The Effects of Wildland Fire and Other Disturbances on the Nonnative Tree Paulownia Tomentosa and Impacts on Native Vegetation

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The Effects of Wildland Fire and Other Disturbances on the Nonnative Tree Paulownia tomentosa and Impacts on Native Vegetation

THESIS

Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of The Ohio State University

Angela R. Chongpinitchai

Graduate Program in Environment and Natural Resources

The Ohio State University

2012

Master's Examination Committee:

Roger Williams, Advisor

Joanne Rebbeck

David Hix

Stephen Matthews

Copyrighted by

Angela Rose Chongpinitchai

2012

Abstract

Increases in nonnative plant species to ecosystems of the United States have become a concern for the management of natural vegetation and ecological processes.

Many exotic plant species are invasive, rapidly colonizing an area and spreading beyond the point of introduction. Nonindigenous plants can change the dynamics of soil properties, alter fire regimes, and interrupt ecological processes, such as nutrient and hydrologic cycles. These exotic plants often have a competitive edge over native species, due to adaptations in their native geographical range or because of a lack of natural predators in introduced habitats. Changes to microclimate conditions and direct competition from exotic plants often lead to a decrease in species richness in a habitat.

Although this has been an issue for decades, little is known about many exotic plant species, particularly how they interact with natural vegetation in introduced habitats.

Increased anthropogenic activity, such as logging, road construction, and prescribed burns, tends to facilitate invasions of exotic species by creating disturbed areas and reducing biodiversity. Paulownia tomentosa, a tree native to China, was first introduced to the U.S. in the 1840s as an ornamental; in recent decades the species has expanded its range since escaping cultivation. There is a lack of knowledge on the role Paulownia plays in introduced habitats – how large and small-scale disturbances facilitate the spread of the species, and how the tree affects natural vegetation composition. This study

ii investigated the response of Paulownia to several disturbances at Shawnee State Forest,

Ohio – decades of logging, tree damage from a 2003 ice storm, a 2009 wildfire, and targeted herbicide control of Paulownia tomentosa and Ailanthus altissima. This study also investigated the impact of Paulownia on vegetation composition and species richness. Herbaceous and woody vegetation was sampled in June-September 2011 across

122 plots to identify which disturbances affected Paulownia colonization and how

Paulownia presence impacted native vegetation composition. Paulownia seedling and sapling stem densities were positively correlated with areas impacted by the 2009 wildfire and the 2003 ice storm. Paulownia tree stem density was positively correlated with areas of greater canopy closure not recently impacted by large disturbances. In areas not impacted by the 2009 wildfire, native vegetation composition was significantly altered when all size classes of Paulownia were present, and species richness was lowest in these areas. Results of this study indicate that Paulownia spreads after natural disturbances and human activity, and that the exotic tree is changing native vegetation species composition.

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Acknowledgments

I would like to thank my advisor, Dr. Roger Williams, and my thesis committee members Dr. Joanne Rebbeck, Dr. David Hix, and Dr. Stephen Matthews, for their help and feedback during my research. I give a special thanks to Dr. Williams for letting me focus my project on what interests me most, and to Dr. Rebbeck for helping me access important data. I’m also grateful for the help and ideas given by Norm Bourg when I encountered field work challenges. I thank all my SENR friends, who I’ve come to know the past 1.5 years, and my friends back home for the much needed good laughs, listening ears, and encouragement along the way. Finally, a shout-out to my family for, well, being my family.

