EFFECT OF SILVICULTURAL TREATMENTS ON THE GROUND LAYER VEGETATION
IN PINE-HARDWOOD STANDS OF THE SOUTHERN APPALACHIAN PLATEAU
by
DANA ALISON VIRONE
A THESIS
Submitted in partial fulfillment of the requirements
for the degree of Master of Science
in the Department of Natural Resources and Environmental Sciences
in the School of Graduate Studies
Alabama A&M University
Normal, Alabama 35762
November 2010
Submitted by DANA ALISON VIRONE in partial fulfillment of the requirements for the
degree of MASTER OF SCIENCE specializing in PLANT AND SOIL SCIENCE.
Accepted on behalf of the Faculty of the Graduate School by the Thesis Committee:
___________________________ Luben Dimov
___________________________ Callie Schweitzer
___________________________ Yong Wang
___________________________ Kozma Naka
_________________________ Dean of the Graduate School
_________________________ Date
ii Copyright by
DANA ALISON VIRONE
2010
iii This thesis is dedicated to my parents, Terry and Nina Wallace, and my husband,
Shane, for their unending support, patience, and encouragement.
iv EFFECT OF SILVICULTURAL TREATMENTS ON THE GROUND LAYER VEGETATION
IN PINE-HARDWOOD STANDS OF THE SOUTHERN APPALACHIAN PLATEAU
Virone, Dana Alison, M.S., Alabama A&M University, 2010. 66 pp.
Thesis Advisor: Dr. Luben Dimov
It is imperative to understand the impact of forest management activities on
species cover, diversity, and richness. This would allow for adequate selection of the
silvicultural activities needed to achieve particular desired future conditions. The effects
of thinning and prescribed burning are studied often, but their combined effects are
investigated only rarely and mostly for their impact on tree species. This study examines
the response of the cover, composition, diversity, and richness of ground layer vegetation
to six treatments: low intensity dormant season prescribed burning applied once, fire
exclusion, heavy thin with residual basal area of 11 m2/ha, light thin with a residual basal
area of 17 m2/ha, un-thinned control, and combinations of these burning and thinning
regimes. The study was carried out in the William Bankhead National Forest (BNF),
northwestern Alabama, in 20-50 year old pine-hardwood stands dominated by planted
loblolly pine (Pinus taeda). Two growing seasons after treatment, species richness,
overall plant cover, and cover of graminoids increased the most, compared to untreated
stands, in the heavy thin alone and the two combination treatments. Stands treated with
the burn alone had no change in overall cover, richness, diversity, or cover of the
individual life form groups. Plant diversity increased the most after the heavy thin only
and heavy thin plus burn treatments. Three growing seasons after treatment, only the
heavy thin plus burn had greater diversity than the control. The results were similar for
richness. As a whole, the more intense the treatment, the greater the increase in cover,
richness, and diversity.
v KEYWORDS: Ground layer vegetation, prescribed burning, thinning, silviculture, forest
management, community composition, herbaceous, Cumberland Plateau
vi TABLE OF CONTENTS
LIST OF TABLES ........................................................................................................... viii LIST OF FIGURES ........................................................................................................... xi CHAPTER 1 - INTRODUCTION AND LITERATURE REVIEW .................................. 1 Introduction ..................................................................................................................... 1 Literature Review ............................................................................................................ 4 CHAPTER 2 - MATERIALS AND METHODS ............................................................. 16 Study Site ...................................................................................................................... 16 Sampling Methods ......................................................................................................... 21 Data Analysis ................................................................................................................ 22 CHAPTER 3 - RESULTS AND DISCUSSION .............................................................. 26 Results ........................................................................................................................... 26 Discussion ..................................................................................................................... 51 APPENDIX – SPECIES LIST .......................................................................................... 57 REFERENCES ................................................................................................................. 61
VITA
vii LIST OF TABLES
Table
Page
1. Change in vegetation attributes compared to control treatment according to different
studies ............................................................................................................................11
2. Initial treatment design ..................................................................................................19
3. Dates when treatments were implemented ....................................................................19
4. Modified treatment design.............................................................................................20
5. Dates of ground layer vegetation sampling ..................................................................24
6. Average cover and frequency per stand for the five most frequently occurring species
of each life form for the second growing season post-treatment .................................27
7. Marginal mean estimates of the change of dependent variables from pre-treatment to
the second growing season post-treatment. ...................................................................29
8. Bray-Curtis indices of similarity for ground layer vegetation communities in the
second-season post-treatment. ......................................................................................33
viii 9. Marginal mean estimates of the change in the percent cover of ground variables from
pre-treatment to the second growing season post-treatment... ...........................................34
10. Marginal mean estimates of the change in cover from pre-treatment to the second
growing season post-treatment for the five species of each life form with the highest
average post-treatment ... ...................................................................................................36
11. Indicator values for indicator species identified in a comparison of unburned and
burned stands in the second season post-treatment............................................................38
12. Indicator values for indicator species identified in a comparison of no thin, heavy thin
and light thin stands in the second season post-treatment... ..............................................39
13. Average cover and frequency per stand for the five most frequently occurring species
of each life form for the third growing season post-treatment...........................................41
14. Marginal mean estimates of the change of dependent variables in the third growing
season following treatment... .............................................................................................42
15. Bray-Curtis indices of similarity for ground layer vegetation communities in the third
season post-treatment... ......................................................................................................46
ix 16. Marginal mean estimates of the change in the percent cover of ground variables from
pre-treatment to the third growing season post-treatment... ..............................................47
17. Marginal mean estimates of the change in cover from pre-treatment to the third
growing season post-treatment for the five species of each life form with the highest
average post-treatment... ....................................................................................................48
18. Indicator values for indicator species identified in a comparison of stands treated with
the no thin, heavy thin, and light thin in the third season post-treatment... .......................50
x LIST OF FIGURES
Figure
Page
1. Schematic drawing of treatment stand with five 0.08 ha plots. Schematic drawing
of the 0.08 ha vegetation plots with sample square layout, area, and distance from
the plot center ..............................................................................................................23
2. Burn and thin treatment interaction on the mean difference in overall cover, forb
cover, graminoid cover, and vine cover in the second season post-treatment ............32
3. Burn and thin treatment interaction on the mean difference in overall richness, forb
richness, graminoid richness, and vine richness, and overall diversity in the second
season post-treatment ...................................................................................................33
4. Burn and thin treatment interaction on the mean change in overall cover, forb cover,
graminoid cover, and vine cover in the third season post-treatment ...........................43
5. Burn and thin treatment interaction on the mean change in overall richness, forb
richness, graminoid richness, vine richness and overall diversity in the third season
post-treatment ..............................................................................................................44
xi ACKNOWLEDGMENTS
I would like to thank my committee members: Dr. Kozma Naka, Dr. Callie
Schweitzer, and Dr. Yong Wang, for their guidance, patience, and advice throughout this
process. Their willingness to share their knowledge and sacrifice their time to help me
grow as a researcher is so appreciated. I especially thank my major advisor, Dr. Luben
Dimov, for his constant support, helpfulness, encouragement, and guidance throughout
this project. Thanks to Vanaraj Ganapathy, Clint Patterson, Dawn Lemke, Allison
Cochran, Daryl Lawson, Stacy Clark, Loretta Lynne Weninegar, Nicole Hupp, and Joel
Zak for sharing their time, talent, and knowledge.
Research support was provided by National Science Foundation, CREST-CFEA.
Additional support came from the Forestry, Ecology, and Wildlife Program in the
Department of Natural Resources and Environmental Sciences, Alabama A&M
University; USDA Forest Service, Southern Research Station, Upland Hardwood
Ecology and Management Research Work Unit; and the Alabama Wildflower Society.
The USDA Forest Service William B. Bankhead National Forest provided logistical and
technical support throughout the study.
xii CHAPTER 1
INTRODUCTION AND LITERATURE REVIEW
Introduction
Maintaining or increasing levels of biodiversity while restoring and sustainably
managing healthy forest ecosystems are among the primary goals of many forest
managers (Gilliam, 2002; Hunter, 1999; Roberts and Gilliam, 1995). As natural and
anthropogenic disturbances impact the composition and health of eastern North American
forests, it is imperative to understand the effects of disturbance on species cover,
diversity, and richness (Clinton and Vose, 2000; Hutchinson et al., 2005). Knowledge of
these dynamics will allow forest managers to make more accurate predictions and better
decisions on how to utilize different forest management practices to achieve desired
future conditions. Prescribed burning and overstory thinning are two intermediate
treatments that can be used in forests with an oak component to impede the successional
replacement of oak by maple, improve forest health, and facilitate oak regeneration
(Chiang et al., 2008). A number of studies address the effects of these treatments
separately and they often focus only on woody vegetation. Few, however, address their
interaction and combined effects or their impact on ground layer vegetation.
Ground layer vegetation includes forbs (perennial, biennial, or annual vascular
plants that do not exhibit secondary growth), graminoids (plants in the families Poaceae,
1 Cyperaceae, or Juncaceae), vines, and woody species less than one to two meters in
height (Elliot and Knoepp, 2004; Gilliam, 2002; Zenner and Berger, 2008). I continue
with the precedent of Joel Zak who examined species less than 1.4 meters in height for
this study in the pre-treatment and first growing season post-treatment sampling periods
(Zak, 2008). The ground layer represents the most diverse layer of vegetation in Eastern
forest ecosystems (Gilliam, 2002). Because thinning can alter the amount of light
intercepted by the forest canopy and burning may favor the survival of some species over
others, it is especially important to monitor the response of the layer to burning and
thinning over time.
In 2003 the United States Forest Service (USFS) enacted the Forest Health and
Restoration Project in the William B. Bankhead National Forest (BNF) in northwestern
Alabama. This project is aimed at restoring degraded pine-dominated pine-hardwood
forests while favoring hardwoods through management activities including prescribed
burning and overstory thinning. In this study I examined the response of ground layer
vegetation to these treatments by quantifying the changes in cover, richness, and diversity
of ground layer species two and three growing seasons after treatment.
The study area was located on the southern Cumberland Plateau in northern
Winston and southern Lawrence counties. Forests of the Cumberland Plateau are among
the most diverse of the Eastern temperate zone forests due to an extremely varied
landscape consisting of mountains, deeply incised stream valleys, floodplains, hills, and a
tableland surface area (Hart and Grissino-Mayer, 2008). The variety of
microenvironmental conditions found throughout the area support species that are more
often found in forests of higher and lower latitudes (Braun, 1942). Cumberland Plateau
2 forests have a long history of human land use and have likely been disturbed for
millennia (Delcourt and Delcourt, 2000). Logging activities increased around the Civil
War with a peak in the 1920s. Current vegetation composition and structure depends on
site characteristics, land-use history, and disturbance events (Hart and Grissino-Mayer,
2008).
