RESPONSE OF FOREST HERPETOFAUNA TO VARYING LEVELS OF
OVERSTORY TREE RETENTION IN NORTHERN ALABAMA
by
ZACHARY FELIX
A DISSERTATION
Submitted in partial fulfillment of the requirements
for the degree of Doctor of Philosophy
in the Department of Plant & Soil Science
in the School of Graduate Studies
Alabama A & M University
Normal, AL 35762
May 2007
RTIFICATE O
F APPROVAL
Submitted by ZACHARY FELIX in partial fulfillment of the requirements for the
degree of DOCTOR OF PHILOSOPHY specializing in WILDLIFE 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
ZACHARY IRA FELIX
2007
iii
This dissertation is dedicated to three of my biggest supporters; my big brother,
Jed Kissane, my uncle, John Patrick Sullivan, and my Father, Bill Felix.
iv
RESPONSE OF FOREST HERPETOFAUNA TO VARYING LEVELS OF
OVERSTORY TREE RETENTION IN NORTHERN ALABAMA
Zachary Felix, M.S. Marshall University, 2001.
Dissertation Advisor: Yong Wang
Since 2002 I have been monitoring the response of a community of reptiles and
amphibians to a gradient of overstory tree removal levels ranging from clearcuts to
control. This project was a collaboration between Alabama A&M, the US Forest Service
and private timber companies. Micro- climate and habitat measures were taken each year
to document changes due to treatments and over time. Tree harvest created a gradient of
conditions from warm and dry daytime conditions on clearcuts to cool more humid
conditions on controls. Microhabitat features also responded to treatments forming a
gradient of open canopies with plentiful herbaceous and woody vegetation, bare ground
and abundant slash and coarse woody debris on clearcut treatments to more closed
canopy stands dominated by leaf litter in control treatments. Many parameters of both
micro- climate and habitat appeared to recover by the 4th year post-treatment in that
values were similar on treated stands to control conditions. Amphibian and reptile
communities were characterized using drift fences, coverboards, and artificial pools. The
most species-rich units were consistently those with intermediate levels of tree retention
(25 and 50% of original basal area). Certain guilds of species showed a significant
response to treatments and also consistent associations with specific microhabitat
variables. Oviposition rates of 4 amphibian species which bred in artificial pools were
affected by treatments. Some species, such as Cope’s gray treefrog, Hyla chrysoscelis,
v
responded favorably, while others, including the mountain chorus frog, Pseudacris
brachyphona, responded negatively. Radiotelemetry of eastern box turtles revealed that,
while movement patterns and home range sizes were not affected by tree removal,
microhabitat use was. In areas with 25-50% of the canopy retained turtles relied heavily
on slash piles for habitat, possibly to provide them with cool, moist conditions. This
project highlights the ways in which forest management and conservation of amphibians
and reptiles are compatible and makes several recommendations for future management
and research in this area.
KEY WORDS: Amphibians, Reptiles, Cumberland Plateau, Silviculture, Shelterwood,
Clearcut
vi
TABLE OF CONTENTS
CERTIFICATE OF APPROVAL…………………………………………………. ii
ABSTRACT AND KEYWORDS………………………………………………… v
LIST OF TABLES………………………………………………………………… xii
LIST OF FIGURES……………………………………………………………….. xvi
CHAPTER 1. INTRODUCTION………………………………………………… 1
Hypotheses……………………………………………………………….. 4
Literature Review………………………………………………………… 5
Bibliography……………………………………………………………… 9
CHAPTER 2. RESPONSE OF MICROCLIMATE AND MICROHABITAT TO
VARIOUS LEVELS OF OVERSTORY TREE RETENTION…………………… 15
Study Area………………………………………………………………… 17
Methods…………………………………………………………………… 20
Sampling………………………………………………………….. 20
Stand density………………………………………………. 20
Microclimate……………………………………………… 21
Microhabitat……………………………………………… 21
vii
Data Analysis…………………………………………………….. 22
Stand density……………………………………………… 22
Microclimate……………………………………………… 22
Microhabitat………………………………………………. 22
Results ……………………………………………………………………. 23
Microclimate……………………………………………… 23
Microhabitat………………………………………………. 24
Discussion………………………………………………………………… 41
Microclimate……………………………………………… 41
Microhabitat………………………………………………. 43
Bibliography….……………………………………………………………. 44
CHAPTER 3. RESPONSE OF REPTILE AND AMPHIBIAN COMMUNITIES TO
VARIOUS LEVELS OF OVERSTORY TREE RETENTION…………………… 48
Study Area………………………………………………………………… 50
Methods…………………………………………………………………… 53
Sampling………………………………………………………….. 53
Herpetofaunal sampling…………………………………… 53
Data analysis………………………………………………………. 55
Relative abundance……………………………………….. 55
Diversity indices………………………………………….. 55
Similarity………………………………………………….. 55
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Canonical Correspondence Analysis……………………… 56
Results …………………………………………………………………….. 56
Relative abundance………………………………………… 57
Diversity indices…………………………………………… 65
Similarity………………………………………………….. 70
Canonical Correspondence Analysis………………………. 76
Discussion………………………………………………………………... 78
Bibliography………………………………………………………………. 81
CHAPTER 4. RESPONSE OF LUNGLESS SALAMANDERS TO VARIOUS
LEVELS OF OVERSTORY TREE RETENTION………………………………. 85
Study Area………………………………………………………………… 86
Methods…………………………………………………………………… 89
Sampling………………………………………………………….. 89
Salamander sampling……………………………………… 89
Data analysis………………………………………………………. 90
Results …………………………………………………………………….. 91
Relative abundance……………………………………….. 91
Demographics…………………………………………….. 91
Body size…………………………………………………. 92
Soil temperature…………………………………………… 92
Discussion………………………………………………………………… 96
ix
Bibliography…….………………………………………………………… 98
CHAPTER 5. EFFECT OF VARIOUS LEVELS OF OVERSTORY TREE
RETENTION ON REPRODUCTIVE OUTPUT OF POOL-BREEDING
AMPHIBIANS……………………………………………………………………. 102
Study Area………………………………………………………………… 103
Methods…………………………………………………………………… 107
Stand density…………………………………………….
107
Artificial pools…………………………………………….. 107
Environmental…………………………………………….. 107
Amphibian sampling……………………………………… 108
Data analysis.…...…………………………………………. 109
Results ……………………………………………………………………. 109
Environmental…………………………………………….. 109
Egg masses........................................................................... 110
Metamorphs......................................................................... 110
Discussion…………………………………………………………………. 122
Bibliography…...………………………………………………………….. 126
CHAPTER 6. MOVEMENTS AND HABITAT USE OF EASTERN BOX
TURTLES IN FOREST STANDS MANAGED FOR TIMBER………………….. 130
Study Area…………………………………………………………………. 132
x
Methods……………………………………………………………………. 134
Radiotelemetry…………………………………………….. 134
Movement and home range………………………………… 135
Macrohabitat use…………………………………………… 136
Microhabitat use…………………………………………… 138
Results ………………………………………………………………………139
Movement………………………………………………….. 139
Home range……………………………………………….. 139
Macrohabitat use………………………………………….. 140
Microclimate……………………………………………… 144
Microhabitat use…………………………………………… 144
Discussion…………………………………………………………………. 147
Bibliography……………………………………………………………….. 151
CHAPTER 7. CONCLUSIONS AND MANAGEMENT
RECOMMENDATIONS…………………………………………………………. 155
Management Recommendations………………………………………….. 155
Research Recommendations………………………………………………. 162
Bibliography….……………………………………………………………. 164
xi
LIST OF TABLES
Table
2.1
Page
Average microclimatic variables for five basal area retention
treatments……………………………………………………………………. 25
2.2
Average microhabitat variables for five basal area retention
treatments………………………………………………………………..
32
2.3
Results of principal components analysis of microhabitat variables…….
39
3.1
Species of amphibians and reptiles, their guild assignment, and their
total captures on five basal area retention treatments…………………………58
3.2
Mean relative abundance of total reptiles, total amphibians, guilds,
and common species on five basal area retention treatments……………….. 59
3.3
Mean indices of amphibian diversity, years separate, 2002-2005 on
five basal area retention treatments…………………………………………. 66
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3.4
Mean indices of amphibian diversity, years combined, 2002-2005
on five basal area retention treatments……………………………………… 66
3.5
Mean indices of reptile diversity, years separate, 2002-2005
on five basal area retention treatments……………………………………… 71
3.6
Mean indices of reptile diversity, years combined, 2002-2005
on five basal area retention treatments………………………………………. 71
3.7
Morisita’s indices of similarity for amphibian communities
2003-2005 on five basal area retention treatments…………………………. 74
3.8
Bray-Curtis indices of similarity for amphibian communities
2003-2005 on five basal area retention treatments…………………………. 74
3.9
Morisita’s indices of similarity for reptile communities
2003-2005 on five basal area retention treatments………………………….. 75
3.10 Bray-Curtis indices of similarity for reptile communities
2003-2005 on five basal area retention treatments………………………….. 75
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4.1
Relative abundance of two species of Plethodon salamanders
for five basal area retention treatments in Jackson County…………………. 93
4.2
Ratio of juvenile:adult of Plethodon dorsalis for five basal area
retention treatments………………………………………………………… 93
4.3
Ratio of male:female of Plethodon dorsalis for five basal
area retention treatments…………………………………………………….. 94
4.4
Average log Mass:Snout Vent Length ratio of Plethodon dorsalis for five
basal area retention treatments……………………………………………… 94
5.1
Biophysical parameters, number of amphibian egg masses,
and number of metamorphs in artificial pools……………………… ……… 111
6.1
Data on eastern box turtles radiotracked and their home
range sizes and overwintering sites………………………………………….. 141
6.2
Home range size estimates of male, female, and all
eastern box turtles radiotracked……………………………………………… 142
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6.3
Results of matched-pair logistic regression for female
eastern box turtles……………………………………………………………. 146
6.4
Results of matched-pair logistic regression for male
eastern box turtles……………………………………………………………. 146
7.1
Major conclusions about effects overstory tree
retention treatments on herpetofauna………………………………………… 157
7.2
Costs and benefits of choosing one treatment versus
choosing another of two alternative treatment types………………………… 158
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LIST OF FIGURES
Figure
Page
2.1
Location and layout of study sites in Jackson County, Alabama…………… 18
2.2
Range of day- and nighttime air temperature across
canopy retention treatments………………………………………………… 26
2.3
Range of day- and nighttime soil temperature across
canopy retention treatments………………………………………………… 27
2.4
Range of day- and nighttime relative humidity across
canopy retention treatments…………………………………………………. 28
2.5
Mean day- and nighttime air temperature across
canopy retention treatments………………………………………………… 29
2.6
Mean day- and nighttime soil temperature across
canopy retention treatments………………………………………………… 30
xvi
2.7
Mean day- and nighttime relative humidity across
canopy retention treatments………………………………………………… 31
2.8
Basal area across canopy retention treatments…………………………
33
2.9
Canopy cover across canopy retention treatments……………………..
33
2.10 Litter depth across canopy retention treatments………………………
34
2.11 Percent cover of leaf litter across canopy retention treatments………..
34
2.12 Percent cover of bare ground across canopy retention treatments…….
35
2.13 Percent cover of herbaceous vegetation across
canopy retention treatments………………………………………………… 35
2.14 Percent cover of woody vegetation across canopy
retention treatments…………………………………………………………. 36
2.15 Percent cover of slash across canopy retention treatments…………………. 36
2.16 Percent cover of rock across canopy retention treatments……………..……. 37
xvii
2.17 Percent cover of coarse woody debris across
canopy retention treatments………………………………………………… 37
2.18 Microhabitat principal component scores across
canopy retention treatments………………………………………………… 40
3.1
Location and layout of study sites in Jackson County, Alabama…………… 51
3.2
Number of species detected in drift fences on
canopy retention treatments………………………………………………… 60
3.3
Relative abundance of amphibians on canopy retention treatments………… 60
3.4
Relative abundance of reptiles on canopy retention treatments…………….. 61
3.5
Relative abundance of aquatic salamanders on
canopy retention treatments………………………………………………… 61
3.6
Relative abundance of terrestrial salamanders on
canopy retention treatments………………………………………………… 62
xviii
3.7
Relative abundance of large-pool frogs on
canopy retention treatments………………………………………………… 62
3.8
Relative abundance of small-pool frogs on
canopy retention treatments…………………………………………………. 63
3.9
Relative abundance of large-bodied snakes on
canopy retention treatments………………………………………………… 63
3.10 Relative abundance of small-bodied snakes on
canopy retention treatments………………………………………………… 64
3.11 Relative abundance of lizards on canopy retention treatments……………... 64
3.12 Relative abundance of Plethodon glutinosus on
canopy retention treatments………………………………………………… 67
3.13 Relative abundance of Bufo americanus on
canopy retention treatments………………………………………………… 67
3.14 Shannon-Wiener diversity for total amphibian captures 2002-2005……….. 68
xix
3.15 Evenness for total amphibian captures 2002-2005………………………….. 68
3.16 Simpson’s diversity (1-dominance) for total
amphibian captures 2002-2005……………………………………………… 69
3.17 Species richness for total amphibian captures 2002-2005…………………. 69
3.18 Shannon-Wiener diversity for total reptile captures 2002-2005……………. 72
3.19 Evenness for total reptiles captures 2002-2005……………………………. 72
3.20 Simpson’s diversity (1-dominance) for total
reptile captures 2002-2005…………………………………………………. 73
3.21 Species richness of total reptile captures 2002-2005……………………….. 73
3.22 Species richness of total reptiles and amphibian
captures 2002-2005…………………………………………………………. 74
3.23 Canonical Correspondence axes ordinating
2003 reptile and amphibian guilds and microhabitat measures…………….. 77
xx
3.24 Canonical Correspondence axes ordinating
2004 reptile and amphibian guilds and microhabitat measures……………… 77
3.25 Canonical Correspondence axes ordinating
2005 reptile and amphibian guilds and microhabitat measures……………… 78
4.1
Location and layout of study sites in Jackson County, Alabama…………… 87
4.2
Relative abundance of Plethodon dorsalis across
canopy retention treatments………………………………………………… 94
4.3
Relative abundance of Plethodon glutinosus across
canopy retention treatments………………………………………………… 94
4.4
Average log Mass:SVL ratio of P. dorsalis across
canopy retention treatments………………………………………………… 95
4.5
Average soil temperature during coverboard surveys
across canopy retention treatments………………………………………… 95
5.1
Location and layout of study sites in Jackson County, Alabama………….. 104
xxi
5.2
Canopy cover (%) above artificial pools
across canopy retention treatments………………………………………….. 113
5.3
Water temperature (oC) of artificial pools
across canopy retention treatments…………………………………………. 113
5.4
Dissolved oxygen content (ppm) of artificial pools
across canopy retention treatments………………………………………… 114
5.5
pH of artificial pools across canopy retention treatments………………….
5.6
Number of Hyla chrysoscelis egg masses from
114
artificial pools across canopy retention treatments………………………….. 115
5.7
Number of Pseudacris brachyphona egg masses from
artificial pools across canopy retention treatments…………………………. 115
5.8
Number of Ambystoma maculatum egg masses
across canopy retention treatments…………………………………………. 116
5.9
Total number of Bufo americanus egg masses
from artificial pools across canopy retention treatments…………………….. 116
xxii
5.10 Total number of Hyla chrysoscelis metamorphs
from artificial pools across canopy retention treatments……………………. 117
5.11 Total number of Pseudacris brachyphona metamorphs
from artificial pools across canopy retention treatments…………………… 117
5.12 Total number of Bufo americanus metamorphs
from artificial pools across canopy retention treatments…………………….. 118
5.13 Relationship between number of egg masses
and number of metamorphs for Hyla chrysoscelis………………………….. 120
5.14 Relationship between number of egg masses
and number of metamorphs for Pseudacris brachyphona…………………… 121
6.1
Distance moved by eastern box turtles on
unharvested areas versus harvested areas…………………………………… 142
6.2
Relationship between minimum convex polygon home range size
and percent of radiolocations on unharvested areas for eastern box turtles…. 143
xxiii
6.3
Relationship between 50% volume fixed kernel home range size
and percent of radiolocations on uncut areas for eastern box turtles……….. 143
6.4
Relationship between 95% volume fixed kernel home range size
and percent of radiolocations on uncut areas for eastern box turtles……….. 144
xxiv
ACKNOWLEDGMENTS
I would to thank my committee members for their advice and guidance through this
degree. I especially thank Dr. Yong Wang for his endless kindness, patience, and
knowledge; all students should be so lucky to have such a great advisor. I am thankful to
the United States Environmental Protection Agency’s Greater Research Opportunities
Fellowship program for financial support. The United States Forest Service provided
funding for equipment and field help, as well as manpower for field help. Thanks to my
labmates for their support and advice including Adrian Lesak, Bill Sutton, John Carpenter,
Florence Chan, and Jill Wick. Field help was provided by the following: Helen Czech,
Idun Guenther, Ryan Sisk, Bill Sutton, David Lamfrom, Cassie Smith, Jeff Crocker,
Mizuki Takahasi, Jessica Wooten, Julia Bartens, Tom Smith, and Pete Davis. Gwen
Tenney provided much needed support during the writing process and to her I am
thankful.
This publication “RESPONSE OF FOREST HERPETOFAUNA TO
VARYING LEVELS OF OVERSTORY TREE RETENTION IN NORTHERN
ALABAMA” was developed under a STAR Research Assistance Agreement No.
U 916242 awarded by the U.S. Environmental Protection Agency. It has not been
formally reviewed by the EPA. The views expressed in this document are solely
those of Zachary Felix and the EPA does not endorse any products or commercial
services mentioned in this publication
xxv
CHAPTER 1
INTRODUCTION
Historically, management of forests by government agencies and private industry
revolved around timber production. A new policy has emerged which places greater
emphasis on ecosystem management, whose goal is to continue using forests for timber
production while maintaining ecosystem integrity (Kessler et al. 1992, Sharitz et al.
1992). For this approach to work, a better understanding of the relationships of
silvicultural practices and populations of forest biota is needed.
Because of their intermediate positions on food webs, efficient production of new
tissue, and large biomass relative to other vertebrate groups (Pough 1983, Hairston 1987,
Petranka and Murray 2001), reptiles and amphibians (herpetofauna) should be viewed as
integral parts of forest ecosystems, and therefore be considered in forest management
plans. For example, biomass of salamanders alone in some forest ecosystems is twice
that of birds and equal to that of small mammals, and their annual production of biomass
exceeds that of birds and mammals combined (Burton and Likens 1975a,b). Wyman
(1998) demonstrated that, by reducing invertebrate numbers, salamanders may reduce
decomposition rates of forest litter by up to 17%, arguably impacting carbon dynamics of
forest ecosystems. Some terrestrial turtles have been identified as vectors of seed
1
dispersal (Liu et al. 2004). As major predators of rodents, snakes can have effects on
control of their populations (Fitch 1949). Rodents, in turn, are capable of impacting plant
community structure (Hayword and Phillipson 1979). These examples point to the
importance of herpetofauna in ecosystems, and show that it is plausible that herpetofauna
can indirectly alter forest processes such as regeneration, and nutrient cycling.
Diversity of both amphibians and reptiles reach exceptionally high levels in the
southeastern United States (Kiester 1971). Reports of global declines in amphibian
populations (Blaustein et al. 1994, Gibbons et al. 2000, Stuart et al. 2004) have also
raised concerns over the effects of habitat perturbations on the group. In the southern
Appalachian region, it has been reported that 48% of amphibian species and 52% of
reptile species are listed as being of conservation concern by state or federal agencies in
some portion of their range in the region (Mitchell et al. 1999).
The four silvicultural systems most commonly used in North America are
selection, seed tree, shelterwood, and clearcut (USDA Forest Service 1973). The
selection method is used to maintain a forest with a mixture of ages, or an uneven-aged
forest. Selection is accomplished by removing trees singly or in small groups. The other
three systems maintain even-aged forests in which all trees fall into one or two age
classes. Clearcutting involves removing most or all trees in one cutting. The seed tree
method is similar to clearcutting, but a small number of trees are left as a source of seeds
for the next generation. The shelterwood method also entails removing most trees, but
the removal is accomplished in a series of partial cuts. The use of clearcutting has been
2
declining on US National Forest lands as alternative methods gain popularity (USDA
Forest Service 1973).
There is a growing body of evidence that suggests silvicultural practices can have
significant effects on populations of herpetofauna and their habitats. Upon removal of the
forest canopy, certain aspects of the microclimate and physical structure of the forest
floor are altered. Increased light penetration to the forest floor may increase ground
surface and soil temperatures thereby reducing moisture, and may result in a reduced leaf
litter layer, along with changes in vegetation structure (Gieger 1965, Chen et al. 1999,
Zheng et al. 2000). It is these changes that may be responsible for changes in species
composition and abundance of reptiles and amphibian populations by affecting
immigration and emigration rates (deMaynadier and Hunter 1995), and increasing
mortality rates (Maiorana 1977, Ash 1988).
Most existing studies investigating the interactions between silviculture and
herpetofauna compare clearcut sites to forested sites, while relatively few studies have
compared a number of intermediate levels of harvest as it relates to herpetofauna (but see
Sattler and Reichenbach, 1998; Brooks, 1999; Harpole and Haas, 1999; Grialou et al.,
2000; Ross et al., 2000, Knapp et al. 2003, Patrick et al. 2006). Unlike previous studies,
the current study was a unique opportunity to explore the interactions of intermediate
levels of overstory tree harvest and the full community of reptiles and amphibians and
their habitat. This was accomplished by comparing herpetofaunal communities among
treatments with a spectrum of overstory tree retention levels including clearcuts (0%),
25%, 50%, and 75% basal area retention treatments and controls. The study investigated
3
whether threshold levels exist, beyond which herpetofaunal communities are significantly
altered. The research also fills a gap in knowledge of the relationships between
silvicultural practices and herpetofaunal communities in the southernmost Appalachians.
This is important because these relationships can vary geographically, and by ecosystem
type (Enge and Marion 1986, McLeod and Gates 1998). Because the study was a
collaborative effort between the US Forest Service (USFS), and Mead-Westvaco
Corporation (Stevenson Land Company), results will enable forest managers to predict
the impact their actions will have on populations of reptiles and amphibians. The
objectives of the study were to compare relative abundance, species richness, species
diversity, and community structure of reptile and amphibian communities among
treatments, and investigate the relationships between these variables and habitat
characters, both biotic and physical. Basic hypotheses tested by this research were:
Ho1: Microclimatic and microhabitat parameters will not differ among treatment types
with different levels of tree retention.
Ho2: Species richness, diversity, and relative abundance of reptiles and amphibians will
not differ across tree retention treatments.
Ho3: Relative abundance and demographic characteristics of lungless salamanders will
not differ across tree retention treatments.
Ho4: Reproductive output of pool-breeding amphibians will not differ across treatments.
Ho5: Movement patterns and habitat use of eastern box turtles will not differ in harvested
and unharvested areas.
This dissertation is arranged in seven chapters. This, the first chapter, serves to introduce
the subject area, list my hypotheses, and review existing literature. Chapters 2-6 are
4
designed to address the hypotheses listed above. Chapter 7 contains an overall
conclusion and management recommendations based on the results of the research. Each
chapter is prepared as a stand alone manuscript for submission to peer-reviewed journals.
Literature Review
While relatively few studies exist relating silvicultural techniques to the
abundance of both reptiles and amphibians in the eastern United States (Enge and Marion
1986, Pais et al. 1988, Caschetta 1993, Phelps and Lancia 1995, McLeod and Gates 1998,
Ross et al. 2000, Renken et al. 2004), studies on amphibians, salamanders in particular,
are more common (Blymer and McGinnes 1977, Bennett et al. 1980, Ash 1988, Petranka
et al. 1994, Mitchell et al. 1997, Chazal and Niewiarowski 1998, Sattler and Reichenbach
1998, Harpole and Haas 1999, Knapp et al 2003, Patrick et al. 2006). Russell et al.
(2004) provided an excellent review of herpetofaunal response to forest management in
the southeastern United States.
In general, many species of reptiles increase in relative abundance upon removal
of the forest canopy, while amphibians tend to decrease in abundance (Russell et al.
2004). This is likely due to differences in physiology and natural history between the two
groups. Compared to reptiles, amphibians have smaller home ranges and are not as
capable of dispersing to more favorable conditions (Zug 1993, Stebbins and Cohen 1995).
Amphibians are also rendered more susceptible to changes in moisture levels and
temperatures associated with habitat change because of their physiology (Spotila 1972,
Duellman and Trueb 1986).
5
Snakes, as a group, tend to increase in abundance and diversity within clearcuts
(Enge and Marion 1986, Phelps and Lancia 1995, McLeod and Gates 1998, Ross et al.
2000). Some studies have shown lizards to be more abundant on clearcuts than adjacent
forests (Phelps and Lancia 1995, McLeod and Gates 1998). Others have shown lizard
abundance does not differ between harvested and unharvested sites, but species
composition does (Enge and Marion 1986, Greenberg et al. 1994). Because turtles are
generally undersampled by traditional trapping methods, trends within the group are
unclear. Results of similar studies are mixed for anurans. Some find higher abundance is
associated with forested sites (McLeod and Gates 1998, Ross et al. 2000, Patrick et al.
2006), but the presence of aquatic breeding habitat is often a more important factor (Enge
and Marion 1986, Ross et al. 2000). In nearly every study, salamanders are found in
smaller numbers in clearcuts than in forested sites, with reductions of up to 70% reported
by some investigators (Pough et al. 1987, Clawson et al. 1997, McLeod and Gates 1998,
Sattler and Reichenbach 1998, Herbeck and Larsen 1999, Ross et al. 2000, Knapp et al.