Vita

May 2009 ...... B.S. Biology, Italian Minor, Gettysburg

College, PA

June-August 2009 ...... U.S. Fish & Wildlife Service, Big Oaks

National Wildlife Refuge, Biology Intern

January-August 2010 ...... Smithsonian Conservation Biology Institute

Ecology Intern

2010 to present ...... Graduate Teaching Associate, School of

Environment and Natural Resources, The

Ohio State University

Fields of Study

Major Field: Environment and Natural Resources

Table of Contents

Abstract ...... ii

Acknowledgments...... iv

Vita ...... v

Table of Contents ...... vi

List of Tables ...... ix

List of Figures ...... xi

Chapter 1: Review of the Literature ...... 1

Botanical and Silvical Characteristics ...... 1

Germination and Seed Bank Viability ...... 3

Paulownia and Disturbance ...... 6

Paulownia and Fire ...... 6

Invasive Properties ...... 8

Means of Control ...... 10

Value and Uses ...... 12

Chapter 2: The Response of Paulownia tomentosa to Disturbances and its Invasive

Potential ...... 14

Introduction ...... 14

Study Area ...... 17

Methods ...... 20

Paulownia Density Statistical Analysis ...... 22

Results ...... 23

Discussion ...... 25

Seedlings ...... 25

Saplings ...... 29

Trees ...... 32

Conclusion ...... 37

Chapter 3: Effects of Paulownia tomentosa on Natural Vegetation ...... 44

Introduction ...... 44

Study Area ...... 47

Methods ...... 50

Paired Plots Statistical Analysis...... 52

Natural Vegetation Statistical Analysis ...... 53

Results ...... 54

Paired Plots ...... 54

MRPP...... 55

Jackknife Species Richness ...... 55

vii

Indicator Species Analysis ...... 55

Discussion ...... 57

Paired Plots ...... 57

MRPP-understory ...... 58

MRPP-seedlings and saplings ...... 63

Jackknife Species Richness ...... 68

Indicator Species-understory ...... 72

Indicator Species-seedlings and saplings ...... 74

Conclusion ...... 78

Future Implications ...... 80

References ...... 87

Appendix A: Maps of Shawnee State Forest, Ohio ...... 96

Appendix B: Harvest data of sample plots at Shawnee State Forest, Ohio 2005-2011 .. 103

Appendix C: Seed-bearing Paulownia tomentosa stems at Shawnee State Forest, Ohio in

2011...... 105

Appendix D: Species area curves for the understory stratum of the four plot types at

Shawnee State Forest, Ohio in 2011 ...... 107

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List of Tables

Table 2.1. Redundancy analysis of Paulownia stem density data – correlations of species ordination axes with environmental variables...... 39

Table 2.2. Percent canopy closure for all sample plots (N = 122) from densiometer readings at Shawnee State Forest, Ohio...... 40

Table 3. 1 Mean slope percent, mean aspect, mean elevation, and soil type (series) for the four plot types (N = 122). FP = fire, Paulownia, FNP = fire, no Paulownia, NFP = no fire, Paulownia, NFNP = no fire, no Paulownia ...... 83

Table 3.2. Summary of multi response permutation procedure on the understory, seedling, and sapling strata relationships associated with Paulownia and fire (N = 122).

Vegetation composition is significantly different at P < 0.05 for comparisons marked with an asterisk. FP = fire, Paulownia, FNP = fire, no Paulownia, NFP = no fire,

Paulownia, NFNP = no fire, no Paulownia ...... 84

Table 3.3. First order jackknife estimates of understory species richness (N = 122).

Regression coefficients (c = expected number of species per unit area, z = rate of species richness increase) are calculated from the species area curve, fit with a power function.

FP = fire, Paulownia, FNP = fire, no Paulownia, NFP = no fire, Paulownia, NFNP = no fire, no Paulownia ...... 85

Table 3.4. Indicator species for understory, seedling, and sapling plot data (N = 122). FP

= fire, Paulownia, FNP = fire, no Paulownia, NFP = no fire, Paulownia, NFNP = no fire, no Paulownia ...... 86

Table B.1 Logging data for the sample plots (N = 45) established in areas that were harvested between 2005-2011 at Shawnee State Forest, Ohio ...... 104

Table C.1 Seed-bearing Paulownia tomentosa stems from the sample plots (N = 61) with the species present in Shawnee State Forest, Ohio 2011. Table B.1 Logging data for the sample plots (N = 45) established in areas that were harvested between 2005-2011 at

Shawnee State Forest, Ohio ...... 106

List of Figures

Figure 2.1. Redundancy analysis triplot of Paulownia tomentosa stem density and environmental variables. HighFire = high fire intensity, LowFire = low fire intensity,

MedFire = moderate fire intensity, NoFire = outside the burn area, Logging = years since last logging activity, IceDmge = 2003 canopy ice damage, No IceDm = no canopy mortality, GroundCo = percent ground cover, AvgVegHt = average vegetation height,

NoHerb = no herbicide application, CanopyCl = canopy closure ...... 41

Figure 2.2 Distribution of Paulownia stem d.b.h. classes at Shawnee State Forest, Ohio in 2011...... 42