The stands in the study area were 20-50 year old mixed pine and hardwoods
dominated by planted loblolly pine (Pinus taeda). The forest has been impacted by both
human and natural disturbances. In the 1970s much of the abandoned agricultural land
from prior European settlement was planted in loblolly pine (USDA Forest Service,
2003). Over the past decade BNF forests have been affected by epidemic-level southern
pine beetle (Dendroctonus frontalis Zimmerman) infestations (USDA Forest Service,
2003). As a result of these major permutations, BNF land managers started using
silvicultural treatments in an attempt to reduce pine density and to regenerate native
hardwood species (USDA Forest Service, 2003).
This study is part of a larger project conducted by the Center for Forest
Ecosystem Assessment (CFEA). CFEA is a collaboration between Alabama A&M
University and the USDA Forest Service and is a Center of Research Excellence in
Science and Technology (CREST) of the National Science Foundation. CFEA is
conducting a multidisciplinary, multi-year study of ecosystem level response to the
implementation of the BNF’s Forest Health and Restoration Management Plan. This
study follows on the work of Joel Zak (2008) who gathered baseline vegetation and
environmental data for the project and examined the initial response of ground layer
vegetation to burning and thinning. The focus of this project is to examine the ground
3 layer’s response two and three growing seasons after treatment and further expand
knowledge of disturbance response in ground layer vegetation.
Hypothesis and Predictions
Ha: There will be a significant thin and burn effect and an interaction effect on overall
ground layer vegetation cover, richness (S’), and diversity (H’), and on the cover and
richness of the life form groups herbs, graminoids, and vines in the second and third
growing seasons post-treatment.
Predictions: Overall cover will increase after a combination of thinning and burning.
Herbaceous cover will increase with burning, thinning, and a combination of burning
and thinning.
Literature Review
The function of ground layer vegetation in managed forest ecosystems has gained
increased attention in recent years (Gilliam, 2002). Ground layer vegetation plays an
important role in contributing to overall forest species richness and diversity, nutrient
cycling, productivity, and aesthetics. Due to these contributions it is argued that ground
layer vegetation is vital to the long-term sustainability of managed forest ecosystems
(Jeffries et al., 2010).
Ground layer vegetation is a major contributor to overall plant species richness
and diversity. In an analysis of the findings from several studies throughout North
America, Gilliam (2007) found that ground layer vegetation makes up more than 80% of
the total plant species richness of a forest.
4 Ground layer vegetation comprises a relatively small portion of total forest
biomass, but often contributes exponentially to overall forest productivity. Only 0.2% of
the aboveground biomass of typical forests in the Northern Hemisphere is composed of
ground layer vegetation, but ground layer vegetation supplies approximately 4% of net
primary productivity (Gilliam, 2007). In a deciduous forest in Indianna, herb litter
accounted for approximately 12% of total litter fall (Welch et al., 2007).
Because ground layer vegetation tends to be short-lived and decomposes more
than twice as quickly as tree litter, it impacts nutrient accumulation and cycling (Gilliam,
2007). In a study conducted in 25 to 40 year old mixed hardwood stands, it was found
that ground layer vegetation comprised only 3% of total aboveground biomass, but
contained from 5 to 12% of the total aboveground nutrient pool of nitrogen, phosphorous,
potassium, calcium, and magnesium (MacLean and Wein, 1977). The role of ground
layer vegetation in nutrient cycling is further illustrated by a study conducted in the
Hubbard Brook Experimental Forest in New Hampshire. Concentrations of nitrogen and
phosphorous were 30% higher in herb foliage than in tree foliage. Concentrations of
magnesium in herb foliage were nearly twice that of tree foliage and concentrations of
potassium in herbs was nearly threefold that of trees (Muller, 2003).
The rise in multiple-use forest management practices has led to an increase in the
value placed on issues such as forest aesthetics. Ground layer vegetation is an important
characteristic of high scenic quality for many forest users (Ribe, 1990). In a slide
evaluation of aesthetic quality in recently cut hardwood stands, 70% of participants rated
green ground cover as being pleasant (Hamilton et al., 1973) and in a study of 31
5 predominately hardwood stands it was found that ground cover, measured in percent
cover, had a positive influence on scenic beauty (Ribe, 1990.)
The sensitivity of the ground layer to disturbance, coupled with the fact that it is
the most diverse layer of vegetation in Eastern forest ecosystems, translates into a need to
monitor and understand the ways it is affected by disturbance (Gilliam, 2002; Roberts
and Gilliam, 1995; Hunter, 1999). Many studies demonstrate the sensitivity of ground
layer vegetation to disturbance (Elliot et al., 1999; Phillips et al., 2004; Sparks et al.,
1998), but often the scale and long-term implications of disturbance on ground layer
vegetation is not well understood. In a study examining landscapes across Europe and
North America, it was shown that plant communities on abandoned agricultural lands
remain reduced in herbaceous species characteristic of forests uncleared for centuries
(Flinn and Vellend, 2005).
The conservation of species is a major goal for many public and private land
managers throughout the world. Biodiversity is valued for both economic and ecological
reasons and is becoming a key factor in management decisions (AF&PA, 2001). In fact,
one of the main goals of the BNF’s Forest Health and Restoration Project is to increase
overall plant diversity (USDA Forest Service, 2003).
Biodiversity is broadly defined to include the physical structures, processes,
species, and genotypes in an area. Species and genetic diversity are often dependent on
structural and process diversity (Palik et al., 2002). Both natural and anthropogenic
disturbances affect the relationships between biodiversity and these structures and
processes. Forest disturbances can range in intensity, frequency, and scale, e.g., from a
low intensity fire to a large scale hurricane. Disturbance scale, timing, frequency, and
6 severity shape the dynamics of forest ecosystems (Hughes and Fahey, 1991).
Disturbances create a variety of structures and processes that then influence the variety
and diversity of species (Palik et al., 2002). Plant communities that contain a broad
diversity of species are better able to adapt to such disturbances (Tillman and Downing
1994).
In this study, I quantified the changes in the cover, composition, and diversity of
ground layer vegetation after two anthropogenic disturbances, prescribed burning and
overstory thinning. The composition and diversity of ground layer vegetation
communities is often explained by variations in environment gradients, site quality, and
interspecific competition (Hughes and Fahey, 1991). Both burning and overstory thinning
can significantly affect these factors.
Prescribed burning can change the composition of tree regeneration. It may
improve oak regeneration, especially when used in combination with overstory reduction
techniques, and is being used for this purpose with increasing frequency on public and
private forest lands (Hutchinson et al., 2005). Iverson et al. (2008) found that oak and
hickory are competitive on dry or intermediate sites after opening the canopy 8.5-19%
and implementing at least two fires. Brose and Van Lear (1998) found that oak and
hickory species are more resilient sprouters than yellow poplar or red maple after fire.
Fire also improved oak stem form and increased growth.
Prescribed fires similar to the ones in this study (low intensity, dormant season
fires) rarely cause significant damage to overstory trees (Hutchinson et al., 2005), but
have a much greater impact on ground layer vegetation. These low intensity fires seldom
have flame lengths greater than one meter in height and usually consume only surface
7 fuels (Elliot et al, 1999). As a result, ground layer vegetative structures are top-killed and
alterations occur in forest floor properties (Hutchinson et al., 2005). These alterations
may include changes in pH, bulk density, availability of nutrients, quantity and quality of
organic matter, microbial biomass, and structure stability (Certini, 2005). A study of the
effects of prescribed fire on a mixed-oak forest in Ohio showed that soil temperature was
elevated for 75 days on mesic sites and 155 days on xeric sites after dormant-season
prescribed fires (Iverson and Hutchinson, 2002).
Ground layer plants respond to fire in a variety of ways. Both the morphological
and chemical properties of a species determine its vulnerability to fire. Typically, more
flammable plants have low moisture contents and fine plant parts, whereas less
flammable plants have higher moisture content and coarser, broad plant parts (Bond and
Van Wilgen, 1996). Thus, plants with small diameter plant part such as pines and grasses,
lose moisture and burn more quickly than plants with broader leaves.
Vines such as blackberry (Rubus spp.) sprout prolifically from underground
rootstocks or basal dormant buds (Langdon, 1981). Many forbs sprout quickly after the
plant is top-killed by fire through creeping rhizomes, stolons, or thickened perennial
rootstocks (Vogl, 1974). Grasses may also survive fire by sprouting through rhizomes
and stolons. In some areas grasses sprout new growth within a few weeks of a low
intensity fire (Landgon, 1981).
Fire also affects the reproductive activities of ground layer vegetation. Seeds from
forbs such as partridge pea (Chamaecrista fasciculata) and tick trefoil (Desmodium spp.)
often respond to fire by increasing germination in the seed bed (Langdon, 1981). Many
8 grasses show increases in flowering and seed production in response to fire (Ahlgren and
Ahlgren, 1960).
The season of occurrence impacts the effects of fire on vegetation. Plant
temperature, internal water relations, dormancy, and food reserves are all variables that
tend to be correlated with season and that determine the magnitude of a plant’s response
to fire (Landgon, 1981). In a study comparing late growing season and late dormant
season fires in restored pine-grassland communities in Arkansas, some plant species
displayed different responses according to the season of the burn. Late growing season
fire reduced panic grass (Dichanthelium spp.) distribution and abundance, while late
dormant season fire increased its distribution and abundance (Sparks et al., 1998).
Timber harvesting practices, including commercial thinning, are common
anthropogenic disturbances in forests and impact all layers of forest vegetation (Zenner
and Berger, 2008). The removal of forest canopy markedly affects the microclimate of
the forest floor by altering levels of solar radiation, air and soil temperature, humidity,
wind, and rainfall (Aussenac, 2000). Changes in these factors typically result in
significant alterations to community structure and species importance with a shift to a
more heterogeneous distribution of species (Hughes and Fahey, 1991). Harvesting may
increase species diversity by removing the dominance of a few species or by increasing
environmental heterogeneity (Zenner and Berger, 2008). In Eastern forest ecosystems,
species diversity is typically the highest two to three years after harvesting operations
(Elliot and Knoepp, 2005). Elliot and Knoepp hypothesized this is due to low resource
competition and high resource availability.
9 A number of studies examine the response of ground layer vegetation to
prescribed burning (e.g., Elliot et al., 1999; Glitzenstein and Streng, 2003; Hutchinson et
al., 2005; Langdon, 1981; Nuzzo et al., 1996; Sparks et al.,1998) and silvicultural
activities such as overstory thinning (Elliot and Knoepp, 2005; Gilliam, 2002; Jenkins
and Parker, 1999; Zenner et al., 2006). However, few studies (Phillips et al., 2004;
Phillips et al., 2007; Zak, 2008) have examined the combined effects of these practices,
especially in upland pine-dominated forests such as the ones found in the BNF.
