., 2006).
Spearman’s correlation coefficient is a statistical measure of the strength of a monotonic
relationship between paired data that is measured from -1 to +1. The statistic values and
power of correlation are as follows: 0.00-0.19=very weak; 0.20-0.39=weak; 0.400.59=moderate; 0.60-0.79=strong; 0.80-1.0=very strong. The following methodology has
been utilized in recent studies and produced reliable habitat models (De Wan et al., 2009;
Hansen et al., 2011).
Focal Species
Species were chosen upon how they were considered to respond to silvilcultural
treatment (in the literature) and based upon on their conservation status. Given that the
BNF has undergone composition and structural changes in recent years many bird species
will also experience changes in possible habitat preference and also in their abundance.
The composition of the forest will continue to change as future desired conditions are met
in the long term, and occupancy models will be able to provide insight to predictors of
detection and occupancy based on environmental and habitat variables.
Worm-eating Warbler
The Worm-eating Warbler is an interior habitat associated species that inhabits
large, intact deciduous and mixed hardwood/coniferous forests. They are considered
habitat specialists, since they most likely only build nest on forested slopes (Hanners &
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Patton, 1998). Dense shrub cover and understory has also been a habitat component
known to influence Worm-eating Warbler occupancy due to its foraging behavior which
consists of gleaning caterpillars off low lying shrubs (Watts & Wilson, 2005; Wenny et
al., 1993). It is listed as a Partners in Flight Watchlist species and bird of conservation
concern given its need for large tracts of forests, small forest gaps and patchy habitat
characteristics created by tree fall (Rich, 2004).
Prairie Warbler
The Prairie Warbler is considered an early successional dependent species that
strives in habitat conditions created by intensive and repeated silvicultural disturbances.
Large openings with clumping of shrubby microhabitats within the larger area are typical
of its breeding habitat, with many sites having much ground cover and few overstory
trees (James, 1971). Shrub-scrub habitats have been declared those that have been
imperiled the most in recent decades, leading to a steep decline in populations of the
Prairie Warbler since the 1960’s (Askins et al., 1990). Frequent prescribed burning is
management tool that has increased occupancy of Prairie Warblers in burned areas
(Blake, 2005; Greenberg et al., 2007; Wick, 2008).
Wood Thrush
The Wood Thrush’s population numbers have decreased by 43% since 1966
across its entire breeding range, making it a flagship species for avian conservation
(Cornell Lab of Ornithology, 2013). Habitat fragmentation is considered the most
detrimental factor causing current population declines (Robinson & Wilcove, 1994). The
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Wood Thrush is a forest interior dwelling species, depending greatly on forest patch size.
In a regional study, Wood Thrush’s chose oak and maple tree species over any other tree
taxonomic groups and selected forests with a high density of saplings in the understory,
higher canopies, moist soils near water, elevated leaf litter, and avoided areas with a high
proportion of coniferous trees (Cornell Lab of Ornithology, 2013). Breeding Wood
Thrush’s were also found to decline sharply in eastern forests with patch sizes less than
80 hectares (200 acres), with other research finding breeding occurring the forest of less
than 80 hectares and with edge, but reproductive success was diminished (Driscoll et al.,
2005). Most studies found that low-intensity silvilcultural practices that do not contribute
to forest fragmentation such as selective harvests and small-scale thinning do not
negatively impact the Wood Thrush (Crawford et al., 1981; Lang et al., 2002; Robinson
& Wilcove, 1994).
Brown-headed Nuthatch
The Brown-headed Nuthatch is susceptible to habitat alteration and fragmentation
throughout its range, endemic to the pine forests of the southeastern U.S. Since 1966 the
population of Brown-headed Nuthatches has decreased by 45%, at an average of two
percent per year (Rich, 2004). It requires mature forest where it excavates nests in snags,
or uses abandoned cavities left by woodpeckers, and forages on pine seed and insects in
nearby live mature pines(Cornell Lab of Ornithology, 2013). Fire suppression has been
thought to have a negative impact on this species since frequent prescribed burns create
habitat by providing snags and the open understory it prefers (Engstrom et al., 1984).
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Results
Wood Thrush
The global model for the Wood Thrush reported a c-hat value of 0.5, indicating
that there is underdispersion within the models. Wood Thrush occupancy in the BNF
was estimated 0.59 (SE=0.10) through model averaging, but is likely being
overestimated. Basal area, or volume of hardwood tree species, and percent of
herbaceous cover was the most influential site covariates included in the top ranking
models for the Wood Thrush totaling 51% of the Akaike weight (Table 11). Wood
Thrush occupancy was positively correlated with basal area of hardwood and slightly
negatively associated with percent of herbaceous cover. Detection probability was
constant and relatively low, 0.17 (SE=0.10) for survey one and 0.18 (SE=0.09) for survey
two. Detection was best modeled as a constant across the survey period, indicating that
Wood Thrush detectibility was not heterogeneous between the surveys and consistent
from year to year. The spearman rank correlation found that the model displayed a very
weak positive monotonic correlation (rs=0.18, P=0.040) between the observed occupancy
in the BNF and expected occupancy modeled predictions.
Worm-eating Warbler
The global model for Worm-eating Warbler showed a slight overdispersion of the
candidate data (c-hat=1.3), so the c-hat value was adjusted to account for models’
overdispersion and standard errors were adjusted. Worm-eating Warbler occupancy in
the BNF was 0.52 (SE=0.12), and was most influenced by overstory height, slope, and
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percent shrub cover. The two top models ranked containing these covariates and totaling
71 % of the Akaike weight. Overstory height, slope, and percent shrub cover all showed
positive correlations with Worm-eating Warbler occupancy. Detection probability varied
among surveys and was 0.24 (SE=0.16) for survey one and 0.52 (SE=0.09) for survey
two. Detection of the Worm-eating Warbler was best modeling with date of survey as the
survey covariate, showing a slight negative correlation with survey date. This indicated
that Worm-eating Warbler detectibility decreased when a later date was chosen to
perform surveys. The spearman rank correlation found that the model displayed a
moderate positive monotonic correlation (rs=0.40, P=0.000) between the observed
occupancy in the BNF and expected occupancy modeled predictions.
Brown-headed Nuthatch
The global model for the Brown-headed Nuthatch reported a c-hat value of 1.1,
indicating that there was only slight overdispersion within the models, so the c-hat value
was not adjusted. Brown-headed Nuthatch occupancy in the BNF was 0.56 (SE=0.16).
The top ranked models showed occupancy of the Brown-headed Nuthatch to be most
influenced by basal area of conifers (wi=0.67). Percent shrub cover was also an
influencing covariate included in both the top ranked model and the fourth ranked model,
but combined Akaike weight (wi=0.27) was fairly low. Overstory height also
contributed, but again had a relatively low combined Akaike weight (wi=0.31). Detection
probability was very low and also varied among surveys, and was 0.18 (SE=0.06) for
survey one and 0.06 (SE=0.07) for survey two. Detection was best modeled with a
negative association with date, implying Brown-headed Nuthatches were detected more
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in the surveys taken earlier in the breeding season. Models only showed very slight
overdispersion of the data, but strong inferences about Brown-headed Nuthatch
occupancy cannot be made, other than they seem to have a positive relationship with
conifer basal area. The spearman rank correlation found that the model displayed a very
weak positive monotonic correlation (rs=0.24, P=0.007) between the observed occupancy
in the BNF and expected occupancy modeled predictions.
Prairie Warbler
The Prairie Warbler’s global occupancy model showed overdispersion within the
dataset (c-hat=1.9), so the c-hat value had to be changed to account for model
uncertainty, resulting in QAIC and ΔQAIC values for competing models. Prairie
Warbler occupancy in the BNF was 0.45 (SE=0.26). The top ranked models showed
occupancy of the Prairie Warbler to be influenced most by overstory height (wi=0.66)
percent canopy cover (wi=0.54) and percent of shrub cover (wi=0.30) (Table 11).
Overstory height and percent canopy cover were both negatively associated, while
percent shrub cover was positively correlated with Prairie Warbler occupancy. Detection
probability varying among surveys, and was 0.31 (SE=0.03) for survey one and 0.46
(SE=0.11) for survey two. Detection was best modeled with a positive association with
temperature. The spearman rank correlation found that the model displayed a moderate
positive monotonic correlation (rs=0.49, P=0.000) between the observed occupancy in the
BNF and expected occupancy modeled predictions. Among survey years, naïve
occupancy and occupancy predictions were highest in the years 2011 and 2012 when the
species had an influx in its population in the BNF.
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Table 8. Rankings of models using Akaike’s Information Criterion (AIC) in program PRESENCE to
explain occupancy (ψ) and detection probability (p) of the Wood Thrush in the Willliam B. Bankhead
National Forest.
Model
AIC
ΔAIC
wi
Likelihood
K
ψ(BA_HW),p(.)
217.41
0.00
0.2423
1.0000
3
ψ(.),p(.)
219.35
1.94
0.0919
0.3791
2
ψ(BA_HW+Herb %),p(.)
219.41
2.00
0.0892
0.3679
4
ψ(BA_HW),p(time)
219.61
2.20
0.0807
0.3329
5
ψ(Herb%),p(.)
220.03
2.62
0.0654
0.2698
3
ψ(Midcanopy %),p(.)
220.32
2.91
0.0566
0.2334
3
ψ(.),p(time)
220.76
3.35
0.0454
0.1873
4
ψ(Shrub %),p(t.)
221.04
3.36
0.0395
0.1628
3
ψ(OS_ HT),p(.)
221.20
3.79
0.0351
0.1503
3
ψ(.),p(Survey)
221.26
3.85
0.0354
0.1459
3
ψ(Canopy %),p(.)
221.31
3.90
0.0345
0.1423
3
ψ(Herb%),p(time)
221.57
4.16
0.0303
0.1249
5
ψ(.),p(temp)
221.71
4.30
0.0282
0.1165
4
ψ(.),p(wind)
222.08
4.67
0.0235
0.0968
4
ψ(.),p(sky)
223.26
5.85
0.0013
0.0537
4
ψ(.),p(Global)
227.66
10.25
0.0014
0.0059
8
a. Occupancy and detection probability were modeled as a constant (.) or as a function of site or survey
specific covariates. Detection probability was also modeled as a function of differences in detection
heterogeneity between survey periods (survey).
Table 9. Rankings of models using Akaike’s Information Criterion (AIC) in program PRESENCE to
explain occupancy (ψ) and detection probability (p) of the Brown-headed Nuthatch in the Willliam B.
Bankhead Nationsl Forest.