Figure 2.3. Paulownia tomentosa growing in a canopy gap in a mature stand not impacted by the 2009 wildfire at Shawnee State Forest, Ohio...... 43

Figure 3.1. Principal components analysis of environmental variables (slope percent, aspect, elevation) for the four plot types (N = 122 plots)...... 82

Figure A.1 Location of Shawnee State Forest in Adams and Scioto Counties, Ohio

...... 97

Figure A.2 Areas in the vicinity of the approximately 1,200 ha 2009 wildfire (red) that were logged from 2005-2011 at Shawnee State Forest, Ohio (green shading). Sample plots (N = 48) established in these logged areas are shown (brown squares), along with the remaining sample plots (N = 74) not established in recently logged areas (pink squares)...... 98

Figure A.3 Areas experiencing 33-100% canopy mortality from the 2003 ice storm at

Shawnee State Forest, Ohio (blue). Although tree damage was more widespread throughout Shawnee State Forest, only the areas where sample plots (pink squares) are located are shown. Access roads (black), hiking trails (green), and bridle trails (brown) are also shown...... 99

All other areas within the fire perimeter are considered low intensity. Sample plots (pink squares), created dozer lines (brown shading), and access roads (black) are also shown..

...... 100

Mapped areas of Paulownia and A. altissima not targeted with herbicide are shown

(green). The perimeter of the approximately 1,200ha fire of April 2009 (red), created dozer lines (brown shading), sample plots (pink squares), access roads (black), hiking trails (green), and bridle trails (brown) are also shown...... 101

Figure A.6 The 433 cruise plots within the 2009 fire perimeter at Shawnee State Forest,

Ohio. Plots were 2.2m radius in size, established by Shawnee State Forest employees in

September 2009. All woody stems over 0.3m tall and with a d.b.h. less than 2.1cm were inventoried within each plot radius...... 102

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Figure D.1 Species area curve of the understory stratum (herbs, vines, woody shrubs) for the 28 FP plots (Fire, Paulownia). A power function is the best fit line; the instantaneous rate of species richness increase is 0.395 and the expected number of species in each unit area is 21.866...... 108

Figure D.2 Species area curve of the understory stratum (herbs, vines, woody shrubs) for the 28 FNP plots (Fire, no Paulownia). A power function is the best fit line; the instantaneous rate of species richness increase is 0.428 and the expected number of species in each unit area is 17.456 ...... 109

Figure D.3 Species area curve of the understory stratum (herbs, vines, woody shrubs) for the 33 NFP plots (No fire, Paulownia). A power function is the best fit line; the instantaneous rate of species richness increase is 0.400 and the expected number of species in each unit area is 19.651 ...... 110

Figure D.4 Species area curve of the understory stratum (herbs, vines, woody shrubs) for the 33 NFNP plots (No fire, no Paulownia). A power function is the best fit line; the instantaneous rate of species richness increase is 0.442 and the expected number of species in each unit area is 15.737 ...... 111

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Chapter 1 – Review of the Literature

Botanical and Silvical Characteristics

Paulownia tomentosa (Thunb.) Siebold & Zucc. Steud., commonly known as

Princess tree, is a deciduous tree native to Eastern Asia, particularly China (Hu 1961). It is a mid-sized tree most notable for its large, heart-shaped leaves and fragrant, showy violet flower clusters that bloom early in spring (Hu 1961). Leaves reaching a meter in length and width are reported, with larger sizes on saplings and root sprouts (Hu 1961,

Carpenter 1983, Preston 1983). Their thin leaves are easily damaged by high winds and rain storms (Hu 1961, Carpenter 1983, Preston 1983). Leaves are densely pubescent, especially on the underside (Hu 1961). Paulownia flowers are perfect, and fruits are egg- shaped capsules that open to release seeds in October, which can germinate readily in favorable conditions, or exhibit a light-induced dormancy until the following year (Hu

1961, Carpenter et al 1983, Young and Young 1992, Kuppinger 2008, Innes 2009). The species is a prolific seed producer, with estimates of 2,000 tiny seeds per fruit capsule and tens of millions of seeds produced per individual mature tree in one season (Millsaps

1936, Tang et al 1980, Carpenter et al 1983, Kuppinger 2008). Winged seeds, each weighing less than a milligram, are wind-dispersed, and can travel several kilometers from a parent tree (Millsaps 1936, Hu 1961, Langdon and Johnson 1994). Distances of

10 km from the nearest mature tree have been estimated (Kuppinger 2008). With a short juvenile period – trees can reach maturity in 8-10 years in natural settings and 3-4 years

1 in crop plantations – Paulownia have the potential to produce billions of seeds in its short lifetime of about seventy years (Hu 1961, Carpenter et al 1983, Beckjord and McIntosh

1983).