A summary of the findings from a number of studies that were carried out in the
Eastern US are presented in Table 1. The current study will fill some gaps in the
literature, such as the effect of thinning on overall cover, and graminoid cover, in
addition to the effect of thinning plus burning on richness (Table 1). Additionally, there
are few studies that examine the effect of thinning, burning, and their combination after
more than one or two growing seasons.
A combination of overstory reduction and burning causes an increase in overall
plant cover and the cover of the individual cover classes of vines, herbs, trees, and
graminoids one growing season after treatment in a shortleaf and loblolly pine
community in South Carolina (Phillips et al., 2004). The increase in light availability
appears to counteract the effects of any negative physical soil disturbance caused by
logging machinery (Phillips et al., 2004).
In the Bankhead National Forest, however, overall cover and vine cover decrease
after burning and thinning in the first season post-treatment (Zak, 2008). Forb cover and
graminoid cover show no change while overall richness increases (Zak, 2008).
10 Table 1. Change in vegetation attributes compared to control treatment according to different studies. ↑=increase, ↓=decrease,
0=no change, (#)=number of growing seasons after treatment
Vegetation attribute
Overstory reduction
Burn
Burn and overstory reduction
0 (1) Sparks et al., 1998
Overall cover
0 (1) Zak, 2008
0 (1) Phillips et al., 2004
↓ (1) Elliot et al., 1999
0 (1) Zak, 2008
↑ (1) Phillips et al., 2004
↑ (1) Phillips et al., 2004
↓ (1) Zak, 2008
0 (2) Elliot et al., 1999
Forb cover
11
↑ (1) Phillips et al., 2004
↑ (1) Phillips et al., 2004
0 (1) Zak, 2008
0 (1) Zak, 2008
0 (2-4) Harrington and Edwards, 1999
↑ (1-2) Elliot et al., 1999
0 (3) Phillips and Waldrop, 2007
0 (3) Phillips et al., 2007
0 (1) Zak, 2008
0 (3) Phillips et al., 2007
0 (4) Harrington and Edwards, 1999
0 (1) Zak, 2008
↑ (1-2) Harrington and Edwards, 1999
↑ (1) Phillips et al., 2004
↑ (1) Phillips et al., 2004
↑ (1) Zak, 2008
0 (1) Zak, 2008
↑ (1-2) Elliot et al., 1999
↑ (3) Phillips et al., 2007
↑ (1-2) Elliot et al., 1999
↑ (1) Phillips et al., 2004
0 (1) Zak, 2008
↓ (1) Zak, 2008
↓ (1-2) Phillips et al., 2004
0 (3-4) Harrington and Edwards, 1999
11 ↑ (3) Phillips et al., 2007
0 (3) Phillips et al., 2007
↑ (1) Phillips et al., 2004
Vine cover
0 (1) Zak, 2008
↓ (1) Sparks et al., 1998
0 (1-3) Harrington and Edwards, 1999
Graminoid cover
↑ (1) Phillips et al., 2004
Table 1(con). Change in vegetation attributes compared to control treatment according to different studies. ↑=increase,
↓=decrease, 0=no change, (#)=number of growing seasons after treatment
Vegetation attribute
Overstory reduction
Burn
0 (1) Zak, 2008
0 (1) Zak, 2008
0 (1-2) Frederickson et al., 1999
Diversity
Overstory reduction and burn
↑ (1) Sparks et al., 1998
0 (9) Kern et al., 2006
Elliot et al., 1999
0 (20) Gilliam, 2002
0 (1-4) Hutchinson et al., 2005
0 (39) Kern et al., 2006
0 (1) Zak, 2008
0 (1-2) Clinton and Vose, 2000
↑ (3) Clinton and Vose, 2000
12 0 (1) Zak, 2008
↑ (1) Sparks et al., 1998
Richness
0 (1) Zak, 2008
Elliot et al., 1999
0 (1-2) Frederickson et al., 1999
Greenburg, 2003
↑ (3) Phillips et al, 2007
Hutchinson et al., 2005
0 (9) Kern et al., 2006
↓ (2) Sparks et al., 1998
0 (29) Kern et al., 2006
↑ (3) Phillips et al., 2007
↑ (2-4) Hutchinson et al., 2005
0 (8) Greenburg, 2003
12 ↑ (1) Zak, 2008
↑ (3) Phillips et al., 2007
Plant diversity was found to be minimally impacted from thinning and burning
combination with no change observed after the first two growing seasons and a slight
increase after the third growing season (Clinton and Vose, 2000; Zak, 2008).
The response of ground layer vegetation after burning alone is more variable than
after thinning and burning combined (Table 1). Overall cover either increases (Phillips et
al., 2004), or decreases (Elliot et al., 1999), or does not change one and two growing
seasons after treatment (Sparks et al., 1998; Elliot et al., 1999; Zak, 2008) The reported
differences could be a result of variation in site-specific and forest type-specific
conditions, and therefore do not allow for simple generalizations. The response of
graminoids, however, is more consistent after burning, with an increase one and two
growing seasons after treatment (Elliot et al., 1999; Phillips et al., 2004; Zak, 2008),
though Sparks et al. (1998) found a decrease in graminiod cover. By the third season after
treatment there was no difference in the cover of trees, herbs, or graminoids (Phillips et
al., 2007). Diversity increased initially (Elliot et al., 1999, Sparks et al., 1998), or did not
change during any of the subsequent five growing seasons (Hutchinson et al., 2005; Zak,
2008) after prescribed burning. Burning also resulted in an increase in richness one
growing season after treatment (Elliot et al., 1999; Sparks et al., 1998; Hutchinson et al.,
2005), but in no change from the initial richness levels after eight growing seasons
(Greenburg, 2003). Evenness increased in the first through the fourth growing seasons
(Hutchinson et al., 2005). While the review of the studies above compares their results in
regards to fire, it is important to note that the differences in the results could be due to a
number of factors. They include variation in the season of fire, as indicated earlier in this
13 review, ecosystem characteristics, as well as duration, maximum temperature, intensity,
and many other fire attributes that are not always reported in the publications.
Another study in western North Carolina focusing only on the impact of fire on
ground layer vegetation showed that diversity, richness and non-woody species cover all
increased with burning in the first and second years after treatment (Elliot et al., 1999).
Interestingly, this effect was only observed on ridge locations. Areas along the mid-slope
actually saw decreases in diversity and richness and a loss of infrequently occurring
species (Elliot et al., 1999). This emphasizes the need to examine responses concurrent
with site-specific and fire-specific characterizations.
In a longleaf pine plantation and a loblolly/shortleaf pine community in South
Carolina, overstory reduction alone caused increases in vine cover one to two growing
seasons after treatment (Harrington and Edwards, 1999; Phillips et al., 2004). Phillips et
al. (2004) hypothesized that the slight increase or decrease of cover in thinned plots may
represent a time lag as cover responds to both light changes and soil disturbances from
logging machinery (Phillips et al., 2004). However, by the third season there was no
change in herb, tree, or vine cover in thinned plots (Phillips et al., 2007) compared to
untreated controls.
Species diversity and richness were not greatly affected by thinning in upland
hardwood forests of Pennsylvania and Alabama (Frederickson et al., 1999; Zak, 2008),
though one study in South Carolina did show an increase in species richness three
growing seasons after treatment (Phillips et al., 2007). Long-term impacts of harvesting
on ground layer diversity were examined by Gilliam (2002) and Kern et al. (2006).
Gilliam found that there was no significant difference in the soil variables and species
14 diversity in clearcut and mature stands 20 years after treatment. Kern et al. (2006) found
that there was no significant difference in diversity or richness 29 years after thinning
treatments, while Gilliam (2002) concluded that the length of time needed for return to
pre-treatment levels can be as short as 20 years.
The inconsistency of the results of the studies outlined above suggest that the
response of ground layer vegetation to burning and thinning is very site-specific and
forest type-specific, and thus does not allow for broad generalizations. Therefore it is
important to study the response of a wide variety of forest types to burning and overstory
reduction (Gilliam, 2002).
15 CHAPTER 2
MATERIALS AND METHODS
Study Site
The study area is located within the William B. Bankhead National Forest (BNF)
in northwestern Alabama (N 34°19’ W 87°21’). The BNF is geographically located on
the southern Cumberland Plateau and encompasses portions of Lawrence, Winston, and
Franklin counties. The BNF is a multiple use forest managed for timber, water, wildlife,
soils and recreation.
The forest areas treated in this study have been heavily impacted by both natural
and anthropogenic disturbances especially in the last century. In the 1970s agricultural
lands and upland hardwood forests were converted to loblolly pine plantations. Since
then the stands examined in this study have experienced few management activities
except for six stands that were part of prescribed burning activities in the past 20 years.
None were burned in the 10 years before the study was initiated (USDA FS, 2003).
The study stands are located in northern Winston and southern Lawrence
counties. The stands for treatment were selected according to the approved treatments to
achieve the desired future conditions described in the management plan of the National
Forest. All control stands are in the Sipsey wilderness area. Soils are composed of sandy
ultisols and sandy loams on limestone bedrock and are well drained and permeable Typic
Hapludults (Smalley, 1982). Ultisols are the most common soil type in southern forests
16 and can originate from limestone parent material. The main characteristic of ultisols is
heavy leaching of clay and nutrients (including calcareous material). The soil pH ranges
from 4.5 to 5.7 (Dillon, 2006). The mean annual temperature is 13o C. Mean annual
precipitation is 147 cm (USGS Station 02450250).
All study stands are on or along ridge lines and are composed of mixed pine and
hardwood species with planted loblolly pine (Pinus taeda) being the species with the
highest basal area. Other commonly occurring tree species identified during initial
vegetation surveys conducted by Zak in 2007 include red maple (Acer rubrum), pignut
hickory (Carya glabra), mockernut hickory (Carya tomentosa), flowering dogwood
(Cornus florida), common persimmon (Diospyros virginiana), American beech (Fagus
grandifolia), yellow poplar (Liriodendron tulipifera), blackgum (Nyssa sylvatica), bigleaf
magnolia (Magnolia macrophylla), sourwood (Oxydendrum aboreum), Virginia pine
(Pinus virginiana), black cherry (Prunus serotina), white oak (Quercus alba), scarlet oak
(Q. coccinea), chestnut oak (Q. montana), and black oak (Q. velutina). Common shrub
species include oak leaf hydrangea (Hydrangea quercifolia), Carolina buckthorn
(Rhamnus caroliniana), maple leaf viburnum (Viburnum acerifolium), and several
species of Vaccinium. The most common forbs include spotted wintergreen (Chimaphila
maculata) and partridge berry (Mitchella repens) and the most common graminoids are
needle grass (Stipa avenacea) and Boott’s sedge (Carex picta). The most common vines
are muscadine (Vitis rotundifolia), poison ivy (Rhus radicans) and greenbrier (Smilax
spp.).