Model
AIC
ΔAIC
wi
Likelihood
K
ψ(BA_Conifer+Shrub%),p(date)
129.92
0.00
0.1816
1.0000
6
ψ(BA_Conifer),p(date)
130.99
1.07
0.1064
0.5857
5
ψ(BA_Conifer+OS_HT),p(date)
131.30
1.38
0.0911
0.5016
6
ψ(BA_Conifer+Shrub%+OS_HT+Herb%),p(date)
131.31
1.39
0.0906
0.4991
8
ψ(BA_Conifer+Herb%),p(date)
131.53
1.61
0.0812
0.4471
6
ψ(BA_Conifer+OS_HT+Herb%),p(date)
131.70
1.78
0.0746
0.4107
7
ψ(.),p(date)
132.27
2.35
0.0561
0.3088
4
ψ(OS_HT),p(date)
132.46
2.54
0.0510
0.2808
5
ψ(BA_Conifer+OS_DBH),p(date)
132.88
2.96
0.0413
0.2276
6
ψ(Herb%),p(date)
133.29
3.37
0.0337
0.1854
5
ψ(Canopy%),p(date)
133.72
3.80
0.0272
0.1496
5
ψ(.),p(survey)
133.86
3.94
0.0253
0.1395
3
126
Table 9 (continued).
Model
AIC
ΔAIC
wi
Likelihood
K
ψ(.),p(sky)
135.13
5.21
0.0134
0.0739
4
ψ(.),p(wind)
135.46
5.54
0.0114
0.0627
4
ψ(.),p(time)
135.83
5.91
0.0095
0.0521
4
ψ(.),p(temp)
135.84
5.92
0.0094
0.0518
4
a. Occupancy and detection probability were modeled as a constant (.) or as a function of site or survey
specific covariates. Detection probability was also modeled as a function of differences in detection
heterogeneity between survey periods (survey).
Table 10. Rankings of models using Akaike’s Information Criterion (AIC) in program PRESENCE to
explain occupancy (ψ) and detection probability (p) of the Worm-Eating Warbler in the Willliam B.
Bankhead Nationsl Forest.
Model
ψ(Slope+Shrub%+OS_HT),p(date)
QAIC
165.76
ψ(Slope+OS_HT),p(date)
166.65
ψ(Shrub%+OS_HT+Herb%),p(date)
ΔQAIC
0.00
wi
0.4354
Likelihood
1.0000
7
K
0.89
0.2790
0.6408
6
169.25
3.49
0.0760
0.1746
8
ψ(Slope),p(date)
170.91
5.15
0.0332
0.0762
5
ψ(OS_HT),p(date)
171.28
5.52
0.0276
0.0633
4
ψ(Slope),p(time+date)
171.97
6.21
0.0195
0.0448
6
ψ(.),p(survey)
173.47
7.71
0.0092
0.0212
3
ψ(.),p(date)
173.52
7.76
0.0090
0.0207
4
ψ(.),p(time)
174.11
8.35
0.0067
0.0154
4
ψ(.),p(time+date)
174.32
8.56
0.0060
0.0138
5
ψ(Canopy %),p(date)
174.49
8.73
0.0055
0.0127
5
ψ(OS_DBH),p(date)
174.69
8.93
0.0050
0.0115
5
ψ(.),p(temp)
175.21
9.45
0.0039
0.0089
4
ψ(.),p(sky)
175.35
9.59
0.0036
0.0083
4
ψ(.),p(wind)
175.46
9.70
0.0034
0.0078
4
ψ(.),p(.)
179.07
13.31
0.0006
0.0013
2
ψ(.),p(Global)
179.83
14.07
0.0004
0.0009
8
a. Occupancy and detection probability were modeled as a constant (.) or as a function of site or survey
specific covariates. Detection probability was also modeled as a function of differences in detection
heterogeneity between survey periods (survey).
127
Table 11. Rankings of models using Akaike’s Information Criterion (AIC) in program PRESENCE to
explain occupancy (ψ) and detection probability (p) of the Prairie Warbler in the Willliam B. Bankhead
Nationsl Forest.
Model
AIC
ΔAIC
wi
Likelihood
K
ψ(%Canopy+Shrub%+OS_HT),p(temp)
107.40
0.00
0.2500
1.0000
7
ψ(%Canopy+OS_HT),p(temp)
107.51
0.11
0.2366
0.9465
6
ψ(OS_HT),p(temp)
109.96
2.56
0.0695
0.2780
5
ψ(Shrub%+OS_HT),p(temp)
110.48
3.08
0.0536
0.2144
6
ψ(.),p(survey)
110.54
3.13
0.0523
0.2091
3
ψ(.),p(.)
110.56
3.14
0.0520
0.2080
2
ψ(OS_HT),p(time)
110.57
3.16
0.0515
0.2060
5
ψ(%Canopy),p(temp)
111.57
3.17
0.0512
0.2049
5
ψ(.),p(temp)
111.85
4.17
0.0311
0.1243
4
ψ(OS_HT),p(time+temp)
112.06
4.45
0.0270
0.1081
6
ψ(.),p(time)
112.17
4.66
0.0243
0.0973
4
ψ(Shrub%),p(temp)
112.31
4.77
0.0230
0.0921
5
ψ(.),p(sky)
112.52
4.91
0.0215
0.0859
4
ψ(.),p(date)
112.52
5.12
0.0193
0.0773
4
ψ(.),p(wind)
112.52
5.12
0.0193
0.0773
4
ψ(.),p(temp+time)
113.38
5.98
0.0503
0.0503
5
ψ(.),p(Global)
115.16
7.76
0.0207
0.0207
11
a. Occupancy and detection probability were modeled as a constant (.) or as a function of site or survey
specific covariates. Detection probability was also modeled as a function of differences in detection
heterogeneity between survey periods (survey).
Table 12. Summary of results following single-season parameterization of occupancy (ψ) and detection
probability (p) of select avian species of conservation concern in the William B. Bankhead National Forest.
Species
Wood Thrush
C-hat
0.5
ψ
0.59
P1
0.17
P2
0.18
Influential Covariates
BA Hardwood (+)
Worm-eating
Warbler
1.3
0.52
0.24
0.52
Overstory height (+); Slope
(+); % Shrub cover (+)
Brown-headed
Nuthatch
1.1
0.56
0.18
0.06
BA Conifer (+);% Shrub
cover(+)
0.46
Overstory height (-); %
Shrub cover(+); % Canopy
cover (-)
Prairie
Warbler
1.9
0.45
0.31
128
Discussion
When using models to describe animal and environmental relationships, it is
important to achieve not necessarily the best result, but the most likely result that can be
interpreted to tell the most about the relationships one is describing. In this portion of the
study, model results varied greatly among individual target species due to many factors
including: detection sample size, habitat variable collection methodology, and individual
species response to changes in habitat complexity. Testing the efficacy of an occupancy
model for predicting relationships among species and habitat variables was important in
this study. Determining if there were any differences in bird/habitat relationships due to
scale (larger scale data collection) and methodology (different collection methodologies
such as the breeding bird survey’s point count methodology and the line transect
methodology used in the first portion of the study) was also important. The comparison
of results between modeling methodology and statistical tests was also explored.
Model performance was restricted in the study for two main reasons. First, the
breeding bird survey was not able to adequately represent the metapopulation or make
inferences about immigration or emigration within a single season because only one
survey is taken in a given year. Repeat visits (3-4) to each site ensure more precise
occupancy predictions (Mackenzie & Royle, 2005). Repeat visits were included to create
a detection history under the assumption that site occupancy would not change in a given
year. This assumption must be made when performing single season modeling
methodology in PRESENCE (Royle et al., 2005). The data show, however, that this
assumption may have been violated, as the model accuracy was especially low for two
target species after performing the Spearman Rank correlation statistical test.
129
Furthermore, births and deaths would have certainly occurred between the years of data
collection, especially in the target migratory bird species (Sandercock et al., 2008) The
assumption that occupancy would not change within a survey year or season, is hard to
preserve in bird studies since survival and reproduction change in response to several
external environmental and biological factors than cannot be successfully accounted for
in modeling studies.
Second, low detectibility had an influence in the modeling results. The Wood
Thrush’s decline throughout the study years lead to a relatively low naïve occupancy
estimate (0.16) for the 2011-2012 years of data collection, resulting in a weak correlation
between observed and predicted occupancy when using the test data in place of the data
used to develop the models. This low correlation was also found for the Brown-headed
Nuthatch which had very low naïve estimation (0.085) for 2011-2012 years of data
collection. The Wood Thrush showed a positive relationship with hardwood BA, and
other studies concluded that they have a strong habitat preference for hardwood forests
(Hill, 1998; Lang et al., 2002). Models may have been improved by using more specific
covariate information such as hardwood species or percentage of hardwood in the
understory or midstory (Wood, 2007). Both low detection and covariate selection were
short comings of this study’s predictive models of occupancy. Although not all habitatwildlife relationships were tested in this study, the results add to and support the current
knowledge base of the species/habitat relationships. The restoration efforts in the BNF
should lead to increases in abundance of both the Wood Thrush and Brown-headed
Nuthatch, but because the process of moving these stands towards hardwood-dominance
will take decades, concurrent positive impacts on these bird species may also take
130
decades. Data used to model the Prairie Warbler and the Worm-eating Warbler resulted
in stronger models compared to the other species. Spearman rank correlation yielded a
moderate positive monotonic correlation between the observed occupancy in the BNF
and the expected or predicted model occupancy. Both of these species had moderate to
relatively high naïve occupancies (>0.5) throughout the study period, contributing to
more robust model outputs. Silviculture treatments of both thinning and burning
implemented throughout the BNF has created desirable habitat for Prairie Warblers
throughout the forest, increasing presence and occupancy of this species of conservation
concern. Similar results for this species were found in species/habitat relationships
among the modeling results and the CCA results. The Worm-eating Warbler showed a
positive association with forest percent overstory cover and percent canopy cover in the
CCA, and in the site-occupancy model these were also the most influential covariates in
the top ranking models. The Prairie Warbler had a positive association with percent
woody cover and a negative association with canopy cover in the CCA, and in the siteoccupancy model there was also a positive association with woody shrub cover and a
negative association with percent canopy cover. These results demonstrated how models
can provide insight to habitat suitability when care is taken so that model assumptions are
met and appropriate methodology and approach is taken when building the models.
Depending on the research goals, a theoretic-information methodology is relevant when
exploring wildlife/habitat relationships. These models can serve to provide much-needed
and currently absent baseline data on habitat associations and unbiased occupancy
estimates for selected birds within the BNF. Since the birds researched in this study are
not only local and regional species of concern, but also species of concern county-wide, it
131
is imperative to collect as much information about their habitat requirements in this
region of the U.S. to transcend to other regions. Furthermore, state managers and
biologists may use the information provided in their wildlife management plans. Because
birds can be good indicators of habitat importance, occupancy modeling may give
managers an applied and targeted conservation and management tool for assessing not
only focal species occupancy, but also overall ecosystem health (Wood, 2007).