2003). In some cases, it appears salamanders can be completely eliminated from
clearcuts (Ash 1988 and 1997, Petranka et al. 1994). Results within each group vary on a
species by species basis in many cases however, and generalities should be avoided when
possible.
Species richness of reptiles and amphibians combined has been found to be
similar between clearcut and control plots, but because some species were found on
clearcuts and not in forested sites, and vice-versa, inclusion of both forested and clearcut
stands raised overall species richness of a forest (Phelps and Lancia 1995, McLeod and
6
Gates 1998). In other studies, species richness of both groups combined was higher on
forested plots than clearcuts (Enge and Marion 1986). Mean combined biomass of
reptiles and amphibians in Florida flatwoods was not different among sites, but was
apportioned differently among taxonomic groups on clearcuts and forested plots (Enge
and Marion 1986).
The few studies that have compared reptile and amphibian abundance in sites with
intermediate levels of harvest have mainly focused on terrestrial salamanders. In
Virginia, it was found that salamander abundance was greater on control plots and plots
with the understory removed by herbicide than on clearcuts or two other treatment types
that removed significant amounts of canopy (Harpole and Haas 1999, Knapp et al. 2003).
While abundance of Plethodon hubrichti, the Peaks of Otter salamander, was lower on
clearcuts compared to control plots, shelterwood cuts that removed 33-64% of basal area
appeared to have minimal impact on abundance (Sattler and Reichenbach 1998). In the
Pacific Northwest, there was no difference in salamander species diversity betweeen
control plots and plots where thinning removed an average of 16% basal area, from 57
m2/ha to 48 m2/ha. But, capture rates of western redback salamanders (Plethodon
vehiculum) were significantly lower on thinned plots post-harvest than pre-harvest
(Grialou et al. 2000). On New England plots with a residual stocking of 50-60%, the
abundance of northern redback salamanders (Plethodon cinereus) was not different than
on control plots (Brooks 1999). As increasing amounts of live trees were removed from
Pennsylvania stands, the abundance of snakes increased, while salamanders decreased.
Results of the study suggest salamander species may negatively respond to removal of
7
live tree basal area beyond a threshold of <15 m2/ha (Ross et al. 2000). This study took
place in a number of stands covering a wide variety of conditions and various forest types,
which may make patterns less evident.
Recently, research into the effects of forest management on herpetofauna has
focused on more controlled experiments and attempting to identify the proximate causes
for observed changes in abundance after harvesting. This understanding of the
mechanisms responsible for observed patterns of abundance after tree harvest is an
important step towards enabling managers to make strong inferences about the effects of
their actions on wildlife (Marzluff et al. 2000). When presented the choice between
emigrating from natal pools into old fields or closed-canopy forests, American toads
(Bufo americanus) and spotted salamanders (Ambystoma maculatum) preferentially chose
forests. Recapture patterns suggested that metamorphs of both species experienced
higher mortality in open fields (Rothermel and Semlitsch 2002). Juvenile and adult
spotted salamanders preferred forest soils over grassland soils, especially in combination
with leaf litter, suggesting that substrate choice may be important for spatial distribution
of amphibians (Rittenhouse et al. 2004). Complete removal of pine litter and coarse
woody debris (CWD) resulted in elevated activity level in mole salamanders (Ambystoma
talpoideum), potentially increasing risk of predation and dessication (Moseley et al.
2004). In the same CWD-removal treatments, diets of southern toads (Bufo terrestris)
did not differ from individuals in control areas, suggesting that CWD is not an important
foraging substrate for the species (Moseley et al 2005). Juvenile mole salamanders
experienced greater water loss in clearcut exclosures than in closed canopy stands, or
8
stands treated to reduce canopy cover by 25%. Survival was lower in clearcut exclosures
than thinned or control stands, and the authors concluded that thinning did not increase
desiccation but clearcutting did (Rothermel and Luhring 2005). Spotted and marbled
(Ambystoma opacum) salamanders experienced higher survival in forest interior
enclosures than in old fields, and survival until sexual maturity was only observed in
forest enclosures (Rothermel and Semlitsch 2006). These types of studies suggest that
amphibian populations respond to tree removal through processes such as decreased
survivorship and microhabitat and substrate selection.
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14
CHAPTER 2
RESPONSE OF MICROCLIMATE AND MICROHABITAT TO
VARIOUS LEVELS OF OVERSTORY TREE RETENTION
Changes to forest vegetation structure associated with silviculture lead to shifts in
microclimatic conditions within a forest stand. These microclimatic shifts can lead to
changes in important ecological functions such as plant regeneration and species
composition (Gray and Spies 1992), and soil respiration (Chen et al. 1999).
Microclimatic conditions in the understory can affect production in the overstory (Gieger
1965). Microclimatic conditions are also a major determinant of the distribution of plant
species in space and time (Shirley 1945, Brosofske et al. 1999). Some forests experience
such high diurnal fluctuations in microclimatic conditions that the only way to attain
adequate tree regeneration is to use a shelterwood method which buffers some of this
variability (Smith et al. 1997, Heithecker and Halpern 2006). Forest structure also
dictates the amount and types of microhabitats available to forest biota, either through
immediate and direct inputs of residual woody debris, altered future inputs such as leaf
litter, or through changes in the amount of nutrients, light, and space available thereby
altering plant growth rates. Microclimate and microhabitat can in turn affect each other
through changes in decomposition and growth rates associated with temperature shifts,
15
changes in air circulation after alteration of canopy architecture, and shifts in water
absorption and retention in response to changes in leaf litter cover (Covington 1981).
These changes in microclimate and microhabitat associated with silviculture are
important because they are critical for determining the distribution and abundance of
organisms residing in a forest stand. Air temperature was shown by Wachob (1996) to be
an important factor in the selection of avian foraging site. Reptile microsite selection is
also affected by microclimatic parameters such as air temperature and relative humidity
(Moore and Gillingham 2006). Percent cover of canopy trees has been found to be an
important factor associated with the presence or absence of amphibians, particularly
salamanders (Welsh and Lind 1995, Harpole and Haas 1999). High abundance of
reptiles and amphibians species that seek cover within logs or under loose bark, or who
are burrowers is associated with abundant coarse woody debris, including downed logs
and stumps (Enge and Marion 1986). Terrestrial amphibian abundance can be positively
associated with amount of coarse woody debris in the form of downed logs (Petranka et
al. 1994, Brooks 1999, Ross et al. 2000). Leaf litter depth and percent cover of
understory vegetation explained 63% of variation in aboveground activity of salamanders
in a study by Pough et al. (1987). DeGraaf and Rudis (1990) found that herpetofaunal
evenness was significantly correlated with litter depth. Changes to depth of leaf litter due
to prescribed burning were responsible for changes in nesting habits of ovenbirds
(Seiurus auricapollis) (Artman et al. 2001). Small mammal abundance in northern
Arizona was positively related to woody debris and shrub coverage (Converse et al.
2006).
16
Understanding the changes in forest microclimate and microhabitats associated
with canopy tree removal could help us understand and possibly predict the ways in
which organisms respond to land uses such as forest management. The time which it
takes microclimate and –habitat variables to return to pre-harvest levels is also important
for understanding the ecological effects of canopy tree removal. The objectives of this
study were to quantify the average and range of several microclimatic variables and the
average of a suite of structural, or microhabitat variables, and to test the null hypotheses
that neither canopy tree retention treatments or time since harvest impact these variables.
Study Area
This study took place in Jackson County, northeastern Alabama (Fig. 2.1). The
area is classed into the Cliff section of the Cumberland Plateau in the Mixed Mesophytic
Forest region by Braun (1950). Bailey et al. (1994) included this area in the Eastern
Broadleaf Forest (Oceanic) Province and Northern Cumberland Plateau Section.
According to Smalley (1982), the sites are located in the Mid Cumberland Plateau region,
the Strongly Dissected Portion subregion, and landtypes 16, 17, and 18 of the Strongly
Dissected Margins and Sides landtype association. The area is characterized by steep
slopes dissecting the Plateau surface and draining to the Tennessee River. Soils are
shallow to deep, stony and gravelly loam or clay, well drained, and formed in colluvium
from those on the Plateau top (Smalley 1982). Climate of the region was described as
temperate with mild winters and moderately hot summers with a mean temperature of 13
17
a)
Miller Mtn.
Jack
Gap
b)
25%
50%
clear
control -cut
clear
-cut
Block 3
75% control
Block 1
Miller Mt.
25%
N
75% 50%
50% 25% clear control
-cut
4-ha units
75%
Block 2
Jack Gap
Figure 3.1 Location of study site in Alabama (a) and layout of experimental design (b),
Jackson County, Alabama.
18
degrees C, and mean precipitation of 149 cm (Smalley 1982). Two sites were used. The
first, Miller Mountain (34o 58’ 11” N, 86o 12’ 21” W), was situated on mainly South,
Southwest facing slopes with elevations ranging from 457-518 m (Figure 2.1a). The
second, Jack Gap (34o 56’ 30” N, 86o 04’ 00” W), had a North aspect with elevations
ranging from 304-475 m. Dominant canopy tree species included oaks, including
Quercus velutina Lamarck, Q. rubra L., Q. alba L., Q. prinus L.; 46% of pretreatment
basal area (BA), hickories (Carya spp.; 15% pretreatment BA), sugar maple (Acer
saccharum Marsh.; 13% pretreatment BA) and yellow poplar (Liriodendron tulipifera L.;
9% pretreatment BA) (Schweitzer 2003). Common understory species included
flowering dogwood (Cornus florida L.), eastern redbud (Cercis canadensis L.), and
sourwood (Oxydendrum arboretum DC.).
The study followed a randomized complete block design with three blocked
replicates of five treatments involving varying levels of basal area retention of trees (Fig
2.1b). Treatments included clearcuts, 25-, 50-, and 75% retention, and controls. The
clearcuts, 25%, and 50% retention treatments were chainsaw-felled and grapple skidded
in a commercial logging operation. In the 25 and 50 percent retention treatments, trees
were marked to leave favoring dominant and codominants with high vigor, especially oak,
ash (Fraxinus spp.), and persimmon (Diosyros virgniana L.). In 75% retention treatment
plots, the midstory was removed by incising trees and applying the herbicide Arsenal
(active ingredient imazapyr) to achieve a shelterwood cut. An average of 941 stems that
were an average of 7.4 cm diameter at breast height (DBH; measured at 1.37 m above
ground) was treated per hectare with herbicide in such a way to retain an intact canopy,
19
but allow increased light penetration to the forest floor (Schweitzer 2003). These
treatments were implemented in order to determine which silvicultural prescription was
most conducive to regenerating oaks on these sites. The 25, 50, and 75 percent retention
treatments were designed as shelterwoods and residual stems are scheduled to be
removed 10 years post harvest. Two blocks were located at Jack Gap, and the other at
Miller Mountain. Each of the 15 experimental units was 4 ha in size. Trees were
harvested during the fall of 2001 and winter of 2002, and herbicide treatment took place
in fall 2001. Although pretreatment data was not obtained for any of the variables
measured in the present study besides basal area, the close proximity of sites, the uniform
forest structure present pretreatment (Schweitzer 2003), and the random assignment of
treatments make comparison of treatments to control plots valid. Post treatment basal
area of treatments was as follows: controls, 24.3 m2/ha (99% retention); 75%, 18.8 m2/ha
(70% retention); 50%, 9.2 m2/ha (38% retention); 25%, 6.3 m2/ha (28% retention); and
clearcut, 1.2 m2/ha (5% retention) (Schweitzer 2003).
Methods
Stand density. During the summer of 2001, prior to treatments, three permanent
measurement plots were established in each experimental unit (Schweitzer 2003). Plot
centers were monumented with a piece of reinforcing steel and a 0.081 ha concentric
subplot was established. Inside this plot all trees ≥ 0.142 m d.b.h. were tagged and
measured at 1.37 m above ground for DBH with a metal diameter tape. In the summers
20
of 2002, 2003, 2004 and 2005 measurement plots were revisited and all tagged trees
within all plots were located and remeasured for DBH.
Microclimate. Microclimatic regimes were sampled with H8 Hobo dataloggers
(Onset Corp., Bourne, MA). Dataloggers were housed in modified 1-liter plastic
containers. The bottom of each container was removed and slots were cut in the
container sides for ventilation. One datalogger was placed at each measurement plot
within each block and data was obtained for three consecutive 24-hour periods during
July of 2002, 2003, 2004, and 2005. Dataloggers recorded hourly air temperature (AT) in
o
C and relative humidity (RH) in percent at 60 cm above ground surface. Soil
temperature (ST) was measured at 7 cm below the soil surface was measured via an
additional soil temperature probe connected to the datalogger.
Microhabitat. Two 20-meter line transects divided into 0.5 meter increments
were utilized at each measurement plot to sample physical attributes of microhabitat
during August and September of 2002, 2003, 2004, and 2005. The point-intersect method
was used to calculate percent cover of the following variables along each transect: leaf
litter, bare soil, herbaceous vegetation (including vines), woody vegetation, slash, rocks >
10 cm length, and coarse woody debris (CWD) >10 cm diameter. Percent coverage was
calculated as the percentage of 0.5 m increments a given variable covered >50% of.
Every 2 meters along transects percent canopy closure was measured at chest height with
a hand-held spherical densitometer, and litter depth to mineral soil was measured with a
ruler to the nearest half-centimeter.
21
Data Analysis
Stand density. Basal area was calculated each year using d.b.h.’s of all trees
measured within 0.081 ha plots.
Microclimate. All data were trimmed so that data collection on all plots within a
block was concurrent. Each 24-hour period was divided into day- and nighttime periods
based on sunrise/sunset schedules. Variables were inspected visually and RH variables
were arcsine transformed to better meet assumptions of normality and equal variance.
Response variables for tests included daily mean and range for day- and nighttime air and
soil temperatures, and relative humidity. Range (maximum – minimum) was used as a
measure of variability rather than standard deviation because of its easy interpretation.
Microhabitat. Microhabitat variables were inspected for normality both visually
using histograms and statistically using Kolmogorov-Smirnov tests (Hair et al. 1998).
Based on these inspections, the following variables were transformed: litter (log inverse),
bare soil, slash and rock (log), CWD (square root), canopy cover (arcsine). The best
transformation was selected based on the original distribution of the variable and through
trial and error (Hair et al. 1998). Principal component analysis (PCA) was used to
condense the 9 original microhabitat variables and basal area to 3 components which
retained approximately 72% of original variation (Bartlett’s Test of Sphericity χ2 = 936.44,
df = 45, P < 0.0001). These principal components (PC’s) represent weighted linear
combinations of the original variables and provide insight into the relationship of
variables and, because they are orthogonal to each other, are useful as predictor variables
in other analyses.
22
Data from the three measurement plots in each unit were averaged for comparison
of means of stand density, microclimate, and microhabitat variables. To test for effects
of year, treatment, and year by treatment interactions on means of all microclimate and
microhabitat variables including PC’s I used ANCOVA with treatment and block as main
factors, year as a covariate, and Tukey tests for mean separation when ANCOVA
indicated differences. All analyses were performed in SAS (SAS 2003) using alpha <
0.05 for significance.
Results
Microclimate. The range of air and soil temperature and relative humidity, both
day- and nighttime, differed by basal area retention treatment (Fig. 2.2-2.4, Table 2.1).
For the range of each variable, mean separations showed two groups, one containing
clearcuts, 25- and 50% treatments, and another with 75% retention and controls (closed
canopy treatments). The range was always smaller on closed canopy treatments than on
cut treatments, both day and night.
The range of both day- and nighttime RH differed by year (Table 2.1), indicating
that variability in RH changed over the course of the study. Range of daytime RH was
higher in 2003, 2004, and 2005 than 2002. Nighttime RH was greater in 2005 than in
2002. Ranges in day- or nighttime soil or air temperatures did not differ by year,
suggesting little changes in temperature variability occurred during the study.
The mean of all variables except nighttime AT differed by treatment (Fig. 2.5-2.7,
Table 2.1). For each variable that differed by treatment, except daytime RH, controls
23
differed from clearcuts. RH was generally highest in the daytime on controls and lowest
on clearcuts with the opposite observed at night. During daytime, AT was generally
highest on clearcuts and lowest in controls with the opposite observed at night. ST was
highest on clearcuts during day and night.
Mean AT differed by year only during daytime, with higher temperatures in 2002
than 2003, 2004, and 2005 and higher values in 2003 than 2005 (Table 2.1). Both dayand nighttime average ST differed by year, with higher values in 2002 than all other years.
Average RH varied by year only for nighttime measures and was higher in 2002 and
2003 than 2004 and 2005.
The averages of daytime ST and AT on harvested plots (clearcut, 25- and 50%
retention) became progressively more similar to conditions on controls through time, and
by 2005 were similar (Fig. 2.5 and 2.6). For daytime average RH, values for clearcuts
were similar to controls by 2005 (Fig. 2.7).
Microhabitat. The means of all microhabitat variables differed by basal area
retention treatment (Fig. 2.8-2.17, Table 2.2). The means of several variables, including
canopy cover, and percent cover of litter and bare ground separated into three groups.
Canopy cover and litter cover were lowest in clearcuts, higher in 25- and 50% retention,
and highest in 75% retention and controls. Bare ground showed the opposite trend, with
highest cover in clearcuts, lower in 25- and 50% retention, and lowest in 75% retention
and controls. Means of woody vegetation cover and CWD cover separated into two
groups, with highest values in clearcuts, 25- and 50% retention, and lowest in 75%
retention and control. Cover of herbaceous vegetation was highest in clearcuts and 25%
24
Table 2.1 Range and average of microclimatic variables for five basal area retention treatments in Jackson County, Alabama, 2002-2005. Means within a row with
different superscript numbers differ (Tukey P<0.05). Day = daytime measures, Night = nighttime measures, AT = air temperature (oC), ST = soil temperature (oC),
RH = relative humidity (%).
P-valueA
mean - treatment
variable
treatment
block
year
year*treat
clearcut
25%
50%
75%
control
Range
Day AT
< 0.0001
0.025
0.749
0.751
20.86±1.221
19.86±0.831
19.30±1.101
10.18±0.792
9.33±0.822
8.82±0.861
9.44±1.041
4.97±0.452
5.53±0.722
Night AT
< 0.0001
0.153
0.944
0.960
11.03±0.931
Day ST
< 0.0001
0.121
0.348
0.557
6.15±0.551
6.71±0.461
5.24±0.681
3.06±0.272
2.50±0.222
Night ST
< 0.0001
0.138
0.140
0.391
4.54±0.361
4.36±0.331
3.71±0.351
2.08±0.132
1.89±0.182
64.48±4.161
64.01±3.571
37.39±5.002
34.81±3.522
Day RH
< 0.0001
0.033
0.0003
0.333
64.66±3.631
Night RH
< 0.0001
0.031
0.0008
0.485
38.99±3.101
41.15±4.211
39.29±4.671
24.99±4.862
21.11±2.472
Average
Day AT
< 0.0001
0.058
<0.0001
0.093
29.20±0.841
28.52±0.641
27.96±0.591
25.32±0.432
24.66±0.472
Night AT
0.448
0.076
0.684
0.990
21.40±0.44
21.53±0.42
21.69±0.39
22.36±0.39
22.16±0.41
Day ST
< 0.0001
0.027
<0.0001
0.042
24.41±0.561
24.47±0.521
23.77±0.481,2
22.37±0.252
21.75±0.263
1
1
1,2
2,3
23.54±0.41
23.20±0.39
22.25±0.23
21.65±0.213
Night ST
< 0.0001
0.045
0.0008
0.075
23.68±0.50
Day RH
0.0079
0.014
0.565
0.296
69.03±3.071,2
67.26±1.862
69.58±2.781,2
76.65±2.851,2
78.92±2.651
92.11±1.801,2
91.61±2.301,2
87.16±2.022
88.48±2.542
Night RH
0.0013
0.040
<0.0001
0.757
94.73±1.021
A
P-values were calculated using ANCOVA, dftreat = 4, dfblock = 2, dfyear = 1. DaveRH, DrngRH, NaveRH, and NrngRH were arcsine transformed to better fit normality
assumptions for analyses, and means are reported for back-transformed values.
Table 2.1 (continued)
mean - year
variable
Range
Day AT
Night AT
Day ST
Night ST
Day RH
Night RH
Average
Day AT
Night AT
Day ST
Night ST
Day RH
Night RH
2002
2003
2004
2005
14.41±1.33
7.27±0.95
5.01±0.64
3.67±0.43
37.74±3.282
25.40±3.042
17.89±1.60
8.36±1.00
4.51±0.61
3.03±0.38
62.41±3.881
31.90±2.791,2
17.54±1.76
9.67±0.93
5.38±0.63
3.77±0.35
55.42±5.431
34.83±4.281,2
14.28±1.49
6.83±0.81
4.18±0.55
2.91±0.36
57.91±5.051
40.94±4.981
29.13±0.671
22.69±0.27
25.03±0.531
24.23±0.411
75.06±1.77
95.20±0.641
27.26±0.662
20.72±0.52
22.71±0.332
22.17±0.302
70.48±2.46
94.37±1.071
26.76±0.582,3
21.67±0.24
22.79±0.322
22.41±0.262
65.49±1.60
85.88±2.262
25.48±0.643
22.17±0.10
22.90±0.432
22.65±0.292
77.37±3.24
87.74±1.922
25
30
a)
Range
20
10
0
N=
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
16
b)
14
Range
12
10
% retention
Clearcut
8
25%
6
50%
4
75%
Control
2
N=
3 3 3 3 3
2002
3 3 3 3
3
3 3 3 3
2003
2004
3
3 3 3 3
3
2005
Year
Figure 2.2 Range of (a) daytime and (b) nighttime air temperature for five basal area
retention treatments in Jackson County, Alabama, 2002-2005.
26
12
a)
10
Range
8
6
4
2
0
N=
3
3
3
3
3
3
3
3
3
3
3
3
3
2
3
3
3
3
3
3
7
b)
6
Range
5
4
% retention
Clearcut
3
25%
2
50%
1
75%
Control
0
N=
3
3 3 3
2002
3
3 3
3 3 3
3
2003
3 3
2 3
2004
3 3
3 3
3
2005
Year
Figure 2.3 Range of (a) daytime and (b) nighttime soil temperature for five basal area
retention treatments in Jackson County, Alabama, 2002-2005.
27
90
a)
80
70
Range
60
50
40
30
20
10
N=
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
100
b)
80
60
Range
% retention
Clearcut
40
25%
50%
20
75%
Control
0
N=
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
2002
2003
2004
2005
Year
Figure 2.4 Range of (a) daytime and (b) nighttime relative humidity for five basal area
retention treatments in Jackson County, Alabama, 2002-2005.
28
36
a)
34
Temperature (C)
32
30
28
26
24
22
20
N=
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
26
b)
Temperature (C)
24
22
% retention
Clearcut
20
25%
50%
18
75%
Control
16
N=
3 3 3 3 3
2002
3 3 3 3
3
3 3 3 3
2003
2004
3
3 3 3 3
3
2005
Year
Figure 2.5 Mean (a) daytime and (b) nighttime air temperature for five basal area
retention treatments in Jackson County, Alabama, 2002-2005.
29
30
a)
Temperature (C)
28
26
24
22
20
18
N=
3
3
3
3
3
3
3
3
3
3
3
3
3
2
3
3
3
3
3
3
27
b)
26
Temperature (C)
25
24
% retention
23
Clearcut
22
25%
21
50%
75%
20
Control
19
N=
3 3 3 3 3
2002
3 3 3 3
3
3 3 3 2
2003
2004
3
3 3 3 3
3
2005
Year
Figure 2.6 Mean (a) daytime and (b) nighttime soil temperature for five basal area
retention treatments in Jackson County, Alabama, 2002-2005.
30
100
a)
Relative humidity (%)
90
80
70
60
50
40
N=
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
110
b)
Relative humidity (%)
100
90
% retention
Clearcut
80
25%
50%
70
75%
Control
60
N=
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
2002
2003
2004
2005
Year
Figure 2.7 Mean (a) daytime and (b) nighttime relative humidity for five basal area
retention treatments in Jackson County, Alabama, 2002-2005.
31
Table 2.2 Average microhabitat variables for five basal area retention treatments in Jackson County, Alabama, 2002-2005. Means within a row with different
superscript numbers differ (Tukey P<0.05).
P-valueA
mean - treatment
variable
treatment
block
year
year*treat
clearcut
25%
50%
75%
control
Basal area
0.504
0.555
0.993
1.00±1.153
9.38±3.362
8.08±1.462
24.90±3.771
23.17±0.921
<0.001
Canopy cover
0.261
27.57±0.503
57.42±0.302
66.14±0.172
91.78±0.091
95.89±0.091
<0.001
<0.001
0.004
Litter depth
NAB
NA
NA
2.01±0.30
2.69±0.17
2.51±0.22
2.83±0.28
3.80±0.33
<0.001
Litter
0.939
0.212
0.194
81.24±3
93.73±2
93.57±2
98.55±1
98.55±1
<0.001
1
2
2
3
6.00±1.26
6.46±1.30
2.52±1.20
1.97±1.253
Bare
15.67±1.27
<0.001
0.041
0.012
0.0062
Herbaceous
0.067
0.127
0.618
62.85±5.461
51.28±4.911,2
63.30±5.251
37.78±4.922,3
24.69±4.223
<0.001
Woody
47.19±5.471
54.93±5.751
50.31±4.951
25.76±2.082
20.94±3.512
<0.001
0.018
<0.001
<0.001
Slash
0.800
0.095
19.39±1.111
8.96±1.212
12.09±1.131,2
2.93±1.243
1.76±1.143
<0.001
0.001
1
1
1,2
2
6.23±1.16
4.35±1.13
2.70±1.14
5.13±1.241,2
Rock
0.040
0.355
0.804
5.39±1.24
0.0086
CWD
0.296
0.295
0.882
10.29±0.051
7.18±0.021
7.42±0.021
2.62±0.022
1.34±0.022
<0.001
0.08±0.831
-0.02±0.851
0.32±0.521
0.60±0.491
PC1
0.859
-0.97±1.322
<0.001
0.0049
<0.001
PC2
0.432
0.77±0.731
0.56±0.721
0.63±0.601
-0.83±0.392
-1.13±0.422
<0.001
<0.001
0.012
0.24±1.061
-0.08±1.011,2
-0.37±0.802
0.25±1.001
PC3
0.212
0.796
-0.05±0.941
0.004
0.033
A
P-values were calculated using ANCOVA, dftreat = 4, dfblock = 2, dfyear = 1. B Litter depth was not tested due to serious interactions between year and treatment
factors.