Paulownia tomentosa is an extremely fast grower; juvenile stems are able to grow a meter or more per year, with one study recording stems growing over 1.5 m in two growing seasons (Hu 1961, Beckjord and McIntosh 1983). Paulownia has the ability to resprout from adventitious buds on the trunk and roots after top-kill from fire, cutting, or other non-fatal damage (Hu 1961). It also exhibits vegetative growth without any prior damage (Innes 2009). Root sprouts can grow even faster than main stems; they have been recorded to grow 5 m in one growing season (Beckjord and McIntosh 1983).

Paulownia can form dense clusters in areas, especially after vegetation clearing disturbances, and this may be due to root sprouts (Hu 1961). There is no research on the contribution of clonal growth to Paulownia populations and spread, although there is on the similar nonnative invasive tree Ailanthus altissima. A. altissima is consistently found in open areas and after disturbances, such as thinning and burning treatments for promoting oak regeneration (Kowarik 1995, Knapp and Canham 2000, Rebbeck et al

2005). However, A. altissima can also be found growing in intact, mature-growth forests, and although seedling mortality rate is high after their first year in closed forests, ramets from clonal growth are present in the understory (Kowarik 1995, Knapp and Canham

2000). A. altissima may be a gap-obligate to initially invade a mature forest, but the species can survive via clonal growth off the parent tree as the canopy closes (Kowarik

1995, Knapp and Canham 2000). Further research is needed to determine if Paulownia uses clonal growth to establish in areas not recently disturbed. Regardless, these

2 characteristics of Paulownia – fast growth, short juvenile period, mass production of wind dispersed seeds, and the ability to sprout – enable the species to easily colonize an open area, even when not in the vicinity of a mature tree (Langdon and Johnson 1994).

Paulownia branches are stout with a hollow pith, but are brittle with thin bark because of its fast-growth, especially when younger (Hu 1961). Saplings and new shoots are unstable because they grow quickly before expanding in diameter (Hu 1961). Given its large, thin leaves, growth form, and brittle branches, downed wood and leaf litter can accumulate in areas.

In its native China, field observations have found that mature Paulownia do not have a strong tap root, most likely as a result of its fast shoot growth; the lateral rooting system is shallow and horizontal in nature (Hu 1961). In contrast, in the southern

Appalachians of the U.S., Paulownia can have a deep, penetrating main root within a few years after germination (Kuppinger et al 2010). Research conducted in Turkey on multiple species of Paulownia as crop plants indicate the genus has a deep rooting system

(Ayan et al 2006).

Germination and Seed Bank Viability

Paulownia seedlings are known to have a weak primary root, often unable to penetrate through leaf litter on a forest floor (Millsaps 1936, Hu 1961, Tang et al 1980).

As a consequence, bare mineral soil is thought to be one of the requirements for

Paulownia germination, and studies have found a negative correlation between increased leaf litter and germination rates (Millsaps 1936, Hu 1961, Carpenter and Smith 1981,

Carpenter et al 1983, Longbrake 2001, Kuppinger 2008). Similarly, Paulownia seeds

3 placed on bare mineral soil, versus those buried to several centimeters, had higher germination rates (Longbrake 2001, Kuppinger 2008)

Paulownia seedlings appear to require not only bare mineral soil for successful germination, but high light levels as well. Carpenter et al (1983) found that longer photoperiods increased Paulownia seedling height growth, root length, and total dry matter production, measured by leaf area size and root length. A doubling of the photoperiod length increased height growth by 100% (Carpenter et al 1983). Although the Paulownia seedlings receiving the shortest photoperiod (8 hours) were the most efficient photosynthesizers, these individuals never reached the height growth observed with the longer photoperiods (Carpenter et al 1983). Longbrake (2001) measured the germination rate of Paulownia across different light levels and substrates using collected seeds selectively placed in the field. She found that seeds placed on bare soil or gravel substrate within a clearcut (full light), had the greatest germination rates (Longbrake

2001).