132
CHAPTER 5
FINAL CONCLUSIONS AND MANAGEMENT
RECOMMENDATIONS
As no single forest management practice can benefit all avian species, a matrix of
successional seres created throughout the landscape can provide the most benefit to the
greatest suite of species. In the southeastern US, we have learned that active forest
management is almost always beneficial for creating and maintaining a variety of habitats
conducive to a variety of birds compared to doing nothing. Our study showed that 6-7
years following initial silvicultural treatments, many bird species responded positively,
and as forest succession continues the bird community will continue to change in
response to the corresponding changes in the microhabitat. There exists a need for the
continuation of monitoring to elucidate more on species and guild responses (Greenberg
et al., 2007; Harrison et al., 2005; Perry & Thill, 2013; Yahner, 1986). The intermediate
disturbance hypothesis states species diversity maximizes when intermediate ecological
disturbances, not too rare or too infrequent, are applied in the system, and was applicable
to responses found in this study (Connell, 1978). It was clear that the management
applied thus far resulted in an intermediate level of disturbance, resulting in viable habitat
and resources for both opportunistic and competitive, and specialist, species to coexist
132
(Wilkinson, 1999). At this stage in the management of these stands, all treatments are
intermediate in their degree of disturbance. A more extreme disturbance, such as
clearcutting, was not included in my study, and inferences beyond intermediate
disturbances such as thinning and prescribed burning are not appropriate. It was found
that over time, frequency or infrequency of disturbance affected species diversity. For
example, over a relatively short time (~6 years) infrequently burned stands did not harbor
any additional species than those utilizing undisturbed sites. Species composition was
similar in these treatment stands, with no clear impact on species diversity. With an
increase in disturbance, there was also an increase in species diversity. Results were
limited by the amount of disturbance under study, with the most disturbed stands having
a single heavy thin and two burns.
This study showed that thinning and infrequently burning created habitat for the
most bird species diversity. However, disturbance- dependent habitat specialists
benefited the most from thinning and burning combined with burns occurring frequently
(every three years). Wick (2008) found that thinning combined with burning had the
greatest negative impacts on the bird community, but only the short -term responses of
one burn were studied and guilds were only accessed, not individual species. We now
know that 6-7 years following treatment, thinning combined with frequent burning (2
burns) provided habitat for several early-successional species that require reoccurring
disturbance, while thinning combined with less frequent burning provided the most viable
habitat for the highest quantity of bird species.
Vegetation and site characteristics associated with burning are short lived, and
more frequent prescribed burns may more continuously provide foraging habitat for
133
many aerial foraging species, while also maintaining a complex herbaceous forest
component. As other studies suggest (Blake, 2005; Greenberg et al., 2007), low intensity
fires alone, akin to those in this study, may not make dramatic positive impacts on the
bird community, nor provide viable habitat for high densities of many early successional
species. When prescribed fire is combined with thinning that targets overstory and
midstory trees, desirable habitat is created for early successional species. Thinning
combined with frequent prescribed burning maintained openness in the stands, whereas
thinning alone created an ephemeral openness that returned to pretreatment conditions 67 years post-thin. In these types of forests, mixed oak-pine, early successional bird
species require a continuation of active forest management, such as frequent fires, to
maintain breeding habitat essentials and the “open” habitat that these species necessitate.
Other species such as the Kentucky Warbler may benefit from the less frequent burns that
briefly open the stands and create small gaps. Because early seral habitats are short lived
and stand composition changes through time, habitat then becomes unsuitable for early
successional species. Management plans can incorporate these changes and benefit a
host of species by using adaptable treatment rotations and by shifting mosaics across the
landscape, increasing the longevity of species occupancy (Evers, 1994).
Occupancy modeling can be used to predict occurrence of a given species in a
management area, but these models depend on input of appropriate covariates and sound
detection histories. The Wood Thrush’s strong correlation with BA of hardwood
indicated that future desired conditions in the BNF should create desirable habitat for this
species, potentially slowing its 5-decade decline. The Prairie Warbler occupancy model
results were influenced by shrub component complexity. A continuation of disturbance
134
regimes in the BNF which maintains shrubs and other understory vegetation should
benefit this species of concern. The Worm-eating Warbler nests on the ground and is
more susceptible to fire. However, because the Worm-eating Warbler has an affinity for
habitats on the most highly sloped terrain where fire is less likely to spread, these areas
may provide a refuge from fire. The gently undulating Plateau surface, a major
topographic feature in the BNF, provides adequate habitat for the Worm-eating Warbler
throughout the forest, regardless of management. The model was heavily weighted by
overstory canopy height, indicating this species requires an overstory canopy. It was
found in this study that thinning that removed half of the basal area did not negatively
impact the Worm-eating Warbler. Both lightly thinning and heavily thinning harvests
still supported the Worm-eating warbler 6-7 years post initial treatment implementation.
Forest management goals and bird conservation have great potential to be coupled
successfully by enhancing communication between managers and research scientists. For
successful conservation, long-term monitoring following implementation of silvicultural
prescriptions is paramount to narrowing the knowledge gap on habitat and bird response.
Application of treatments such as thinning and burning, and their associated impacts,
must be done with regard to forest composition and structure, landscape position, and
targeted desired conditions.
135
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APPENDICES
APPENDIX A: DESCRPITIVE TABLES
Table 13. Birds previously encountered in BNF research stands and their associated guilds: Nest location
(G, ground; S, shrub; T, tree; C, cavity) (Ehrlich et al., 1986), Migration destination (N, Neotropical
migrant; T, temperate migrant; R, resident) (Sauer et al., 1996; Imhof, 1976), Habitat association (O/E,
open-edge; I/E, interior-edge; I, interior) (Blake & Karr, 1987; Freemark & Collins, 1992), and forage guild
(A, aerial; F, foliage; G, ground; B, bark) (Ehrlich et al., 1986).
Species
Code
ACFL
AMRO
BAWW
BTGW
BGGN
BLGR
BHVI
BLJA
BWWA
BHCB
BHNU
BRTH
CACH
CARW
CEWR
DOWO
EABL
EAPH
EATO
Common Name
Acadian Flycatcher
American Robin
Black-and-white
Warbler
Black-throated
Green Warbler
Blue-gray
Gnatcatcher
Blue Grosbeak
Blue-headed Vireo
Blue Jay
Blue-winged
Warbler
Brown-headed
Cowbird
Brown-headed
nuthatch
Brown Thrasher
Carolina chickadee
Carolina Wren
Cerulean Warbler
Downy
Woodpecker
Eastern Bluebird
Eastern Phoebe
Eastern Towhee
Scientific Name
Empidonax virescens
Turdus migratorius
Mniotilta varia
Nesting
Guild
T
T
G
Migration
Guild
N
R
T
Habitat
Guild
I
O/E
I
Forage
Guild
A
G
B
Dendroica virens
T
N
I
F
Polioptila caerulea
T
T
I/E
F
Guiraca caerulea
Vireo solitarius
Cyanocitta cristata
Vermivora
cyanoptera
Molothrrus ater
S
T
T
G
N
N
R
N
O/E
I/E
I/E
O/E
G
F
F
F
P
R
O/E
G
Sitta pusilla
C
R
I
B
Toxostoma rufum
Poecile carolinensis
Tryothorus
ludovicianus
Setophaga cerulea
Picoides villosus
S
C
C
T
R
R
O/E
I/E
O/E
G
F
G
T
C
N
R
I
I/E
F
B
Sialia sialis
Sayornis phoebe
Pipilo
erythrophthalmus
C
C
G
R
R
N
O/E
I/E
I/E
G
G
G
149
Table 13 (continued).
Species
Code
ETTI
EAWP
GRCA
GCFL
HAWO
HOWA
INBU
KEWA
LOWA
MODO
NOCA
NOFL
NOMO
NOPA
OVEN
PIWA
PIWO
PRWA
RBWO
REVI
RHWO
RTHU
SCTA
SUTA
WBNU
WEVI
WEWA
WOTH
YBCH
YBCU
YTVI
YTWA
Common Name
Eastern Tufted
Titmouse
Eastern Wood
Peewee
Gray Catbird
Great Crested
Flycatcher
Hairy Woodpecker
Hooded Warbler
Indigo Bunting
Kentucky Warbler
Louisiana
Waterthrush
Mourning Dove
Northern Cardinal
Northern Flicker
Northern
Mockingbird
Northern Parula
Ovenbird
Pine Warbler
Pileated
Woodpecker
Prairie Warbler
Red-bellied
Woodpecker
Red-eyed Vireo
Red-headed
Woodpecker
Ruby-throated
Hummingbird
Scarlet Tanager
Summer Tanager
White-breasted
Nuthatch
White-eyed Vireo
Worm-eating
Warbler
Wood Thrush
Yellow-breasted
Chat
Yellow-billed
Cuckoo
Yellow-throated
Vireo
Yellow-throated
Warbler
Scientific Name
Baeolophus bicolor
Nesting
Guild
C
Migration
Guild
N
Habitat
Guild
I/E
Forage
Guild
F
Contopus virens
T
R
I/E
A
Dumetella
carolinensis
Myiarchus crinitus
S
T
O/E
G
C
R
I/E
A
Picoides villosus
Setophaga citrine
Passerina cyanea
Geothlypis formosa
Seiurus motacilla
C
S
S
G
G
N
N
N
N
R
I
I
O/E
I/E
I/E
B
F
F
G
G
Lenaida macroura
Cardinalis cardinalis
Colaptes auratus
Minus polygottos
T
S
C
S
R
R
R
T
O/E
I/E
O/E
E
G
G
G
G
Setophaga americana
Seiurus aurocapillus
Setophaga pinus
Dryocopus pileatus
T
G
T
C
N
N
R
T
I/E
I
I/E
I
F
G
B
B
Setophaga discolor
Melanerpes carolinus
S
C
N
R
O/E
I/E
F
B
Vireo olivaceus
Melanerpes
erythrocephalus
Archilochus colubris
S
C
N
R
I/E
O/E
F
A
T
N
O/E
N
Piranga olivacea
Piranga ruba
Sitta carolinensis
T
T
C
N
R
T
I
I/E
I
F
F
B
Vireo griseus
Helmitheros
vermivorus
Hylocichla mustelina
Icteria virens
S
G
N
N
O/E
I
F
F
T
S
N
N
I/E
O/E
G
F
Coccyzus americanus
T
N
I/E
F
Vireo flavifrons
T
N
I/E
F
Setophaga dominica
T
N
I/E
B
150
Table 14. Habitat characteristics of sixteen vegetation variables used to assess habitat associations of the
avian community on 36 stands in the William B. Bankhead Forest.