Table 2.2 (continued)
mean- year
variable
2002
2003
2004
2005
Basal area
12.97±9.63
13.30±9.83
13.49±9.89
13.47±10.1
Canopy cover
56.27±0.763
75.45±1.131,2
66.13±0.742,3
83.9±0.191
Litter depth
3.29±0.03
2.45±0.30
2.43±0.20
2.90±0.22
Litter
94.11±
95.37±
94.91±
96.29±
Bare
5.28±1.371,2
8.17±1.321
4.53±1.301,2
3.11±1.232
Herbaceous
33.72±5.05
66.03±4.12
39.92±4.39
52.25±5.97
Woody
24.00±1.762
41.75±4.641
42.50±5.481
51.1±6.101
Slash
5.69±1.38
5.04±1.36
8.64±1.31
6.82±1.19
Rock
5.30±1.18
4.76±1.17
3.72±1.21
4.69±1.16
CWD
5.69±0.07
4.31±0.04
4.03±0.06
6.97±0.06
PC1
-0.25±1.132
-0.15±1.172
-0.09±0.892
0.48±0.551
PC2
-0.31±0.802
-0.04±0.972
-0.03±1.052
0.38±1.071
PC3
0.31±0.961
0.04±1.071,2
-0.33±1.002
-0.02±0.81,2
2
Litter depth was not tested due to serious interactions between year and treatment factors.
32
Basal Area (m-square/ha)
40
30
20
% retention
Clearcut
10
25%
50%
0
75%
Control
-10
N=
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
2002
2003
2004
3
3 3 3 3
2005
Year
Figure 2.8 Basal area (m2/ha) for five basal area retention treatments in northeastern
Alabama, 2002-2005.
120
% Canopy Cover
100
80
% retention
60
Clearcut
25%
40
50%
20
75%
Control
0
N=
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
2002
2003
2004
2005
YEAR
Figure 2.9 Canopy cover (%) for five basal area retention treatments in Jackson County,
Alabama, 2002-2005.
33
7
6
Litter Depth (cm)
5
4
% retention
Clearcut
3
25%
2
50%
1
75%
Control
0
N=
3
3 3 3
3
2002
3 3
3 3 3
3
2003
3 3
3 3
3 3
2004
3 3
3
2005
YEAR
Figure 2.10 Litter depth (cm) for five basal area retention treatments in Jackson County,
Alabama, 2002-2005.
110
100
% Litter
90
% retention
80
Clearcut
70
25%
50%
60
75%
Control
50
N=
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
2002
2003
2004
2005
YEAR
Figure 2.11 Percent cover of leaf litter for five basal area retention treatments in Jackson
County, Alabama, 2002-2005.
34
50
% Bare Ground
40
30
% retention
20
Clearcut
10
25%
50%
0
75%
Control
-10
N=
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
2002
2003
2004
3
3 3 3 3
2005
YEAR
Figure 2.12 Percent cover of bare ground for five basal area retention treatments in
Jackson County, Alabama, 2002-2005.
% Herbaceous Vegetation
100
80
60
% retention
Clearcut
40
25%
50%
20
75%
Clearcut
0
N=
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
2002
2003
2004
2005
YEAR
Figure 2.13 Percent cover of herbaceous vegetation for five basal area retention
treatments in Jackson County, Alabama, 2002-2005.
35
100
% Woody Vegetation
80
60
% retention
40
Clearcut
20
25%
50%
0
75%
Control
-20
N=
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
2002
2003
2004
2005
YEAR
Figure 2.14 Percent cover of woody vegetation for five basal area retention treatments in
Jackson County, Alabama, 2002-2005.
40
% Slash
30
20
% retention
Clearcut
10
25%
50%
0
75%
Control
-10
N=
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
2002
2003
2004
3
3 3 3 3
2005
YEAR
Figure 2.15 Percent cover of slash for five basal area retention treatments in Jackson
County, Alabama, 2002-2005.
36
20
% Rock
10
% retention
Clearcut
0
25%
50%
75%
Control
-10
N=
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
2002
2003
2004
3
3 3 3 3
2005
YEAR
Figure 2.16 Percent cover of rock for five basal area retention treatments in Jackson
County, Alabama, 2002-2005.
% Coarse Woody Debris
30
20
% retention
10
Clearcut
25%
0
50%
75%
Control
-10
N=
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
2002
2003
2004
3
3 3 3 3
2005
YEAR
Figure 2.17 Percent cover of coarse woody debris for five basal area retention treatments
in Jackson County, Alabama, 2002-2005.
37
retention and lowest in controls. Slash cover was highest on clearcuts, lower in 25%
retention, and lowest in 75% retention and controls.
The following variables differed across years: canopy cover, bare ground, and
woody vegetation (Table 2.2). Canopy cover was highest in 2005 and lowest in 2002.
Bare ground was highest in 2003, and lowest in 2005. Woody vegetation was lowest in
2002, and highest in 2003, 2004, and 2005. The effects of treatments diminished over
time for canopy cover, litter depth, litter cover, and bare ground cover, and by 2005 these
variables, with exception of canopy cover, were similar across treatments. Both
herbaceous and woody vegetation cover continued to increase so that treatment effects
were more pronounced each successive year after harvest. For other variables such as
slash, CWD, and rock, the magnitude of the treatment effect remained constant over time.
Eigenvector values for percent cover of bare ground were highly negative for the
first principal component (PC1), while percent cover of litter, litter depth, and canopy
cover were highly positive (Table 2.3). PC1 is therefore called the “canopy/litter
component” and treatments with high values for PC1 had high canopy cover and high
coverage of deep litter, and little bare ground. On PC2, eigenvectors for basal area were
highly negative while percent cover of woody and herbaceous vegetation, slash and
CWD were highly positive. Termed the “ground structure component”, treatments with
high values for PC2 have low basal area and high cover of woody and herbaceous
vegetation, slash and CWD. Eigenvectors for percent cover of rock were highly positive
38
Table 2.3 Results of principal components analysis of microhabitat
variables for five basal area retention treatments in Jackson County,
Alabama, 2002-2005.
Eigenvalues and
Principal Component
Eigenvectors
1
2
3
Eigenvalue
4.57
1.50
1.08
% variation
45.70
14.98
10.84
cumulative % variation
45.70
60.68
71.52
Eigenvectors*
canopy cover
-0.544
-0.082
0.653
litter
-0.106
-0.109
0.899
litter depth
-0.162
0.191
0.788
bare
0.202
0.113
-0.869
basal area
0.445
-0.166
-0.753
woody
0.122
-0.041
0.809
herbaceous
-0.290
0.041
0.571
slash
-0.336
-0.230
0.724
CWD
-0.169
0.170
0.742
rock
-0.038
0.057
0.960
* Varimax rotation applied to eigenvectors to aid in interpretation.
Eigenvectors are weightings of original variables on each principal
component. Signs of eigenvectors indicate direction of relationship.
for PC3, termed the “rock component”. All principal components varied by both
treatment and year (Table 2.2). Mean PC1 values were higher on 25, 50, and 75%
retention and control than on clearcut treatments (Fig. 2.18). PC2 values were higher on
clearcuts, 25 and 50% than 75% retention and controls. PC3 values were highest on
clearcuts, 25% retention and controls. Values of both PC1 and PC2 were higher in 2005
than the previous three years.
39
3
a
2
PC 1
1
0
-1
-2
N=
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
2.0
b
1.5
1.0
PC 2
.5
0.0
-.5
-1.0
-1.5
-2.0
N=
3
3
3
3
2.0
c
1.5
1.0
PC 3
.5
% retention
0.0
Clearcut
-.5
25%
-1.0
50%
75%
-1.5
Control
-2.0
N=
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
2002
2003
2004
2005
Year
Figure 2.18 Microhabitat principal component scores for five basal area retention
treatments in Jackson County, Alabama, 2002-2005. (a) PC1, (b) PC2, (c) PC3.
40
Discussion
Microclimate. As expected, canopy removal associated with tree removal led to
changes in microclimatic conditions within forest stands. All variables measure differed
across treatments except nighttime air temperature. The reason nighttime AT was not
different across treatments is unclear. Response to treatment was variable-specific in our
study. Different microhabitat components often respond differently to changes in
structural features of a forest (Chen et al. 1999). Most variables exhibited a gradient in
average values corresponding to the gradient in forest structure created by the treatments,
with extremes in either clearcuts or controls and considerable overlap between
intermediate treatments. Mean daytime AT showed two main groups, highs in treatments
which were harvested and the canopy opened (clearcut, 25%, and 50%), and lows in
treatments with intact canopy (75% retention and control). The highest average daytime
RH was observed in the control, but the lowest was in the 25% treatment, not the clearcut.
It is well accepted that opening the forest canopy creates warmer, drier conditions
(Geiger 1965, Brosofske et al. 1997). These results suggest that the retention of up to
50% of overstory trees does little to ameliorate the effects relative to clearcut harvesting
on microclimatic conditions in a stand. A similar conclusion was reached in forests of
the Pacific Northwest (Heithecker and Halpern 2006). Shelterwoods reduced soil
temperature relative to clearcuts in Oregon (Childs and Flint 1987).
Nighttime and daytime patterns in variation with respect to treatment were
opposite for RH and AT. During daytime hours humidity is held at ground level by the
forest canopy, while at night RH levels rose in the forest, but RH in the clearcuts rose by
41
a larger amount, making them moister than controls. Nighttime AT was consistently
cooler on cut stands than controls, but not significantly so. In Douglas-fir forests in
Washington air temperatures did not differ between clearcuts and those receiving a partial
cut (Chen et al. 1999). Soil temperature showed a gradient of high values in clearcuts to
lowest values on controls both day and night. The continued warmth in clearcut soils at
nighttime is likely due to the large heat storing capacity of soils (Chen et al. 1999). So,
the effects of treatments on microclimate vary by time of day. During the daytime
clearcuts are both warmer in terms of both soil and air temperature and drier compared to
control stands, but at nighttime air temperatures are not different between these two stand
types, but clearcuts are more moist and soil temperature is warmer. These differences
could have important implications for predicting a species’ response to treatments. For
example, terrestrial salamanders of the genus Plethodon are nocturnal foragers on the
forest floor and forage only at times when enough moisture is available (Jaeger 1978).
The nighttime microclimatic conditions on clearcut stands would therefore seem to be
amenable to foraging for this group.
These data suggest a significant amount of change in microclimatic conditions on
these stands within 4 years. Both soil and air temperatures, which spiked in response to
treatments in 2002 were similar to control levels by 2005. Nighttime RH was highest in
2002 and 2003 due to high values in cut treatments, but were similar to levels
approximating controls by 2005. Researchers in hardwood forests in the northeast found
that 5 years post-harvest air and soil temperatures showed no evidence of emulating
preharvest levels (Liechty et al. 1992). In the Ozarks of Missouri spatial and temporal
42
variation of microclimate 2 years post-harvest began to approximate control values
(Zheng et al. 2000).
Whereas the means of microclimatic variables responded as a gradient to various
levels of canopy removal, variability of microhabitat variables responded to a threshold,
which was manifested by the degree of canopy opening. Once the canopy was opened to
any degree, variability increases approximately the same amount. This is evidenced by
the existence of two groups of means for the range of each variable; all cut treatments
(clearcut, 25%, and 50%) and both closed canopy treatments (herbicide-treated 75%
retention, and controls). This suggests that it makes little difference in terms of
microclimatic variability whether you remove 50% of canopy trees, or all canopy trees.
There was no evidence that range of microclimate variability became closer to
control conditions within the time period sampled. The range of both AT and ST did not
change over time, and the range of RH actually increased for both day- and nighttime
conditions.
Microhabitat. The changes observed in microhabitats relative to canopy tree
removal are similar to those seen by other researchers (Phelps and Lancia 1995, Converse
et al. 2006, Greenberg 2001). Similar to microclimatic variables, the response of
microhabitat variables to canopy tree removal was variable-specific. For example, the
variables associated with canopy and litter (canopy cover, litter cover, and bare ground
cover) fell into 3 groups with respect to treatment response; clearcuts, 50- and 25%
treatments, and 75% and controls. This indicates that, in terms of leaf litter, clearcut
stands are distinct from stands with intermediate levels of harvest, which are distinct from
43
stands with an intact canopy (75% and control). This component of microhabitat
corresponds well to the first principal component, which was lower in clearcuts than
other treatments. Variables such as woody debris and slash responded in two groups;
those on cut stands (clearcut, 25- and 50% retention treatments) and those on uncut
stands (75% and control). These variables corresponded to information in the second
principal component. Herbaceous vegetation was one of the only variables that differed
between 75% and control treatments, indicating that the main effect herbicide-treatment
removal of midstory has on microhabitats in a forest stand is an increase in herbaceous
vegetation cover.
The way in which microhabitat variables changed over time after harvest was
also variable-specific. Litter/canopy variables showed a decrease in magnitude of
treatment effect over time, and by 2005 values were similar across treatments.
Vegetative growth, both herbaceous and woody, continued to increase on all cut stands
throughout the sampling period. Other variables such as slash, CWD, and rock coverage
did not change over the time period sampled.
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47
CHAPTER 3
RESPONSE OF REPTILE AND AMPHIBIAN COMMUNITIES TO VARIOUS
LEVELS OF OVERSTORY TREE RETENTION
Forest managers are increasingly interested in balancing the needs of maintaining
a flow of forest products with conserving biological diversity and maintaining forest
health (Sharitz et al. 1992, Ehrlich 1996). Two important components of this biodiversity
in the southeastern United States are amphibian and reptile species. These groups
comprise a large portion of vertebrate species in many ecosystems in the Southeast
(Russell et al. 2004) and can account for a majority of vertebrate biomass in some cases
(Congdon et al. 1986, Petranka and Murray 2001). Concern about the conservation status
of the two groups (Gibbons et al. 2000, Stuart et al. 2004) has increased interest in the
effects that widespread land uses such as forest management have on these animal
populations.
Research has shown that, in general, many reptile species are benefited by canopy
removal associated with silvicultural activities, while many amphibians, and salamanders
in particular, seem to decrease in abundance after harvesting (reviewed by Russell et al.
2004, Patrick et al. 2006). These trends are somewhat species specific (Greenberg et al.
48
1994) and tend to vary by geographic area and ecosystem type (Enge and Marion 1986,
McLeod and Gates 1998).
Most research on herpetofaunal response to harvesting has focused on clearcutting
and the few studies comparing reptile and amphibian abundance in plots with
intermediate levels of harvest (shelterwoods, two-aged harvests) have mainly focused on
terrestrial salamanders (Bartman 2001, Sattler and Reichenbach 1998). Fredericksen and
others (2000) inventoried herpetofaunal communities in Pennsylvania forest stands which
had undergone a variety of management activities and found that both reptile and
amphibian communities changed in a predictable pattern as a result of harvesting. The
only stand-level experimental study of herpetofaunal response to several levels of tree
removal in the Southeast was completed by Adams and others (1996) in Kentucky.
Greenberg (2001) studied reptile and amphibian communities in wind-created gaps in the
southern Appalachians of North Carolina, and called for future studies investigating the
response of herpetofauna and associated microhabitats and microclimates over a gradient
of canopy removal.
Changes in herpetofaunal community structure after canopy removal are likely
due in part to shifts in available microhabitat (deMaynadier and Hunter 1995). The
amount and arrangement of key microhabitat features such as coarse woody debris
(CWD), leaf litter, and canopy cover dictate an individual’s access to sites for
reproduction, resting, migrating, and reproduction (Halverson et al. 2003, Moseley et al.
2004, Rothermel and Luhring 2005). It is therefore important to understand relationships
49
between amphibian and reptile abundance and changes in microhabitat parameters
associated with canopy removal.
The objectives of this study were to 1) determine response of reptiles and
amphibians to canopy tree removal in terms of relative abundance, diversity, and species
richness, 2) determine if response of the two groups is proportional to the amount of
canopy trees removed, or if thresholds exist beyond which effects are more pronounced,
and 3) examine relationships between relative abundance and treatment-related changes
in microhabitat features. This information will help inform forest managers in the
southern Cumberland Plateau region about the impacts canopy removal has on this
important group.
Study Area
This study took place in Jackson County, northeastern Alabama (Fig. 3.1). The
area is classed into the Cliff section of the Cumberland Plateau in the Mixed Mesophytic
Forest region by Braun (1950). Bailey et al. (1994) included this area in the Eastern
Broadleaf Forest (Oceanic) Province and Northern Cumberland Plateau Section.
According to Smalley (1982), the sites are located in the Mid Cumberland Plateau region,
the Strongly Dissected Portion subregion, and landtypes 16, 17, and 18 of the Strongly
Dissected Margins and Sides landtype association. The area is characterized by steep
slopes dissecting the Plateau surface and draining to the Tennessee River. Soils are
shallow to deep, stony and gravelly loam or clay, well drained, and formed in colluvium
from those on the Plateau top (Smalley 1982). Climate of the region was described as
50
a)
Miller Mtn.
Jack
Gap
b)
25%
50%
clear
control -cut
clear
-cut
Block 3
75% control
Block 1
Miller Mt.
25%
N
75% 50%
50% 25% clear control
-cut
4-ha units
75%
Block 2
Jack Gap
Figure 3.1 Location of study site in Alabama (a) and layout of experimental design (b),
Jackson County, Alabama.
51
temperate with mild winters and moderately hot summers with a mean temperature of 13
degrees C, and mean precipitation of 149 cm (Smalley 1982). Two sites were used. The
first, Miller Mountain (34o 58’ 11” N, 86o 12’ 21” W), was situated on mainly South,
Southwest facing slopes with elevations ranging from 457-518 m (Figure 3.1a). The
second, Jack Gap (34o 56’ 30” N, 86o 04’ 00” W), had a North aspect with elevations
ranging from 304-475 m. Dominant canopy tree species included oaks, including
Quercus velutina Lamarck, Q. rubra L., Q. alba L., Q. prinus L.; 46% of pretreatment
basal area (BA), hickories (Carya spp.; 15% pretreatment BA), sugar maple (Acer
saccharum Marsh.; 13% pretreatment BA) and yellow poplar (Liriodendron tulipifera L.;
9% pretreatment BA) (Schweitzer 2003). Common understory species included
flowering dogwood (Cornus florida L.), eastern redbud (Cercis canadensis L.), and
sourwood (Oxydendrum arboretum DC.).
The study followed a randomized complete block design with three blocked
replicates of five treatments involving varying levels of basal area retention of trees (Fig
3.1b). Treatments included clearcuts, 25-, 50-, and 75% retention, and controls. The
clearcuts, 25%, and 50% retention treatments were chainsaw-felled and grapple skidded
in a commercial logging operation. In the 25 and 50 percent retention treatments, trees
were marked to leave favoring dominant and codominants with high vigor, especially oak,
ash (Fraxinus spp.), and persimmon (Diosyros virgniana L.). In 75% retention treatment
plots, the midstory was removed by incising trees and applying the herbicide Arsenal
(active ingredient imazapyr) to achieve a shelterwood cut. An average of 941 stems that
were an average of 7.4 cm diameter at breast height (DBH; measured at 1.37 m above
52
ground) was treated per hectare with herbicide in such a way to retain an intact canopy,
but allow increased light penetration to the forest floor (Schweitzer 2003). These
treatments were implemented in order to determine which silvicultural prescription was
most conducive to regenerating oaks on these sites. The 25, 50, and 75 percent retention
treatments were designed as shelterwoods and residual stems are scheduled to be
removed 10 years post harvest. Two blocks were located at Jack Gap, and the other at
Miller Mountain. Each of the 15 experimental units was 4 ha in size. Trees were
harvested during the fall of 2001 and winter of 2002, and herbicide treatment took place
in fall 2001. Although pretreatment data were not obtained for any of the variables
measured in the present study besides basal area, the close proximity of sites, the uniform
forest structure present pretreatment (Schweitzer 2003), and the random assignment of
treatments make comparison of treatments to control plots valid. Post treatment basal
area of treatments was as follows: controls, 24.3 m2/ha (99% retention); 75%, 18.8 m2/ha
(70% retention); 50%, 9.2 m2/ha (38% retention); 25%, 6.3 m2/ha (28% retention); and
clearcut, 1.2 m2/ha (5% retention) (Schweitzer 2003).
Methods
Herpetofaunal sampling. Communities of amphibians and reptiles were sampled
using straight-line drift fences adjacent to woody vegetation measurement plots
(Schweitzer 2003). One drift fence was installed within 20 m of the outside perimeter of
each vegetation plot, for a total of 45 fences (3 fences per experimental unit X 15 units).
Fences were installed between April and July of 2002. Fences were constructed out of 61
53
cm high black silt fencing, and were 15 m long. One 19-liter pitfall bucket was situated
at both ends of each fence. A rectangular funnel trap (91cm X 38cm X 35cm)
constructed of 0.6 cm mesh hardware cloth and with a 15 cm inside opening was installed
on either side of each fence at its midpoint. Drift fences were spaced at least 15 m from
each other and from edges of experimental units. All fences on one block were opened
simultaneously and checked daily. In general, one block was opened for a week at a time.
A trap night was defined as one drift fence opened for a 24-h period. Fences were
opened between late July and mid-August in 2002 for a total of 54 trap nights. Fences
were opened between early April and mid-September 2003 for 240 trap nights. In 2004
trapping took place between early April and early August for 282 trap nights. In 2005
fences were opened between late March and mid-August and then again between early
October and late November for 321 trap nights.
Each animal was measured for snout-vent length (SVL) using either dial calipers
or a pocket tape measure, weighed using Pesola scales, and sexed based on secondary
sexual characteristics or probed for the presence of hemipenes. Each animal was also
given a plot-specific mark to identify recaptures. In terms of marking, lizards,
salamanders, and frogs were toe-clipped, snakes received a notched ventral scale, and
turtles were marked by filing a notch in marginal scutes. Recaptured animals were not
included in analyses to avoid double counting.
54
Data analysis
Relative abundance. Data from the three drift fences in each unit were combined
for comparison of relative abundance. An index of relative abundance was calculated by
dividing the total number of individuals captured by the number of nights trapped.
Species were grouped into guilds based on their taxa and ecology. To test for effects of
year, treatment and year X treatment interactions on relative abundance of all reptile and
all amphibians, guilds and abundant species (> 30 individuals/year) I used ANCOVA
with year, treatment and block as main factors and Tukey test for mean separation when
ANCOVA indicated differences.
Diversity Indices. The same ANCOVA model was used to test for differences in
Shannon-Weiner index of diversity, evenness, Simpson’s diversity (1-dominance), and
species richness of amphibians and reptiles for 2003, 2004, and 2005 separately. Indices
of diversity were not derived for 2002 because of the low number of trap nights in the
year. In a separate analysis, average values of amphibian, reptile, and total herpetofaunal
species richness were compared using combined data from 2002 through 2005 using a
one-way ANOVA.
Similarity. Morisita’s and Bray-Curtis indices of similarity (Magurran, 1988)
were computed by treatment using total count data from 2002-2005 for amphibians and
reptiles separately. Reptile and amphibian species are notoriously hard to detect and our
perceptions of the composition of communities change greatly over time because of this
(Gibbons et al. 1997). Therefore, analyzing captures combined across all years sampled
55
may be more informative than analyzing captures from each year separately. All
analyses were performed in SAS (SAS 2003) using alpha < 0.05 for significance.
Canonical Correspondence Analysis. Canonical Correspondence Analysis (CCA)
(PCORD for Windows) was used to investigate variation in abundance of guilds as they
relate to microhabitat measures (see Chapter 2). This procedure is a direct gradient
analysis technique in that it compares community composition directly to environmental
variables across a gradient (Palmer 1993). CCA is a type of ordination, and therefore not
a hypothesis testing technique. It is a special form of multivariate regression that
produces several orthogonal axes consisting of the maximum possible correlation
between sites and species or groups (Palmer 1993). This technique is well-suited to this
project because of the gradient in microhabitat conditions created by the tree removal
treatments. The abundance of reptile and amphibian guilds and microhabitat measures
(see Chapter 2 for microhabitat variable descriptions and methods) from the 45
measurement plots from 2003, 2004, and 2005 were run in separate analyses. An
additional variable, distance to pool, was included and measured by georeferencing the
location of pools in which amphibians bred during the study and measuring distance from
these to drift fences using ArcView.
Results
A total of 40 species of amphibians and reptiles were captured, 21 amphibian and
19 reptile species (Table 3.1). A total of 2949 individual animals were captured; 2491 of
these were amphibians and 458 were reptiles. The most abundant species, Bufo
56
americanus, the American toad, comprised 1786 (60.6 %) of total individuals captured.
Because of the low number of trap nights in 2002, it was assumed that the total number of
species present on the study site was not adequately assessed. However, a graph of the
number of species detected over time during 2003 (Fig. 3.2) shows that the sampling
effort put forth was adequate for detecting a majority of trappable species present. Based
on this observation it was assumed that sampling efforts in 2004 and 2005 were adequate
as they were larger than that of 2003.