Other studies have demonstrated that Paulownia seeds can germinate in reduced light conditions. Although Longbrake (2001) had the most success with germination of seeds in cleared areas with full sun, she also found Paulownia germinating on forest edges where light levels were reduced. Similarly, Kuppinger (2008) had significantly higher germination for seeds in 50% shade versus those in full sun, although fate of the seeds was only monitored for two months, and other variables, such as soil moisture, were not kept constant.

There have been various studies, with contrasting results, on the effects of stratification on germination of Paulownia seeds. In a study by Carpenter and Smith

(1981), stratification, gibberellic acid, and cold dry storage of seeds effectively reduced the light requirement for germination of Paulownia. Of the three treatments, stratified seeds displayed the greatest germination – defined as the amount of time to the development of a radicle – in the dark (Carpenter and Smith 1981). Kuppinger’s (2008) dissertation work, however, found that stratified seeds had the lowest germination rates when compared to those that were dry stored.

The viability of Paulownia’s seed bank remains a point of contention. In studies placing seed bags in the field, decreased germination rates over several months indicate short-lived viability (Kuppinger 2008). Kuppinger (2008) also cited the tiny size and small carbohydrate reserve of Paulownia seeds as further evidence for lack of long-term viability. In the only truly in situ experiment, Hyatt and Casper (2000) found that although Paulownia creates a large seed bank, mortality is high. Survival rate of seeds was less than 30% after two years in the soil (Hyatt and Casper 2000). In contrast,

Longbrake (2001) found that seeds could survive up to fifteen years in the soil. This was based on extrapolation of data of the highest mortality percentages of Paulownia seeds recorded after seed bags were placed in the field (Longbrake 2001). Laboratory experiments have also concluded that Paulownia seeds remain viable up to two cycles of cold storage, and would thus be able to germinate in the seed bank (Carpenter and Smith

1981).

Paulownia and Disturbance

Paulownia tomentosa is a disturbance-dependent species. Even in its native

China, the tree is limited to isolated individuals and patches, often in marginal areas, playing but a minor role in the composition of the mesophytic forests there (Hu 1961).

Hu (1961) reported that only when human activity or other events destroy vegetation cover does Paulownia grow densely. Paulownia seems similarly restricted in its geographical range in the United States as an introduced species. The exotic tree is a main component of the forests in central Virginia following Hurricane Camille in 1969, but with the lack of any recent soil-clearing disturbances, Paulownia does not appear to be self-regenerating (Williams 1993b). The age distribution of Paulownia indicates little recruitment of the species; Williams (1993b) attributes this trend to the lack of any large- scale disturbances to the area since the hurricane. Similarly, in the southern

Appalachians, Paulownia seedlings are growing in abundance following an increase in prescribed burns for managerial reasons (Kuppinger et al 2010). Results, however, show

Paulownia spread consistently decreasing with years since the last fire, with habitat area reduced to only the driest outcroppings of the region within ten years of the last burn

(Kuppinger et al 2010). In Great Smoky Mountains National Park, Paulownia trees are dense in numbers along roadways and trails, areas disturbed by anthropogenic activities

(Langdon and Johnson 1994).

Paulownia and Fire

Paulownia is not specifically a fire adapted species, and most fire severities will result in top-kill of stems (Innes 2009). The brittle and hollow branches, as well as the

6 large leaves, will easily burn and contribute to the amount of flammable materials in a forest (Hu 1961, Innes 2009). However, the ability of the species to sprout following top- kill gives Paulownia an advantage post-fire; even if stems do not survive, Paulownia can root sprout – root systems are considered insulated from heat damage even in high severity fires (Innes 2009). Because Paulownia germination appears at least partially dependent on cleared soils and higher light levels, recently burned areas provide excellent conditions for colonization by the nonnative plant; the tree has been noted to rapidly invade areas after wildfire and prescribed burns in the Appalachians (Langdon and

Johnson 1994, Kuppinger et al 2010). Paulownia is very tolerant of dry, sunny areas and low pH soils, allowing the species to take advantage of areas impacted by a fire (Tang et al 1980, Kuppinger et al 2010).