Habitat Variable
Abbreviation
Ground Cover:Litter (%)
litter
Ground Cover: Herbaceous
plants(%)
herb
Ground Cover: Woody
plants (%)
woody
Bare ground cover (%)
bare
Litter depth (mm)
litterD
Canopy cover (%)
canopy
Forest level 1present (%)
GC
Forest level 2 present (%)
US
Forest level 3 present (%)
MS
Forest level 4 present (%)
OS
Total BA (ft2/ac)
Pine BA (ft2/ac)
Hardwood BA (ft2/ac)
BA
bapine
bahw
Snag BA (ft2/ac)
basnag
Tree species richness (per
stand)
TreeRich
Stand tree density (per
stand)
TreeDen
151
Table 15. Habitat site-specific covariates used in site occupancy models for four focal bird species in the
William B. Bankhead Forest.
Habitat Covariate
Abbreviation
Slope
Slp
Aspect
Asp
Elevation
Elev
Conifer BA
(ft2/ac)
Hardwood BA
(ft2/ac)
ConBA
HwBA
Overcanopy (%)
OvCan
Midcanopy (%)
MidCan
Shrub cover (%)
ShrubC
Herbaceous cover (%)
HerbC
Litter depth
Lit
Overstory species
component
OverComp
Overstory DBH
OvsDBH
Table 16. Survey-specific covariates used in site occupancy models for four focal bird species in the
William B. Bankhead Forest.
Survey Covariate
Abbreviation
Date
Date
Time
Time
Temperature
Temp
Wind Condition
Wind
Sky Condition
Sky
152
Figure 40. Habitat sampling datasheet.
153
Figure 41. Transect/distance sampling datasheet.
154
Figure 42. Habitat sampling datasheet.
155
APPENDIX B: MICROHABITAT AND AVIAN RESPONSE TABLES
Table B.1. Mean + standard error and results from Multivariate Analysis of Variance (MANOVA) of
microhabitat and forest structure variables of six silvicultural treatments (n =4 for each treatment) in the
Bankhead National Forest. Treatment and block were the between subjects factors, and year (pretreatment,
1-yr post, and 6-7 post-treatment) was the within subject factor.
Community Variable
Treatments
C
Bare Ground (%)
HT
LT
HTxHB
LTxHB
SE
0.0
Mean
0.0
SE
0.0
Mean SE
0.0
0.0
Mean SE
0.0 0.0
Mean SE
0.0 0.0
Mean
0.0
0.0
1.4
1.5
1.4
1.1
0.4
7.5
4.7
1.4
1.8
12.9 13.7
12.9 1.9
12.9 0.6
12.9 56.1
12.9 26.5
12.9
PreA 9.3
1B 11.2
6.1
13.5
6.1
20.7
6.1
26.8
6.1
22.5
6.1
8.3
6.1
5.6
14.6
5.6
20.8
5.6
23.2
5.6
23.2
5.6
20.0
5.6
A
8.4
9.0
32.9
9.0
13.9
9.0
8.0
9.0
38.4
9.0
30.7
9.0
A
5.1
3.5
7.1
3.5
15.7
3.5
15.3
3.5
14.9
3.5
8.1
3.5
1AB
6.8
3.5
8.6
3.5
17.5
3.5
20.7
3.5
19.4
3.5
13.9
3.5
IntAB 34.0
PreA 99.0
6.7
26.3
6.7
82.2
6.7
86.0
6.7
63.4
6.7
63.8
6.7
0.4
99.5
0.4
99.5
0.4
99.2
0.4
99.7
0.4
99.4
0.4
99.5
2.0
97.5
2.0
97.6
2.0
98.2
2.0
90.8
2.0
92.8
2.0
Int
Pre
97.4
12.7 74.4
12.7 97.0
12.7 99.3
12.7 42.8
12.7 73.3
12.7
0.0
0.1
0.3
0.1
0.0
0.1
0.0
0.1
0.0
0.1
0.0
0.1
1
0.0
0.1
0.3
0.1
0.0
0.1
0.0
0.1
0.0
0.1
0.0
0.1
0.8
0.5
2.1
0.5
0.0
0.5
0.0
0.5
0.8
0.5
0.3
0.5
2.3
0.9
0.7
0.9
1.7
0.9
1.7
0.9
2.4
0.9
1.0
0.9
1.4
0.9
1.0
0.9
3.0
0.9
2.2
0.9
3.1
0.9
2.8
0.9
IntB 0.0
Pre 4.7
0.3
0.6
0.3
1.2
0.3
0.3
0.3
0.0
0.3
0.0
0.3
0.4
3.3
0.4
3.6
0.4
4.8
0.4
4.6
0.4
4.7
0.4
1
7.8
0.7
3.7
0.7
4.9
0.7
4.7
0.7
3.4
0.7
5.0
0.7
Int
5.4
1.0
4.4
1.0
4.1
1.0
4.0
1.0
3.6
1.0
4.1
1.0
Pre
86.2
2.2
86.6
2.2
78.6
2.2
82.1
2.2
81.2
2.2
80.3
2.2
1
91.0
5.3
90.4
5.3
62.3
5.3
64.2
5.3
50.9
5.3
69.8
5.3
95.1
2.6
94.9
2.6
95.7
2.6
93.5
2.6
77.4
2.6
83.6
2.6
19.7
2.9
21.0
2.9
17.0
2.9
23.7
2.9
20.3
2.9
22.3
2.9
11.3
2.3
8.0
2.3
10.0
2.3
13.3
2.3
14.7
2.3
10.7
2.3
IntA 27.0
0.0
27.0
0.0
27.0
0.0
27.0
0.0
27.0
0.0
27.0
0.0
Year Mean
PreA 0.0
1B
Int
Herbaceous Cover (%)
Int
Woody Cover (%)
Litter Cover (%)
Pre
1A
B
Rock (%)
Int
CWD (%)
Pre
AB
A
1
Litter Depth (cm)
Canopy (% closure)
Int
Forest Level 1
B
Treatment Effect
Pre
1B
A
1.4
1.4
156
1.4
P(treat) P(year) P(treat*year)
SE
0.0
df(5,12) df(3,12) df(5,12)
0.03
0.02 0.05
CABABLTBABHTABHTBABLTB
0.36
0.31
0.05
0.00
0.00
0.00
CABABLTBABHTABHTBABLTB
0.02
0.01
0.05
CABABLTBABHTABHTBABLTB
0.04
0.02
0.24
0.65
0.00
0.43
0.02
0.29
0.41
BACABHTBCLTBCDHTBCDLTCD
0.00
0.00
0.00
BACABHTBCLTBCDHTBCDLTCD
0.63
0.00
0.56
Table B.1 (continued).
Community Variable
Treatments
C
Forest Level 2
Year Mean
PreA 20.3
22.0
1B
Forest Level 4
Basal Area
Tree Abundance
Basal Area: Hardwoods
Basal Area: Pines
LTxHB
SE
2.2
HT
Mean
19.7
SE
2.2
Mean SE
19.7 2.2
Mean SE
21.3 2.2
Mean
20.3
SE
2.2
2.3
23.0
2.3
8.3
2.3
6.3
5.7
5.7
2.3
2.3
2.3
P(treat) P(year) P(treat*year)
21.7
3.5
11.0
3.5
24.3
3.5
23.7
3.5
7.7
3.5
5.0
3.5
3.1
20.0
3.1
20.3
3.1
10.3
3.1
18.7
3.1
19.7
3.1
1
11.7
2.2
22.3
2.2
8.0
2.2
5.3
2.2
5.0
2.2
6.7
2.2
Int
21.3
3.8
16.7
3.8
16.0
3.8
12.7
3.8
7.0
3.8
6.7
3.8
Pre
26.7
2.6
17.3
2.6
26.7
2.6
24.3
2.6
24.3
2.6
26.3
2.6
df(5,12) df(3,12) df(5,12)
0.01
0.00 0.00
0.08
0.00
0.02
0.33
0.02
0.68
0.00
0.00
0.86
0.00
0.00
0.00
0.00
0.00
0.33
0.00
0.20
0.00
0.00
0.03
0.68
0.00
0.00
1
25.7
3.0
20.3
3.0
18.3
3.0
19.3
3.0
21.0
3.0
17.7
3.0
Int
26.7
1.3
26.7
1.3
20.0
1.3
22.3
1.3
19.3
1.3
24.7
1.3
Pre
126.4
12.7
113.7
12.7 127.8
12.7 121.5 12.7 123.7 12.7 127.5
12.7 0.00
1
132.1
7.0
121.6
7.0
47.2
7.0
63.9
7.0
48.1
7.0
60.2
7.0
147.5
5.9
159.4
5.9
66.1
5.9
78.5
5.9
58.2
5.9
81.2
5.9
5.1
0.8
5.3
0.8
5.7
0.8
5.9
0.8
5.9
0.8
4.5
0.8
1A
5.2
0.8
5.1
0.8
3.2
0.8
4.1
0.8
3.9
0.8
3.1
0.8
IntB
Pre
5.8
1.0
6.1
1.0
6.5
1.0
6.7
1.0
6.3
1.0
4.9
1.0
53.7
5.4
64.8
5.4
56.9
5.4
45.6
5.4
49.8
5.4
55.9
5.4
1
53.3
2.6
63.1
2.6
15.8
2.6
18.6
2.6
15.9
2.6
20.7
2.6
Pre
AB
Int
54.2
3.0
69.2
3.0
17.1
3.0
20.0
3.0
16.3
3.0
22.3
3.0
Pre
11.2
4.7
10.5
4.7
10.4
4.7
16.8
4.7
11.4
4.7
7.2
4.7
1
44.5
7.7
44.4
7.7
31.1
7.7
18.9
7.7
18.9
7.7
21.1
7.7
Int
16.6
5.1
13.7
5.1
10.3
5.1
17.8
5.1
12.7
5.1
9.1
5.1
PreA 115.6
1B 118.9
9.6
107.2
9.6
124.6
9.6
104.7 9.6
119.7
9.6
21.2
96.7
21.2 42.2
21.2 77.8
21.2
21.2 36.7
104.0 9.6
21.2 37.8
Int
Pre
133.6
7.1
145.7
7.1
55.8
7.1
61.8
7.1
46.1
7.1
72.0
7.1
0.2
0.9
0.4
0.9
1.5
0.9
4.4
0.9
4.7
0.9
0.5
0.9
B
8.9
1.6
4.4
1.6
5.5
1.6
1.1
1.6
2.2
1.6
2.2
1.6
6.2
0.7
3.0
0.7
1.0
0.7
0.6
0.7
2.0
0.7
1.11
0.7
AB
Basal Area: Snags
HTxHB
Mean
23.0
14.3
Int
Tree Species Richness
LT
SE
2.2
Int
Pre
A
Forest Level 3
B
Treatment Effect
1
Int
AB
BACABHTBCLTBCDHTBCDLTCD
BACABHTBCLTBCDHTBCDLTCD
BBCCBCLTABHTABLTBABHTBA
BBCCBCLTABHTABLTBABHTBA
a. Abbreviated labels are denoted as C = control, FB =frequent burn only (3 year interval), HT= heavily
thinned LT= lightly thinned, HTxFB= heavily thinned with frequent burn (3 year interval) LTxFB= lightly
thinned with frequent burn (3 year interval)
b. Different letters among years for community variable shows a significant difference, p≤0.05.
c. Different letters among treatments indicates a significant difference among treatments, ordered from
lowest to highest values, p≤0.05.