17 BNF lands are part of the Mixed Mesophytic Forest Association (Braun, 1942). In
the study stands, pretreatment basal area ranged from 28 to 30 m2/ha. Loblolly pine
contributed an average of 87% of the total basal area (Schweitzer and Wang, In Press).
Experimental Design and Treatments
The experiment was designed as a randomized complete block design replicated
four times (Table 2). This design includes nine treatments consisting of three low
intensity dormant season burn regimes (unburned control, frequent burn applied once
every 3 to 5 years, and infrequent burn applied once every 8 to 10 years) and three
thinning regimes (heavy thin with a residual basal area of 11 m2/ha, light thin with a
residual basal area of 17 m2/ha, and an untreated control) intended to favor hardwoods,
and combinations of these burning and thinning levels. Each treatment was replicated
four times, in a block arrangement. A total of thirty-six stands were treated. The
experimental unit is defined as a stand. All stands are over 8 hectares in size. Initial
treatment implementation began in 2005 and concluded in 2008 (Table 3).
Thinning was conducted by commercial logging companies and hardwoods were
preferentially retained. A feller-buncher was used for thinning. After thinning, the light
thin stands were reduced to 12 m2/ha and the heavy thin stands were reduced to 16 m2/ha.
The burns were implemented using a combination of flanking, backing, and striphead fires with hand ignition. Mean fire temperature was 48°C (Clark and Schweitzer, in
press). Due to the timing of the experiment only two burning frequencies were included
in this study (unburned control and frequent 3 to 5 year burn.) Since sampling was carried
out in 2008 and 2009, third year post-treatment (2010) data from Block 4 was not
collected. Data from Block 1 was not included in analyses due to insufficient pretreatment data availability. The modified experiment design is shown in Table 4.
18 Table 2. Initial treatment design. All treatments were replicated four times.
Treatment number
Treatment description
1
control
2
infrequent burn, no thin 1
3
frequent burn, no thin 2
4
no burn, heavy thin 3
5
no burn, light thin 4
6
frequent burn, heavy thin
7
frequent burn, light thin
8
infrequent burn, heavy thin
9
infrequent burn, light thin
1
Infrequent burn = Burn every 8-10 years
2
Frequent burn = Burn every 3-5 years
3
Heavy thin = Reduce basal area to 11 m2/ha
4
Light thin = Reduce basal area to 17 m2/ha
Table 3. Dates when treatments were implemented.
Block Thin
Burn
1
Aug – Sept 2005
Feb – Mar 2006
2
Apr – Sep 2006
Feb – Mar 2007
3
Apr – Sep 2006
Feb – Mar 2007
4
May – Sep 2007
Feb – Mar 2008
19 Table 4. Modified treatment design and number of sampled replications two and three
growing seasons after treatment.
Treatment
Treatment description
number
Replications 2 years
Replications 3 years
after treatment
after treatment
1
control
3
2
2
burn, no thin
3
2
3
no burn, heavy thin1
3
2
4
no burn, light thin2
3
2
5
burn, heavy thin
4
2
6
burn, light thin
4
2
1
Heavy thin = Reduce basal area to 11m2/ha
2
Light thin = Reduce basal area to 17 m2/ha
20 Sampling Methods
Five permanently marked vegetation plots were sampled in each stand. Each plot
measures 0.08 ha and is marked with rebar at the plot center. Plots were established in
2005 and 2006 by Dr. Callie Schweitzer’s team (USDA Forest Service Southern
Research Station, PO Box 1568, Normal, AL 35762).
Sampling within each plot followed sampling procedures initially used by Zak
(2008). The sampling area per plot was decreased from the 105 m2 measured
pretreatment to 80 m2 following Zak’s findings that 70m2 is sufficient to capture 90% of
species in an average stand (Zak, 2008).
I quantified the percent foliar cover for all vascular plants occurring below 1.4 m
over an area of 16 m2 systematically located within the vegetation plots. Within each plot,
one 1.0 m2 subplot was located at 3.0 m and three 1.0 m2 subplots were located at 15.0 m
from plot center in each cardinal direction. I located the inner subplots north, east, south,
and west from plot center and arranged them with the lower left, upper left, upper right,
and lower right corners, respectively, laying over the point that was 3.0 m from the plot
center (Figure 1). For the outer subplots, I divided a 4.0 m2 square area whose center laid
over a point 15.0 m from the plot center into four equal squares. I established a subplot in
three of those squares, excluding the lower left, upper left, upper right and lower right 1
m2 square plot from the 4 m2 plots located to the north, east, south, and west of plot
center, respectively (Figure 1).
For every vascular plant present in the subplot I recorded foliar cover regardless
of whether or not it was rooted in the subplot. Ground cover variables such as pine and
broadleaf litter, down woody debris (where the diameter at the widest part is over 2.5
21 cm), tree bole, mineral soil, nonvascular plants, and old skid trails were given a cover
estimate after foliar cover was estimated. The cover of each species and ground variable
was estimated to the nearest 1cm2 per quadrat. Then the cover estimates for each quadrat
in a plot were added and the overall percent cover of each species and ground variable for
the plot was determined. Species that occupied a space less than 1cm2 in size were
recorded only as present species for richness and diversity measures.
All species were grouped according to three life form groups: forbs, graminoids
and vines. This classification system is consistent with recent publications on ground
layer vegetation (Elliot et al., 1999; Jones et al., 2009). To aid in calculations of species
indices estimates, all plants were identified to species whenever possible. Specific
nomenclature follows Radford et al. (1968).
Second growing season post-treatment sampling occurred from May through June
2008 for Blocks 2 and 3 and from August through September of 2009 for Block 4 (Table
5.) Third growing season post-treatment sampling occurred from May through July of
2009 for Blocks 2 and 3. Analysis of early-spring vernal species was not available due to
time constraints and lack of pre-treatment data. These species show varying response to
disturbance and future monitoring is recommended.
Data Analysis
For each variable (overall cover, richness, diversity; cover and richness of forbs,
graminoids, and vines) the pre-treatment value was subtracted from the post-treatment
value and the difference was used as the dependent variable in each model. Differences
among the treatments in mean cover change from pre-treatment to post-treatment were
22 3 m2 Treatment Stand ( > 9 ha) Sample square area Plot Center (PC)
1 m2 0.08 ha vegetation plots
3.0m
15.0m
0.08 ha vegetation plot Distances to PC from sample square area
Figure 1. Schematic drawing of a treatment stand with five 0.08 ha plots (left) and of the
0.08 ha vegetation plots with sample square layout, area, and distance from the plot
center (right).
23 Table 5. Dates of ground layer vegetation sampling.
Block
Pre-treatment
First year post-
Second year post-
Third year post-
treatment
treatment
treatment
August 2006
July 2007
July 2008
1
June 2005
2
April – June 2006 June – July 2007
May – June 2008
May-July 2009
3
April – June 2006 June – July 2007
May – June 2008
May-July 2009
4
June – July 2006
August-September 2009
July – August 2008
analyzed using a mixed model in SAS version 9.1. This model was utilized to account for
random effects of the plots within each of six treatments and generalized least squares
estimation was used to account for the hierarchical structure of the data. Block was a
random effect in the model and treatment was used as a fixed effect. Tukey’s adjustment
was used for multiple comparisons of significant least-square mean differences.
Diversity was calculated using the Shannon index (Magurran, 1988). This index
s
was calculated using the formula H = −∑ pi ln pi where s is the number of species in the
j =1
sample and pi is the proportion of all individuals in sample that belongs to the ith species. The Shannon index indicates the level of uncertainty associated with predicting the
species of an individual selected at random from a given community. The Shannon index
ranges from zero, where there is no diversity, to approximate five in the most diverse
communities (Magurran, 1988).
24 The Bray-Curtis similarity coefficients (Magurran, 1988) were calculated by
treatment type for both the second and third growing seasons post-treatment. Similarity
analyses were performed as described in Krebs (1999).
Percent cover data for all vine, forb, and graminoid species was analyzed using
indicator species analysis through PC-ORD version 5.0. Indicator species analysis
(Dufrene and Legendre, 1997) calculates indicator values for each species. The analysis
was performed once for each post-treatment season using two groups of stands classified
by burning (no burn, burn) and once for each post-treatment season using three groups of
stands classified by thinning (no thin, heavy thin, light thin). This analysis method places
equal emphasis on fidelity (restriction to plots of a particular group) and constancy
(frequency of occurrence in plots of that group). A species with a high indicator value
will have high fidelity to a particular group and high constancy in that group (Jeffries et
al., 2010). Species that had an indicator value more than 15 points higher for one group
than the others and a p-value ≤0.05 after a Monte Carlo procedure based on 1000 random
assignments were considered to be good indicator species.
25 CHAPTER 3
RESULTS AND DISCUSSION
Results
Response after two growing seasons
In the twenty stands sampled in the second growing season post-treatment, there
were forty-seven woody species in the ground layer. I also found seventy-five non-woody
ground layer species. They consisted of forty-one forb species, fifteen graminoid species,
and nineteen vine species.
The vines Vitis rotundifolia, Smilax rotundifolia, Rhus radicans, and Smilax
glauca, along with the graminoid, Carex picta, occurred in every treatment stand. V.
rotundifolia had an average cover of 7.93%, which was the highest of all ground layer
species (Table 6).After C. picta, Dichanthelium boscii and Stipa avenacea were the most
frequently occurring graminiods and were both found in 90% of the stands with an
average cover of 3.35% and 3.26% respectively.
Forbs were less common overall. The most frequently occurring forbs were
Chamaecrista fasciculata, Solidago arguta, and Lespedeza repens, all of which occurred
in 55% of the stands and had an average cover of 0.31%, 0.11%, and 0.02% respectively.
Hypericum hypercoides and Lobelia siphilitica were both found in 50% of the stands.
When comparing pre-treatment vegetation cover with the cover two growing seasons
after treatment, analyzed using a mixed model, I found that control stands (no treatment)
26 Table 6. Average cover and frequency per stand for the five most frequently occurring species of
each life form for the second growing season post-treatment.