Relative abundance. The relative abundance of amphibians was not different
across canopy retention treatments, but was greater in 2002 and 2003 than 2004 and 2005
(Fig. 3.3, Table 3.2). Reptile abundance was greater in 25% and 50% retention
treatments than 75% and control treatments, and greater for clearcut treatments than
controls (Fig. 3.4, Table 3.2).
Because American toads were an order of magnitude more abundant than most other
species, they were not included in any guild. The remaining 39 reptile and amphibian
species were grouped into seven guilds (Table 3.1). Amphibians were classified into
terrestrial and aquatic salamanders based on their reproductive mode, and large- and
small pool frogs depending on whether they breed in large pools containing fish or small
fishless pools. Reptiles were grouped into lizards, turtles, and either small (≤ 50 cm total
length), or large (> 50 cm) snakes.
Only two guilds differed across treatments in terms of mean relative abundance
(Fig. 3.5-3.11, Table 3.2). The relative abundance of large snakes and lizards differed
among canopy retention treatments (Fig. 3.9 & 3.11, Table 3.2). Large snake abundance
57
Table 3.1 Species of amphibians and reptiles, their guild assignment, and their total captures
on five basal area retention treatments in Jackson County, Alabama 2002-2005.
Guild assignment
Treatment
Species
N
clearcut 25% 50% 75% control
Aquatic salamanders
Ambystoma maculatum
2
0
1
0
0
1
Ambystoma opacum
1
0
0
1
0
0
Ambystoma talpoideum
6
0
2
1
2
1
Eurycea lucifuga
11
1
3
2
1
4
Hemidactylium scutatum
2
0
0
2
0
0
Notophthalmus viridescens
27
0
8
12
4
3
Psueudotriton ruber
56
15
12
4
14
11
Terrestrial salamanders
Aneides aeneus
2
0
1
0
0
1
Plethodon dorsalis
73
15
3
21
34
0
Plethdon glutinosus
273
38
48
71
50
66
Large pool frogs
Acris crepitans
1
0
1
0
0
0
Rana catesbeiana
80
6
14
27
20
13
Rana clamitans
75
7
16
24
19
9
Bufo americanus
1786
179
242
269
671
425
Small pool frogs
Gastrophryne carolinensis
7
2
1
1
3
0
Hyla chrysoscelis
9
1
3
1
2
2
Pseudacris brachyphona
11
0
2
3
3
3
Pseudacris crucifer
4
0
1
0
1
2
Rana palustris
8
0
5
1
2
0
Rana utricularia
12
3
2
2
4
1
Scaphiopus holbrookii
3
0
0
1
2
0
Large-bodied snakes
Agkistrodon contortrix
14
5
2
1
4
2
Coluber constrictor
16
5
7
4
0
0
Crotalus horridus
1
0
0
1
0
0
Elaphe obsoleta
4
0
0
3
1
0
Heterodon platirhinos
7
2
3
2
0
0
Lampropeltis getula
1
0
1
0
0
0
Lampropeltis triangulum
3
0
2
1
0
0
Thamnophis sirtalis
26
8
5
5
8
0
Small-bodied snakes
Carphophis amoenus
82
19
15
17
19
12
Diadophis punctatus
12
4
0
4
2
2
Storeria dekayi
1
0
0
1
0
0
Storeria occipitomaculata
3
0
1
2
0
0
Virginia valeriae
16
3
3
4
4
2
Lizards
Anolis carolinensis
3
0
3
0
0
0
Eumeces fasciatus
86
25
22
26
6
7
Eumeces laticeps
23
3
7
6
5
2
Sceloporus undulatus
135
28
52
41
10
4
Scincella lateralis
7
2
2
3
0
0
Turtle
Terrapene carolina
18
9
4
5
0
0
58
Table 3.2 Mean relative abundance of total reptiles, total amphibians, guilds, and common species on five basal area retention treatments in Jackson County,
Alabama 2002-2005. Means within a row with different superscript numbers differ (Tukey P<0.05).
P-value
mean - treatment
Taxa
treatment
block
year
year* treat
clearcut
25%
50%
75%
reptiles
0.001
0.004
0.137
0.957
0.13±0.091,2
0.19±0.161
0.13±0.061
0.08±0.072,3
large snakes
0.011
0.114
0.233
0.079
0.028±0.0301
0.018±0.0141,2
0.022±0.0211,2
0.016±0.0151,2
small snakes
0.301
0.792
0.0003
0.100
0.055±0.094
0.029±0.035
0.048±0.057
0.036±0.031
lizards
0.002
0.0005
0.002
0.199
0.078±0.0551,2
0.138±0.1601
0.091±0.0721,2
0.034±0.0612
amphibians
0.076
0.0001 0.0004
0.891
0.310±0.310
0.500±0.640
0.780±0.630
0.970±1.000
large-pool frogs
0.49
0.004
0.003
0.402
0.021±0.033
0.058±0.085
0.113±0.233
0.094±0.252
small-pool frogs
0.068
0.004
0.042
0.874
0.006±0.008
0.015±0.015
0.008±0.010
0.016±0.016
Bufo americanus
0.146
0.002
0.919
0.977
0.035±0.049
0.045±0.057
0.047±0.054
0.118±0.171
aquatic salamanders
0.903
0.022
0.482
0.525
0.024±0.034
0.031±0.031
0.022±0.024
0.023±0.027
terrestrial salamanders
0.223
0.046
0.129
0.088
0.058±0.055
0.072±0.091
0.132±0.132
0.079±0.099
Plethodon glutinosus
0.516
0.533
0.032
0.493
0.009±0.011
0.011±0.007
0.014±0.009
0.012±0.009
Table 3.2 (continued)
Taxa
reptiles
large snakes
small snakes
lizards
amphibians
large-pool frogs
small-pool frogs
Bufo americanus
aquatic salamanders
terrestrial salamanders
Plethodon glutinosus
2002
0.23±0.19
0.020±0.035
0.083±0.0921
0.135±0.1601
0.910±0.8201
0.194±0.2961
0.000±0.0002
0.022±0.017
0.028±0.042
0.060±0.110
NA
mean - year
2003
2004
0.10±0.08
0.12±0.07
0.018±0.014
0.018±0.013
0.026±0.0192
0.030±0.0162
0.051±0.0632 0.070±0.0541,2
0.870±0.8101
0.320±0.2202
0.028±0.0312
0.035±0.0412
0.018±0.0161
0.012±0.0111
0.141±0.158
0.039±0.039
0.027±0.022
0.022±0.019
0.089±0.044
0.058±0.039
0.017±0.0081 0.011±0.0081,2
2005
0.07±0.05
0.013±0.011
0.012±0.0132
0.039±0.0362
0.420±0.4102
0.013±0.0102
0.011±0.0121
0.053±0.057
0.022±0.020
0.118±0.131
0.009±0.0072
59
control
0.11±0.173
0.002±0.0042
0.019±0.021
0.023±0.0332
0.600±0.390
0.038±0.052
0.007±0.010
0.074±0.083
0.022±0.019
0.065±0.041
0.016±0.006
30
# of species detected
25
20
15
Log.Clearcut
(1)
Log.25%
(3)
Log.50%
(4)
Log.75%
(2)
Log.Control
(5)
10
5
1
5
9
13
17
21
25
29
33
37
41
45
49
53
57
61
65
69
73
77
81
85
89
93
0
Trap
Trap
daysnights
Figure 3.2 Number of species detected in drift fences over time on five basal area
retention treatments in Jackson County, Alabama, 2003.
3.5
3.0
Relative abundance
2.5
2.0
% retention
1.5
Clearcut
1.0
25%
.5
50%
75%
0.0
Control
-.5
N=
3
3
3
2003
3
3
3
3
3
3
3
2004
3
3
3
3
3
2005
Year
Figure 3.3 Relative abundance of amphibians on five basal area retention treatments in
Jackson County, Alabama, 2002-2005.
60
.4
Relative abundance
.3
.2
% retention
Clearcut
.1
25%
50%
0.0
75%
Control
-.1
N=
3
3
3
3
3
3
2003
3
3
3
3
3
3
2004
3
3
3
2005
Year
Figure 3.4 Relative abundance of reptiles on five basal area retention treatments in
Jackson County, Alabama, 2002-2005.
.03
Relative abundance
.02
% retention
.01
Clearcut
25%
0.00
50%
75%
Control
-.01
N=
2 3 3 3 3
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
2002
2003
2004
2005
Year
Figure 3.5 Relative abundance of aquatic salamanders on five basal area retention
treatments in Jackson County, Alabama, 2002-2005.
61
.10
Relative abundance
.08
.06
% retention
.04
Clearcut
.02
25%
50%
0.00
75%
Control
-.02
N=
2 3 3 3 3
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
2002
2003
2004
2005
Year
Figure 3.6 Relative abundance of terrestrial salamanders on five basal area retention
treatments in Jackson County, Alabama, 2002-2005.
Relative abundance
.2
.1
% retention
Clearcut
0.0
25%
50%
75%
Control
-.1
N=
2 3 3 3 3
3 3 3 3 3
3 3 3 3 3
2002
2003
2004
3
3 3 3 3
2005
Year
Figure 3.7 Relative abundance of large-pool frogs on five basal area retention treatments
in Jackson County, Alabama, 2002-2005.
62
.012
Relative abundance
.010
.008
.006
% retention
Clearcut
.004
25%
.002
50%
0.000
75%
Control
-.002
N=
2 3 3 3 3
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
2002
2003
2004
2005
Year
Figure 3.8 Relative abundance of small-pool frogs on five basal area retention treatments
in Jackson County, Alabama, 2002-2005.
.03
Relative abundance
.02
% retention
.01
Clearcut
25%
0.00
50%
75%
Control
-.01
N=
2 3 3 3 3
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
2002
2003
2004
2005
Year
Figure 3.9 Relative abundance of large-bodied snakes on five basal area retention
treatments in Jackson County, Alabama, 2002-2005.
63
.08
.07
Relative abundance
.06
.05
% retention
.04
.03
Clearcut
.02
25%
.01
50%
0.00
75%
Control
-.01
N=
2 3 3 3 3
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
2002
2003
2004
2005
Year
Figure 3.10 Relative abundance of small-bodied snakes on five basal area retention
treatments in Jackson County, Alabama, 2002-2005.
.12
Relative abundance
.10
.08
.06
% retention
Clearcut
.04
25%
.02
50%
0.00
75%
Control
-.02
N=
2 3 3 3 3
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
2002
2003
2004
2005
Year
Figure 3.11 Relative abundance of lizards on five basal area retention treatments in
Jackson County, Alabama, 2002-2005.
64
was greater in clearcuts than controls and lizards were more abundant in 25% treatments
compared to 75% and control treatments. Lizards were more abundant in 2002 than 2003
and 2005. Small snakes and large pool frogs were more abundant in 2002 than 20032005. Small pool frogs were less abundant in 2002 compared to 2003-2005.
Only one species, Plethodon glutinosus, the slimy salamander, was captured in
sufficient numbers (N ≥ 30 individuals) in 2003, 2004, and 2005 to test for differences in
mean abundance by treatment and year, and one species, the American toad, satisfied this
criterion for 2002-2005. Slimy salamanders did not differ by treatment, but did across
years (Fig. 3.12, Table 3.2). More slimy salamanders were captured in 2003 than 2005.
American toad abundance was not different across treatments or among years (Fig. 3.12,
Table 3.2). American toads did not differ by treatment or across years (Fig. 3.13, Table
3.2).
Diversity Indices. None of the amphibian diversity indices measured differed
across canopy retention treatments when years were analyzed separately. ShannonWeiner indices were lower in 2002 than 2003-2005. Simpson’s diversity was lower in
2002 than in 2004 and 2005 (Table 3.3). When all captures from between 2002 and 2005
were combined and then analyzed the following indices did not differ among treatments:
Shannon-Weiner (F4,8=1.63, P = 0.257) (Fig. 3.14), evenness (F4,8=0.72, P = 0.602) (Fig.
3.15), Simpson’s diversity (F4,8=1.30, P = 0.349) (Fig. 3.16). Species richness, however,
differed by treatment (F4,8=5.42, P = 0.021). Species richness of amphibians between
2002 and 2005 was lower in clearcuts compared to 25% treatments (Fig. 3.17, Table 3.4).
Of the 21 species of amphibians captured, 11 of these were never captured on clearcuts,
65
Table 3.3 Mean indices of amphibian diversity, years separate, 2002-2005 on five basal area retention treatments, Jackson County,
Alabama. Means within a row with different superscript numbers differ (Tukey P<0.05).
P-value
mean - treatment
Index
treatment
block
year
year*treat
clearcut
25%
50%
75%
Shannon Wiener
0.068
0.006
0.0001
0.884
0.67±0.58
0.98±0.52
1.01±0.34
0.73±0.41
Evenness
0.134
0.0003
0.637
0.043
0.79±0.20
0.74±0.19
0.64±0.14
0.58±0.25
Simpson’s Diversity
0.088
0.125
0.001
0.939
0.34±0.29
0.47±0.25
0.52±0.16
0.37±0.21
Richness
0.143
0.0001
NA
0.529
3.50±2.39
5.17±2.66
5.25±2.18
4.92±2.61
Table 3.3 (continued)
Index
Shannon Wiener
Evenness
Simpson’s Diversity
Richness
2002
0.43±0.392
0.76±0.22
0.25±0.222
2.33±1.40
mean - year
2003
2004
1
0.86±0.29
1.07±0.431
0.53±0.22
0.74±0.18
0.42±0.161,2 0.53±0.211
5.93±2.12
4.93±1.94
2005
0.94±0.431
0.66±0.21
0.47±0.211
5.40±2.64
Table 3.4 Mean indices of amphibian diversity, years combined, 2002-2005 on five basal area retention treatments,
Jackson County, Alabama. Means within a row with different superscript numbers differ (Tukey P<0.05).
P-value
mean - treatment
Index
treatment
block
clearcut
25%
50%
75%
control
Shannon Wiener
0.257
0.624
0.95±0.48
1.26±0.18
1.33±0.26
0.90±0.20
0.86±0.14
Evenness
0.602
0.551
0.53±0.14
0.53±0.09
0.59±0.11
0.41±0.10
0.46±0.23
Simpson’s Diversity
0.349
0.934
0.44±0.21
0.54±0.11
0.63±0.08
0.39±0.10
0.41±0.15
11.0±3.461 10.0±3.611,2 10.0±3.611,2 9.0±4.581,2
Richness
0.021
0.001
6.0±2.652
66
control
0.73±0.29
0.61±0.26
0.39±0.16
4.42±2.39
.04
Relative abundance
.03
.02
% retention
Clearcut
.01
25%
50%
0.00
75%
Clearcut
-.01
N=
3
3
3
3
3
3
3
2003
3
3
3
3
3
2004
3
3
3
2005
Year
Figure 3.12 Relative abundance of Plethodon glutinosus on five basal area retention
treatments in Jackson County, Alabama, 2002-2005.
.7
.6
Relative abundance
.5
.4
% retention
.3
Clearcut
.2
25%
.1
50%
75%
0.0
Control
-.1
N=
3 3 3 3 3
3 3 3 3 3
3 3 3 3 3
2002
2003
2004
3
3 3 3 3
2005
Year
Figure 3.13 Relative abundance of Bufo americanus on five basal area retention
treatments in Jackson County, Alabama, 2002-2005.
67
1.8
Shannon-Wiener diversity
1.6
1.4
1.2
1.0
.8
.6
.4
.2
N=
3
3
3
3
3
Clearcut
25%
50%
75%
Control
% retention treatment
Figure 3.14 Shannon-Wiener diversity for total amphibian captures 2002-2005.
.8
.7
Evenness
.6
.5
.4
.3
.2
N=
3
3
3
3
3
Clearcut
25%
50%
75%
Control
% retention treatment
Figure 3.15 Evenness for total amphibian captures 2002-2005.
68
.8
Simpson's Diversity
.7
.6
.5
.4
.3
.2
N=
3
3
3
3
3
Clearcut
25%
50%
75%
Control
% retention treatment
Figure 3.16 Simpson’s diversity (1-dominance) for total amphibian captures 2002-2005.
16
14
# of species
12
10
8
6
4
2
N=
3
3
3
3
3
Clearcut
25%
50%
75%
Control
% retention treatment
Figure 3.17 Species richness for total amphibian captures 2002-2005.
69
compared to 4 and 7 species never captured on 50% retention and control treatments
respectively. There were no amphibian species captured only on control treatments.
Mean Shannon-Weiner index for reptiles was higher in clearcut, 25% and 50% treatments
than controls when years were analyzed separately (Table 3.5). Simpson’s diversity of
reptiles was higher in clearcut, 25% and 50% treatments than 75% and controls, and 75%
treatments were higher than controls. Mean species richness of reptiles was higher on
50% treatments than 75% and controls, and higher on clearcuts and 25% treatments than
on controls. Reptile diversity indices did not differ over time (Table 3.5). When total
captures were analyzed together none of the following indices varied by treatment:
Shannon-Weiner (F4,8=3.42, P = 0.066) (Fig. 3.18), evenness (F4,8=0.213, P = 0.924) (Fig.
3.19), Simpson’s diversity (F4,8=1.20, P = 0.381) (Fig. 3.20).
Reptile richness, however, was higher in clearcut, 25% and 50% treatments than
controls, and higher in 50% than 75% treatments (F4,8=11.41, P = 0.0002) (Fig. 3.21,
Table 3.6).
Total species richness of amphibians and reptiles combined for all captures 20022005 varied by treatment (F4,8=5.15, P = 0.024) (Fig. 3.22). Total herpetofaunal species
richness was higher in 25- and 50% retention treatments than controls.
Similarity. Both Morisita’s and Bray-Curtis indices of similarity for amphibian
communities showed that a given treatment was generally most similar to treatments with
the closest amount of basal area retained (Table 3.7 & 3.8). That is, clearcut treatments
were most similar to 25% treatments, which were most similar to 50%, and so on. BrayCurtis similarity showed that amphibian communities on 75% and control treatments
70
Table 3.5 Mean indices of reptile diversity, years separate, 2002-2005 on five basal area retention treatments, Jackson County, Alabama. Means
within a row with different superscript numbers differ (Tukey P<0.05).
P-value
mean - treatment
Index
treatment
block
year
year*treat
clearcut
25%
50%
75%
control
1
1
1
1,2
Shannon Wiener
0.007
0.006
0.459
0.088
1.44±0.46
1.23±0.36
1.47±0.33
1.02±0.55
0.69±0.572
Evenness
0.218
0.996
0.459
0.411
0.90±0.10
0.87±0.10
0.90±0.07
0.95±0.08
0.96±0.07
Simpson’s Diversity
0.008
0.018
0.592
0.056
0.70±0.171
0.64±0.131
0.72±0.091
0.56±0.282
0.41±0.313
Richness
<0.001
0.016
0.900
0.870
4.83±2.291,2
4.50±1.881,2 5.08±2.431 3.33±1.442,3 2.00±1.543
Table 3.5 (continued)
Index
Shannon Wiener
Evenness
Simpson’s Diversity
Richness
2002
0.75±0.53
0.94±0.10
0.44±0.29
2.20±1.47
mean - year
2003
2004
1.17±0.50
1.43±0.44
0.93±0.08
0.90±0.08
0.62±0.21
0.69±0.20
4.07±1.79
5.53±1.96
2005
1.32±0.42
0.90±0.10
0.67±0.16
4.00±2.33
Table 3.6 Mean indices of reptile diversity, years combined, 2002-2005 on five basal area retention treatments,
Jackson County, Alabama. Means within a row with different superscript numbers differ (Tukey P<0.05).
P-value
mean - treatment
Index
treatment
block
clearcut
25%
50%
75%
Shannon Wiener
0.066
0.365
1.97±0.07
1.77±0.07
1.95±0.17
1.71±0.21
Evenness
0.924
0.918
0.83±0.04
0.82±0.11
0.82±0.04
0.88±0.05
Simpson’s Diversity
0.381
0.430
0.81±0.03
0.76±0.05
0.80±0.04
0.78±0.07
Richness
0.002
0.162
10.67±1.151,2 9.0±1.731,2
11.0±2.001
7.0±1.002,3
71
control
1.29±0.50
0.84±0.15
0.64±0.21
4.67±1.533
2.2
Shannon-Wiener diversity
2.0
1.8
1.6
1.4
1.2
1.0
.8
.6
N=
3
3
3
3
3
Clearcut
25%
50%
75%
Control
% retention treatement
Figure 3.18 Shannon-Wiener diversity for total reptile captures 2002-2005.
1.0
Evenness
.9
.8
.7
.6
N=
3
3
3
3
3
Clearcut
25%
50%
75%
Control
% retention treatment
Figure 3.19 Evenness for total reptiles captures 2002-2005.
72
.9
Simpson's diversity
.8
.7
.6
.5
.4
.3
N=
3
3
3
3
3
Clearcut
25%
50%
75%
Control
% retention treatment
Figure 3.20 Simpson’s diversity (1-dominance) for total reptile captures 2002-2005.
14
12
# of species
10
8
6
4
2
N=
3
3
3
3
3
Clearcut
25%
50%
75%
Control
% retention treatment
Figure 3.21 Species richness of total reptile captures 2002-2005.
73
30
# of species
20
10
0
N=
3
3
3
3
3
Clearcut
25%
50%
75%
Control
% retention treatment
Figure 3.22 Species richness of total reptiles and amphibian captures 2002-2005.
Table 3.7 Morisita’s indices of similarity for amphibian communities 2003-2005 on five
basal area retention treatments, Jackson County, Alabama.
treatment
clearcut
25%
50%
75%
control
clearcut
--1.000
0.999
0.964
0.989
25%
1.000
--1.000
0.967
0.988
50%
0.999
1.000
--0.954
0.982
75%
0.964
0.967
0.954
--0.994
control
0.989
0.988
0.982
0.994
---
Table 3.8 Bray-Curtis indices of similarity for amphibian communities 2003-2005 on five
basal area retention treatments, Jackson County, Alabama.
treatment
clearcut
25%
50%
75%
control
clearcut
--0.792
0.685
0.443
0.577
25%
0.792
--0.858
0.563
0.719
50%
0.685
0.858
--0.597
0.777
74
75%
0.443
0.563
0.597
--0.764
control
0.577
0.719
0.777
0.764
---
were especially similar to each other; likewise communities on clearcut, 25% and 50%
were relatively more similar to each other than to 75% and control. The same pattern of
reptile similarity indices was seen across treatments as with amphibians, with more
similar treatments showing more similar reptile communities (Table 3.9 & 3.10). Control
treatments appeared especially dissimilar from other treatments in terms of reptile
communities.
Table 3.9 Morisita’s indices of similarity for reptile communities 2003-2005 on five basal
area retention treatments, Jackson County, Alabama.
treatment
clearcut
25%
50%
75%
control
clearcut
--0.979
1.003
0.834
0.788
25%
0.979
--1.023
0.744
0.677
50%
1.003
1.023
--0.775
0.738
75%
0.834
0.744
0.775
--0.983
control
0.788
0.677
0.738
0.983
---
Table 3.10 Bray-Curtis indices of similarity for reptile communities 2003-2005 on five
basal area retention treatments, Jackson County, Alabama.
treatment
clearcut
25%
50%
75%
control
clearcut
--0.785
0.819
0.617
0.429
25%
0.785
--0.860
0.488
0.365
50%
0.819
0.860
--0.509
0.362
75
75%
0.617
0.488
0.509
--0.701
control
0.429
0.365
0.362
0.701
---
Canonical Correspondence Analysis. Based on the CCA analysis of microhabitat
measures and drift fence captures in 2003, 28% of the variation in relative abundance of
the seven guilds can be explained by the first two axes. The first axis explained 18.6% of
this variation (Eigenvalue = 0.214, Pearson correlation of guild-microhabitat variables R
= 0.78) and the second axis 9% (Eigenvalue = 0.103, R = 0.727). Analysis of 2004
guild/microhabitat relationships revealed that the first axis explained 12.5% of variation
(Eigenvalue = 0.127, R = 0.65) and the second 7.2% (Eigenvalue = 0.127, R = 0.62) for a
total of 19.7% of variation explained. The first and second axes in 2005 explained 14.6%
(Eigenvalue = 0.178, R = 0.71) and 9.8% (Eigenvalue = 0.119, R = 0.65) of variation,
respectively, for a total of 24.4%.
The position of microhabitat variables along the first two axes in each year
correspond to the gradient in conditions created by canopy retention treatments (See
Chapter 2) (Fig. 3.23-3.25). On one end of the gradient are the variables woody
vegetation, herbaceous vegetation, slash and coarse woody debris (CWD). Opposite of
these are variables such as litter, canopy, basal area, and distance to pool. The relative
abundance of reptile and amphibian guilds were consistently positioned along this
gradient and several showed a relationship with specific microhabitat variables.
Terrestrial salamanders, and to a lesser degree aquatic salamanders, consistently related
with basal area. Lizard abundance appeared to be related to slash and woody vegetation
variables. Large snakes were positively related with variables such as herbaceous and
woody vegetation. Large and small pool frogs grouped closely together in 2004 and
2005, but did not appear related to any microhabitat variable measured.
76
large-pool
frogs
litter
small-pool
frogs
large snakes
woody veg
aquatic salamanders
canopy cover
basal area
herbaceous veg
Terrestrial salamanders
small
snakes
lizards
Figure 3.23 First and second Canonical Correspondence axes with reptile and amphibian
guilds and microhabitat variables, Jackson County, Alabama, 2003.
large-pool
frogs
small-pool
frogs
canopy cover
litter
distance to
pool
basal area
aquatic salamanders
woody veg
slash
lizards
small snakes
Terrestrial salamanders
herbaceous veg
bare
large snakes
Figure 3.24 First and second Canonical Correspondence axes with reptile and amphibian
guilds and microhabitat variables, Jackson County, Alabama, 2004.