Interestingly, processed Paulownia wood is highly flame retardant (Li and Oda

2007). The species’ unique cell tissue structure – commonly described as similar to honeycomb in its porosity – and lack of lignins give it a high ignition point; although the wood will carbonize, it will not ignite (Li and Oda 2007). This unusual property of

Paulownia wood has contributed to its popularity as a building material (Hu 1961, Li and

Oda 2007).

There have been several studies on smoke as a germination signal to Paulownia seeds. Todorovic et al (2005) found that when liquid smoke was applied to light-induced seeds, germination occurred, but when applied to seeds that already completed the phytochrome stage – the second of three steps of successful germination – radicle development was stunted. Smoke enhances the sensitivity of Paulownia seeds to light, which can aid in successful germination when light levels are lower, but liquid smoke

7 exposure does not postpone scotodormancy, a phenomenon where seeds prolonged in darkness lose light-sensitivity (Todorovic et al 2010). When comparing dry Paulownia seeds to water soaked seeds, the dry seeds absorb more liquid smoke quicker, resulting in a higher germination percentage (Todorovic et al 2010).

As Paulownia seeds are small and delicate, any on the top soil would be destroyed by a fire, but even buried seeds may not survive higher temperatures.

Kuppinger (2008) found that buried Paulownia seeds did not germinate post-fire when temperatures reached above 100°C. An experiment in vitro found more specific results – optimal germination temperatures for Paulownia tomentosa seeds were between 23°C and 27°C, with inhibitory effects at temperatures just above 30°C (Todorovic et al 2010).

Invasive Properties

The definition of the word “invasive” varies by context and author. Some define invasive as an introduced species able to establish a self-sustaining population, while others the ability of a nonindigenous plant to spread its range beyond the initial area of introduction (Williamson and Fitter 1996, Allendorf and Lundquist 2003, Martin et al

2009). Paulownia has characteristics commonly associated with and predictive of an invasive species: small, lightweight wind-dispersed seeds, a short time (one growing season) between large seed crops, fast growth, short juvenile period, vegetative reproduction, and perfect flowers (Rejmanek and Richardson 1996, Goodwin et al 1999,

Herron et al 2007, Martin et al 2009). In a model by Herron et al (2007), Paulownia is listed as an invasive tree because of these traits. Similarly, others cite the ability of

Paulownia to germinate in an area where there was no previous population and its ability

8 to colonize large areas – due to the patchwork of habitats across a landscape – as reasons for its invasiveness (Langdon and Johnson 1994, Kuppinger et al 2010). Paulownia acts as an r-strategist and is dependent on disturbance for establishment to some extent; it is not surprising Paulownia can spread to new areas, as most invasions are associated with disturbed habitats, both by natural and human activities ( Rejmanek and Richardson

1996).

Several studies show that not only are certain biological characteristics crucial to a plant being invasive, but also the geographical range of the species in its native habitat

(Williamson and Fitter 1996, Goodwin et al 1999, Herron et al 2007). Plant species with large native latitudinal ranges are more successful as invaders in introduced habitats because of the plants’ ability to adapt to new conditions, having already been exposed to wide environmental gradients in their places of origin, and possibly their dispersal ability

(Williamson and Fitter 1996, Goodwin et al 1999, Herron et al 2007). However,

Paulownia is restricted to certain areas in its native China, which are determined not only by vegetation-clearing disturbances, but by cold gradients more north than its current latitudinal distribution of 30° N (Hu 1961). With a small native geographical range,

Paulownia is lacking a trait that may have a strong influence on the probability of a plant’s invasiveness. However, in a study on the vegetation of a mountainous oceanic island, alien species were constrained by their pre-adaptation to large gradients in their native habitats, making expansion in introduced areas more difficult for the “invasive” species than for the indigenous species (Kitayama and Mueller-Dombois 1995). In this study, a larger native range did not necessarily correlate with a wider distribution in introduced habitats, making it possible this trait does not play a significant role in

9 determining invasiveness Kitayama and Mueller-Dombois 1995). However, the alien plant invasions on the island were determined by natural disturbances and cattle grazing, both of which destroyed native plant cover, fortifying the idea that exotic plants are mostly disturbance-dependent (Kitayama and Mueller-Dombois 1995).