Life Form
Scientific Name
Common Name
Frequency
(%)
Cover
(%)
Chamaecrista fasciculata
Partridge pea
55
0.31
Solidago arguta
Atlantic goldenrod
55
0.11
Lespedeza repens
Creeping lespedeza
55
0.02
Hypericum hypercoides
St. Andrew’s cross
50
0.09
Lobelia siphilitica
Great blue lobelia
50
0.03
Carex picta
Boott’s sedge
100
0.95
Dichanthelium commutatum
Variable panic grass
90
3.35
Stipa avenacea
Needle grass
90
3.26
Dichanthelium boscii
Bosc’s panic grass
85
1.52
Dichanthelium dichotomum
Cypress panic grass
85
1.42
Vitis rotundifolia
Muscadine
100
7.93
Smilax rotundifolia
Roundleaf greenbrier
100
1.54
Rhus radicans
Poison ivy
100
0.95
Smilax glauca
Cat greenbrier
100
0.57
Rubus argutus
Southern blackberry
95
0.84
Forb
Graminiod
Vine
27 and stands that were burned alone displayed no significant change in overall cover or the
cover of forbs, graminoids, and vines (Table 7). Stands that were treated with the heavy
thin alone, burn and heavy thin, and burn and light thin all experienced increases in
overall cover, forb cover, graminoid cover, and vine cover compared to pre-treatment.
Interestingly, the light thin alone did not result in differences compared to pre-treatment
in any category except graminoid cover.
Stands that were treated with the heavy thin alone showed increases, compared to
the control stands, in the change in overall cover, graminoid cover, and vine cover, but
stands that were lightly thinned alone did not show differences from control in any of
these categories (Table 7). Neither the light thin alone nor the heavy thin alone resulted in
a change in forb cover compared to the control. The two combination treatments (burn
and light thin, burn and heavy thin) showed increases from the control stands in overall
cover and graminoid cover, but not vine cover. Forb cover change was different from the
control stands for the burn and heavy thin but not in the burn and light thin.
There was a change in overall species richness from pre-treatment in all
treatments except the light thin alone and the burn and light thin (Table 7). Overall
richness decreased in the control (-4.47 species) and burn alone stands (-7.73 species),
but increased in the heavy thin alone (3.53 species) and burn and heavy thin stands (3.50
species).
There was a change from pre-treatment in forb richness only in the burn and
heavy thin stands where there was an increase of 2.63 species (Table 7). Post-treatment
graminiod richness increased in all treatments except the control and burn alone, where it
remained unchanged. Post-treatment change in graminiod richness was lower in the
28 Table 7. Marginal mean estimates of the change of dependent variables from pre-treatment to the second growing season posttreatment. Tukey-Kramer adjustment for multiple comparisons of significant treatment effects (α ≤ 0.05). Means in the same
row with same letter are not different. A * symbol indicates that the mean estimate is significantly different from zero.
29 Control
Burn Alone
Heavy Thin
Alone
Light Thin
Alone
Burn + Heavy
Thin
Burn + Light
Thin
Cover%
-4.13 ± 3.97a
-1.59 ± 3.97a
24.57 ± 3.97b*
5.27 ± 4.12a
27.53 ± 3.44b*
29.99 ± 3.44b*
Forb Cover%
0.10 ± 0.60a
-0.28 ± 0.60a
1.66 ± 0.60ab*
-0.19 ± 0.62a
3.34 ± 0.52b*
1.29 ± 0.52ab*
Gram Cover%
0.21 ± 2.02a
0.38 ± 2.02a
13.82 ± 2.02b*
4.28 ± 2.09a*
21.42 ± 1.75b*
21.19 ± 1.75b*
Vine Cover%
-1.27 ± 1.75a
0.12 ± 1.75a
8.25 ± 1.75b*
3.36 ± 1.81ab
3.99 ± 1.52ab*
3.58a ± 1.52b*
Richness (S’)
-4.47 ± 1.47ab*
-7.73 ± 1.47a*
3.53 ± 1.47c*
-1.29 ± 1.52bc
3.50 ± 1.27c*
1.75 ± 1.27c
Forb Rich (SF’)
-1.03 ± 1.19ab
-2.10 ± 1.19a
1.59 ± 1.19ab
-2.05 ± 1.23ab
2.63 ± 1.09b*
2.04 ± 1.09ab
Gram Rich(SG’)
-0.98 ± 0.84a
-0.53 ± 0.84a
3.92 ± 0.84b*
3.59 ± 0.89b*
2.20 ± 0.77ab*
3.31 ± 0.77b*
Vine Rich(SV’)
-0.33 ± 0.41a
-0.67 ± 0.41a
0.27 ± 0.41a
0.50 ± 0.43a
0.65 ± 0.36a
-0.25 ± 0.36a
Diversity (H’)
-0.06 ± 0.08a
-0.09 ± 0.08a
0.27 ± 0.08bc*
0.03 ± 0.08ab
0.48 ± 0.07c*
0.12 ± 0.07ab
29 control stands (-0.98 species) than it was in the stands subjected to the heavy thin alone.
(3.92 species), light thin alone (3.59 species) and burn and light thin (3.31 species). Vine
richness showed no change from pre-treatment numbers and from the control for any of
the treatments.
Two growing seasons after the treatments, overall ground layer diversity did not
change in four of the treatments, but increased in the other two: in the heavy thin alone
(0.27) and in the burn and heavy thin (0.48; Table 7). For both of these treatments the
change in diversity was greater than in the control stands.
There was an interaction between burning and thinning (Figure 2) for overall
cover (p<0.01) and graminoid cover (p<0.01). However, there was no interaction
observed in the models for any other type of vegetation cover, richness, and diversity
(Figure 2, Figure 3).
As could be expected from the results listed earlier, the Bray-Curtis index of
similarity showed that stands that were heavily thinned only and stands that were burned
and thinned showed the most similarities (Table 8). Stands that were burned alone,
heavily thinned and burned, and thinned alone were the least similar. Burned stands were
the most similar to control stands, while control stands were the most similar to burned
only stands and stands that were lightly thinned and burned.
The change in ground cover variables displayed few differences among treatments
(Table 9). Bare soil cover decreased 3.28% from pre-treatment levels in burn and heavy
thin stands. This could be related to the increases in vegetation cover in those stands. The
changes in cover of down woody debris, non-vascular plants and fungi, rocks, and stumps
were not different among the six treatment types. The cover of down woody debris
30 Figure 2. Burn and thin treatment interaction on the mean difference in overall cover
(p<0.01), forb cover (p=0.16), graminoid cover (p<0.01), and vine cover (p=0.21) in the
second season post-treatment.
31 Figure 3. Burn and thin treatment interaction on the mean difference in overall richness
(p=0.10), forb richness (p=0.10), graminoid richness (p=0.41), and vine richness
(p=0.35), and overall diversity (p=0.30) in the second season post-treatment.
32 Table 8. Bray-Curtis indices of similarity for ground layer vegetation communities for the six treatment types in the second
season post-treatment. Greater value indicates greater similarity.
Treatment
Control
Burn Alone
Burn
Heavy
Light
Burn and
Burn and
Alone
Thin Alone
Thin Alone
Heavy Thin
Light Thin
0.54
0.49
0.55
0.38
0.41
1.00
0.26
0.31
0.24
0.26
1.00
0.69
0.72
0.74
1.00
0.50
0.59
1.00
0.74
Control
1.00
Heavy Thin Alone
33 Light Thin Alone
Burn and Heavy Thin
Burn and Light Thin
1.00
33 Table 9. Marginal mean estimates of the change in the percent cover of ground variables
from pre-treatment to the second growing season post-treatment across 20 treatment
stands. Tukey-Kramer adjustment for multiple comparisons of significant treatment
effects (α ≤ 0.05). Means in the same row with same letter are not different. A * symbol
indicates that the mean estimate is significantly different from zero.
Control
Burn
Alone
Heavy
Thin
Alone
Light
Thin
Alone
Burn+
Heavy
Thin
Burn+
Light
Thin
Bare Soil
0.06 b
-0.79ab
0.14b
-0.27ab
-3.28a*
-0.65ab
Down Woody Debris
0.07a
0.21a
2.06a*
0.07a
0.43a
1.42a*
Non-Vascular Plants/Fungi
0.13a*
0.01a
-0.12a
-0.13a
0.00a
0.07a
Rock
0.06a
0.01a
0.01a
0.00a
0.00a
0.01a
Stump
-0.02a
0.00a
0.48a*
0.15a
0.42a*
0.28a*
34 increased in the heavy thin (2.06%) and in the burn and light thin (1.42%), but remained
the same in the other treatments. The cover of non-vascular plants and fungi increased in
the control stands by 0.13%, but did not change under any treatment. The rock cover
remained at pre-treatment levels for all treatments, while the cover of tree stems or
stumps increased after heavy thin alone (0.48%), burn and heavy thin (0.42%), and burn
and light thin (0.28%).
The five species of each life form with the highest average second season posttreatment percent cover were evaluated to examine the ways in which individual species
respond to the treatments (Table 10). C. fasciculata and D. rotundifolium were the only
forbs that showed differences among the treatment types in cover change from pretreatment to post-treatment. In both cases the cover changes in the burn and heavy thin
stands were greater (C. fasciculata, 1.07%; D. rotundifolium, 0.85%) than in the control,
burn alone, light thin alone, or heavy thin alone stands.
The five graminoids with the greatest average percent cover all had greater
change in cover in the burn and heavy thin stands than the control or burn alone stands.
D. boscii, D. commutatum, and S. avenacea also had greater change in cover in the burn
and light thin stands than the control or burn alone stands. S. avenacea had the greatest
increase in cover within a treatment type with an increase of 8.01% in the burn and light
thin stands.
35 Table 10. Marginal mean estimates of the change in cover from pre-treatment to the second growing season post-treatment for
the five species of each life form with the highest average post-treatment cover across 20 treatment stands. Tukey-Kramer
adjustment for multiple comparisons of significant treatment effects (α ≤ 0.05). Means in the same row with same letter are not
different. A * symbol indicates that the mean estimate is significantly different from zero.