77
canopy cover
aquatic salamanders
large-pool
small-pool
frogs
frogs
Terrestrial
salamanders
basal area
CWD
distance to
pool
slash
woody veg
lizards
herbaceous
veg
large snakes
litter depth
small snakes
Figure 3.25 First and second Canonical Correspondence axes with reptile and amphibian
guilds and microhabitat variables, Jackson County, Alabama, 2005.
Discussion
Overall, it appears that amphibian response to canopy removal on these sites is
either neutral or negative. While no changes were observed in amphibian diversity, or in
relative abundance in amphibian guilds, a couple of negative responses were observed.
Species richness of amphibians was lowest in clearcuts and total abundance of
amphibians dropped in 2004 and 2005 relative to 2002 and 2003. This drop in abundance
could have been related to macroclimatic conditions such as yearly rainfall, or to a
delayed response to treatments. Reptiles, on the other hand, responded favorably to
canopy removal. Lizards were most common in 25% retention treatments, while large-
78
bodied snakes reached their highest abundance on clearcut treatments. Total reptile
abundance was highest on 25% treatments and lowest on controls. Reptile diversity and
species richness were highest on cut treatments (clearcut, 25% and 50% retention) and
lowest on controls.
Other researchers have similarly shown that amphibian response to canopy
removal in the Southeast is variable and that reptiles more predictably respond favorably.
In Virginia, salamanders decreased in abundance after reducing basal area to 41% of
pretreatment levels (18 m2 basal area) (Knapp et al. 2003). Other researchers (Bartman
2001, Sattler and Reichenbach 1998) have found that, while clearcutting reduced
terrestrial salamander numbers, shelterwood cuts that retained 60-30% of initial basal
area had no measurable effect on salamander abundance. On the northwest edge of the
Cumberland Plateau amphibian diversity was lower on two-age harvested stands with 3.5
m2 residual basal area than unharvested controls, but species richness and abundance did
not differ while reptile abundance and species richness were higher on clearcuts and twoaged harvests with 3.5-7 m2 residual basal area than controls (Adams et al. 1996).
Amphibians and reptiles showed opposite linear relationships in terms of species richness
and basal area of forest stands in Pennsylvania, with amphibians increasing with
increasing basal area and reptiles decreasing (Fredericksen et al. 2000). Amphibian
richness, diversity, and abundance did not differ between control stands or salvagelogged wind gaps with 50-70% of pre-disturbance basal area in North Carolina, while
reptile richness, diversity and abundance were all higher in gaps (Greenberg 2001).
79
One of the major questions of this research was whether the response of reptile
and amphibian groups was proportional to the amount of canopy removed. If the
response was proportional you would expect to see a gradient in abundance, diversity or
richness over the various levels of tree retention treatments. If, however, a threshold
existed in the amount of canopy removed then you would expect to see more drastic
changes beyond a certain level of canopy removal or retention. Results were mixed for
reptiles, with large-bodied snake abundance varying in proportion with canopy removal,
but lizard abundance greater in intermediate levels of harvest (25- and 50% retention) and
lower in 75% and controls. Reptile diversity and species richness increased in both
intermediate levels of harvest (50- and 25% retention) and clearcuts, indicating that any
level of harvest which resulted in an opening of the forest canopy benefits reptiles. The
only other study of herpetofaunal response to a gradient of canopy removal concluded
that amphibian and reptile response was comparable for treatments with 3.5 - 7 m2
residual basal area and clearcuts relative to controls (Adams et al. 1996). This suggests
that effects on herpetofauna, positive or negative, were as apparent in two-aged harvests
as in clearcuts. In our study, the positive effects of canopy removal observed for reptiles
were apparent and more pronounced even in stands with intermediate levels of canopy
retention (25- and 50%).
The abundance of reptile and amphibian guilds was related to treatment-related
changes to microhabitat availability. Canopy retention treatments created a gradient in
microhabitat availability ranging from clearcuts with abundant herbaceous and woody
vegetation, slash, CWD, to control stands with high canopy cover, high coverage of deep
80
leaf litter, and high basal area (see Chapter 2). Terrestrial salamanders, and to a smaller
extent aquatic salamanders, were most often captured in areas with high basal area. In
north Georgia hardwood forest stands abundance of both terrestrial and aquatic
salamanders was related to increasing stand age and basal area (Ford et al. 2002). Lizard
abundance was most strongly related to the amount of slash and woody vegetation in
open stands. Slash likely provides lizards with opportunities for basking
thermoregulation and cover. It was conjectured that logging slash was an important
microhabitat for reptiles on South Carolina clearcuts (Phelps and Lancia 1995). Largebodied snakes were captured most often in areas with high coverage of herbaceous
vegetation and bare ground. Open habitats with abundant herbaceous vegetation are
preferred by a wide variety of large-bodied snakes such as black racers Coluber
constrictor, and black rat snakes Elaphe obsoleta (Durner and Gates 1993, Keller and
Heske 2000).
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prescriptions in the Daniel Boone National Forest, Kentucky. Proceedings of the
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Congdon, J.D., J.L. Greene, and J.W. Gibbons. 1986. Biomass of freshwater turtles: a
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deMaynadier, P.G., and Hunter, M.L., Jr. 1995. The relationship between forest
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Durner, G.M. and J.E. Gates. 1993. Spatial ecology of black rat snakes on Remington
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Ehrlich, P.R. 1996. Conservation in temperate forests: what do we need to know and do?
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Enge, K.M, and W.R. Marion. 1986. Effects of clearcutting and site preparation on
herpetofauna of a north Florida flatwoods. Forest Ecology and Management 14:
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Ford, W.M., B.R. Chapman, M.A. Menzel, and R.H. Odom. 2002. Stand age and habitat
influences on salamanders in Appalachian cove hardwood forests. Forest Ecology
and Management 155: 131-141.
Frederickson, T.S., B.D. Ross, W. Hoffman, E. Ross, M.L Morrison, J. Beyea, M.B.
Lester, and B.N. Johnson. 2000. The impact of logging on wildlife: a study in
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Gibbons, J.W., V.J. Burke, J.E. Lovich, R.D. Semlitsch, T.D. Tuberville, J.R. Bodie, J.L.
Greene, P.H. Niewiarowski, H.H. Whiteman, D.E. Scott, J.H.K. Pechmann, C.R.
Harrison, S.H. Bennett, J.D. Krenz, M.S. Mills, K.A. Buhlmann, J.R. Lee, R.A.
Seigel, A.D. Tucker, T.M. Mills, T. Lamb, M.E. Dorcas, J.D. Congdon, M.H.
Smith, D.H. Nelson, M.B. Dietsch, H.G. Hanlin, J.A. Ott, and D.J. Karapatakis.
1997. Perceptions of species abundance, distribution, and diversity: lessons from
four decades of sampling on a government-managed reserve. Environmental
Management 21: 259-268.
Gibbons, J.W., D.E. Scott, T.J. Ryan. 2000. The global decline of reptiles, déjà vu
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Greenberg, C.H. 2001. Response of reptile and amphibian communities to canopy gaps
created by wind disturbance in the southern Appalachians. Forest Ecology and
Management 148: 135-144.
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Greenberg, C.H., D.G. Neary, and L.D. Harris. 1994. Effect of high-intensity wildfire and
silvicultural treatments on reptile communities in sand-pine scrub. Conservation
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Halverson, M.A., D.K. Skelly, J.M. Kiesecker, and L.K. Freidenberg. 2003. Forest
mediated light regime linked to amphibian distribution and performance.
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Keller, W.L. and E.J.Heske. 2000. Habitat use by three species of snakes at the Middle
Fork Fish and Wildlife Area, Illinois. Journal of Herpetology 34: 558-564.
Knapp, S.M., C.A. Haas, D.N. Harpole, and R.L. Kirkpatrick. 2003. Initial effects of
clearcutting and alternative silvicultural practices on terrestrial salamander
abundance. Conservation Biology 17: 752-762.
McLeod, R.F., and J.E. Gates. 1998. Response of herpetofaunal communities to forest
cutting and burning at Chesapeake Farms, Maryland. American Midland
Naturalist 139: 164-177.
Magurran, A.E. 1988. Ecological diversity and its measurement. Princeton University
Press, Princeton, NJ.
Moseley, K.R., S.B. Castleberry, and W.M. Ford. 2004. Coarse woody debris and pine
litter manipulation effects on movement and microhabitat use of Ambystoma
talpoideum in a Pinus taeda stand. Forest Ecology and Management 191: 387-396.
Palmer, M.W. 1993. Putting things in even better order: the advantages of canonical
correspondence analysis. Ecology 74: 2215-2230.
Patrick, D.A., M.L. Hunter, and A.J. Calhoun. 2006. Effects of experimental forestry
treatments on a Maine amphibian community. Forest Ecology and Management
234: 323-332.
Petranka, J.W., and Murray, S.S. 2001. Effectiveness of removal sampling for
determining salamander density and biomass: a case study in an Appalachian streamside
community. Journal of Herpetology 35: 36-44.
Phelps, J.P., and R.A. Lancia. 1995. Effects of a clearcut on the herpetofauna of a South
Carolina bottomland swamp. Brimleyana 22: 31-45.
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Rothermel, B.B., and T.M. Luhring. 2005. Burrow availability and dessication risk of
mole salamanders (Ambystoma talpoideum) in harvested versus unharvested
forest stands. Journal of Herpetology 39: 619-626.
Russell, K.R., T.B. Wigley, W.M. Baughman, H.G. Hanlin, and W.M. Ford. 2004.
Respsonses of southeastern amphibians and reptiles to forest management: A
review. Pgs. 319-334 In General Technical Report SRS-75. Asheville, NC: U.S.
Department of Agriculture, Forest Service, Southern Research Station.
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Institute Inc., Cary, NC, USA.
Sattler, P., and N. Reichenbach. 1998. The effects of timbering on Plethodon hubrichti:
Short-term effects. Journal of Herpetology 32: 399-404.
Schweitzer, C.J. 2003. First-year response of an upland hardwood forest to five levels of
overstory tree retention. In K.F. Connor, ed. Proceedings of the 12th biennial
southern silvicultural research conference. Gen. Tech. Rep. SRS-71. Asheville,
NC: U.S. Department of Agriculture, Forest Service, Southern Research Station.
Sharitz, R.R., L.R. Boring, D.H. Van Lear, and J.E. Pinder III. 1992. Integrating
ecological concepts with natural resource management of southern forests.
Ecological Applications 2: 226-237.
Smalley, G.W. 1982. Classification and evaluation of forest sites on the Mid-Cumberland
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Forest Service, Southern Forest Experiment Station.
Stuart, S.N., J.S. Chanson, N.A. Cox, B.E. Young, A.S.L. Rodrigues, D.L. Fischman, and
R.W. Waller. 2004. Status and trends of amphibian declines and extinctions
worldwide. Science 306: 1783-1786.
84
CHAPTER 4
RESPONSE OF LUNGLESS SALAMANDERS TO VARIOUS LEVELS OF
OVERSTORY TREE RETENTION
Lungless salamanders of the family Plethodontidae have received much attention
in recent years because of their unique ecological value and sensitivity to environmental
changes (Welsh and Droege 2001, Davic and Welsh 2004). These animals can reach
extremely high levels of biomass in deciduous forests of the eastern United States
(Burton and Likens 1975a, Petranka and Murray 2001), surpassing biomass of other
vertebrate groups in the same systems. Because of their numbers and unique
physiological adaptations (Pough 1983) lungless salamanders play an important role in
nutrient cycling in forest ecosystems (Burton and Likens 1975b). For these reasons,
salamanders have been the focus of much research on the effects of canopy removal
associated with forest management (Russell et al. 2004).
Although it is generally accepted that clearcutting forest stands in the eastern
United States results in either a reduction in numbers (Pough et al. 1987, Petranka et al.
1994, Ash 1997, Harper and Guynn 1999, Knapp et al. 2003) or complete disappearance
(Ash 1997) of Plethodontid salamanders, debate remains about the effects of intermediate
levels of tree removal. Some studies have shown that removal of up to 50% of basal area
85
results in no observable change to abundance of salamanders (Sattler and Reichenbach
1998, Brooks 1999, Brooks 2001, McKenny et al. 2006). Other research has shown that
retaining 50-60% of overstory trees can reduce numbers for at least 4 years after harvest
(Knapp et al. 2003, Morneault et al 2004).
Beyond effects on abundance of salamanders, canopy removal can impact
demographic attributes such as percentage of juveniles (Sattler and Reichenbach 1998,
Knapp et al. 2003), and growth of individuals as indicated by changes to mass or ratio of
mass to length (Knapp et al 2003, Karraker and Welsh 2006). These more subtle impacts
could have important ramifications for the long-term viability of populations. The
objectives of this study were to compare the relative abundance, population structure, and
body condition of terrestrial salamanders across a range of canopy retention treatments in
upland hardwood forests of northern Alabama.
Study Area
This study took place in Jackson County, northeastern Alabama (Fig. 4.1). The
area is classed into the Cliff section of the Cumberland Plateau in the Mixed Mesophytic
Forest region by Braun (1950). Bailey et al. (1994) included this area in the Eastern
Broadleaf Forest (Oceanic) Province and Northern Cumberland Plateau Section.
According to Smalley (1982), the sites are located in the Mid Cumberland Plateau region,
the Strongly Dissected Portion subregion, and landtypes 16, 17, and 18 of the Strongly
Dissected Margins and Sides landtype association. The area is characterized by steep
slopes dissecting the Plateau surface and draining to the Tennessee River. Soils are
86
a)
Miller Mtn.
Jack
Gap
b)
25%
50%
clear
control -cut
clear
-cut
Block 3
75% control
Block 1
Miller Mt.
25%
N
75% 50%
50% 25% clear control
-cut
4-ha units
75%
Block 2
Jack Gap
Figure 4.1 Location of study site in Alabama (a) and layout of experimental design (b),
Jackson County, Alabama.
87
shallow to deep, stony and gravelly loam or clay, well drained, and formed in colluvium
from those on the Plateau top (Smalley 1982). Climate of the region was described as
temperate with mild winters and moderately hot summers with a mean temperature of 13
degrees C, and mean precipitation of 149 cm (Smalley 1982). Two sites were used. The
first, Miller Mountain (34o 58’ 11” N, 86o 12’ 21” W), was situated on mainly South,
Southwest facing slopes with elevations ranging from 457-518 m (Figure 4.1a). The
second, Jack Gap (34o 56’ 30” N, 86o 04’ 00” W), had a North aspect with elevations
ranging from 304-475 m. Dominant canopy tree species included oaks, including
Quercus velutina Lamarck, Q. rubra L., Q. alba L., Q. prinus L.; 46% of pretreatment
basal area (BA), hickories (Carya spp.; 15% pretreatment BA), sugar maple (Acer
saccharum Marsh.; 13% pretreatment BA) and yellow poplar (Liriodendron tulipifera L.;
9% pretreatment BA) (Schweitzer 2003). Common understory species included
flowering dogwood (Cornus florida L.), eastern redbud (Cercis canadensis L.), and
sourwood (Oxydendrum arboretum DC.).
The study followed a randomized complete block design with three blocked
replicates of five treatments involving varying levels of basal area retention of trees (Fig
4.1b). Treatments included clearcuts, 25-, 50-, and 75% retention, and controls. The
clearcuts, 25%, and 50% retention treatments were chainsaw-felled and grapple skidded
in a commercial logging operation. In the 25 and 50 percent retention treatments, trees
were marked to leave favoring dominant and codominants with high vigor, especially oak,
ash (Fraxinus spp.), and persimmon (Diosyros virgniana L.). In 75% retention treatment
plots, the midstory was removed by incising trees and applying the herbicide Arsenal
88
(active ingredient imazapyr) to achieve a shelterwood cut. An average of 941 stems that
were an average of 7.4 cm diameter at breast height (DBH; measured at 1.37 m above
ground) was treated per hectare with herbicide in such a way to retain an intact canopy,
but allow increased light penetration to the forest floor (Schweitzer 2003). These
treatments were implemented in order to determine which silvicultural prescription was
most conducive to regenerating oaks on these sites. The 25, 50, and 75 percent retention
treatments were designed as shelterwoods and residual stems are scheduled to be
removed 10 years post harvest. Two blocks were located at Jack Gap, and the other at
Miller Mountain. Each of the 15 experimental units was 4 ha in size. Trees were
harvested during the fall of 2001 and winter of 2002, and herbicide treatment took place
in fall 2001. Although pretreatment data was not obtained for any of the variables
measured in the present study besides basal area, the close proximity of sites, the uniform
forest structure present pretreatment (Schweitzer 2003), and the random assignment of
treatments make comparison of treatments to control plots valid. Post treatment basal
area of treatments was as follows: controls, 24.3 m2/ha (99% retention); 75%, 18.8 m2/ha
(70% retention); 50%, 9.2 m2/ha (38% retention); 25%, 6.3 m2/ha (28% retention); and
clearcut, 1.2 m2/ha (5% retention) (Schweitzer 2003).
Methods
Salamander sampling. Artificial cover objects (coverboards) (Fellers and Drost
1994) were used to monitor terrestrial salamander abundance on experimental treatment
units. This method has been used effectively by several researchers to detect changes in
89
salamander abundance after canopy removal (Brooks 1999, Morneault et al. 2004). A
grid of 30 pine boards (5cm X 20cm X 30cm) was placed at each of 3 vegetation plots on
each unit established by Dr. Callie Schweitzer of the USDA Forest Service to monitor the
response of woody vegetation to treatments (90/unit X 15 units = 1350 boards total).
Boards were placed in direct contact with the forest floor without removal of leaf litter
during the spring of 2002. Each coverboard grid was at least 15 m from other grids and
edges of treatment units. Coverboards were checked 11 times between December 3rd,
2004 and May 4th, 2005 and another 11 times between January 31st, 2005 and April 15th,
2006. All boards on one block were checked within a 24 hr period and 6-20 days passed
between successive sampling periods. Salamanders were hand captured, measured for
snout-vent length (SVL) with calipers to the nearest mm, weighed to the nearest gram
with Pesola scales and given a grid-specific toe clip. Soil temperature was taken in
duplicate at each coverboard grid with a soil thermometer (REO TEMP, San Diego, CA)
at 10 cm.
Data analysis. An index of relative abundance was calculated by dividing the
total number of salamanders captured on an experimental unit each year by the number of
visits. To test for effects of year, treatment, and year X treatment interactions on relative
abundance indices of salamander species I used ANCOVA with treatment and block as
main factors, year as a covariate, and Tukey tests for mean separation when ANCOVA
indicated differences. To explore the effects of canopy retention treatments on body
condition of salamanders, an index was created by dividing log-transformed mass by
SVL. The mean mass:length ratio was compared across treatments and years using the
90
same ANCOVA model. To test for differences in the ratio of juveniles:adults and
males:females across the treatments each year a χ2 test was used. All analyses were done
using SAS (SAS 2003) with p ≤ 0.05 for significance.
Results
In 2005 a total of 304 zigzag salamanders (Plethodon dorsalis), 66 slimy
salamanders (Plethodon glutinosus) were captured. In addition to these lungless
salamanders 19 worm snakes (Carphophis amoenus), 6 ringneck snakes (Diadophis
punctatus), 5 ground skinks (Scincella lateralis), 3 spotted salamanders (Ambystoma
maculatum), and a five lined skink (Eumeces fasciatus) were captured. In 2006, 262
zigzag and 52 slimy salamanders were captured, as well as 13 worm snakes, 3 five lined
skinks, 1 ringneck snake, 1 northern red salamander (Pseudotriton ruber), and a
redbellied snake (Storeria occipitomaculata).
Relative abundance. Mean relative abundance did not differ by treatment or by
year for zigzag or slimy salamanders (Table 4.1, Fig. 4.2 and 4.3).
Demographics. Only zigzag salamanders were captured in sufficient numbers to
compare demographic trends across treatments. The χ2 test assumes that > 80% of
categories have an expected value > 5 (Zar 1996) and slimy salamanders did not meet
this assumption. In both 2005 and 2006 the ratio of juvenile to adult zigzag salamanders
differed by treatment (Table 4.2). In 2005 a high number of juveniles per adult were
captured in 25% treatments. In 2006, a low number of juveniles per adult were captured
in clearcuts compared to other treatments. Male:female ratios also differed across
91
treatments in 2005 and 2006 (Table 4.3). In 2005 sex ratios in 25- and 50% treatments
were skewed towards males. In 2006 male-biased ratios were observed in clearcut and
75% retention treatments.
Body size. Only zigzag salamanders were captured in sufficient numbers to
compare mass:length ratios across treatments. The ratio of mass to length was higher on
clearcuts than 25% and control treatments (Fig. 4.4, Table 4.4). This ratio was higher in
2005 than 2006.
Soil temperature. Mean soil temperature was not different among canopy
retention treatments (F = 0.37, P = 0.829) (Fig. 4.5), but was higher in 2006 (9.41 ± 1.14)
than 2005 (8.76 ± 1.21) (F = 8.34, P = 0.0085).
Discussion
Zigzag salamanders were never observed on the clearcut or 25% treatment in
block 1 in either 2005 or 2006. This block is on a south-facing aspect and is generally
warmer and drier than blocks 2 and 3. It has been observed that canopy removal effect is
more dramatic on dry sites where moisture may be more limiting (Petranka et al. 1994). I
did not detect a difference in relative abundance caused by canopy removal as other
researchers have (Pough et al. 1987, Petranka et al. 1994, Harper and Guynn 1999,
Knapp et al. 2003). It is possible that canopy removal did not sufficiently impact
moisture and temperature levels as to limit growth and reproduction of salamanders on
these sites. There was no difference observed in soil temperature across treatments. Leaf
litter depth and cover was comparable on cut and uncut plots by the late summer of 2005
(see Chapter 2). Cool moist climatic conditions during the sampling period (December or
92
Table 4.1Relative abundance of two species of Plethodon salamanders for five basal area retention treatments in Jackson County,
Alabama,
2005 and 2006.
P-value
mean - treatement
Species
treatment
block
year
year*treat
clearcut
25%
50%
75%
control
P. dorsalis
0.208
<0.001 0.421
0.584
1.03±0.95 1.58±1.70 2.09±1.67
1.79±0.64
2.09±0.82
P. glutinosus
0.244
0.106
0.466
0.303
0.11±0.13 0.33±0.14 0.39±0.36
0.44±0.38
0.52±0.49
Table 4.1 (continued)
Species
P. dorsalis
P. glutinosus
mean - year
2005
2006
1.84±1.32 1.59±1.14
0.40±0.38 0.32±0.30
Table 4.2 Ratio of juvenile:adult of P. dorsalis for five basal area retention treatments in Jackson County,
Alabama, 2005 and 2006.
treatment
Year
χ2
P-value
Clearcut
25%
50%
75%
Control
2005
65.78 < 0.0001
0.15:1
0.32:1
0.18:1
0.15:1
0.18:1
2006
411.35 < 0.0001
0.14:1
0.59:1
0.40:1
0.34:1
0.26:1
93
Table 4.3 Ratio of male:female of P. dorsalis for five basal area retention treatments in Jackson County,
Alabama, 2005 and 2006.
treatment
Year
χ2
P-value
Clearcut
25%
50%
75%
Control
2005
75.93 < 0.0001
0.88:1
1.04:1
1.07:1
0.70:1
0.60:1
2006
70.07 < 0.0001
1.17:1
0.93:1
0.63:1
1.24:1
0.88:1
Table 4.4 Average log Mass:SVL ratio of P. dorsalis for five basal area retention treatments in Jackson County, Alabama,
2005 and 2006. Means within a row with different superscript numbers differ (Tukey P<0.05).
P-value
mean – treatment
Index
treatment
block
year
year*treat
clearcut
25%
50%
75%
control
mass:svl
0.031
0.0054 <0.01
0.625
0.0077± 0.0071±
0.0073±
0.0075±
0.0071±
1
2
1,2
1,2
0.0004
0.0007
0.0007
0.0009
0.00062
Table 4.4 (continued)
mean - year
Index
2005
2006
mass:svl
0.0078±
0.00041
0.0068±
0.00052
94
Figure 4.2 Relative abundance of Plethodon dorsalis for five basal area retention
treatments in Jackson County, Alabama, 2002-2005.
1.4
1.2
Relative abundance
1.0
.8
% retention
.6
Clearcut
.4
25%
.2
50%
75%
0.0
Control
-.2
N=
3
3
3
3
3
3
3
3
2005
3
3
2006
Year
Figure 4.3 Relative abundance of Plethodon glutinosus for five basal area retention
treatments in Jackson County, Alabama, 2002-2005.
.009
logMass:SVL
.008
% basal area
Clearcut
25%
.007
50%
75%
Control
.006
N=
2
2
3
3
3
2
2005
2
2
2006
Year
95
3
3
Figure 4.4 Average log Mass:SVL ratio of P. dorsalis for five basal area retention
treatments in Jackson County, Alabama, 2005 and 2006.
13
Soil temperature (C)
12
11
10
% retention
Clearcut
9
25%
8
50%
7
75%
Control
6
N=
9
9
9
9
9
9
2005
9
9
9
9
2006
Year
Figure 4.5 Average soil temperature (oC) for five basal area retention treatments in
Jackson County, Alabama, 2005 and 2006.
January through April or May) may also buffer the effects that canopy removal have on
microclimatic conditions experienced by salamanders. It is also possible a type II
statistical error has been committed and there is an actual difference in abundance that
has gone undetected. Although this is certainly a possibility, it has been shown that
terrestrial salamander abundance is remarkably constant through time and that they are
generally amenable to population monitoring because of this low variability in counts
(Welsh and Droege 2001).