157
Table B.2. Mean + standard error and results from Multivariate Analysis of Variance (MANOVA)
of bird species response to six silvicultural treatments (n =3 for each treatment) in the Bankhead
National Forest. Treatment and block were the between subject factors, and year (pretreatment, 1yr post, and 6-7 post-treatment) was within subject factor.
Treatments
C
HT
HB
Treatment Effect
LTxHB
HTxHB
LT
Year Mean
1.0
SE
0.4
Mean
0.0
SE Mean SE Mean SE Mean SE
0.4 0.0 0.4 0.0 0.4 0.8 0.4
Mean
2.7
SE
0.4
1AB
0.7
0.3
0.6
0.3
0.6
0.3
0.0
0.3
0.0
0.3
0.6
0.3
A
6
0.3
0.1
0.0
0.1
0.0
0.1
0.0
0.1
0.0
0.1
0.0
0.1
A
0.1
0.4
0.1
0.4
0.1
0.0
0.1
0.0
0.1
0.0
0.1
1.8
0.9
4.1
0.9
2.2
0.9
1.6
0.9
0.7
0.9
Species
Acadian flycatcher
PreB
Empidonax virescens
Black-and-white warbler
7
Pre
0.0
2.4
0.9
Mniotilta varia
1
1.5
0.8
1.7
0.8
1.2
0.8
2.1
0.8
0.0
0.8
0.0
0.8
6
0.7
0.6
0.8
0.6
1.8
0.6
0.6
0.6
1.4
0.6
1.8
0.6
7
1.7
0.8
0.3
0.8
3.7
0.8
2.1
0.8
1.8
0.8
0.0
0.8
Blue-gray gnatcatcher
Pre
1.4
1.2
0.7
1.2
0.0
1.2
0.7
1.2
2.7
1.2
0.7
1.2
Polioptila caerulea
1
0.0
0.5
0.4
0.5
0.6
0.5
1.4
0.5
0.5
0.5
1.4
0.5
6
0.3
0.3
1.1
0.3
0.7
0.3
0.3
0.3
0.6
0.3
1.4
0.3
7
0.0
1.5
0.3
1.5
0.4
1.5
1.1
1.5
5.3
1.5
0.6
1.5
Black-throated green warbler
Pre
1.3
0.6
0.0
0.6
0.6
0.6
1.1
0.6
1.6
0.6
1.4
0.6
Setophaga virens
1
0.7
0.3
0.7
0.3
1.0
0.3
0.0
0.3
0.5
0.3
0.0
0.3
6
1.0
0.5
0.3
0.5
1.1
0.5
1.0
0.5
1.1
0.5
0.7
0.5
7
2.3
1.2
0.0
1.2
0.0
1.2
1.1
1.2
3.3
1.2
1.4
1.2
Blue jay
Pre
0.0
0.8
1.0
0.8
1.5
0.8
1.4
0.8
0.0
0.8
0.0
0.8
Cyannocitta cristata
1
0.7
0.6
0.6
0.6
0.4
0.6
0.7
0.6
1.3
0.6
1.4
0.6
6
1.0
0.7
1.6
0.7
1.0
0.7
1.0
0.7
1.5
0.7
1.2
0.7
0.6
0.5
0.9
0.5
1.7
0.5
1.0
0.5
0.3
0.5
0.6
0.5
Brown-headed cowbird
Pre
A
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
Molothrus ater
1B
0.0
0.5
0.0
0.5
0.8
0.5
0.7
0.5
2.1
0.5
1.3
0.5
6AB
0.0
0.4
0.0
0.4
0.5
0.4
0.0
0.4
0.4
0.4
0.6
0.4
AB
0.0
0.4
0.0
0.4
0.4
0.4
0.0
0.4
1.6
0.4
0.0
0.4
Brown-headed nuthatch
Pre
A
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
Sitta pusilla
1A
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
B
6
0.0
0.6
0.0
0.6
0.3
0.6
0.9
0.6
2.0
0.6
1.9
0.6
AB
0.0
0.4
0.0
0.4
0.0
0.4
0.0
0.4
1.3
0.4
0.7
0.4
C
5.1
1.2
2.6
1.2
6.9
1.2
3.5
1.2
6.2
1.2
5.9
1.2
BC
1
1.9
1.2
4.6
1.2
6.0
1.2
5.2
1.2
3.1
1.2
2.7
1.2
6A
1.1
0.9
3.0
0.9
1.5
0.9
1.6
0.9
1.0
0.9
3.1
0.9
7AB
Pre
0.7
0.7
4.0
0.7
2.2
0.7
0.0
0.7
2.9
0.7
3.8
0.7
Carolina wren
1.0
1.1
0.3
1.1
0.6
1.1
1.1
1.1
3.3
1.1
2.0
1.1
Thyrothorus ludovicianus
1
1.0
0.5
0.7
0.5
0.4
0.5
2.5
0.5
2.5
0.5
2.7
0.5
6
1.3
0.8
0.3
0.8
1.0
0.8
2.0
0.8
2.3
0.8
0.0
0.8
7
1.4
0.7
1.2
0.7
0.8
0.7
0.4
0.7
2.0
0.7
1.8
0.7
7
7
7
Carolina chickadee
Poecile carolinensis
Pre
Downy woodpecker
Pre
A
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
Picoides pubescens
A
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
B
6
0.0
0.7
0.9
0.7
0.9
0.7
1.3
0.7
0.6
0.7
2.2
0.7
B
0.6
0.6
1.3
0.6
0.0
0.6
0.7
0.6
1.3
0.6
1.4
0.6
1
7
158
P(treat*year)
P(block) P(treat)
P(year)
df(2,12) df(5,12)
df(3,12)
0.66
<0.005
<0.005
0.16
0.01
0.15
0.46
0.58
0.38
0.63
0.19
0.03
0.07
0.28
0.65
0.85
0.88
0.54
0.82
0.10
<0.005
0.02
0.48
CABALTAHTABLTBABHTBB
0.27
<0.005
0.01
0.47
CABAHTALTABLTBBCHTBC
0.18
0.15
<0.005
0.07
0.34
0.32
0.61
0.41
0.64
0.34
<0.005
0.47
df(5,12)
0.01 LTAHTAHTBABACABLTBB
LTBBAHTBACABLTABHTB
Table B.2 (continued).
Treatments
C
HB
HT
Treatment Effect
LT
HTxHB
LTxHB
Species
Eastern phoebe
Year Mean
Pre 0.0
SE
0.0
Mean
0.0
SE Mean SE Mean SE Mean SE
0.0 0.0 0.0 0.0 0.0 0.0 0.0
Mean
0.0
SE
0.0
Sayomis phoebe
1
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
6
0.2
0.2
0.0
0.2
0.0
0.2
1.0
0.2
0.3
0.2
0.0
0.2
0.0
0.3
0.0
0.3
0.6
0.3
0.7
0.3
0.3
0.3
0.0
0.3
Eastern towhee
7
Pre
A
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
Pipilo erythrophthalmus
1A
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
B
6
0.0
0.6
0.0
0.6
0.7
0.6
0.9
0.6
2.8
0.6
3.3
0.6
0.0
0.9
0.0
0.9
2.0
0.9
0.4
0.9
2.7
0.9
1.3
0.9
Eastern tufted titmouse
7B
Pre
0.7
0.6
0.3
0.6
0.8
0.6
1.4
0.6
2.6
0.6
1.9
0.6
Baeolophus bicolor
1
0.3
0.4
0.7
0.4
1.8
0.4
1.0
0.4
0.5
0.4
0.0
0.4
6
1.0
0.6
0.6
0.6
1.8
0.6
1.3
0.6
0.6
0.6
1.6
0.6
7
2.1
0.5
1.3
0.5
2.6
0.5
0.7
0.5
2.0
0.5
1.9
0.5
A
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
AB
0.0
0.4
0.0
0.4
0.8
0.4
1.4
0.4
0.8
0.4
0.7
0.4
B
6
0.0
0.8
0.3
0.8
1.3
0.8
1.3
0.8
1.8
0.8
1.2
0.8
7B
Pre
0.4
0.7
1.0
0.7
0.4
0.7
0.4
0.7
1.1
0.7
2.1
0.7
Great-crested flycatcher
1.3
0.9
2.7
0.9
0.4
0.9
1.1
0.9
2.5
0.9
1.3
0.9
Myiarchus crinitus
1
1.4
0.6
1.6
0.6
0.8
0.6
1.4
0.6
2.6
0.6
2.0
0.6
6
0.8
0.5
0.4
0.5
0.6
0.5
0.3
0.5
0.3
0.5
1.4
0.5
0.4
0.5
1.6
0.5
0.0
0.5
0.0
0.5
0.0
0.5
1.9
0.5
2.6
2.2
2.8
2.2
6.0
2.2
4.4
2.2
4.1
2.2
3.5
2.2
Eastern wood-peewee
Contopus virens
Pre
1
7
Hooded warbler
Setophaga citrina
Pre
A
B
1
2.1
1.1
0.7
1.1
1.6
1.1
2.5
1.1
0.8
1.1
1.4
1.1
AB
6
2.0
0.8
0.7
0.8
4.1
0.8
2.2
0.8
2.7
0.8
3.0
0.8
3.5
1.1
0.3
1.1
3.5
1.1
4.3
1.1
0.0
1.1
0.0
1.1
Indigo bunting
7AB
Pre
1.8
1.7
1.4
1.7
3.9
1.7
3.9
1.7
5.1
1.7
3.8
1.7
Passerina cyanea
1
0.7
2.2
1.0
2.2
7.1
2.2
3.6
2.2
8.3
2.2
4.7
2.2
6
0.6
0.8
0.8
0.8
2.2
0.8
2.9
0.8
4.0
0.8
8.3
0.8
7
0.0
0.7
0.3
0.7
3.0
0.7
2.2
0.7
7.0
0.7
5.7
0.7
Kentucky warbler
Pre
0.4
0.7
0.4
0.7
1.2
0.7
1.8
0.7
0.0
0.7
0.7
0.7
Oporornis formosus
1
0.7
0.6
0.7
0.6
1.2
0.6
1.4
0.6
1.3
0.6
0.0
0.6
6
0.0
0.3
0.0
0.3
0.3
0.3
0.6
0.3
0.0
0.3
1.1
0.3
7
0.0
0.6
0.0
0.6
0.6
0.6
0.4
0.6
1.3
0.6
0.0
0.6
Mourning dove
Pre
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
Zenaida macroura
1
0.0
0.6
0.0
0.6
1.0
0.6
2.1
0.6
0.0
0.6
0.0
0.6
6
0.0
0.2
0.0
0.2
0.0
0.2
0.0
0.2
0.3
0.2
0.4
0.2
7
0.0
0.3
0.0
0.3
0.0
0.3
0.8
0.3
0.4
0.3
0.0
0.3
AB
2.1
1.1
3.4
1.1
2.2
1.1
1.8
1.1
1.8
1.1
4.5
1.1
A
1.0
0.5
0.7
0.5
2.2
0.5
2.1
0.5
0.5
0.5
0.0
0.5
6B
1.5
0.9
1.9
0.9
4.8
0.9
3.3
0.9
3.3
0.9
3.7
0.9
B
1.7
1.5
1.3
1.5
4.5
1.5
1.0
1.5
5.9
1.5
3.8
1.5
Northern cardinal
Cardinalis cardinalis
Pre
1
7
159
P(block) P(treat)
P(year)
P(treat*year)
df(2,12) df(5,12)
0.70
0.11
df(3,12)
0.01
df(5,12)
0.13
0.87
0.01
<0.005
0.11 CABALTABHTABLTBBHTBB
0.03
0.17
0.04
0.56
0.62
0.04
0.04
0.68 CABABHTABLTABHTBABLTBB
0.62
0.27
0.01
0.43
0.32
0.50
0.03
0.75
0.07
0.02
0.30
0.37
0.02
0.34
0.26
0.70
0.27
0.25
0.08
0.08
0.93
0.13
0.01
0.52
Table B.2 (continued).