Life Form
Scientific Name
Control
Burn Alone
Heavy Thin
Alone
Light Thin
Alone
Burn +
Heavy Thin
Burn +
Light Thin
Chamaecrista fasciculata
Erechtites hieraciifolia
Mitchella repens
Desmodium rotundifolium
Solidago arguta
0.00a
0.00a
0.00a
0.01a
-0.01a
0.00a
0.00a
0.00a
-0.03a
-0.05a
0.35a*
0.84a*
-0.03a
0.08a
0.13a*
0.02a
0.38a
-0.31a
0.01a
0.05a
1.07b*
0.04a
-0.23a
0.85b*
0.08a
0.24a
0.16a
0.00a
0.38ab*
0.08a
Chasmanthium sessiliflorum
Dichanthelium boscii
Dichanthelium commutatum
Dichanthelium dichotomum
Stipa avenacea
0.00a
0.04a
0.08a
0.05a
0.18a
-0.06a
0.05a
0.14a
0.00a
0.18a
1.39ab*
0.91ab
5.65b*
1.73ab*
2.66ab*
0.36a
0.60ab
0.94a
0.75a
1.21ab
3.32b*
4.14b*
5.52b*
3.51b*
3.80b*
0.44a
3.84b*
5.83b*
1.54ab*
8.01c*
Rhus radicans
Rubus argutus
Smilax glauca
Smilax rotundifolia
Vitis rotundifolia
0.12a
0.00a
-0.13a
-0.80a
-0.45a
0.05a
-0.02a
0.38a
-0.89a
0.56ab
-0.03a
1.16ab*
0.29a
0.31a
5.61b*
-0.44a
0.69ab
0.08a
-0.59a
2.55ab
-1.56a*
2.26b*
-0.47a
1.01a
3.08ab*
-1.22a*
0.41ab
0.07a
-0.38a
3.96ab*
Forb
36 Graminoid
Vine
36 The vine, R. argutus, had greater changes in cover in the burn and heavy thin
(2.26%) treatment than in the control (0.00%) or burn alone (-0.02%) treatments. The
change in cover for V. rotundifolia was greater in the heavy thin alone stand (5.61%) than
it was in the control stand (-0.45%).
In the second post-treatment season the indicator species analysis, where the
groups were burned and unburned stands, identified five species for the burned stands
(Table 11). The graminoids identified were C. picta and D. boscii. Forbs included H.
hypericoides and Viola sp. The only vine indicator species was P. quinquefolia.
In an indicator species analysis where the grouping was by level of thinning (no
thin, heavy thin, light thin), eight species indicated a heavy thin (Table 12). Of these three
were forbs (Antennaria plantaginifolia, Lespedeza cuneata, and L. repens,) four were
graminoids (Chasmanthium sessiliflorum, D. commutatum, D. dichotomum, and Panicum
anceps,) and one was a vine (Rubus argutus.) These are all early-successional, lightdependent species. The vines Bignonia capreolata and Gelsemium sempervirens along
with the forb Chimaphila maculate were indicators of the no thin. These species are
typically found in forested ecosystems. The only light thin indicator was the graminoid
Danthonia sericea.
Response after three growing seasons
In the third post-treatment growing season sampling of the ground layer
vegetation I observed 45 woody species and sixty-seven non-woody species over twelve
treatment stands. Thirty forb species, seventeen vine species, and fourteen graminoid
species were recorded.
37 Table 11. Indicator values for indicator species identified in a comparison of unburned and burned stands in the second season
post-treatment. Bold indicator values assign the indicator species to either burned or unburned stands. P-values in the last
column show robustness of the given species as an indicator using the Monte Carlo test of significance.
Species
Common Name
Life Form
Burn Indicator
Indicator Value
Value
p-value
Carex picta
Boott’s sedge
graminoid
18
82
0.02
Dichanthelium boscii
Bosc’s panic grass
graminoid
12
77
0.03
Hypericum hypericoides
St Andrew’s cross
forb
5
58
0.05
vine
8
63
0.03
forb
0
55
0.02
38 Parthenocissus quinquefolia Virginia Creeper
Viola sp.
Violet
38 No Burn
Table 12. Indicator values for indicator species identified in a comparison of no thin, heavy thin and light thin stands in the
second season post-treatment. Bold indicator values assign the indicator species to either unthined, heavily thinned, or lightly
thinned stands. P values in the last column show robustness of the given species as an indicator using the Monte Carlo test of
significance.
Species
Common Name
Life Form
Heavy Thin
Light Thin
indicator
indicator
indicator
value
value
value
p-value
39 Antennaria plantaginifolia
Pussytoes
forb
0
63
2
0.01
Bignonia capreolata
Crossvine
vine
46
0
1
0.03
Chasmanthium sessiliflorum
Longleaf woodoats
graminoid
0
73
13
0.02
Chimaphila maculata
Pipsissewa
forb
48
1
0
0.05
Danthonia sericea
Downy danthonia
graminoid
0
1
65
0.01
Dicanthelium commutatum
Variable panic grass
graminoid
1
59
39
0.02
Dichanthelium dichotomum
Cypress panic grass
graminoid
0
69
31
0.05
Gelsemium sempervirens
Yellow jassamine
vine
66
10
1
0.04
Lespedeza cuneata
Chinese lespedeza
forb
0
57
0
0.02
Lespedeza repens
Creeping lespedeza
forb
1
70
8
0.02
Panicum anceps
Beaked panic grass
graminoid
0
46
3
0.05
Rubus argutus
Southern blackberry
vine
2
73
25
0.01
39 No Thin
The most common species in the third growing season post-treatment were
similar to the most common species in the second season post-treatment (Table 6). The
most frequently occurring species overall were again, V. rotundifolia, S. rotundifolia, R.
radicans, and C. picta. They occurred in 100% of the stands (Table 13). V. rotundifolia
had the highest average percent cover at 8.33 percent.
After C. picta, S. avenacea and D. boscii were the most frequently occurring
graminiods and were found in 92% of the stands with an average cover of 2.06% and
1.00% respectively.
Forbs were again much less common overall. The most frequently occurring forbs
were S. arguta and C. fasciculata which both occurred in 58% of stands and had an
average percent cover of 0.08% and 0.05% respectively. Polystichum acrostichoides,
Desmodium rotundifolium, and Euphorbia corollata were found in 50% of stands and
had average covers of 0.07%, 0.04% and 0.03% respectively.
Cover, richness and diversity measurements in the third season post-treatment
(Table 14) were similar to the second season post-treatment. The only changes were that
change in diversity for the heavy thin alone treatment (0.28) was no longer different than
the change in the control stand (-0.10) and the change in forb cover in the burn and heavy
thin (0.68%) was no longer different than the change in the control (-0.06%).
There were burn by thin interactions for overall cover (p<0.01), graminoid cover
(p<0.01), and overall richness (p=0.02; Figure 4, Figure 5). The burn by thin interaction
was not a significant effect for the overall richness two growing seasons after the
treatment (Figure 3), but was an effect three growing seasons after treatment.
40 Table 13. Average cover and frequency per stand for the five most frequently occurring
species of each life form for the third growing season post-treatment.
Life Form
Scientific Name
Common Name
Frequency
(%)
Cover
(%)
Solidago arguta
Atlantic goldenrod
58
0.08
Chamaecrista fasciculata
Partridge pea
58
0.05
Polystichum acrostichoides
Christmas fern
50
0.07
Desmodium rotundifolium
Prostrate tick trefoil
50
0.04
Euphorbia corollata
Flowering spurge
50
0.03
Carex picta
Boott’s sedge
100
0.60
Stipa avenacea
Needle grass
92
2.06
Dichanthelium boscii
Bosc’s panic grass
92
1.00
Dichanthelium commutatum
Variable panic grass
83
1.64
Dichanthelium dichotomum
Cypress panic grass
83
0.31
Vitis rotundifolia
Muscadine
100
8.33
Smilax rotundifolia
Roundleaf greenbrier
100
2.02
Rhus radicans
Poison ivy
100
0.95
Rubus argutus
Southern blackberry
92
0.85
Berchemia scandens
Alabama supple jack
92
0.38
Forb
Graminiod
Vine
41 Table 14. Marginal mean estimates of the change of dependent variables in the third growing season following treatment.
Tukey-Kramer adjustment for multiple comparisons of significant treatment effects (α ≤ 0.05). Means in the same row with
same letter are not different. A * symbol indicates that the mean estimate is significantly different from zero.
42 Control
Burn Alone
Heavy Thin
Alone
Light Thin
Alone
Burn+ Heavy
Thin
Burn+ Light
Thin
Cover%
-5.95 ± 4.05a
-2.89 ±4.05 a
27.69 ± 4.05b*
1.65 ± 4.05a
19.56 ± 4.05b*
25.34 ± 4.05b*
Forb Cover%
-0.06 ± 0.29a
-0.30 ± 0.29a
0.37 ± 0.29a
-0.09 ± 0.29a
0.68 ±0.29 a*
0.73 ± 0.29a*
Gram Cover%
-0.32 ± 2.21a
0.18 ±2.21 a
10.53 ± 2.21bc*
2.59 ± 2.21ab
11.50 ± 2.21bc*
18.99 ± 2.21c*
Vine Cover%
-2.12 ± 2.12a
0.20 ± 2.12a
10.93 ± 2.12b*
3.02 ± 2.12ab
6.23 ± 2.12ab*
5.26 ± 2.12ab*
Richness (S’)
-4.80 ± 1.36ab*
-7.60 ± 1.36a*
7.30 ± 1.36d*
0.00 ± 1.36bc
5.50 ± 1.36cd*
4.60 ± 1.36cd*
Forb Rich (SF’)
-1.02 ± 0.81ab
-1.89 ±0.81 a*
1.53 ± 0.81b
-0.98 ± 0.81ab
0.67 ± 0.81ab
0.96 ± 0.81ab
Gram Rich(SG’)
-0.78 ± 1.00a
-0.21 ± 1.00ab
4.52 ± 1.00c*
3.75 ± 1.00bc*
3.08 ± 1.00abc*
5.28 ± 1.00c*
Vine Rich(SV’)
-0.61 ± 0.86a
-0.01 ± 0.86a
1.71 ± 0.86a*
-0.49 ± 0.86a
1.54 ± 0.86a
0.81 ±0.86 a
Diversity (H’)
-0.10 ± 0.11ab
-0.19 ±0.11 a
0.28 ± 0.11bc*
0.09 ± 0.11abc
0.43 ± 0.11c*
0.13 ± 0.11abc
42 Figure 4. Burn and thin treatment interaction on the mean change in (clockwise from
upper left) overall cover (p<0.01), forb cover (p=0.21), graminoid cover (p<0.01), and
vine cover (p=0.17) in the third season post-treatment.
43 Figure 5. Burn and thin treatment interaction on the mean change in (clockwise from
upper left) overall richness (p=0.02), forb richness (p=0.15), graminoid richness
(p=0.35), vine richness (p=0.70) and overall diversity (p=0.53) in the third season posttreatment.
44 There were no interactions between year and either treatment type on the overall
cover or the cover of vines in the second and third seasons post-treatment. There were
year by thin interactions for both forbs (p<0.01) and graminoids (p=0.05).
The Bray-Curtis index coefficients of similarity in the third growing season posttreatment show that heavy thin alone stands were the most similar to stands that received
the combination treatments (Table 15). The stands that were burned alone were the most
similar to the control stands, and vice versa, but most dissimilar with the heavy and light
thins alone, as well as the combination treatments.
The only ground variable with differences among the treatment types was nonvascular plants/fungi (Table 16). The cover change of this variable was lower in the
heavy thin alone stands (-0.26%) than in the control stands (0.22%).