Other researchers have reported a lack of response in salamander numbers after
intermediate levels of tree harvesting. The average number of Peaks of Otter salamander
(Plethodon hubrichti) captures remained constant and comparable to control numbers
96
after shelterwoods that retained 33-67% of basal area (Sattler and Reichenbach 1998).
Research by Brooks (1999 and 2001) has failed to detect a response in redback
salamander (Plethodon cinereus) numbers in thinned forests. Oak forests thinned to 5060% residual stocking 12-21 years previous contained as many salamanders as unthinned
forests (Brooks 1999). Population size of redback salamanders on single-tree and groupselection treatments with a target basal area of 18 m2/ha was not different than uncut
controls (McKenny et al. 2006). In western forests, Grialou and others (2000) found that
stands thinned from 57 m2/ha to 48 m2/ha (16% reduction in basal area) showed
comparable salamander capture rates to controls. Thinned stands in northwestern
California showed comparable salamander abundance to unthinned stands (Karraker and
Welsh 2006).
No clear trends in zigzag salamander population structure were observed across
treatments. Populations of Plethodon metcalfi on North Carolina clearcuts contained less
reproductive males than nearby intact stands (Ash et al. 2003). The prevalence of
juvenile zigzag salamanders was reduced in clearcuts during 2006. The proportion of
juvenile slimy salamanders (Plethodon glutinosus) was higher in uncut than cut stands in
Virginia and West Virginia (Knapp et al. 2003). The most obvious difference between
treatments was that zigzag salamanders were more massive at a given length on clearcuts
than other treatments. Changes to body size and mass relationships have received
relatively little attention. Though the average SVL of adult salamanders did not differ
between clearcut and intact stands, salamanders on clearcuts were more massive than
those in intact stands (Ash et al. 2003). California Plethodontid salamanders of the genus
97
Ensatina weighed more at a given length on control plots than on thinned plots, but no
difference was observed on clearcuts (Karraker and Welsh 2006). In Virginia, gravid
female Desmognathus ochrophaeus showed a similar to response to zigzags in this study,
with more mass per length on cut plots than uncut (Knapp et al. 2003).
These results indicate that, while there were some indications terrestrial
salamanders responded to removal of overstory trees, the response was not as dramatic as
some previous researchers have observed. This is the first reported investigation of its
kind on the southern Cumberland Plateau and any response may be specific to the
particular geology and hydrology of the area (Smalley 1982). Forests in this region likely
recover more quickly than forests at higher latitudes and elevations and therefore
salamander response may be relatively short-lived. Populations of red-backed
salamanders are known to recover within 4 years of removal of 50% of basal area as far
north as Ontario, Canada (Morneault et al. 2004). These populations should be
monitored in the future, however, to determine long-term effects, especially after residual
stems are removed from shelterwood systems approximately 10 years after the initial
harvest.
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101
CHAPTER 5
EFFECT OF VARIOUS LEVELS OF OVERSTORY TREE RETENTION ON
REPRODUCTIVE OUTPUT OF POOL-BREEDING AMPHIBIANS
Forest managers are increasingly interested in weighing the consequences their
actions exert on biodiversity (Lindenmayer and Franklin 2002). The response of
amphibians, in particular, to forest management has received much attention lately
(deMaynadier and Hunter 1995, Russell et al. 2004), likely because of the sensitivity of
the group to habitat disturbances such as canopy removal (Patrick et al. 2006).
Because of their unique bi-phasic life history, understanding the impact of
disturbances on amphibians requires knowledge of effects in both the aquatic and
terrestrial environment (Semlitsch 1998, Semlitsch 2003). Much of the research on
amphibian response to canopy removal has either focused on the terrestrial environment
(Chazal and Niewiarowski 1998, deMaynadier and Hunter 1999) or the effects on the
terrestrial and aquatic environments are confounded (Clawson et al. 1997, Phelps and
Lancia 1995) in that observed trends in abundance could be related to changes in
recruitment from aquatic breeding sites or altered survivorship in terrestrial habitat. It is
also unclear whether captured animals were in a given area to forage, rest, or breed.
Research on the effects of forest management on amphibians is becoming increasingly
102
experimental. For example, the new Land-use Effects on Amphibians Populations
(LEAP) project (Rothermel and Luhring 2005, Patrick et al. 2006) controls for the
amount of aquatic habitat present by testing for effects of different forestry treatments on
habitat use of amphibians around a single pool.
Still, no study exists examining how harvesting trees impacts the number of eggs
deposited in and metamorphs leaving aquatic breeding sites in an experimental setting.
Newly metamorphosed individuals drive amphibian population dynamics (Berven 1990,
Semlitsch 2003), and an understanding of how their abundance changes after timber
harvest would bring us closer to a mechanistic understanding of amphibian response
(Marzluff et al. 2000). Coupled with an understanding of how terrestrial juveniles and
adults cope with climatic and habitat changes after tree harvest, knowledge of how
individual species’ reproductive dynamics are altered would increase our ability to
predict direction and magnitude of population changes.
The objectives of this study were to quantify oviposition rates and production of
newly metamorphosed amphibians in forest stands receiving several levels of canopy tree
retention treatments. Biophysical parameters of aquatic habitat and their response to
canopy removal were also evaluated.
Study Area
This study took place in Jackson County, northeastern Alabama (Fig. 5.1). The
area is classed into the Cliff section of the Cumberland Plateau in the Mixed Mesophytic
Forest region by Braun (1950). Bailey et al. (1994) included this area in the Eastern
103
a)
Miller Mtn.
Jack
Gap
b)
25%
50%
clear
control -cut
clear
-cut
Block 3
75% control
Block 1
Miller Mt.
25%
N
75% 50%
50% 25% clear control
-cut
4-ha units
75%
Block 2
Jack Gap
Figure 5.1 Location of study site in Alabama (a) and layout of experimental design (b),
Jackson County, Alabama.
104
Broadleaf Forest (Oceanic) Province and Northern Cumberland Plateau Section.
According to Smalley (1982), the sites are located in the Mid Cumberland Plateau region,
the Strongly Dissected Portion subregion, and landtypes 16, 17, and 18 of the Strongly
Dissected Margins and Sides landtype association. The area is characterized by steep
slopes dissecting the Plateau surface and draining to the Tennessee River. Soils are
shallow to deep, stony and gravelly loam or clay, well drained, and formed in colluvium
from those on the Plateau top (Smalley 1982). Climate of the region was described as
temperate with mild winters and moderately hot summers with a mean temperature of 13
degrees C, and mean precipitation of 149 cm (Smalley 1982). Two sites were used. The
first, Miller Mountain (34o 58’ 11” N, 86o 12’ 21” W), was situated on mainly South,
Southwest facing slopes with elevations ranging from 457-518 m (Figure 5.1a). The
second, Jack Gap (34o 56’ 30” N, 86o 04’ 00” W), had a North aspect with elevations
ranging from 304-475 m. Dominant canopy tree species included oaks, including
Quercus velutina Lamarck, Q. rubra L., Q. alba L., Q. prinus L.; 46% of pretreatment
basal area (BA), hickories (Carya spp.; 15% pretreatment BA), sugar maple (Acer
saccharum Marsh.; 13% pretreatment BA) and yellow poplar (Liriodendron tulipifera L.;
9% pretreatment BA) (Schweitzer 2003). Common understory species included
flowering dogwood (Cornus florida L.), eastern redbud (Cercis canadensis L.), and
sourwood (Oxydendrum arboretum DC.).
The study followed a randomized complete block design with three blocked
replicates of five treatments involving varying levels of basal area retention of trees (Fig
5.1b). Treatments included clearcuts, 25-, 50-, and 75% retention, and controls. The
105
clearcuts, 25%, and 50% retention treatments were chainsaw-felled and grapple skidded
in a commercial logging operation. In the 25 and 50 percent retention treatments, trees
were marked to leave favoring dominant and codominants with high vigor, especially oak,
ash (Fraxinus spp.), and persimmon (Diosyros virgniana L.). In 75% retention treatment
plots, the midstory was removed by incising trees and applying the herbicide Arsenal
(active ingredient imazapyr) to achieve a shelterwood cut. An average of 941 stems that
were an average of 7.4 cm diameter at breast height (DBH; measured at 1.37 m above
ground) was treated per hectare with herbicide in such a way to retain an intact canopy,
but allow increased light penetration to the forest floor (Schweitzer 2003). These
treatments were implemented in order to determine which silvicultural prescription was
most conducive to regenerating oaks on these sites. The 25, 50, and 75 percent retention
treatments were designed as shelterwoods and residual stems are scheduled to be
removed 10 years post harvest. Two blocks were located at Jack Gap, and the other at
Miller Mountain. Each of the 15 experimental units was 4 ha in size. Trees were
harvested during the fall of 2001 and winter of 2002, and herbicide treatment took place
in fall 2001. Although pretreatment data was not obtained for any of the variables
measured in the present study besides basal area, the close proximity of sites, the uniform
forest structure present pretreatment (Schweitzer 2003), and the random assignment of
treatments make comparison of treatments to control plots valid. Post treatment basal
area of treatments was as follows: controls, 24.3 m2/ha (99% retention); 75%, 18.8 m2/ha
(70% retention); 50%, 9.2 m2/ha (38% retention); 25%, 6.3 m2/ha (28% retention); and
clearcut, 1.2 m2/ha (5% retention) (Schweitzer 2003).
106
Methods
Stand density. During the summer of 2001, prior to treatments, one permanent
0.081 ha measurement plot was randomly established in each experimental unit by Dr.
Callie Schweitzer of the USDA Forest Service’s Southern Research Station. Plot centers
were monumented and all trees ≥ 0.142 m diameter at breast height (DBH) in the plot
were tagged and measured at 1.37 m height for DBH using steel diameter tapes. In the
summers of 2002, 2003, 2004 and 2005 measurement plots were revisited and all tagged
trees were located and DBH remeasured. All live trees > 14.2 cm DBH were used to
calculate basal area at each plot yearly.
Artificial pools. Within each unit, and adjacent to measurement plots, a group of
3 artificial pools were installed. Pools were black plastic, 91 cm X 61 cm X 46 cm in
size, and held 60 l of water. Pools were arranged in a triangular fashion
approximately1.5 meters apart and were buried flush with the ground and allowed to fill
with rainwater. Pools were installed in the fall of 2002 and sampling was limited during
the summer of 2003 while amphibians colonized them. In order to maintain semi-natural
conditions within pools all water was removed from each pool during late fall of 2002,
2003, and 2004. Natural pools found on or near the study site were also generally small
in size and dried at least annually, rendering them fishless and relatively free of predators.
Environmental. Response of biophysical parameters within pools was monitored
monthly February-August, October and November of 2004 and March-June, August and
September of 2005. Water temperature (oC) (WT) and dissolved oxygen (ppm) (DO)
were measured in each pool at 10 cm depth using a YSI DO200 probe (YSI Inc., Yellow
107
Springs, OH) and pH was measured with an Oakton pH Testr probe (Oakton Instruments,
Vernon Hills, IL). In September of 2004 and 2005, canopy cover was estimated using a
spherical densiometer held at chest level. Percent reduction in photosynthetically active
radiation compared to full sun was measured at each pool in September 2005 using an
AccuPAR Linear Par Ceptometer, Model PAR-80 (Decagon Devices, Inc., Pullman,
WA).
Amphibian sampling. During the summer of 2003 notes were taken on the
presence of amphibian eggs or larvae every 7-14 days to assess amphibian usage of pools.
Between February and October 2004 and 2005 pools were sampled every 7-14 days ( x =
9 days) to enumerate amphibian egg masses and metamorphs. Sampling involved
visiting each pool and counting the total number of egg masses of each species in a unit
(total for 3 pools). Eggs were typically attached to leaves or sticks that had fallen into
pools, but also to the sides of pools. Survey frequency was based on hatching time for
study species so that eggs would not be recounted on subsequent surveys, with the
exception of the spotted salamander, Ambystoma maculatum, whose eggs were large
enough and in small enough numbers to be individually tracked between surveys. While
counting eggs, all visible amphibian metamorphs were also captured. Additionally, 5
sweeps were made in each pool with a dipnet. When a metamorph was captured
sweeping continued until 3 consecutive sweeps were made without capturing additional
individuals. Metamorphs were defined by the presence of fully developed front limbs,
corresponding to Gosner stage 42 or greater (Gosner 1960).
108
Data analysis
Each variable was averaged for each experimental unit each year for statistical
analyses. Average pH was calculated by first converting pH to H+ ion concentration,
averaging the H+ ion concentrations and converting back to pH. To test for year and
treatment effects with biophysical variables (WT, DO, pH) and mean total number of egg
masses and metamorphs PC’s I used ANCOVA with treatment and block as main factors,
year as a covariate, and Tukey tests for mean separation when ANCOVA indicated
differences. To determine if the number of metamorphs produced in a given unit each
year was related to the number of eggs deposited by that species, I used simple linear
regression. To test for the effects of treatment on percent light reduction in 2005, a 1way ANOVA was used. These analyses were performed in SAS (SAS 2003) using alpha
< 0.05 for significance. Univariate contrasts in the GLM procedure of SPSS were used to
test for 1rst-4th order trends in each year for all variables.
Results
All environmental variables except percent light reduction differed by treatment
(Table 5.1). Canopy cover was higher on 75% and control treatments than on clearcut,
25- and 50% treatments, with a linear trend in 2004 and 2005 increasing with basal area
retention (Fig. 5.2). WT was higher on clearcut, 25- and 50% than control treatments.
WT showed a linear trend in 2004, decreasing with increased basal area retention, and a
quadratic trend in 2005 with one low in clearcut, higher values in 25- and 50% treatments,
and another low in control treatments (Fig. 5.3) . DO was higher on the clearcut and 50%
109
treatments than control (Fig. 5.4), and pH was higher on clearcut than control treatments
(Fig. 5.5). Both DO and pH decreased linearly with basal area retention in 2004. Trends
were linear again in 2005 for pH, while a 4th order trend was seen in DO for 2005.
Canopy cover, water temperature and pH were all higher in 2005 than 2004.
Eggs were deposited in artificial pools by three species of amphibians (Hyla
chrysoscelis, Cope’s gray treefrog; Pseudacris brachyphona, mountain chorus frog; and
Bufo a. americanus, eastern American toad) during the summer of 2003. Ambystoma
maculatum first deposited eggs in the winter of 2004. By fall 2003, 97% (44/45) of
individual pools were colonized by amphibians.
The number of egg masses deposited by H. chrysoscelis and P. brachyphona
differed by tree retention treatment (Table 5.1). More egg masses of Hyla chrysoscelis
were deposited in clearcut than 75% and control treatments (Fig. 5.6). In both 2004 and
2005 a linear trend was detected with more H. chrysoscelis egg masses in clearcuts than
control treatments. More egg masses were deposited by P. brachyphona in control than
25% and clearcut treatments, with a linear trend in both years from more eggs in controls
and less in clearcuts (Fig. 5.7). While the number of egg masses laid by A. maculatum
was not significant, in both 2004 and 2005 eggs were deposited only in the 75% and
control treatments on 2 out of 3 blocks (Fig. 5.8). No differences were found in B.
americanus egg mass number across treatments and eggs were only laid in 25%
treatments in 2004 and in 75% treatments in 2005 (Fig. 5.9).
Metamorphs of three species (H. chrysoscelis, P. brachyphona, and B.
americanus) were detected in pools (Figs. 5.10-5.12).
110
Table 5.1 Results of ANCOVA comparison of biophysical parameters, number of amphibian egg masses, and number of
metamorphs in artificial pool on five basal area retention treatments in Jackson County, Alabama, 2004 and 2005. Means
within a row with different superscript numbers differ (Tukey P<0.05).
treatment
Environmental
canopy
Water temperature (oC)
Dissolved oxygen (ppm)
pH
Light reduction*
Egg mass #
Hyla chrysoscelis
Ambystoma maculatum
Pseudacris brachyphona
Bufo americanus
Metamorph #
Hyla chrysoscelis
Pseudacris brachyphona
Bufo americanus
P-value
block year
year*
treat
clearcut
25%
mean
50%
75%
control
<0.001
0.007
<0.001
0.013
0.317
0.005
0.102
0.066
0.024
0.075
0.031
0.009
0.129
0.038
NA
0.168
0.138
0.534
0.979
NA
32.67±28.102
20.70±0.751
6.59±1.281
8.24±0.591
79.26±22.28
56.50±21.272
20.65±1.191
5.14±1.801,2
7.94±0.651,2
73.24±23.05
59.33±28.212
20.83±1.641
6.15±2.111
7.93±0.651,2
71.88±29.15
90.00±1.261
19.95±1.011,2
3.64±0.802,3
7.71±0.281,2
89.17±5.23
93.67±1.751
18.70±1.172
2.56±0.703
7.26±0.342
97.10±1.68
0.001
0.068
0.003
0.120
0.029
0.205
0.511
0.365
0.567
0.841
<0.001
0.248
0.971
0.580
0.196
0.021
89.33±41.621
0.00±0.00
50.83±50.892
0.00±0.00
63.17±42.561,2,3
0.00±0.00
77.17±79.482
1.67±2.66
65.50±62.561,2
0.00±0.00
102.33±124.631,2
0.00±0.00
12.83±13.962,3
4.50±5.28
169.33±108.661,2
0.33±0.82
3.67±8.983
6.00±8.63
230.67±175.771
0.00±0.00
0.199
0.364
0.590
0.077
0.092
0.565
0.041
0.314
0.151
0.155
0.228
0.619
4.00±7.51
8.67±8.31
0.00±0.00
2.83±2.04
7.33±4.84
1.67±1.67
3.50±4.04
9.00±8.72
2.67±2.67
0.50±0.84
12.33±5.65
0.33±0.33
0.00±0.00
20.33±25.01
0.00±0.00
*Light reduction only measured in 2005.
111
Table 5.1 (continued)
mean
Environmental
canopy
Water temperature (oC)
Dissolved oxygen (ppm)
pH
Light reduction*
Egg mass #
Hyla chrysoscelis
Ambystoma maculatum
Pseudacris brachyphona
Bufo americanus
Metamorph #
Hyla chrysoscelis
Pseudacris brachyphona
Bufo americanus
2004
2005
59.80±32.672
19.65±1.422
4.44±1.87
7.64±0.512
NA
73.07±25.891
20.69±1.131
5.19±2.21
8.00±0.631
82.13±19.30
50.67±47.69
1.93±3.92
44.40±50.812
0.67±1.80
43.13±52.81
2.27±5.98
207.73±127.631
0.13±0.52
3.53±5.181
13.80±16.77
1.87±4.69
0.80±1.572
9.27±7.07
0.00±0.00
*Light reduction only measured in 2005.
112
120
100
% canopy cover
80
60
% retention
Clearcut
40
25%
20
50%
0
75%
Control
-20
N=
3
3
3
3
3
3
3
2004
3
3
3
2005
Year
Figure 5.2 Canopy cover (%) above artificial pools on five basal area retention treatments
in Jackson County, Alabama, 2004 and 2005.
24
Water temperature (C)
23
22
21
% retention
20
Clearcut
19
25%
18
50%
75%
17
Control
16
N=
3
3
3
3
3
3
2004
3
3
3
3
2005
Year
o
Figure 5.3 Water temperature ( C) of artificial pools on five basal area retention
treatments in Jackson County, Alabama, 2004 and 2005.
113
10
Dissolved oxygen (ppm)
8
6
% retention
Clearcut
4
25%
50%
2
75%
Control
0
N=
3
3
3
3
3
3
3
3
2004
3
3
2005
Year
Figure 5.4 Dissolved oxygen content (ppm) of artificial pools on five basal area retention
treatments in Jackson County, Alabama, 2004 and 2005.
9.5
9.0
pH
8.5
% retention
8.0
Clearcut
7.5
25%
50%
7.0
75%
Control
6.5
N=
3
3
3
3
3
3
2004
3
3
3
3
2005
Year
Figure 5.5 pH of artificial pools on five basal area retention treatments in Jackson County,
Alabama, 2004 and 2005.
114
# of egg masses
200
100
% retention
Clearcut
0
25%
50%
75%
Control
-100
N=
3
3
3
3
3
3
3
2004
3
3
3
2005
Year
Figure 5.6 Total number of Hyla chrysoscelis egg masses from artificial pools on five
basal area retention treatments in Jackson County, Alabama, 2004 and 2005.
600
500
# of egg masses
400
300
% retention
Clearcut
200
25%
100
50%
0
75%
Control
-100
N=
3
3
3
3
3
3
2004
3
3
3
3
2005
Year
Figure 5.7 Total number of Pseudacris brachyphona egg masses from artificial pools on
five basal area retention treatments in Jackson County, Alabama, 2004 and 2005.
115
30
# of egg masses
20
% retention
10
Clearcut
25%
0
50%
75%
Control
-10
N=
3
3
3
3
3
3
3
2004
3
3
3
2005
Year
Figure 5.8 Total number of Ambystoma maculatum egg masses from artificial pools on
five basal area retention treatments in Jackson County, Alabama, 2004 and 2005.
7
6
# of egg masses
5
4
% retention
3
Clearcut
2
25%
1
50%
75%
0
Control
-1
N=
3
3
3
3
3
3
2004
3
3
3
3
2005
Year
Figure 5.9 Total number of Bufo americanus egg masses from artificial pools on five
basal area retention treatments in Jackson County, Alabama, 2004 and 2005.
116
30
# of metamorphs
20
% retention
10
Clearcut
25%
0
50%
75%
Control
-10
N=
3
3
3
3
3
3
3
2004
3
3
3
2005
Year
Figure 5.10 Total number of Hyla chrysoscelis metamorphs from artificial pools on five
basal area retention treatments in Jackson County, Alabama, 2004 and 2005.
70
60
# of metamorphs
50
40
% retention
30
Clearcut
20
25%
10
50%
75%
0
Control
-10
N=
3
3
3
3
3
3
2004
3
3
3
3
2005
Year
Figure 5.11 Total number of Pseudacris brachyphona metamorphs from artificial pools
on five basal area retention treatments in Jackson County, Alabama, 2004 and 2005.
117
# of metamorphs
20
10
% retention
Clearcut
25%
0
50%
75%
Control
-10
N=
3
3
3
3
3
3
2004
3
3
3
3
2005
Year
Figure 5.12 Total number of Bufo americanus metamorphs from artificial pools on five
basal area retention treatments in Jackson County, Alabama, 2004 and 2005.
No species differed by treatment in terms of metamorph number (Table 5.1). However,
the general pattern in number of egg masses counted across treatments held for the
number of metamorphs counted for each species. A linear trend was observed in H.
chrysoscelis metamorph number during 2004 with more observed in clearcuts than
controls (Fig. 5.10). More H. chrysoscelis metamorphs were observed in 2004 than 2005.
The number of Pseudacris brachyphona metamorphs did not differ among treatments
(Fig. 5.11).
Metamorphs of Bufo americanus were captured only in 2004 in the 25%, 50%,
and 75% retention treatments (Fig. 5.12) The relationship between metamorph and egg
number was marginally significant for H. chrysoscelis in 2004 (P = 0.057, R2 = 0.25,
118
metamorphs = 0.78 + 0.054 eggs) and significant in 2005 (P = 0.02, R2 = 0.35,
metamorphs = 0.44 + 0.007 eggs) (Fig. 5.13). The number of P. brachyphona
metamorphs counted in a given unit was not related to the number of eggs for 2004 (P =
0.745, R2 = 0.008) or 2005 (P = 0.906, R2 = 0.001) (Fig. 5.14).
119
20
# of metamorphs
a)
10
0
-10
-20
0
20
40
60
80
100
120
140
# of egg masses
6
b)
5
# of metamorphs
4
3
2
1
0
-1
-20
0
20
40
60
80
100
120
140
160
# of egg masses
Figure 5.13 Relationship between number of egg masses and number of metamorphs for
Hyla chrysoscelis in (a) 2004 and (b) 2005.
120
70
a)
60
# of metamorphs
50
40
30
20
10
0
-10
-50
0
50
100
150
200
400
500
# of egg masses
30
b)
# of metamorphs
20
10
0
-10
0
100
200
300
# of egg masses
Figure 5.14 Relationship between number of egg masses and number of metamorphs for
Pseudacris brachyphona in (a) 2004 and (b) 2005.
121
Discussion
The observed patterns in egg mass number across treatments could be explained
by at least two mechanisms. One is that adult amphibians are seeking out breeding
habitat in the different treatments and depositing eggs in artificial pools based on
conditions in the aquatic environment within the pools. This could be explained by either
male or female choice. In most anuran mating systems males arrive at breeding sites first
and form a chorus and then females arrive and select a male before mating (Wells 1977).
It has been shown that males differentially select calling sites and that females deposit
eggs in some sites more than others dependant on the presence or absence of various cues
(Resetarits and Wilbur 1991). Factors that are known to affect egg deposition by
amphibians are the presence of conspecifics and predators (Resetarits and Wilbur 1989,
Petranka et al. 1994), water depth (Crump 1991), and pathogens (Kiesecker and Skelly
2000). It is believed that selection would favor males who choose sites where they
maximize access to mates and females who choose sites that maximize the survivorship
of their offspring (Resetarits and Wilbur 1991).
Forest canopy cover above aquatic breeding sites is known to be an important
factor determining the growth and survival of larvae of several amphibian species
(Werner and Glennemeier 1999, Skelly et al. 2002, Halverson et al. 2003, Lauck et al.
2005). It appears that, while larvae of most species perform better in open canopy than
closed canopy pools, there are some species that thrive in closed canopy pools while
others experience very low survivorship in these environments (Werner and Glennemeier
1999, Skelly et al. 2002). These differences appear to be related to food resource
122
availability in closed versus open pools in the form of periphyton and to water
temperature and dissolved oxygen (Werner and Glennemeier 1999, Skelly et al. 2002,
Halverson et al. 2003).