Treatments
C
Species
Northern parula
HB
HT
Treatment Effect
LT
HTxHB
LTxHB
Year Mean
PreA 0.0
SE
0.0
Mean
0.0
SE Mean SE Mean SE Mean SE
0.0 0.0 0.0 0.0 0.0 0.0 0.0
Mean
0.0
SE
0.0
A
1
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
6AB
0.0
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.8
0.3
7B
0.0
0.6
1.1
0.6
0.4
0.6
0.3
0.6
1.1
0.6
0.6
0.6
A
0.7
1.1
2.7
1.1
0.6
1.1
0.7
1.1
2.7
1.1
1.2
1.1
AB
1
0.4
0.5
1.4
0.5
0.0
0.5
0.0
0.5
0.0
0.5
0.6
0.5
6AB
0.4
0.8
1.4
0.8
0.6
0.8
0.3
0.8
0.0
0.8
1.6
0.8
7B
Pre
0.4
0.3
0.6
0.3
0.8
0.3
0.0
0.3
0.0
0.3
0.0
0.3
Pileated woodpecker
0.0
0.6
0.0
0.6
1.5
0.6
0.0
0.6
0.7
0.6
1.4
0.6
Drycopus pileatus
1
0.7
0.4
0.6
0.4
0.4
0.4
0.4
0.4
1.7
0.4
0.0
0.4
6
0.0
0.4
0.9
0.4
0.3
0.4
0.9
0.4
1.1
0.4
3.2
0.4
7
0.7
0.6
1.7
0.6
0.0
0.6
0.7
0.6
0.8
0.6
1.3
0.6
A
5.4
1.9
6.1
1.9
5.2
1.9
6.4
1.9
7.2
1.9
6.8
1.9
AB
1
2.9
1.8
1.6
1.8
6.1
1.8
6.0
1.8
6.4
1.8
8.2
1.8
6B
1.5
0.7
0.9
0.7
5.7
0.7
4.5
0.7
3.2
0.7
4.9
0.7
AB
5.3
1.5
2.2
1.5
4.6
1.5
2.5
1.5
6.0
1.5
6.5
1.5
A
0.0
0.5
1.0
0.5
0.4
0.5
0.0
0.5
1.3
0.5
0.0
0.5
AB
0.0
1.3
1.0
1.3
6.2
1.3
1.5
1.3
3.3
1.3
1.4
1.3
6B
0.0
1.0
0.0
1.0
3.8
1.0
4.6
1.0
5.7
1.0
9.0
1.0
B
Setophaga americana
Ovenbird
Seiurus aurocapillus
Pine warbler
Setophaga pinus
Pre
Pre
7
Prairie warbler
Setophaga discolor
Pre
1
0.0
1.0
0.7
1.0
4.6
1.0
2.9
1.0
5.5
1.0
5.3
1.0
Red-bellied woodpecker
Pre
A
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
Melanerpes carolinus
1A
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
B
0.0
0.3
0.5
0.3
1.5
0.3
1.0
0.3
1.1
0.3
2.8
0.3
7B
7
6
0.0
0.5
1.7
0.5
0.4
0.5
0.7
0.5
0.5
0.5
0.7
0.5
Red-eyed vireo
Pre
C
7.2
1.8
8.5
1.8
7.6
1.8
7.1
1.8
10.3
1.8
9.8
1.8
Vireo olivaceus
B
1
7.4
1.3
6.3
1.3
3.8
1.3
3.6
1.3
6.9
1.3
5.4
1.3
6A
4.6
0.9
1.9
0.9
3.2
0.9
3.0
0.9
3.4
0.9
2.8
0.9
AB
0.9
2.3
0.9
3.5
0.9
2.9
0.9
2.1
0.9
3.9
0.9
Red-headed woodpecker
7
Pre
6.4
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
Melanerpes erythrocephalus
1
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
6
0.0
0.6
0.3
0.6
0.3
0.6
0.3
0.6
0.3
0.6
2.5
0.6
0.4
7
0.0
0.4
0.0
0.4
0.0
0.4
0.3
0.4
2.0
0.4
1.3
Scarlet tanager
Pre
2.3
0.9
2.6
0.9
2.8
0.9
2.8
0.9
3.0
0.9
2.6
0.9
Piranga olivacea
1
2.4
0.8
1.0
0.8
2.0
0.8
2.9
0.8
2.0
0.8
2.0
0.8
6
1.3
1.0
2.8
1.0
1.9
1.0
1.7
1.0
0.7
1.0
2.9
1.0
7
1.6
0.5
1.0
0.5
1.5
0.5
1.4
0.5
1.3
0.5
0.0
0.5
Summer tanager
Pre
0.0
0.6
1.3
0.6
0.8
0.6
1.1
0.6
2.0
0.6
3.8
0.6
Piranga rubra
1
0.4
0.7
0.4
0.7
1.0
0.7
1.7
0.7
2.1
0.7
1.3
0.7
6
1.0
1.0
0.5
1.0
0.3
1.0
2.2
1.0
0.8
1.0
3.1
1.0
7
2.0
0.5
1.6
0.5
0.4
0.5
0.0
0.5
0.0
0.5
1.9
0.5
160
P(block) P(treat)
P(year)
P(treat*year)
df(2,12) df(5,12)
df(3,12)
df(5,12)
0.08
0.66
<0.005
0.76
0.09
0.06
0.11
0.87
0.95
0.26
0.41
0.05
0.66
0.12
0.02
0.55
0.02
<0.005
<0.005
0.00
0.05
<0.005
<0.005
0.01
0.06
0.35
<0.005
0.34
0.11
0.07
<0.005
0.01
0.25
0.94
0.04
0.81
0.07
<0.005
0.73
0.27
CALTAHTABABHTBABLTBB
CAHTBABLTABHTABBBLTBB
HTACABAHTBALTALTBB
Table B.2 (continued).
Treatments
C
HB
HT
Treatment Effect
LT
HTxHB
LTxHB
Species
White-breasted nuthatch
Year Mean SE
Pre 0.7 0.7
Mean SE Mean SE Mean SE Mean SE
0.0 0.7 0.0 0.7 0.3 0.7 1.3 0.7
Mean
2.1
SE
0.7
Sitta carolinensis
1
0.0
0.7
1.1
0.7
0.0
0.7
0.7
0.7
2.1
0.7
0.7
0.7
6
0.3
0.2
0.0
0.2
0.0
0.2
0.6
0.2
0.3
0.2
0.4
0.2
7
0.0
0.2
0.3
0.2
0.0
0.2
0.4
0.2
0.3
0.2
0.0
0.2
White-eyed vireo
Pre
A
0.7
0.5
0.4
0.5
0.4
0.5
0.0
0.5
0.0
0.5
0.7
0.5
Vireo griseus
1A
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
6B
0.7
1.6
0.0
1.6
2.4
1.6
4.2
1.6
6.5
1.6
6.2
1.6
7AB
0.3
0.5
0.4
0.5
4.3
0.5
3.2
0.5
2.9
0.5
1.9
0.5
PreA
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
A
1
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
6B
0.6
0.4
0.3
0.4
0.6
0.4
0.0
0.4
0.4
0.4
0.0
0.4
0.3
0.2
0.0
0.2
0.4
0.2
0.0
0.2
0.0
0.2
0.0
0.2
Worm-eating warbler
7AB
Pre
3.8
1.9
1.7
1.9
5.0
1.9
3.7
1.9
6.1
1.9
2.8
1.9
Helmitheros vermivorus
1
3.5
0.8
1.5
0.8
1.6
0.8
1.8
0.8
2.1
0.8
2.0
0.8
6
2.0
0.9
2.2
0.9
3.0
0.9
3.6
0.9
2.4
0.9
3.7
0.9
7
3.2
1.6
0.9
1.6
2.7
1.6
4.2
1.6
2.9
1.6
4.4
1.6
Yellow-bil ed cuckoo
PreA
1.7
0.9
2.1
0.9
1.0
0.9
2.8
0.9
5.1
0.9
2.6
0.9
Coccyzus americanus
B
1
0.4
0.6
0.3
0.6
0.0
0.6
0.4
0.6
1.3
0.6
0.6
0.6
B
6
0.6
0.5
0.4
0.5
0.9
0.5
0.0
0.5
0.7
0.5
1.2
0.5
7B
0.7
0.3
0.0
0.3
0.6
0.3
0.0
0.3
0.0
0.3
0.0
0.3
Yellow-breasted chat
PreA
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
Icteria virens
1AB
0.0
0.6
0.3
0.6
2.3
0.6
1.4
0.6
1.3
0.6
0.0
0.6
6C
0.0
1.9
3.9
1.9
4.0
1.9
4.6
1.9
6.8
1.9
7.6
1.9
Wood thrush
Hylocichla mustelina
P(block) P(treat)
P(year) P(treat*year)
df(2,12) df(5,12)
df(3,12)
df(5,12)
0.98
0.26
0.11
0.35
0.90
0.05
<0.005
0.02
0.99
0.41
0.06
0.95
0.06
0.25
0.25
0.93
0.48
0.36
<0.005
0.10
0.19
0.01
<0.005
A AB AB AB B B
0.16 C B LT HT LTB HTB
7B 0.0 0.9 0.0 0.9 3.1 0.9 2.2 0.9 5.7 0.9 3.2 0.9
a. Abbreviated labels are denoted as C = control, FB = frequent burn only (three year interval), HT=
heavily thinned LT= lightly thinned, HTxFB= heavily thinned with frequent burn
(three year interval) LTxFB= lightly thinned with frequent burn (three year interval)
b. Different letters among years for community variable shows a significant difference, p≤0.05.
c. Different letters among treatments indicates a significant difference among treatments, ordered from
lowest to highest density, p≤0.05.