The five species of each life form with the highest average third season posttreatment percent cover (Table 17) showed some differences from the second season
post-treatment (Table 9). Among the forbs, the change in cover of C. fasciculata once
again showed differences among the treatment types with change in cover in the heavy
thin alone stands (0.18%) being higher than in the control (0.00%) or burn alone stands
(0.00%). The cover change of H. hypercoides was higher in the heavy thin alone stands
(0.21%) than in the light thin alone stands (-0.09%).
Differences in cover change among the treatment types for graminoids were
reduced in the third season post-treatment. D. commutatum was the only graminoid
species to show a greater change in cover in the burn and heavy thin stands (4.64%) than
in the control (0.07%), burn alone (0.09%), or light thin alone (0.39%) stands. The
change in cover of S. avenacea was higher in the burn and light thin stands (6.63%) than.
45 Table 15. Bray-Curtis indices of similarity for ground layer vegetation communities for the six treatment types in the third
season post-treatment. Greater value indicates greater similarity.
Treatment
Control
Burn Alone
Heavy Thin Alone
46
Burn
Heavy
Light
Burn and
Burn and
Alone
Thin Alone
Thin Alone
Heavy Thin
Light Thin
0.58
0.42
0.50
0.43
0.48
1.00
0.25
0.28
0.23
0.27
1.00
0.65
0.80
0.72
1.00
0.63
0.57
1.00
0.80
Control
1.00
Light Thin Alone
Burn and Heavy Thin
Burn and Light Thin
1.00
46 Table 16. Marginal mean estimates of the change in the percent cover of ground variables
from pre-treatment to the third growing season post-treatment across 12 treatment stands.
Tukey-Kramer adjustment for multiple comparisons of significant treatment effects (α =
0.05). Means in the same row with same letter are not different. A * symbol indicates that
the mean estimate is significantly different from zero.
Control
Burn
Alone
Heavy
Thin
Alone
Light
Thin
Alone
Burn+
Heavy
Thin
Burn+
Light
Thin
Bare Soil
-0.01a
0.05a
0.11a
0.00a
-0.04a
0.69a*
Down Woody
Debris
Non-Vascular
Plants/Fungi
-0.81a
0.54a
1.18a
0.99a
1.49a
1.75a
0.22a*
-0.22ab*
-0.26b*
-0.17ab
-0.05ab
0.01ab
Rock
0.01a
0.00a
-0.02a
0.00a
-0.02a
0.00a
Stump
-0.03a
0.00a
0.43a*
0.03a
0.44a*
0.47a*
47 Table 17. Marginal mean estimates of the change in cover from pre-treatment to the third growing season post-treatment for
the five species of each life form with the highest average post-treatment cover across 12 treatment stands. Tukey-Kramer
adjustment for multiple comparisons of significant treatment effects (α = 0.05). Means in the same row with same letter are not
different. A * symbol indicates that the mean estimate is significantly different from zero.
Life Form
Scientific Name
Control
Burn Alone
Heavy Thin
Alone
Light Thin
Alone
Burn +
Heavy Thin
Burn +
Light Thin
Chamaecrista fasciculata
Erechtites hieraciifolia
Hypericum hypericoides
Polystichum acrostichoides
Solidago arguta
0.00a
0.00a
0.00ab
0.00a
-0.01a
0.00a
0.00a
0.00ab
0.00a
-0.03a
0.18b*
0.11a
0.21b*
-0.12a
0.08a
0.03ab
0.00a
-0.09a
-0.26a
0.03a
0.05ab
0.31a*
0.11ab
-0.04a
0.11a
0.06ab
0.00a
0.14ab
-0.31a*
0.15a
Carex picta
Chasmanthium sessiliflorum
Dichanthelium boscii
Dichanthelium commutatum
Stipa avenacea
0.08a
0.00a
0.00a
0.07a
-0.07a
0.24a
0.05a
0.04a
0.09a
-0.04a
1.44b*
2.00a*
1.43ab*
2.69ab*
0.18a
0.27a
0.04a
0.29a
0.39a
0.76a
0.73ab*
0.44a
1.76ab*
4.64b*
2.94ab*
0.74ab*
0.72a
2.40b*
1.74ab*
6.63b*
Berchemia scandens
Rhus radicans
Rubus argutus
Smilax rotundifolia
Vitis rotundifolia
-0.10a
-0.13a
-0.08a
0.64b
-2.10a
-0.01a
0.10a
-0.03a
-1.43a*
1.16ab
-0.40a*
0.33a
2.01b*
0.60ab
8.24b*
-0.09a
-0.18a
0.67ab
0.28ab
0.72ab
0.02a
-1.05a*
2.03b*
-0.13ab
5.13ab*
-0.08a
-0.11a
0.14a
-0.12ab
5.79ab*
Forb
48
Graminoid
Vine
48 in the control (-0.07%), burn alone (-0.04%), heavy thin alone (0.18%), or light thin alone
(0.76%) stands. However, the change in S. avenacea cover in the burn and light thin was
not significantly different from the change in cover in the burn and heavy thin treatment
The vine R. argutus had greater changes in cover in the heavy thin alone (2.01%)
and burn and heavy thin (2.03%) treatments than in the control (-0.08%), burn alone
(-0.03%), or burn and light thin (0.14%) treatments. The change in cover for V.
rotundifolia was greater in the heavy thin alone stand (8.24%) than it was in the control
stand (-2.10%).
The only vines to show a decrease in cover due to treatment implementation were
S. rotundifolia which decreased 1.43% in the burn alone stands, R. radicans, which
decreased 1.05% in the burn and heavy thin stands, and B. scadens, which decreased
0.40% on the heavy thin alone stands.
In the third season post-treatment the indicator species analysis identified eight
species for the heavy thin but identified no species for the burn or no burn stands (Table
18). Of the eight species identified for the heavy thin two were vines (B. scandens, R.
argutus), three were forbs (E. hieraciifolia, H. hypercoides, C. fasciculata), and three
were graminoids (C. picta, C. sessiliflorum, D. commutatum).
49 Table 18. Indicator values for indicator species identified in a comparison of stands treated with the no thin, heavy thin, and
light thin in the third season post-treatment. Bold indicator values assign the indicator species to either the no thin, heavy thing,
or light thin stands. P-values in the last column show robustness of the given species as an indicator using the Monte Carlo test
of significance.
Species
Common Name
Life Form
Heavy Thin
Light Thin
indicator
indicator
indicator
value
value
value
p-value
50 Berchemia scandens
Alabama supple jack
vine
7
63
27
0.03
Carex picta
Boott’s sedge
graminoid
11
61
28
0.03
Chasmanthium sessiliflorum
Longleaf woodoats
graminoid
1
70
21
0.05
Dicanthelium commutatum
Variable panic grass
graminoid
1
70
28
0.02
Erechtites hieraciifolia
American burnweed
forb
0
75
0
0.05
Hypericum hypericoides
St Andrew’s cross
forb
0
70
7
0.02
Chamaecrista fasciculata
Partridge pea
forb
0
64
22
0.03
Rubus argutus
Southern blackberry
vine
0
79
20
0.01
50 No Thin
Discussion
Many of my results are consistent with results from other studies (Harrington and
Edwards, 1999; Phillips and Waldrop, 2007) and with the finding that light availability
was the dominant factor in herbaceous vegetation response in a study examining pine
thinning in South Carolina (Harrington and Edwards, 1999). Removal of forest canopy
immediately affects ground layer vegetation by increasing light availability (Thomas et
al., 1999) which then increases levels of photosynthesis in the surviving understory and
midstory (Aussenac, 2000).
Though light availability does appear to drive the differences in cover change
between the stands that were not thinned and the thinned stands, it does not explain the
differences observed in the stands that were lightly thinned alone and the stands that were
heavily thinned alone and both burned and thinned. There was a significant posttreatment increase in cover in the heavy thin stands and the stands treated with the
combination treatments while there was no change from pre treatment levels in the light
thin alone stands. Schweitzer and Wang (in press) found that the amount of full sun
penetrating the canopy was similar for the light (43% of full sun) and heavy thinned
stands (52% of full sun) after treatment. Therefore, light availability is not likely to be the
main cause of the observed differences. Similar studies have shown that factors other
than light availability, such as litter depth, slash cover, soil drainage, and nutrient
availability also affect the response of ground layer vegetation to disturbance
(Fredericksen et al, 1999).
Overall ground layer vegetation richness increased in the second and third
growing seasons post-treatment in stands that were heavily thinned and in stands that
51 were burned and thinned. These results are consistent with a study in mixed hardwood
forests in Ohio where ground layer vegetation richness increased in the first three years
after a commercial thinning from below (Phillips et al., 2007). Conversely, a study of the
initial response of ground layer vegetation richness to increasing levels of harvest
intensity in hardwood forests in Pennsylvania showed no differences in overall ground
layer richness among the different harvest intensities. Residual basal areas ranged from
0.5 m2/ha to 42.3m2/ha. There were, however, other factors such as litter cover, blueberry
cover, and percent slope that displayed significant relationships to species richness
(Frederickson et al., 1999). These results emphasize the varying response of ground layer
vegetation to silvicultural activities and the need for site-specific information and
analyses.
Ground layer vegetation response to burning alone was variable among similar
studies. I observed no change in ground layer vegetation cover in the second or third
season after prescribed burn treatment. The Bray-Curtis similarity analyses showed that
the stands that were burned alone were the most similar to stands that were untreated.
This is consistent with other studies where cover tends to increase in the first season after
burning, but show no difference from pre-treatment conditions by the second or third
growing season after treatment (Elliot et al., 1999; Phillips et al., 2007). The lack of
impact of burning alone on individual species after the first two seasons post-treatment is
illustrated by the results of my indicator species analysis. In the second growing season
after treatment five species were indicators of burned stands. By the third year, however,
there were no species that were indicators of burned stands.
52 The intensity of burn affects vegetation response. Elliot et al. (1999) found that
high intensity burns (≥800°C) increased cover and diversity more than low intensity
burns (≤80°C) which have little or no impact on ground layer vegetation cover or
composition. Phillips et al. (2007) found that burning doubled the richness of ground
layer vegetation in stands that were burned at an average temperature of 152 degrees
Celsius. The burns in my study were of low intensity (mean fire temperature of 104°C)
and the resulting changes in ground layer vegetation cover were negligible.
The change in cover of graminoids was substantially higher than that of vines or
forbs and appeared to drive the observed increases in overall cover in the stands treated
with the heavy thin alone and the two combination treatments. Dichanthelium boscii, D.
commutatum, D. dichotomum and Stipa avenacea were major components of stands that
experienced increases in graminoid cover. These graminoids are early-successional,
disturbance-responsive species that quickly respond to the additional resources available
post-treatment (Jeffries et al., 2010).