In the current study canopy removal impacted biophysical conditions in aquatic
habitat in ways consistent with previous research. Elevated water temperature, dissolved
oxygen, and pH are known to occur in open canopy pools (Werner and Glennemeier
1999, Skelly et al. 2002, Lauck et al. 2005). These factors are associated with both larval
microhabitat use and within-pond oviposition site choice (Noland and Ultsch 1981,
Dougherty et al. 2005). Species differences in thermal tolerance correspond to their
spatial distribution relative to canopy closure, with those more tolerant of warmer
temperatures found more often in less shaded pools (Blaustein et al. 1999).
Because canopy cover is so important in determining the performance of larval
amphibians through its impact on resource availability and abiotic conditions, the
prediction could be made that it should also affect oviposition rates. While research has
shown that the distribution of amphibian species is related to canopy cover, it is unknown
if patterns are due to oviposition choice (Werner and Glennemeier 1999, Halverson et al.
2003). This phenomenon could be responsible for the observed pattern of egg mass
number across treatments in this study. Hyla chrysoscelis may be an “open canopy
specialist” species (sensu Skelly et al 2002) and find optimal conditions for larval growth
in open pools. Pools in harvested areas where H. chrysoscelis laid the most eggs had the
highest water temperature, dissolved oxygen, and pH. On the other hand both Pseudacris
brachyphona and Ambystoma maculatum may have selected conditions in the closed
123
canopy treatments as optimal. Depending on their physiology, species are known to
differ in their preference for water temperature and dissolved oxygen concentrations
(Noland and Ultsch 1981).
It is also possible that temporal or “priority effects” (Alford and Wilbur 1985)
impact observed patterns of oviposition. Species which breed later in the season, such as
H. chrysoscelis, may oviposit based on the distribution of species which have already
bred (P. brachyphona and A. maculatum) to avoid competition and or predation (Wilbur
1984, Resatarits and Wilbur 1989, Petranka et al. 1994).
Another possible mechanism explaining observed changes in the number of egg
masses deposited across treatments is the effect that treatment-related changes to the
terrestrial environment had on the amount of adults capable of reaching pools to breed.
Clearcut areas are known to impede movement of amphibians (Gibbs 1998, Rothermel
and Semlitsch 2002, Chan-McLeod 2003). The main factors affecting the permeability of
clearcuts to frogs in the Pacific Northwest were precipitation and air temperature (ChanMcLeod 2003). Air temperature in clearcuts was significantly higher in clearcut
treatments during most of this study (See Chapter 2), but approached levels similar to
control treatments by 2005.
Without further experimental investigation, it is impossible to separate the effects
of either differential oviposition in various treatments or the filtering effect that the
terrestrial environment may have on amphibians intent on depositing eggs in different
treatments. Regardless of the mechanisms, the patterns observed in the number of eggs
deposited and metamorphs produced in the various treatments potentially have important
124
implications for population dynamics as they relate to canopy retention treatments. For H.
chrysoscelis, the number of egg masses was an indication of how many metamorphs
exited pools. This relationship does not hold for P. brachyphona. It is possible that a
relationship does exist between egg mass number and metamorph number, but
metamorphs of P. brachyphona are more variable in abundance and harder to detect. Or,
it could be that more metamorphs are produced in pools with fewer eggs due to density
dependent survivorship (Berven 1990), or that tadpoles experienced increased
survivorship in open canopy pools where less eggs were deposited (Werner and
Glennemeier 1999, Skelly et al. 2002, Halverson et al. 2003). Further research is
necessary to clarify this, especially since there are some indications that the number of
metamorphs is higher in control treatments in some years. Since the number and quality
of metamorphs produced is the primary driver of amphibian population dynamics
(Pechmann et al. 1989, Berven 1990, Semlitsch et al. 1996), the changes observed in this
study may have important implications for the effects of canopy removal on the viability
of amphibian populations.
One important piece of information which is currently missing is the fate of
metamorphs produced in the various treatments. Work by Rothermel and Semlitsch
(2002) suggested that juveniles of both Bufo americanus and Ambystoma maculatum
experienced higher mortality in old fields when compared to closed canopy forests. And,
because juvenile marbled salamanders, Ambystoma opacum, and Ambystoma maculatum
survival was higher in enclosures in forests than in old fields, it was proposed that
125
breeding sites surrounded by open habitat may be population sinks (Rothermel and
Semlitsch 2006).
These data suggest that canopy removal may have important implications for
population dynamics of amphibian populations in similar forested ecosystems. However,
many questions remain. Further research into the number of adult males and females
attending to artificial pools would pinpoint the role of male versus female choice in
oviposition patterns observed. An experimental approach could be used to determine
whether conditions in the aquatic or terrestrial environment experienced by frogs drives
the differences. And, knowledge of the fate of metamorphosing amphibians in different
treatments would be very helpful in determining the full impact of treatments on
population dynamics.
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CHAPTER 6
MOVEMENTS AND HABITAT USE OF EASTERN BOX TURTLES IN FOREST
STANDS MANAGED FOR TIMBER
Eastern box turtles, Terrapene c. carolina inhabit the mesic forests of the eastern
United States and are reported to be abundant in areas where open habitats are
interspersed with cool, moist areas with closed canopies (Dodd 2001). Although
improper forest management has been implicated as an agent of habitat degradation for
this declining species (Dodd 2001), little is known about habitat use and movement
patterns by this species in managed forests. This information is required by forest
managers who would like to include biodiversity considerations in their decision making
process.
Box turtles exist in a surprisingly narrow range of environmental conditions
(Reagan 1974, Dodd 2001). This is accomplished, in part, by construction and use of
microhabitats known as forms (Stickel 1950). Forms are simple depressions in the
substrate, and provide favorable conditions of high humidity and low temperature relative
to average ambient conditions (Reagan 1974).
Turtles select microhabitats with
vegetation structure that provides for suitable ranges in microclimate (Converse and
Savidge 2003, Rossell et al. 2006). In Nebraska, forms of ornate box turtles (T. o.
130
ornata) are associated with abundant litter and shrub layers (Converse and Savidge 2003).
Microhabitats of Arkansas three-toed box turtles (T. c. triunguis) are associated with high
coverage of litter and/or grass (Reagan 1974).
Considering this intimate coupling of microclimate and microhabitat, I predicted
that shifts in climate due to canopy disturbance associated with silviculture would lead to
shifts in microhabitat use by turtles. Because temperature and humidity should be more
limiting in the drier, warmer conditions in cut areas (Geiger 1965, Chen et al. 1999), I
predicted that turtles would be associated with specific vegetation structural features that
serve as shelter in these areas. The identification of these specific structural features is an
important step in providing land managers with information needed to make turtlefriendly decisions. Steps could then be taken to conserve or even maximize the amount
of these features in a forest stand.
Animals move as little as is necessary to obtain necessary resources, thereby
maximizing energy use and minimizing risk of predation. Eastern box turtles have very
low metabolic rates and minimize movements and resultant metabolic costs as part of
their life history strategy (Penick et al. 2002). It has been found that the size of a box
turtle’s home range is a function of habitat quality, with smaller home ranges in areas of
plentiful food and shelter resources than where these are scarce (Stickel 1950, Nieuwolt
1996). Research by Curtin (1997) showed that box turtles residing in habitat fragments
had larger home ranges compared to those in contiguous habitat (8.7 vs. 2.5 ha). In
contrast, Delaware T. c. carolina in forest fragments moved somewhat less than animals
in more contiguous areas (Iglay et al. 2007).
131
Because expected shifts in climate
associated with canopy removal should make microhabitats availability more limiting, I
predicted home ranges would be larger in cut areas.
The objectives of this study were to 1) test for relationships between canopy
removal treatments and average movements and home range size, 2) determine if box
turtles exhibit selection at the macrohabitat level 3) quantify approximate climatic
conditions experienced by turtles in different macrohabitats, and 4) compare microhabitat
selection on cut and uncut areas.
Study Area
This study took place in Jackson County, northeastern Alabama. The area is
classed into the Cliff section of the Cumberland Plateau in the Mixed Mesophytic Forest
region by Braun (1950). Bailey et al. (1994) included this area in the Eastern Broadleaf
Forest (Oceanic) Province and Northern Cumberland Plateau Section. According to
Smalley (1982), the sites are located in the Mid Cumberland Plateau region, the Strongly
Dissected Portion subregion, and landtypes 16, 17, and 18 of the Strongly Dissected
Margins and Sides landtype association. The area is characterized by steep slopes
dissecting the Plateau surface and draining to the Tennessee River. Soils are shallow to
deep, stony and gravelly loam or clay, well drained, and formed in colluvium from those
on the Plateau top (Smalley 1982). Climate of the region was described as temperate
with mild winters and moderately hot summers with a mean temperature of 13 degrees C,
and mean precipitation of 149 cm (Smalley 1982). Two sites were used. The first, Miller
Mountain (34o 58’ 11” N, 86o 12’ 21” W), was situated on mainly South, Southwest
132
facing slopes with elevations ranging from 457-518 m. The second, Jack Gap (34o 56’
30” N, 86o 04’ 00” W), had a North aspect with elevations ranging from 304-475 m.
Dominant canopy tree species included oaks, including Quercus velutina Lamarck, Q.
rubra L., Q. alba L., Q. prinus L.; 46% of pretreatment basal area (BA), hickories (Carya
spp.; 15% pretreatment BA), sugar maple (Acer saccharum Marsh.; 13% pretreatment
BA) and yellow poplar (Liriodendron tulipifera L.; 9% pretreatment BA) (Schweitzer
2003). Common understory species included flowering dogwood (Cornus florida L.),
eastern redbud (Cercis canadensis L.), and sourwood (Oxydendrum arboretum DC.).
The study followed a randomized complete block design with three blocked
replicates of five treatments involving varying levels of basal area retention of trees (Fig
2.1b). Treatments included clearcuts, 25-, 50-, and 75% retention, and controls. The
clearcuts, 25%, and 50% retention treatments were chainsaw-felled and grapple skidded
in a commercial logging operation. In the 25 and 50 percent retention treatments, trees
were marked to leave favoring dominant and codominants with high vigor, especially oak,
ash (Fraxinus spp.), and persimmon (Diosyros virgniana L.). In 75% retention treatment
plots, the midstory was removed by incising trees and applying the herbicide Arsenal
(active ingredient imazapyr) to achieve a shelterwood cut. An average of 941 stems that
were an average of 7.4 cm diameter at breast height (DBH; measured at 1.37 m above
ground) was treated per hectare with herbicide in such a way to retain an intact canopy,
but allow increased light penetration to the forest floor (Schweitzer 2003). These
treatments were implemented in order to determine which silvicultural prescription was
most conducive to regenerating oaks on these sites. The 25, 50, and 75 percent retention
133
treatments were designed as shelterwoods and residual stems are scheduled to be
removed 10 years post harvest. Two blocks were located at Jack Gap, and the other at
Miller Mountain. Each of the 15 experimental units was 4 ha in size. Trees were
harvested during the fall of 2001 and winter of 2002, and herbicide treatment took place
in fall 2001. Although pretreatment data was not obtained for any of the variables
measured in the present study besides basal area, the close proximity of sites, the uniform
forest structure present pretreatment (Schweitzer 2003), and the random assignment of
treatments make comparison of treatments to control plots valid. Post treatment basal
area of treatments was as follows: controls, 24.3 m2/ha (99% retention); 75%, 18.8 m2/ha
(70% retention); 50%, 9.2 m2/ha (38% retention); 25%, 6.3 m2/ha (28% retention); and
clearcut, 1.2 m2/ha (5% retention) (Schweitzer 2003).
Methods
Radiotelemetry. Turtles were captured opportunistically and during visual
surveys during periods of high turtle activity, especially after rain. When captured,
turtles were measured for carapace length with calipers to the nearest mm, weighed to the
nearest gram with pesola scales, and marked by filing marginal scutes for identification
(Cagle 1939). Turtles were fitted with radiotransmitters (LF-1-//-357-RS-8, L.L.
Electronics, Mahomet, IL), which were epoxied along the bottom of their carapace above
their rear limb with the antenna glued extending forward along the marginal scutes.
Transmitter packages weighed 10 g, or less than 3 % of the smallest turtles’ weight.
Turtles were returned to point of capture within 12 hours of transmitter attachment and
134
then relocated every 3-10 days between 0800 and 2000 hrs (Merlin 12, Custom
Electronics of Urbana, Nikomas, FL). Upon relocation, a digital thermohygrometer
(Forestry Suppliers Inc., Jackson, MS) was used to measure air temperature (oC) and
relative humidity (%) at the turtle’s location (TurT and TurRH respectively), and ambient
conditions at 1 meter above the ground in the shade (AmbT and AmbRH respectively). A
group of microhabitat variables were also measured at the turtle’s location, and at a point
a random direction and distance (5 -15 meters) from the turtle. Percent cover of litter (lit),
bare ground (bar), herbaceous vegetation (her), woody vegetation (woo), slash (sla),
coarse woody debris (cwd), and rock (roc) were estimated using line intercept along two
perpendicular 1-m line transects intersecting at the turtle. Overhead canopy cover (can)
was measured at chest level with an ocular densiometer. Distance to nearest tree > 10 cm
d.b.h., nearest slash pile (defined as an aggregation of sticks > 30 cm vertical height and
≥3 stems), and nearest coarse woody debris > 10 cm diameter were measured with a tape
measure. In 2005, basal area was estimated using a JIM-GEM Cruz-All prism (Forestry
Suppliers Inc., Jackson, MS). Locations were marked with a handheld GPS unit (eTrex
Legend, Garmin Ltd., Olathe, KS). Means are reported as ± 1 standard deviation.
Movement and home range. Turtle locations were brought into a geographic
information system (GIS) and analyzed using ArcView 9.1. Turtle locations were used to
calculate 100% minimum convex polygons (MCP), and 50- and 95% volume fixed kernel
(FK50 and FK95) home range estimates using least-squares cross validation in the Home
Range Extension for ArcView (Rodgers and Carr 2002). Distances between successive
moves less than 12 days apart were calculated using Hawth’s Tools, a plug-in for
135
ArcView. Although MCP estimators have been criticized because they potentially
include large areas in which the study animal never spends time (White and Garrott 1990),
recent work by Row and Blouin-Demers (2006) suggests they may perform better than
kernel methods in estimating home range size in herpetofuana. To test for an affect of
harvesting on movement patterns, I compared the means of movements made on
harvested areas and unharvested areas (see below for definition of harvested and
unharvested). I tested for a relationship between estimated home range size of each turtle
(MCP, FK50, and FK95) and the proportion of the turtle’s points occurring on
unharvested areas using simple linear regression. A significant relationship would
indicate that the amount of harvesting within a turtle’s home range impacts the size of
their home range.
Macrohabitat use. Habitat on the study site was classified into the following
categories: harvested, unharvested, or roadside. Harvested areas were defined by the
boundaries of experimental units harvested to retain 25- or 50% of overstory trees.
Unharvested areas were defined as study units treated to retain 75% of basal area, control
units, or untreated areas outside of experimental units. The combination of 25- and 50%
retention treatments and of 75% retention and control treatments was done because of the
large amount of similarity in both microhabitat and microclimate conditions between
pairs (see Chapter 2), and because it allowed for greater sample sizes of radiolocations in
each habitat. Roadside areas were defined as a 15-meter area on both sides of roads.
This buffer size was based on the distance between georeferenced roads and the edges of
experimental units as determined using a GIS, and through communication with Greg
136
Janzen, Stevenson Lands Company, Scottsboro, AL, about the distance normally
harvested alongside roads during road construction. Habitat classification was
accomplished in ArcView by drawing polygons around the perimeters of experimental
units treated for 25- and 50% retention, drawing polygons around units treated for 75%
retention and controls, and applying a 15-m buffer to an existing roads layer. Using these
polygons, all turtle points were attributed as one of these three habitat types.
Compositional analysis (Aebischer et al. 1993) was used to compare turtles’ use
of harvested, unharvested, and roadside habitats relative to their availability. This type of
analysis uses an individual study animal as a sample unit and allows the researcher to
rank habitats according to preference (Aebischer et al. 1993, Garshelis 2000). In this
context, amount of each habitat available was calculated by first applying a 50-m buffer
to each turtle point representing habitat available to a turtle. This buffer was within the
average distance moved by turtles and ample time passed between successive locations so
that this area should be available for turtles to use. These buffers were merged and the
proportion of each habitat type found within this new buffer was estimated. Proportional
habitat use was determined by dividing the number of locations in a given habitat type by
the total number of locations for the turtle. Compositional analysis was carried out in
SPSS (SPSS 1997). A χ2 test was used to test whether the proportion of all radiolocations
in harvested and unharvested habitats was equal across seasons in 2004 and 2005.
Proportion of points in roadside was not tested because of low expected values (Zar
1996). All dates in April and May were classified as spring, July and August as summer,
and September and October as fall.
137
Microhabitat use. A separate data set was created for all turtle locations on
harvested and unharvested habitats. Roadside points were not included in microhabitat
analyses because of low sample sizes (n = 15). Because preliminary univariate analyses
showed that male and female turtles used different microhabitat features, locations on
harvested areas were split into male (n = 69) and female (n = 63) locations, and
unharvested locations were split into male (n = 88) and female (n = 97) locations.
Matched-pairs logistic regression was used (Compton et al. 2002) to model microhabitat
use versus availability in four groups; cut and uncut habitats for males and females. The
analyses were performed in SAS (SAS 2003) using PROC Logistic with a no intercept
model. This form of regression is analogous to a paired t-test in that it compares each
turtle location with its associated random location rather than pooling all locations. This
is appropriate because of the spatial and temporal proximity of turtle and random
locations. The model coefficients are interpreted as functions of differences in habitat
between used and random rather than absolute measures.
The same suite of 5 models was run for each of the four groups, and the most
parsimonious model was chosen using Akaike’ Information Criterion (AIC) (Burnham
and Anderson 2002). Model performance was evaluated based on change in AIC value,
with models within 4 AIC units of the best model supported. Variable importance was
evaluated using AIC weights (Burnham and Anderson 2002). Variables used in analyses
were chosen based on exploratory analyses of correlations between all variables. No
variable showed significant correlation (R2≥0.60) with any other variable used. Model 1
contained the following variables: litter (lit), bare ground (bar), herbaceous vegetation
138
(her), woody vegetation (woo), slash (sla), rock (roc), coarse woody debris (cwd). Model
2 contained lit, roc, and bar and, if supported, would indicate the importance of ground
cover variables. Model 3 was comprised of woo, cwd, and sla. Support for model 3
would suggest the importance of structural variables at the ground level. Model 4
contained canopy cover (can) and her and was theorized to indicate importance of
canopy openness and resulting growth of grasses and other herbaceous vegetation. If
model 5, which contained only can, was supported, this would indicate that turtles’
habitat selection was based solely on canopy openness or closure.
Results
Movement. In 2003, four female box turtles were tracked. In 2004 and 2005 two
male and four females, and five males and four females, respectively, were tracked. The
average number of radiolocations was 28.37±8.28 per turtle and the average number days
turtles were tracked was 364.89±138.15. The average distance between successive
moves was 53.32 ± 20.55 m (Table 6.1). The average distance moved by males (62.27 ±
23.53 m) was not different than that moved by females (48.10 ± 17.56 m) (n = 19, t = 1.50, P = 0.15). The average distance between successive moves on cut areas (44.30 ±
40.04 m, n = 165) was not different than the average distance between successive moves
on uncut areas (51.55 ± 44.43 m, n = 216) (t = -1.65, P = 0.10) (Fig. 6.1).
Home range. Minimum convex polygon estimates of home range size averaged
2.55 ± 1.95 ha (Table 6.2). Fixed kernel estimators using 50- and 95% volume contours
averaged 0.76 ± 0.67 and 2.91 ± 2.71 ha respectively. No differences in home range size
139
were detected between sexes (Table 6.2). No relationship was detected between the
home range size of a given turtle and the percentage of it’s locations occurring in uncut
areas using MCP (n = 19, R2 = 0.154, P = 0.096) (Fig. 6.2), FK50 (n = 19, R2 = 0.022, P
= 0.544) (Fig. 6.3), or FK95 (n = 19, R2 = 0.074, P = 0.261) (Fig. 6.4).
Macrohabitat use. Neither males (Wilk’s Λ = 0.341, F3,4 = 2.58, P = 0.19) nor
females (Wilk’s Λ = 0.602, F3,9 = 1.98, P = 0.19) exhibited non-random macrohabitat use.
When sexes were combined however, turtles used macrohabitats different than at random
(Wilk’s Λ = 0.588, F3,16 = 3.74, P = 0.033). Ranked in terms of their preference,
macrohabitats followed the sequence cut>roadside>uncut. The preference for cut
habitats over both roadside and uncut habitats was significant, but preference for roadside
over control was not significant. The proportion of radiolocations in cut and uncut areas
did not differ between seasons in 2004 (χ2 = 0.98, df = 2, P = 0.95) or in 2005 (χ2 = 2.69,
df = 2, P = 0.25). The overwintering sites used by 17 turtles were located. For three
turtles, two consecutive overwintering sites were recorded. Turtles always overwintered
either inside of or at the edge of their home range. No turtle made a large move outside
its home range to overwinter. The majority of turtles with more radiolocations on cut
areas overwintered on cut areas and vice versa for turtles with more on uncut areas. Two
turtles (T14 and T15) with a majority of their locations on cut areas overwintered on
uncut areas.
140
Table 6.1. Sex, size, number of days and locations radiotracked, average distance moved, percentage of radiolocations
on unharvested areas, and macrohabitat in which ovewintering occurred for 19 eastern box turtles, Jackson county,
Alabama, 2003-2005. MCP = minimum convex polygon home range estimator, FK = fixed kernel home range estimator.
ID
Sex
Carapace
Days
# of
MCP (ha) 50% FK (ha) 95% FK (ha)
% locations
Overx move.
2
4
5
11
12
16
20
22
46
49
50
7
15
17
18
21
23
44
F
F
F
F
F
F
F
F
F
F
F
M
M
M
M
M
M
M
length (mm)
123
123
131
135
135
132
140
136
122
128
129
137
133
139
139
136
140
137
tracked
468
342
332
477
290
348
508
225
657
372
277
348
315
172
94
618
400
334
locs.
34
34
19
29
17
30
35
34
41
31
11
31
27
27
13
41
28
29
1.67
4.23
4.15
0.34
1.20
2.10
7.92
3.34
1.75
1.47
0.38
1.17
1.29
5.78
4.07
0.80
1.97
2.57
0.40
1.95
2.41
0.05
0.31
0.59
0.19
1.75
0.28
1.13
0.34
0.57
0.55
1.03
1.08
0.32
1.18
0.28
* indicates a turtle for which 2 overwintering sites were located.
141
1.82
7.39
10.33
0.20
1.42
2.77
0.94
6.09
1.31
0.24
1.23
2.43
2.22
4.68
4.75
1.39
4.32
1.32
(m)
50.3
40.0
77.8
21.9
44.4
41.1
81.3
61.7
35.9
40.9
48.0
36.6
45.1
86.6
98.7
41.4
66.5
61.1
unharvested
97
40
78
4
0
96
87
11
97
13
0
100
11
84
39
5
100
18
winter loc.
control*
control
control
cut*
cut
control
control
control
cut
cut
control
control
control
cut*
control
cut
Table 6.2 Home range size estimates of male, female, and all eastern box turtles
radiotracked in Jackson County, Alabama 2003-2005. MCP = minimum convex polygon,
FK50 = 50% fixed kernel estimator, FK95 = 95% fixed kernel estimator.
home range
estimator
MCP
FK50
FK95
Male (n = 7)
ha
2.52 ± 1.81
0.72 ± 0.37
3.02 ± 1.53
Female (n = 12)
ha
2.56 ± 2.11
0.79 ± 0.82
2.84 ± 3.29
All (n = 19)
ha
2.55 ± 1.95
0.76 ± 0.67
2.91 ± 2.71
Sex t-test
t = 0.048, P = 0.96
t = 0.220, P = 0.83
t = -0.132, P = 0.90
Length of movement (m)
300
200
100
0
-100
N=
165
216
Cut
Control
Macrohabitat type
Figure 6.1 Distance moved by eastern box turtles on control areas versus cut areas,
Jackson County, Alabama, 2003-2005.
142
10
MCP area (ha)
8
6
4
2
0
-20
0
20
40
60
80
100
120
% of radiolocations on uncut
Figure 6.2 Relationship between minimum convex polygon home range size (ha) and
percent of radiolocations on uncut areas for eastern box turtles, Jackson County, Alabama,
2003-3005.
2.5
50% FK area (ha)
2.0
1.5
1.0
.5
0.0
-20
0
20
40
60
80
100
120
% of radiolocatios on uncut
Figure 6.3 Relationship between 50% volume fixed kernel home range size (ha) and
percent of radiolocations on uncut areas for eastern box turtles, Jackson County, Alabama,
2003-3005.
143
12
95% FK area (ha)
10
8
6
4
2
0
-20
0
20
40
60
80
100
120
% of radiolocations on uncut
Figure 6.4 Relationship between 95% volume fixed kernel home range size (ha) and
percent of radiolocations on uncut areas for eastern box turtles, Jackson County, Alabama,
2003-3005.
Microclimate. On uncut areas mean AmbT (24.61 ± 5.16) was not different than
mean TurT (24.58 ± 5.21) (t = 0.357, df = 218, P = 0.71), but AmbRH (61.51 ± 15.46)
was significantly lower than TurRH (67.96 ± 13.82) (t = -11.12, df = 208, P = <0.0001).