161
Table B.3. Mean + standard error and results from Multivariate Analysis of Variance (MANOVA) of bird
community variables to six silvicultural treatments (n =3 for each treatment) in the Bankhead National
Forest. Treatment and block was the between subject factors and year (pretreatment, 1-yr post, and 6-7
post-treatment) was within subject factor.
Treatment Effect
Treatments
C
Community Variable
Species Richness
HTB
LTB
P(treat) P(year) P(treat*year)
Mean
12.4
SE
1.0
Mean
12.9
SE
1.0
Mean
13.7
SE
1.0
Mean
14.3
SE
1.0
Mean
14.8
1B
10.0
0.6
10.8
0.6
10.8
0.6
11.6
0.6
11.5
0.6
11.6
SE df(5,12) df(3,12) df(5,12)
1.0 0.04 0.00
0.98
0.6
A
13.1
0.5
14.3
0.5
15.2
0.5
14.7
0.5
14.3
0.5
14.8
0.5
A
12.3
0.7
13.5
0.7
14.1
0.7
14.0
0.7
14.7
0.7
14.1
0.7
99.6
8.3
99.1
8.3
103.3
8.3
109.4
8.3
114.1
8.3
118.6
8.3
B
1
79.9
5.1
86.6
5.1
86.6
5.1
92.8
5.1
91.8
5.1
92.8
5.1
6A
104.9
3.5
115.1
3.5
115.7
3.5
115.8
3.5
102.3
3.5
104.3
3.5
A
99.4
4.1
118.7
4.1
117.8
4.1
114.1
4.1
118.6
4.1
125.6
4.1
A
0.9
0.0
0.9
0.0
0.9
0.0
0.9
0.0
0.9
0.0
0.9
0.0
AB
0.9
0.0
0.9
0.0
0.9
0.0
0.9
0.0
0.9
0.0
0.9
0.0
6AB
0.9
0.0
1.0
0.0
0.9
0.0
0.9
0.0
0.9
0.0
0.9
0.0
B
0.9
0.0
1.0
0.0
1.0
0.0
0.9
0.0
1.0
0.0
0.9
0.0
2.5
0.1
2.4
0.1
2.5
0.1
2.6
0.1
2.7
0.1
2.6
0.1
1A
2.4
0.1
2.6
0.1
2.7
0.1
2.8
0.1
2.6
0.1
2.5
0.1
B
6
2.6
0.1
2.8
0.1
3.0
0.1
3.0
0.1
2.9
0.1
3.0
0.1
AB
2.5
0.1
2.6
0.1
2.8
0.1
2.8
0.1
2.9
0.1
2.7
0.1
PreA
11.3
2.4
11.9
2.4
9.8
2.4
12.5
2.4
17.8
2.4
17.0
2.4
B
7.6
2.7
5.2
2.7
10.2
2.7
15.5
2.7
12.0
2.7
12.9
2.7
6A
7.9
1.3
9.1
1.3
12.9
1.3
11.4
1.3
9.8
1.3
14.9
1.3
A
13.7
2.0
7.8
2.0
9.7
2.0
6.4
2.0
17.2
2.0
12.0
2.0
AB
10.6
3.2
13.7
3.2
16.8
3.2
15.2
3.2
17.1
3.2
17.9
3.2
1A
9.0
3.5
8.3
3.5
19.6
3.5
12.1
3.5
16.5
3.5
10.8
3.5
B
10.9
9.0
5.5
9.0
20.4
9.0
47.5
9.0
27.4
9.0
33.9
9.0
AB
9.3
3.4
4.5
3.4
22.7
3.4
15.7
3.4
24.8
3.4
20.9
3.4
A
5.9
2.5
5.3
2.5
8.7
2.5
6.9
2.5
8.3
2.5
4.3
2.5
B
1
5.1
1.5
4.5
1.5
3.6
1.5
3.4
1.5
2.8
1.5
2.0
1.5
6A
2.7
1.0
3.9
1.0
5.5
1.0
5.4
1.0
6.2
1.0
10.2
1.0
A
4.6
2.3
1.6
2.3
8.4
2.3
5.8
2.3
7.3
2.3
4.9
2.3
PreA
6.8
2.1
5.1
2.1
8.5
2.1
6.2
2.1
13.3
2.1
11.1
2.1
B
1
4.8
2.1
8.7
2.1
9.7
2.1
10.0
2.1
10.0
2.1
7.9
2.1
6A
5.2
1.6
6.1
1.6
8.1
1.6
10.4
1.6
8.6
1.6
16.8
1.6
A
6.5
2.0
11.4
2.0
6.6
2.0
4.3
2.0
12.1
2.0
13.5
2.0
Pre
A
7
Pre
1
7
Shannon-Weiner Diversity
LT
SE
1.0
7
Species Evenness
HT
Year Mean
PreA 12.4
6
Relative Abundance
B
Pre
A
7
0.03
0.00
0.38
0.10
0.05
0.65
0.00
0.00
0.61
0.06
0.09
0.03
0.00
0.04
0.10
0.57
0.05
0.27
0.03
0.87
0.03
0.21
0.00
0.53
CABABLTBABHTABHTBABLTB
Nesting Guild
Tree
1
7
Shrub
Pre
6
7
Ground
Pre
7
Cavity
7
Parasite
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
B
1
0.9
0.4
0.0
0.4
0.6
0.4
0.6
0.4
1.7
0.4
1.0
0.4
6A
0.0
0.3
0.0
0.3
0.4
0.3
0.0
0.3
0.4
0.3
0.5
0.3
A
0.0
0.4
0.0
0.4
0.4
0.4
0.0
0.4
0.8
0.4
0.0
0.4
Pre
7
A
162
BACABHTBCLTBCDHTBCDLTCD
Table B.3 (continued).
Treatments
C
Community Variable
Foraging Guild
Ground
Foliage
Bark
Arial
Year
B
Mean
SE
PreA
3.1
B
1
13.0
6A
A
HT
Mean
SE
1.4
4.4
5.2
16.3
3.4
1.5
7
3.2
2.0
PreA
24.4
1B
Treatment Effect
LT
HTB
Mean
SE
Mean
SE
1.4
3.8
1.4
9.6
5.2
10.3
5.2
4.9
1.5
1.5
8.3
1.5
18.1
2.3
2.0
9.6
2.0
7.4
4.7
22.8
4.7
30.4
4.7
2.7
4.7
16.1
4.9
17.1
4.9
29.0
4.9
22.9
6A
20.2
2.5
17.6
2.5
27.4
2.5
7A
20.5
4.1
13.0
4.1
27.1
4.1
PreA
6.8
1.7
6.6
1.7
8.9
1B
3.9
2.1
5.0
2.1
6A
3.1
2.3
3.4
7A
7.8
2.1
6.4
PreA
1.8
0.6
B
1
1.6
6A
1.0
A
LTB
Mean
SE
1.4
4.8
5.2
21.9
1.5
2.0
P(treat) P(year) P(treat*year)
Mean
SE
1.4
6.8
1.4
5.2
24.6
5.2
8.6
1.5
8.8
1.5
12.2
2.0
6.6
2.0
4.7
32.6
4.7
4.9
41.2
26.0
4.9
20.4
4.9
29.0
2.5
32.1
2.5
46.7
2.5
21.2
4.1
32.8
4.1
28.7
4.1
1.7
7.4
1.7
8.6
1.7
8.8
1.7
8.4
2.1
8.5
2.1
8.2
2.1
6.4
2.1
2.3
8.8
2.3
9.0
2.3
8.7
2.3
15.1
2.3
2.1
7.7
2.1
6.1
2.1
10.4
2.1
9.3
2.1
2.2
0.6
0.6
0.6
0.9
0.6
2.6
0.6
3.2
0.6
0.7
2.0
0.7
1.3
0.7
2.3
0.7
2.7
0.7
3.1
0.7
1.0
1.0
1.0
1.1
1.0
1.6
1.0
2.1
1.0
3.7
1.0
7
0.9
1.0
2.6
1.0
0.4
1.0
0.6
1.0
2.8
1.0
4.6
1.0
PreAB
19.8
3.7
21.5
3.7
24.6
3.7
24.9
3.7
33.8
3.7
28.4
3.7
A
1
17.3
4.1
14.0
4.1
19.0
4.1
19.1
4.1
24.2
4.1
16.9
4.1
6B
14.7
3.2
13.2
3.2
26.7
3.2
27.4
3.2
36.9
3.2
46.0
3.2
7AB
20.3
3.6
8.7
3.6
28.8
3.6
22.0
3.6
30.9
3.6
25.9
3.6
A
3.9
1.2
3.1
1.2
3.9
1.2
2.6
1.2
4.5
1.2
1.7
1.2
1B
1.2
1.4
3.1
1.4
7.0
1.4
3.2
1.4
3.0
1.4
2.8
1.4
6A
1.3
0.8
2.4
0.8
2.4
0.8
2.1
0.8
4.2
0.8
6.1
0.8
7A
2.1
1.7
2.3
1.7
3.2
1.7
3.1
1.7
7.0
1.7
1.7
1.7
PreA
12.0
2.9
11.3
2.9
15.2
2.9
13.6
2.9
18.9
2.9
20.7
2.9
B
7.8
3.4
9.8
3.4
18.1
3.4
18.0
3.4
16.2
3.4
15.0
3.4
6A
9.7
1.7
9.0
1.7
16.9
1.7
18.6
1.7
15.0
1.7
24.2
1.7
A
7
11.8
2.1
14.3
2.1
15.4
2.1
7.0
2.1
22.0
2.1
23.8
2.1
PreA
12.3
4.2
9.3
4.2
17.7
4.2
12.4
4.2
17.5
4.2
14.7
4.2
1B
10.1
2.2
8.2
2.2
7.7
2.2
9.7
2.2
7.4
2.2
6.8
2.2
6AB
7.5
1.5
8.9
1.5
14.0
1.5
10.3
1.5
10.3
1.5
14.9
1.5
AB
7
12.0
2.1
6.0
2.1
12.1
2.1
12.1
2.1
10.0
2.1
6.8
2.1
PreA
17.7
3.5
23.8
3.5
21.1
3.5
23.6
3.5
32.2
3.5
29.3
3.5
df(5,12) df(3,12) df(5,12)
0.00
0.00
0.53
CABAHTABLTABLTBBCHTBBC
0.00
0.02
0.25
BBCCBCLTABHTABLTBABHTBA
0.11
0.66
0.36
0.01
0.83
0.88
HTACABLTABBABHTBABLTBB
0.00
0.00
0.03
BBCCBCLTABHTABLTBABHTBA
0.22
0.98
0.13
0.00
0.70
0.05
0.41
0.01
0.55
0.02
0.01
0.02
CABALTABHTABHTBABLTBB
0.00
0.00
0.01
CABALTABHTAB LTBBHTBB
Migratory Guild
Neotropical
Temperate
Resident
Pre
1
CABALTABHTABHTBABLTBB
Habitat Guild
Interior
Interior/Edge
Open/Edge
1B
14.8
2.8
17.2
2.8
21.5
2.8
23.0
2.8
19.0
2.8
19.3
2.8
6A
14.6
1.9
14.1
1.9
22.2
1.9
21.3
1.9
19.1
1.9
29.4
1.9
7A
20.6
3.6
17.1
3.6
21.2
3.6
10.0
3.6
29.2
3.6
27.1
3.6
A
2.8
2.1
2.5
2.1
4.7
2.1
4.3
2.1
7.5
2.1
6.3
2.1
AB
1
1.6
3.5
3.0
3.5
14.9
3.5
9.7
3.5
13.5
3.5
8.6
3.5
6B
2.4
3.5
1.7
3.5
7.1
3.5
16.8
3.5
23.0
3.5
31.9
3.5
7AB
1.4
1.8
2.2
1.8
16.0
1.8
10.0
1.8
21.2
1.8
17.4
1.8
Pre
a. Abbreviated labels are denoted as C = control, FB = frequent burn only (three year interval), HT=
heavily thinned LT= lightly thinned, HTxFB= heavily thinned with frequent burn (three year interval)
LTxFB= lightly thinned with frequent burn (three year interval)
b. Different letters among years for community variable shows a significant difference, p≤0.05.