After graminoids, vines contributed the most to the non-woody cover component
of ground layer vegetation after treatment. Vitis rotundifolia had the highest cover of any
vine in both the second and third seasons after treatment. It changed the most in cover in
the heavy thin alone stands. In temperate forests, liana (woody vine) abundance is the
highest in disturbed areas (Burton et al., 1998). Liana presence is of particular importance
to forest managers because they appear to influence tree growth at all stages of
regeneration (Ladwig and Meiners, 2009).
The decrease in cover of the vine S. rotundifolia on the burn alone stands is
consistent with findings from a study on the Cumberland Plateau in Kentucky where S.
53 rotundifolia cover decreased on once and twice burned forest sites (Arthur et al., 1998). It
is believed that fire suppression in the eastern United States increases the density and size
of briers in forest understory (Arthur et al., 1998).
Forb composition shifted from more shade-tolerant species to early successional,
disturbance-responsive species that are favored by increased light availability and higher
soil moisture and fertility characteristics (Jeffries, 2010). Both C. fasciculata and D.
rotundifolium are legumes which occur much more frequently on burned sites (Kush and
Meldahl, 2000). The results from my study, however, indicate that a single burn not
coupled with any thinning treatment is not sufficient to increase the cover of these
species, which appeared to favor burned sites where the overstory density was reduced
the most.
The results of my indicator species analysis were consistent with a similar study
conducted on the Piedmont of North Carolina (Jeffries, 2010). The author reports that
Danthonia sericia, Dichanthelium commutatum, and D. dichotomum were all present
after intensive harvesting in a loblolly pine forest community. In my study, these species
were all indicators of thinned stands.
Zak (2008) found that the overall cover of ground layer species was reduced by
thinning and burning in the first growing season following the treatments. Graminoid
cover increased only in the stands that were thinned alone and vines decreased in stands
that were burned and thinned. These results differ from my results in the second and third
growing seasons post-treatment where overall cover and graminoid cover increased after
the heavy thin and the burn and thin and vine cover increased in the heavy thin alone and
showed no difference from the control in the combination treatments. The differences in
54 the results from the first growing season post-treatment and the second and third growing
seasons post-treatment demonstrate the response pattern of ground layer vegetation to
disturbance.
During the second growing season post-treatment, ground layer vegetation in this
study quickly increased in cover in heavily treated areas. There was little change in cover
variables from the second to the third growing season post-treatment with the only
changes being a decrease in overall cover in the burn and heavy thin stands, an increase
in graminoid cover in the burn and heavy thin stands, and an increase in forb cover in the
heavy thin alone stands. These results indicate a possible plateau of plant growth as the
available and nutrients are captured. Further monitoring is necessary to determine the
continued response cycle post-disturbance.
Conclusions and Management Implications
The effects of burning and thinning on ground layer vegetation varied according
to the intensity and type of disturbance introduced. Overall cover and the cover of
graminoids were the highest in the stands treated with the heavy thin alone and the two
combination treatments. Vine cover increased the most in stands that were heavily
thinned and these stands should be monitored for V. rotundifolia growth to ensure
negative impacts on tree regeneration are mitigated. The stands treated with the burn
alone had no change in overall cover or the cover of the individual life form groups in
either season. The only cover category that changed due to the light thin alone was
graminoid cover which increased in the second season, but returned to pre-treatment
levels by the third season.
55 These results indicate that the most beneficial conditions for increasing the cover
of ground layer vegetation occurred in stands that were most heavily disturbed: stands
treated with the heavy thin alone and the combination treatments. Thinning appears to be
the main factor in these changes with burning having an additive effect.
In forests where conservation of biodiversity is a targeted management goal, it
appears that burning and thinning can be implemented without causing significant
decreases in species richness or diversity. If a management goal is to increase graminoid
richness managers should utilize a heavy thin or a burn and either light or heavy thin. A
combination of burning and heavy thinning will increase forb richness and overall species
diversity. Species monitoring should be implemented, however, to ensure weedy or
invasive species are not dominating community composition and that species richness
levels are maintained throughout the disturbance response cycle.
56 APPENDIX – SPECIES LIST
Family
Amaryllidaceae
Apiaceae
Apiaceae
Asclepiadaceae
Asclepiadaceae
Aspidiaceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Brassicaceae
Campanulaceae
Convolvulaceae
Dioscoreaceae
Ericaceae
Ericaceae
Euphorbiaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Gentianaceae
Gentianceae
Hypericaceae
Genus
Hypoxis
Sanicula
Thaspium
Asclepias
Asclepias
Polystichum
Antennaria
Antennaria
Aster
Aster
Coreopsis
Elephantopus
Erechtites
Eupatorium
Eupatorium
Gnaphalium
Helianthus
Pityopsis
Rudbeckia
Solidago
Solidago
Solidago
Prenanthes
Lobelia
Calystegia
Dioscorea
Chimaphila
Epigaea
Euphorbia
Desmodium
Desmodium
Lespedeza
Lespedeza
Lespedeza
Mimosa
Sabatia
Obolaria
Hypericum
Species
hirsuta
canadensis
barbinode
tuberosa
variegata
acrostichoides
plantaginifolia
solitaria
dumosus
solidagineus
major
tomentosus
hieracifolia
capillifolium
rotundifolium
obtusifolium
hirsutus
graminifolia
hirta
arguta
caesia
odora
serpentonia
siphilitica
spithamaea
villosa
maculata
repens
corollata
glabellum
rotundifolium
cuneata
procumbens
repens
microphylla
angularis
virginica
gentianoides
57 Life form
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
Hypericaceae
Iridaceae
Iridaceae
Lamiaceae
Oxalidaceae
Pteridaceae
Rubiaceae
Violaceae
Violaceae
Violaceae
Cyperaceae
Cyperaceae
Cyperaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Anacardiaceae
Aristolochiaceae
Bignoniaceae
Caprifoliaceae
Caprifoliaceae
Celastraceae
Liliaceae
Liliaceae
Liliaceae
Loganiaceae
Passifloraceae
Passifloraceae
Rhamnaceae
Rosaceae
Rosaceae
Vitaceae
Vitaceae
Vitaceae
Hypericum
Iris
Sisyrinchium
Pycanthemum
Oxalis
Pteridium
Mitchella
Viola
Viola
Viola
Carex
Carex
Scleria
Andropogon
Chasmanthium
Danthonia
Danthonia
Dichanthelium
Dichanthelium
Dichanthelium
Dichanthelium
Melica
Panicum
Saccharum
Stipa
Toxicodendron
Aristolochia
Bignonia
Lonicera
Lonicera
Euonymus
Smilax
Smilax
Smilax
Gelsemium
Passiflora
Passiflora
Berchemia
Rubus
Rubus
Parthenocissus
Vitis
Vitis
hypericoides
verna
albidum
loomisii
stricta
aquilinum
repens
blanda
hastata
palmata
cherokiensis
picta
oligantha
virginicus
sessiliflorum
sericea
spicata
boscii
commutatum
dichotomum
laxiflorum
mutica
anceps
alopecuroides
avenacea
radicans
serpentaria
capreolata
japonica
sempervirens
americana
bona-nox
glauca
rotundifolia
sempervirens
incarnata
lutea
scandens
argutus
flagellaris
quinquefolia
aestivalis
rotundifolia
58 forb
forb
forb
forb
forb
forb
forb
forb
forb
forb
graminoid
graminoid
graminoid
graminoid
graminoid
graminoid
graminoid
graminoid
graminoid
graminoid
graminoid
graminoid
graminoid
graminoid
graminoid
vine
vine
vine
vine
vine
vine
vine
vine
vine
vine
vine
vine
vine
vine
vine
vine
vine
vine
Aceraceae
Anacardiaceae
Annonaceae
Aquifoliaceae
Aquifoliaceae
Araliaceae
Betulaceae
Betulaceae
Caprifoliaceae
Cornaceae
Cupressaceae
Ebenaceae
Ericaceae
Ericaceae
Ericaceae
Ericaceae
Ericaceae
Ericaceae
Fabaceae
Fabaceae
Fabaceae
Fagaceae
Fagaceae
Fagaceae
Fagaceae
Fagaceae
Fagaceae
Fagaceae
Fagaceae
Fagaceae
Hamamelidaceae
Juglandaceae
Juglandaceae
Lauraceae
Magnoliaceae
Magnoliaceae
Moraceae
Nyssaceae
Oleaceae
Oleaceae
Oleaceae
Oleaceae
Pinaceae
Acer
Rhus
Asimina
Ilex
Ilex
Aralia
Corylus
Ostrya
Viburnum
Cornus
Juniperus
Diospyrus
Kalmia
Oxydendron
Rhododendron
Vaccinium
Vaccinium
Vaccinium
Cercis
Chamaecrista
Robinia
Fagus
Quercus
Quercus
Quercus
Quercus
Quercus
Quercus
Quercus
Quercus
Liquidambar
Carya
Carya
Sassafras
Liriodendron
Magnolia
Morus
Nyssa
Chionanthus
Forestiera
Fraxinus
Ligustrum
Pinus
rubrum
copalliana
triloba
longipes
opaca
spinosa
cornuta
virginiana
acerfolium
florida
virginiana
virginiana
latifolia
arboreum
canescens
arboreum
pallidum
stamineum
canadensis
fasciculata
pseudoacia
grandifolia
alba
coccinea
falcata
marilandica
montana
rubra
stellata
velutina
styraciflua
glabra
tomentosa
albidum
tulipifera
macrophylla
rubra
sylvatica
virginicus
ligustrina
americana
sinense
echinata
59 woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
Pinaceae
Pinaceae
Pinaceae
Rhamnaceae
Rosaceae
Rosaceae
Rosaceae
Saxifragaceae
Styracaceae
Ulmaceae
Verbenaceae
Pinus
Pinus
Tsuga
Rhamnus
Amelenchiar
Crateagus
Prunus
Hydrangea
Styrax
Ulmus
Callicarpa
taeda
virginiana
canadensis
caroliniana
arborea
sp.
serotina
quercifolia
grandifolius
alata
americana
60 woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
woody
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66 VITA
Dana Alison Virone, daughter of Terry and Nina Wallace, was born April 8, 1980
in Ozark, Alabama. She graduated from Carroll High School, Ozark, Alabama in 1998. In
2002, she received a Bachelor of Science in biology from Troy University. She worked
for the National Park Service from 2002 until 2006 and for the United States Holocaust
Memorial Museum from 2006 until 2008. She married Shane Joseph Virone on October
6, 2007. In May 2008, she entered graduate school at Alabama A&M University, Normal,
Alabama.
67