On cut areas AmbT (25.98 ± 5.56) was higher than TurT (25.43 ± 5.54) (t = 3.67, df =
144, P = <0.0001), and AmbRH (62.09 ± 16.24) was lower than TurRH (69.37 ± 13.69)
(t = -11.323, df = 140, P = <0.0001).
Microhabitat use. The best model selected by AIC for explaining differences
between female turtle and random locations on uncut areas was model 1 (y = 4.83 lit +
1.18 bar + 2.81 her + 0.96 woo + 6.03 sla + 3.51 roc + 5.15 cwd + 0.028 can) (Table 6.3).
144
Within this model, the following variables were significant (Wald χ2 P < 0.05): her, sla,
and cwd. Based on AIC wi, this model was 99% likely to be the best model. This model
correctly classified 72% of locations. On cut plots, the most parsimonious model for
female turtle microhabitat was model 3 (y = 0.74 woo + 4.26 sla + 1.40 cwd), which was
77% likely to be the best candidate and 71% classification accuracy. Only sla was
significant in this model. Model 1 was also supported for females on cut plots (y = 1.18
lit – 5.34 bar + 1.97 her + 2.14 woo + 5.39 sla + 2.71 roc + 2.55 cwd + 0.01 can), which
was 23% likely to be the best model and contained only one significant variable; sla.
For males, on uncut areas the best and only supported model was model 1 (y =
6.92 lit – 2.78 bar + 4.53 her + 3.75 woo + 11.81 sla + 10.13 roc + 8.14 cwd – 0.19 can)
(Table 6.4). Significant variables in this model included lit, her, woo, roc, and cwd. This
model classified 83% of locations. On cut areas, male locations were best differentiated
from random points by model 3 (y = 0.63 woo + 6.11 sla + 2.11 cwd), which had an 85%
probability of being the best model and 77% classification accuracy. Slash was the only
significant variable in the model. Model 1 (y = 0.42 lit – 14.67 bar + 2.21 her + 0.50 woo
+ 6.99 sla + 1.25 roc + 2.89 cwd + 0.017 can) was also supported for males on cut areas,
and was 15% likely to be the best model
145
Table 6.3. Results of matche pairs logistic regression for female box turtles
Control models – sensitivity 72.2 %
litt + bar + her* + woo + sla* +roc + cwd* + can
woo + cwd* + sla*
can + her*
can
litt + roc + bar
Cut models – sensitivity 71.4 %
woo + cwd + sla*
litt + bar + her + woo + sla* + roc + cwd + can
can
can + her
litt + roc + bar
sig.
AIC
∆i
wi
<0.0001
<0.0001
0.018
0.547
0.789
100.23
109.22
130.41
136.09
139.42
0.00
8.99
38.81
35.86
39.19
0.989
0.011
0.000
0.000
0.000
<0.0001
0.0002
0.547
0.826
0.866
70.65
73.11
88.97
90.96
92.61
0.00
2.46
18.32
20.31
21.96
0.774
0.226
0.000
0.000
0.000
Figure 6.3. Results of matched-pairs logistic regression for female box turtles.
Table 6.4 Results of matched-pair logistic regression for male eastern box turtles
Control models – sensitivity 82.8 %
sig.
AIC
∆i
litt* + bar + her* + woo* + sla + roc* + cwd* + can
woo + cwd* + sla*
litt + roc* + bar
can* + her*
can*
Cut models - sensitivity 76.8 %
woo + cwd + sla*
litt + bar + her + woo + sla* + roc + cwd + can
litt + roc + bar
can
can + her
146
wi
<0.0001
<0.0001
0.0011
0.003
0.017
72.03
98.59
111.89
113.43
116.97
0.00
26.56
39.86
41.40
44.94
1.000
0.000
0.000
0.000
0.000
<0.0001
<0.0001
0.120
0.605
0.840
61.70
65.09
95.85
97.39
99.31
0.00
3.39
34.15
35.69
37.61
0.845
0.155
0.000
0.000
0.000
Discussion
Timber harvesting at the scale and intensity studied did not appear to have drastic
impacts on movement patterns by box turtles. The average distance moved by turtles on
harvested and unharvested areas did not differ, and no significant relationship between
harvesting and home range existed. This is somewhat surprising considering the
significant changes to climatic and habitat features on cut areas, and the results of
previous research. It has been demonstrated that box turtle home range size can be
affected by habitat quality (Stickel 1950, Nieuwolt 1996, Curtin 1997). Box turtles
which live in isolated woodlots appear to move shorter distances than those living in
areas surrounded by forests (Iglay et al. 2007). It is possible that shifts in climatic
conditions experienced by turtles were compensated for through observed shifts in
microhabitat use, and that movements remained unchanged. Although it was suggested
by Stickel (1950) that the majority of a box turtles home range is visited in a relatively
short time, it is also possible that some turtles in the current study were not tracked long
enough to determine the full extent of their home ranges. This phenomenon has been
described for studies of this species (Weatherby et al. 1998). Large numbers of
individual animals need to be radio-tracked in order to make comparisons due to high
levels of variation in movement patterns (Marshall et al. 2006). This said, the two largest
home ranges were of turtles which spent the majority of their time on uncut areas.
Inspection of these home ranges showed that these turtles made large movements to areas
with open canopy, possibly to reach ephemeral food sources or nesting habitat (Stickel
1950). In Deleware female Terrapene carolina inhabiting the interior of forest patches
147
moved further to nest than those with home ranges nearer to open habitats (Kipp 2003).
One such movement was made a by a female during hot weather to a road rut pool where
she was found completely buried underwater in mud. Movements of this nature have
been observed in Tennessee and also enlarged home ranges (Donaldson and Echternacht
2005).
The MCP estimates of home range size obtained in this study (range 0.34-7.92,
x = 2.6 ha) are comparable to those of previous research. Average MCP home range
estimators for this species include 4.05 ha in New York (Madden 1975), and 0.38 and 1.9
ha in Tennessee (Davis 1981, Donaldson and Echternacht 2005). The lack of sexual
differences in home range size and length of average movement in this study have been
noted by other box turtle researchers (Stickel 1950, Schwartz and Schwartz 1974, Stickel
1989).
Compositional analysis revealed that box turtles prefer forest stands in which 5075% of the forest canopy has been removed. Although no studies have commented on
box turtle habitat use in forest stands after canopy removal, eastern box turtles are known
to use open grassland or pasture habitat (Dodd 2001). Use of open areas by three-toed
box turtles in Arkansas was most common in spring and turtles shifted to closed canopy
forests in summer (Reagan 1974). Florida box turtles (T. c. bauri) use open lawns and
sea oat meadows more during winter and spring during mild temperatures and high
humidity (Dodd et al. 1994). No such seasonal shift was observed in this study. It has
been surmised that box turtles move to areas of high canopy cover for overwintering as
these areas could provide the most protection from temperature extremes (Reagan 1974,
148
Madden 1975). In this study box turtles did not seem to show a large preference for cut
or uncut areas as places to overwinter. However, in two cases turtles with a majority of
their locations on harvested areas moved to and overwintered in unharvested control
areas. No mortality associated with overwintering was observed. Turtles overwintered in
spots with deep litter inside of some type of hole or depression. Several times turtles
were found overwintering in old stump holes, some overwintered at the base of trees or
rocks, and some inside of thick tangles of Smilax vines.
It is possible that preference for harvested areas was related to food availability.
The omnivorous diet of eastern box turtles includes various types of fruits and other plant
material, fungi, and arthropods (Dodd 2001). Fruiting plants, such as blackberries (Rubus
allegheniensis) which grew abundantly on harvested areas at study sites, are known to
draw aggregations of box turtles (Dodd et al. 1994). While overall arthropod abundance
was lower in wind created gaps in North Carolina, some groups were more abundant in
disturbed areas (Greenberg and Forrest 2003). These could serve as important prey for
box turtles, but abundance of macroarthropods is generally a poor predictor of vertebrate
predator abundance (Greenberg and Forrest 2003). The preference for harvested areas
could also stem from physiological benefits gained from climatic shifts after harvesting.
This does not seem likely however since conditions appear to be more limiting in
harvested areas. In uncut areas, air temperature (AT) experienced by turtles did not differ
from ambient, but ambient relative humidity (RH) was lower than turtle RH. In
harvested areas, however, AT was higher and RH was lower ambiently than at turtle sites.
149
On unharvested areas males used microhabitats with more litter, herbaceous and
woody vegetation, coarse woody debris, and rocks than random, while females used sites
with more herbaceous vegetation, slash, and coarse woody debris. Vegetative ground
cover and litter were important components of three-toed box turtle microhabitats in
Arkansas (Reagan 1974). Female T. c. carolina in North Carolina selected locations with
more exposed soil than males, but the amount of woody debris, litter, and canopy cover at
used sites did not differ from those available (Rossell et al. 2006). On cut areas, both
males and females used microhabitats with more slash than random locations. This
indicates that the main microhabitat feature turtles are using to differentiate optimal
habitat from those available on harvested areas is slash. These piles of residual logging
debris may provide turtles with cool, moist conditions necessary for thermoregulation and
maintaining water balances. It has been shown that leaf litter in close proximity to dead
woody debris retains more moisture than in open areas (Andrew et al. 2000). Slash is
viewed as important escape cover for a variety of vertebrate and invertebrates in managed
forests (Smith et al. 1997). The decision to retain or remove slash after harvesting by
burning or chipping is made based on factors such as economics, aesthetics, recreational
opportunities, wildlife habitat, and nutrient retention and storage (Covington 1981, Smith
et al. 1997). Studies of the thermal biology and physiological tradeoffs of habitat use of
box turtles in similarly managed forest stands would likely prove fruitful. It should be
noted that the model used, paired logistic regression, told us only which microhabitat
variables are being used more than random. Other variables may be important to turtles
150
on harvested areas, but only slash was used significantly more than available at random
sites.
Commercial harvesting of 50-75% of overstory trees in this region may be
compatible with preservation of populations of eastern box turtles, at least at the scale
studied. Harvesting over a larger area may have very different impacts than the 4 ha cuts
in this study (Lindenmayer and Franklin 2002). Two female turtles (T12 and T50) were
tracked for 290 and 270 days and were never found on unharvested areas. Both turtles
successfully overwintered on harvested areas. Other turtles had less than 10% of their
locations on unharvested areas. Future research should concentrate on radiotracking box
turtles on areas similarly harvested of larger sizes to determine if the species can exist in
areas devoid of unharvested reserves. Based on the results of this study, I would strongly
recommend the retention of residual logging slash after harvest as it was found to be a
critical feature of box turtles habitat.
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CHAPTER 7
CONCLUSIONS AND MANAGEMENT RECOMMENDATIONS
The usefulness of applied ecological research such as this study should be judged
based on recommendations it produces for forest managers thereby allowing them to
make decisions that best benefit reptile and amphibian populations. Considering that
conservation of biodiversity, two components of which are reptiles and amphibians, is but
one of many factors that forest managers base their decisions upon, recommendations
should be realistic and flexible. With this in mind, I offer some recommendations to
forest managers along with cautions based on limitations to my research, reflections upon
the efficiency of various methods used in my research, and ideas for future research into
this field of ecology based on the results of this dissertation and insights gained during
execution of the project.
Management Recommendations
Inferences drawn from this research, and therefore management recommendations
offered, are necessarily limited in scope. Results apply to forested lands on the
escarpment of the southern Cumberland Plateau. Experimental units used in this study
were embedded in a landscape composed largely of contiguous mature forest. How such
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treatments would impact amphibian and reptile communities in different ecoregions, or in
a different landscape context is impossible to predict. Inferences are also limited to 4 ha
stands. Harvesting larger or smaller areas would likely have very different impacts.
Results are also limited to relatively short time span relative to the typical rotation time in
this type of forest. There were some indications in this research that the response of
some groups was not immediate, and that a period of time was necessary before
observing any trends. The 25-75% retention treatments in this study were applied as a
shelterwood silvicultural system and therefore residual stems will be removed from
stands 10 years post-harvest. The responses observed in this study should be applicable
to the first 5 years post-harvest on forest stands receiving a two-aged harvest as long as
they have similar stand structure.
It is also important to note that responses of forest herpetofauna after canopy
removal are unlikely to be limited to those reported in this investigation. I am confident
that type II statistical errors have been committed in conducting this research. That is, I
am sure that some responses have gone undetected by the investigation. Though this is a
well-designed experiment relative to most previous similar investigations, low replication
is a limiting factor in detecting responses of variable processes to treatments (Marzluff et
al. 2000). Many amphibian populations in particular are extremely variable in time,
making detecting trends very difficult (Pechmann et al. 1991).
Considering these caveats, the responses of herpetofauna revealed by this
investigation are summarized in table 7.1. These responses represent all significant
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Table 7.1 Major conclusions about effects of 5 levels of overstory tree retention
treatements on herpetofauna in Jackson County, Alabama 2002-2005. Responses are
drawn from results reported in chapters 3 and 5 and denote the direction and nature of
response.
Variable
Reptile richness
Reptile abundance
Large snake abundance
Lizard abundance
H. chrysoscelis egg mass #
P. brachyphona egg mass #
A. maculatum egg mass #
Amphibian richness
Response to canopy retention
negative - decrease with increasing retention past 50%
negative - decrease with increasing retention past 50%
negative - gradual decrease with increasing retention
negative - gradual decrease with increasing retention
negative - gradual decrease with increasing retention
positive - gradual increase with increasing retention
positive - sharp increase past 75%
positive - sharp increase past 25%
patterns presented in chapters 3-5 and are categorized as either a positive or negative
response to canopy retention. Some responses were gradual and increased or decreased
consummate with amount of basal area retained. Others changed more rapidly with
retention past a certain level.
The direction and nature of these responses formed the basis for compiling a list
of costs and benefits a manager would incur should they chose one treatment over
another (Table 7.2). In this way a manager can determine what impacts they might
expect to observe as a result of their actions. For the sake of simplicity treatments were
grouped in two cases based on the similarity of observed responses. A group termed
“Intermediate cuts” included both 25- and 50% retention treatments. Though the target
level of retention was considerably different between these treatments, due to limitations
of applying such large scale experiments on an operational basis, these two treatments
were actually quite similar. No significant differences in herpetofaunal responses were
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Table 7.2 Costs and benefits of choosing one treatment versus choosing another of two
alternative treatment types. ▲ = increase in a parameter and ▼ = decrease in parameter.
Treatment
benefits
costs
vs. intermediate cuts:
vs. intermediate cuts:
Clearcut
▲ abundance of large-bodied
▼ richness of amphibians and
snakes
overall herpetofauna
▲ reproductive output by Cope’s
▼ reproductive output by
gray treefrog
mountain chorus frog
vs. closed canopy:
▲ richness of reptiles
▲ abundance of total reptiles,
large-bodied snakes, and lizards
▲ reproductive output by Cope’s
gray treefrog
vs. clearcut:
Intermediate cuts
(25-50% retention) ▲ richness of amphibians and
overall herpetofauna
▲ reproductive output by
mountain chorus frog
Closed Canopy
(75% retention
and control)
vs. closed canopy:
▲ richness of reptiles and overall
herpetofauna
▲ abundance of total reptiles,
large-bodied snakes, and lizards
▲ reproductive output by Cope’s
gray treefrog
vs. intermediate cuts:
▲ reproductive output by
mountain chorus frog
presence of reproductive output
by spotted salamander
▲
vs. clearcut:
▲ richness of amphibians
▲ reproductive output by
mountain chorus frog
▲ presence of reproductive output
by spotted salamander
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vs. closed canopy:
▼ richness of amphibians
▼ reproductive output by
mountain chorus frog
▼ absence of reproductive
output by spotted
salamander
vs. clearcut:
▼ abundance of large-bodied
snakes
▼ reproductive output by
Cope’s gray treefrog
vs. closed canopy:
▼ reproductive output by
mountain chorus frog
▼ absence of reproductive
output by spotted
salamander
vs. intermediate cuts:
▼ richness of reptiles and
overall herpetofauna
▼ abundance of total reptiles,
large-bodied snakes, and
lizards
▼ reproductive output by
Cope’s gray treefrog
vs. clearcut:
▼ richness of reptiles
▼ abundance of total reptiles,
large-bodied snakes, and
lizards
▼ reproductive output by
Cope’s gray treefrog
observed between these treatments. The same reasoning applies to the grouping of the
75% retention and control treatments into the “Closed canopy” group.
The range of treatments applied in this study created a gradient of conditions, and,
as expected, the responses of herpetofauna followed the same gradient. Some species or
groups were more abundant on one end of the spectrum and some the other. Generally,
reptile community parameters tended to reach maximum values with decreasing retention
while amphibian community parameters tended to maximize with increasing retention.
These trends, however, are not simply linear. For example, the cost of decreasing canopy
tree retention in terms of reduction in amphibian species richness was observed only after
retention of less than 25% of overstory trees. The benefits of decreasing retention in
terms of increasing reptile species richness and abundance, as well as increased lizard
abundance, were as pronounced at 25- and 50% retention as they were at 0% retention
(clearcut). In other words, intermediate cuts came with many of the benefits achieved in
clearcut treatments with fewer of the costs associated incurred with clearcut treatments.
For this reason, managers whose objectives include the conservation of amphibians and
reptiles might limit the use of clearcuts in favor of intermediate levels of cutting. Closed
canopy conditions offer unique benefits. For example, reproduction of spotted
salamanders was only observed in 75% retention and control treatments.
It is important to consider the effects canopy removal/retention can exert on
herpetofauna at several scales. Within-habitat, or alpha diversity (Whittaker 1960) is
increased in this ecosystem by removing 50% of overstory trees. This is inferred from
the observation that overall herpetofauanal diversity was greater in 25- and 50% retention
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treatments compared to controls. Because there are a number of species that occurred in
considerable numbers only on harvested plots, and other species that appear to require
closed canopy conditions for reproduction, the existence of forest stands with various
levels of overstory tree retention should increase Beta, or between-habitat diversity
(Whittaker 1960). In other words, there is greater herpetofaunal diversity in the 60 ha
study area where this research was conducted than you would expect to find in a 60 ha
forest comprised entirely of contiguous closed canopy forest. At the next largest scale,
termed Gamma diversity by Whittaker (1960), and for our example the Southern
Cumberland Plateau region, timber harvesting would not appreciably decrease or increase
species diversity because all of the species present on these study sites are present in the
region. In fact, managing for diversity at the smaller, say Beta, scale only may come at a
cost in terms of regional diversity. For example, I saw that two species of amphibians,
the mountain chorus frog and spotted salamander, concentrated their reproductive efforts
more in uncut stands. Spotted salamanders only laid eggs in these stands. The Cope’s
gray treefrog, on the other hand, laid more eggs in clearcut stands. Because of this
pattern one might argue that the total number of amphibians is nearly equal between the
two stand types, and so their value for amphibians is equal. However, because Cope’s
gray treefrog populations are stable and persist in human dominated landscapes (Cline
2005), while both mountain chorus frogs and spotted salamanders are becoming
increasingly rare throughout their respective ranges (Mitchell and Pauley 2005, Savage
and Zamudio 2005) increasing habitat for treefrogs at the expense of the other two
species is effectively reducing regional amphibian diversity.
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One more layer of complexity added to the situation is that if a forest manager
needs to harvest a set amount of wood fiber to supply their mill or meet certain financial
goals, they would have to disturb 25-50% as much land area if they retain 25-50% of
ovestory trees upon harvesting. Essentially the question is: does harvesting twice as
much area half as intensively have the same net impact as simply clearcutting? Although
the results of this research can act as a guide when answering this question, because there
is necessarily a spatial component to the question that is far beyond the scope of my
research, inferences are weak or even dangerous. For example, harvesting 50% of
overstory trees in this study did not reduce amphibian species relative to controls. But,
although spotted salamanders were observed on intermediate cuts outside of the breeding
season they only laid eggs in closed canopy treatments. The size and arrangement of
experimental units may have permitted the movement of individuals from one treatment
to another in order to satisfy requirements of completing their life cycle. Harvesting over
larger areas may preclude this phenomenon thereby eliminating certain species from the
area. Many reptiles and amphibians have different habitat requirements in different parts
of the life cycle.
It is also important to note that when a forest manager is weighing the costs and
benefits of these different management activities they are doing so in a context of all
available options, not just the ones studied here. For example, although clearcutting had
negative consequences for amphibian species richness, a forest manager may be
considering the pros and cons or clearcutting versus a land sale or conversion to a pine
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monoculture. In this situation, clearcutting followed by natural hardwood regeneration to
reclaim the site is likely to be more beneficial to amphibians than either alternative.
If the choice of management activity includes any of the harvesting techniques
discussed here, there are certain steps a manager can take to benefit amphibians and
reptiles. One of these is retention of residual logging debris, particularly tree tops left as
slash piles. Lizard and slash abundance were related on the study sites and the presence
of slash may be important for the group. Radiotelemetry of eastern box turtles revealed
that on cut stands box turtles rely heavily on slash piles for shelter. These structures
likely are important for helping box turtles to maintain proper body temperatures and
water balances in the warmer, drier conditions on cut stands. Slash piles likely benefit a
variety of other organisms in harvested stands and their retention is strongly encouraged.
Research Recommendations
One lesson learned during execution of this project was the importance of asking
directed and realistic questions. A huge amount of time was spent collecting and
organizing data on climatic conditions in the various treatments with no specific objective.
In the end, only a small subset of this data was used in analyses. Being clear in the
beginning of the project with what was going to be done with the data would have saved
much time and energy. The same might be said of drift fence trapping. In the beginning
of the investigation I had hopes of inferring the response of many of the species present
on the sites to treatments. In the end, there were only two guilds of reptiles which
responded predictably to treatments. In hindsight it is apparent that the data set produced
162
by drift fence trapping is typical of most ecological data sets; of the species captured
many are rare, and most common species are general in their habitat requirements. In my
case, 21 of the 40 species were represented by the capture of less than 10 individuals, 28
species less than 20 individuals. Neither of the species which were captured in sufficient
numbers for statistical analyses differed in abundance between treatments. The most
useful information for comparison of treatments was species richness, a measure that
could be estimated relatively quickly and confidently compared to the amount of
sampling completed. With this knowledge it might be a more efficient use of resources
to open traps until a complete sample of the species present is obtained on each treatment.
The amount of sampling required could be estimated based on plots of cumulative
species detected over sampling effort similar to figure 3.2.
The use of artificial pools to study amphibian response to forest management
appears to offer much promise. I would suggest further research that combines intense
mark-recapture studies over time of individuals which visit pools on treatments to
estimate movement patterns and demographic parameters such as growth and survival
rates. These pools are relatively inexpensive, easy to install and maintain, and readily
sampled.
The lack of adequate replication is a serious issue in this type of study. The
processes under investigation when assessing response of reptiles and amphibians are
variable enough that traditional hypothesis testing techniques have limited utility in some
cases. Study designs that maximize replication should be used when possible. In the
current study it may have been possible to add an additional replicate of the clearcut and
163
control treatments since they are more common in the landscape. Then, the 25- and 50%
treatments could have been grouped together since they were so similar. It is very
appealing to attempt to detect responses to such a wide gradient, but realistically it is very
difficult because of statistical limitations.
Based on experiences gained during this study I strongly urge wildlife researchers
to form cooperative relationships with researchers working on silviculture and other
aspects of forest management. The chances of getting such large scale experiments
applied at these scales solely for the study of wildlife populations are slim at best.
Partnering with scientists conducting such applied forest ecology research ensures that
treatments that are investigated are relevant to contemporary forest management and
increases the probability of producing usable results. Working together also allows for
data pooling and the chance to learn from people who have an entirely different
knowledge base than you. The credibility gained by associating yourself with someone
respected by other forest managers is likely also very important when reporting
management recommendations.
Bibliography
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M.J. Lannoo, ed. Amphibian Declines: The Conservation Status of the United
States Species. University of California Press, Berkeley.
Marzluff, J.M., M.G. Raphael, and R. Sallabanks. 2000. Understanding the effects of
forest management on avian species. Wildlife Society Bulletin 28: 1132-1143.
Mitchell, J.C., and T.K. Pauley. 2005. Mountain chorus frog, Pseudacris brachyphona
Cope, 1889. Pp. 465-466. In M.J. Lannoo, ed. Amphibian Declines: The
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Conservation Status of the United States Species. University of California Press,
Berkeley.
Pechmann, J. H. K., D. E. Scott, R. D. Semlitsch, J. P. Caldwell, L. J. Vitt, J. W. Gibbons.
1991. Declining amphibian populations: The problem of separating human
impacts from natural fluctuations. Science 253:892-895.
Savage, W.K., and K.R. Zamudio. 2005. Spotted salamander, Ambystoma maculatum
Shaw, 1802. Pp. 621-627. In M.J. Lannoo, ed. Amphibian Declines: The
Conservation Status of the United States Species. University of California Press,
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Whittaker, R.H. 1960. Vegetation of the Siskiyou Mountains, Oregon and California.
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165
VITA
Zachary Ira Felix, originally son of Kathlyn and Robert Paul, was born Zachary
Ira Paul on July 21rst, 1976 in Albuquerque, New Mexico. He was adopted in 1994 and
metamorphosed into his new identity as Zachary Ira Felix, son of Kathlyn and William
Felix. He attended SUNY Cobleskill in Cobleskill, NY and achieved his A.A.S. in
Fisheries and Wildlife Technology in 1996. From there he went on to work on his B.S.
degree in Environmental Forest Biology from SUNY Environmental Science and
Forestry in Syracuse, NY which he achieved in 1999. An M.S. degree in Biological
Sciences was subsequently earned at Marshall University in the great state of West
Virginia in 2001. After a short tenure in Aruba wrestling venomous serpents Zachary
was accepted into the doctoral program at Alabama Agricultural and Mechanical
University. After 5.5 years of toil the Ph.D. was conferred to Felix in May, 2007.