c. Different letters among treatments indicates a significant difference among treatments, ordered from
lowest to highest density, p≤0.05
163
164
ACFL
BAWW
BGGN
BHCO
BHNU
BHVI
BLJA
BWWA
BTGW
CACH
CAWR
DOWO
EABL
EAPH
EATO
EAWP
GCFL
HOWA
INBU
KEWA
NOCA
NOFL
NOPA
MODO
OVEN
PIWA
PIWO
PRWA
RBWO
REVI
RHWO
SCTA
SUTA
ETTI
WBNU
WEVI
WEWA
WOTH
YBCH
YBCU
YTVI
Species
Stand (Block + Treatment)
B1T1 B1T2 B1T3 B1T4 B1T5 B1T6 B1T7 B1T8 B1T9 B2T1 B2T2 B2T3 B2T4 B2T5 B2T6 B2T7 B2T8 B2T9 B3T1 B3T2 B3T3 B3T4 B3T5 B3T6 B3T7 B3T8 B3T9 B4T1 B4T2 B4T3 B4T4 B4T5 B4T6 B4T7 B4T8 B4T9
0
0
1
0
0
0
0
0
1
0
0
1
0
0
0
0
0
0
0
2
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
1
1
2
2
4
3
2
2
2
2
0
3
3
1
0
3
4
2
4
1
4
2
0
0
4
3
1
1
1
3
1
1
1
1
3
0
0
0
2
1
0
1
1
0
0
0
0
0
0
3
0
0
1
0
0
1
1
2
0
1
1
1
1
0
2
1
1
1
2
3
0
0
0
1
0
1
1
1
1
0
0
0
0
0
0
2
0
1
1
0
0
0
1
0
2
0
1
0
0
0
0
0
0
0
0
1
0
0
0
0
1
1
0
1
0
0
0
0
0
0
0
2
1
0
1
0
0
0
0
0
1
0
0
0
0
0
0
1
2
2
3
1
1
0
0
3
0
0
1
0
0
0
0
0
0
0
0
3
0
0
0
2
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
1
1
1
0
2
1
1
1
3
1
2
1
0
0
1
0
0
0
1
0
1
1
1
0
0
1
1
1
2
1
0
0
1
1
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
1
0
0
1
0
0
1
1
2
2
0
3
2
2
0
1
0
0
3
0
3
1
0
0
1
0
2
1
0
0
2
0
0
0
2
0
0
0
2
0
1
2
1
0
0
0
5
2
1
3
0
3
0
0
3
2
1
1
4
4
0
1
1
3
0
1
0
5
1
0
2
2
0
1
1
0
3
1
0
2
3
0
1
2
2
1
1
0
0
1
0
0
1
0
1
0
0
0
0
1
0
1
0
3
2
1
2
2
1
1
0
2
1
2
0
0
0
1
0
2
0
1
0
1
0
0
0
1
1
2
0
0
0
2
1
0
0
0
2
1
0
1
1
0
1
0
0
1
1
0
2
1
2
0
0
0
0
0
0
0
0
0
0
0
0
0
0
2
0
1
0
0
0
0
0
0
0
1
0
1
0
0
0
1
0
0
0
0
0
0
0
0
1
0
0
1
0
0
0
1
0
1
0
1
1
0
0
1
0
0
0
0
0
0
1
0
0
0
0
0
0
0
1
1
0
0
1
0
0
0
2
0
0
3
1
0
0
0
0
0
0
3
1
4
1
0
0
0
1
0
0
1
3
2
0
2
0
1
2
4
5
5
0
0
1
0
0
1
1
0
0
1
0
0
1
0
0
1
2
1
3
0
0
1
1
1
2
0
1
0
0
3
0
3
0
3
3
2
3
1
1
3
0
0
1
0
0
0
0
0
2
0
0
0
1
1
0
0
2
2
0
0
0
2
0
1
3
3
0
2
0
1
2
1
1
1
1
1
4
4
2
0
3
3
2
2
0
2
5
0
0
6
3
7
0
0
2
2
0
0
3
4
2
1
0
5
5
3
1
1
4
0
0
2
1
0
1
3
0
0
0
0
0
1
2
5
2
3
3
0
0
0
3
0
6
4
1
1
1
0
1
1
4
4
6
5
2
0
0
0
0
1
1
1
1
2
0
0
0
1
0
0
0
0
2
0
0
0
0
0
0
0
1
3
0
0
0
1
1
0
1
3
2
2
4
0
3
3
5
4
2
2
2
3
3
2
3
2
1
1
1
2
2
4
2
2
3
2
2
2
2
3
2
2
2
2
2
2
1
0
0
0
1
0
1
0
0
0
0
0
0
0
0
0
0
1
2
0
1
0
0
0
0
0
0
0
0
0
0
2
0
0
1
0
1
0
0
0
0
0
0
0
0
0
0
0
3
0
1
1
0
1
1
0
2
0
1
0
2
1
1
0
0
2
1
1
1
1
2
1
3
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
2
1
0
0
0
0
0
0
0
0
0
1
1
0
0
0
1
0
1
0
0
1
1
1
0
1
0
0
0
0
0
1
0
1
0
2
1
0
0
0
0
1
0
3
5
2
0
0
1
0
1
1
2
2
4
3
2
3
0
5
3
2
1
4
2
7
4
6
7
9
2
3
5
3
4
3
5
5
2
4
2
4
5
3
4
3
4
1
1
1
0
1
1
2
1
2
1
1
4
0
0
1
1
1
1
1
0
1
0
2
1
1
1
2
0
2
1
1
2
1
3
1
1
0
0
1
4
2
2
5
2
5
0
0
0
1
2
4
3
6
5
0
0
0
5
3
3
1
5
6
0
1
0
2
5
8
8
6
5
0
0
1
1
1
1
1
2
1
0
1
1
0
1
1
1
1
0
0
0
1
0
0
0
0
2
1
0
1
1
2
1
1
2
2
0
5
4
2
2
3
2
2
0
3
7
2
2
2
2
1
1
2
2
7
2
3
2
2
1
1
1
2
6
3
0
2
2
1
1
4
5
0
0
0
1
0
0
1
1
0
0
0
0
0
1
2
1
2
0
0
0
0
0
0
3
1
2
1
0
1
1
1
1
1
2
0
0
3
2
0
2
1
2
2
1
1
0
1
0
1
1
2
3
1
2
1
0
3
0
1
1
1
1
1
1
2
1
1
0
3
3
2
2
1
2
1
0
0
0
1
0
0
3
2
1
0
0
0
1
1
1
2
0
2
1
0
0
2
0
0
3
0
1
1
2
1
0
2
0
0
2
0
0
1
0
2
0
0
2
2
2
1
1
2
1
1
1
4
2
2
3
1
3
2
0
2
1
2
1
3
1
2
1
1
2
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
1
1
0
0
0
1
0
0
0
2
1
1
1
1
0
2
1
3
1
1
1
4
1
1
1
1
2
3
2
1
6
3
0
1
0
3
2
2
1
6
4
2
2
0
0
4
2
2
5
4
3
2
2
4
3
2
1
4
1
6
5
0
2
6
0
0
2
3
2
4
2
2
4
1
3
4
2
3
5
4
4
2
2
1
1
6
0
0
0
0
0
0
1
0
0
1
0
0
0
0
0
0
0
1
0
2
0
0
0
0
0
0
0
1
2
0
2
0
0
0
0
0
0
0
1
4
4
3
5
3
3
0
0
0
2
2
5
2
4
9
0
0
0
3
1
2
2
10
2
0
3
0
1
4
7
9
8
5
0
0
1
0
1
0
1
1
0
0
0
0
1
0
0
0
1
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
2
4
2
0
0
0
0
0
1
0
0
0
0
0
1
0
0
0
1
0
0
1
0
2
0
0
1
1
Table B.3. Raw data from 2013 bird survey data collected on 36 research stands in the Bankhead National Forest and used in CCA analysis.
VITA
Emily Summers, the daughter of Randy and Brenda Summers, was born on
September 1, 1988 in Sherwood, TN. She attended and graduated from Auburn
University in 2010 with a undergraduate degree in Zoology. Upon completing her BS
degree, she came to Alabama A&M University in 2011 to pursue a master’s degree in
Plant and Soil Science, concentrating in Wildlife Ecology.