Additionally, some non-invasive Populus species are incorrectly classified by models as invasive because they exhibit many of the previously mentioned traits; however, their short seed viability is likely a reason preventing these species from becoming invasive (Rejmanek and Richardson 1996). Seed bank viability of Paulownia remains unclear, but this factor could attribute to the extent of its invasiveness.

Determining the likelihood and the extent of invasion by a species are also dependent on the stage of invasion examined and is tied, in part, to the characteristics of the invaded habitat (Herron et al 2007). Thus, it is possible Paulownia exhibits greater invasive success in certain areas than others.

Means of Control

As aforementioned, the characteristics of Paulownia – ability to sprout and tolerance to dry, sunny areas – likely make prescribed burns an ineffective method of control for the species. Chemical control, however, has been proven effective, but multiple repeat treatments are necessary (Miller 2007). Herbicide injection and basal bark spray are effective for larger stems, but follow-up treatments are necessary for the subsequent resprouts (Miller 2007). Foliar application works for Paulownia seedlings and for the resprouts common after the two previously mentioned methods (Miller 2007).

Mechanical means can also be effective in controlling Paulownia. Girdling will top-kill the tree, but sprouting will require a follow-up herbicide treatment (Miller 2007).

This is a common method of control for large trees that have not yet reached maturity.

Young seedlings can be dug or pulled by hand, but this is a laborious method, especially since Paulownia can grow from broken fragments left in the soil (Miller 2007).

Similarly, mowing or cutting seedlings will prevent further spread of the species, but the resprouts will require repeated treatment, as this method will not remove a population

(Miller 2007).

Currently, there are no known natural predators to Paulownia in introduced habitats (Innes 2009). In its native China, cultivated Paulownia often experiences rot from a fungus when small, dead branches are not pruned (Hu 1961). This can occur with trees in natural settings as well, although less common, resulting in a standing, hollow trunk (Hu 1961). The most common disease to Paulownia in Asia is a phytoplasm, referred to as witches’ broom, a bacterial infection that is transmitted by insects (Hiruki

1999, Yue et al 2008). Witches’ broom has killed many Paulownia in China and Japan, causing millions of dollars in economic loss when it infects cultivated trees (Yue et al

2008). Witches’ broom causes yellowing, stunted growth, and reduced vigor in

Paulownia, ultimately leading to premature death of a tree (Hiruki 1999, Yue et al 2008).

This phytoplasm has infected Paulownia for decades in Asia, but the bacteria and vector are not known to be present in the U.S. (Hiruki 1999, Yue et al 2008).

A study has found that Paulownia tomentosa produces multiple anti-herbivore structures throughout its growth (Kobayashi et al 2008). Bowl-shaped organs, glandular hairs, and dendritic trichomes are produced at specific times of development of leaves

11 and shoots, aiding in the protection of young stems and reproductive structures

(Kobayashi et al 2008). The bowl-shaped organs secrete nectar that repels ants, while the glandular hairs and dendritic trichomes trap feeding insects (Kobayashi et al 2008).

Although there is no specific research on the effectiveness of these structures against predators in introduced habitats, it is likely they serve the same purposes, and may even protect from foraging by deer and other herbivorous mammals.

Value and Uses

High quality Paulownia wood is very lightweight yet durable when processed, making it ideal for many uses (Hu 1961). In its native eastern Asia, Paulownia wood has been coveted for centuries as the material to craft temples, furniture, musical instruments, tools, and wardrobes (Hu 1961, Preston 1983). In Japan, the traditional bridal chest is carved from only the finest grain of Paulownia wood (Hu 1961, Preston 1983). The tree has also been revered for its medicinal powers and its religious association since ancient times (Hu 1961, Preston 1983). The continual importance of Paulownia for both cultural and economic purposes in Asia has created a high demand for importing the wood, as most of the stands in its native range were destroyed for agriculture and urbanization (Hu

1961). Even with its cultivation, the supply within Asia cannot support the demand for the wood, especially with many trees becoming infected by witches’ broom (Yue et al

2008).

Paulownia was first introduced to the U.S. in the mid 1840s as an ornamental, planted in gardens, city parks, and along roads (Tang et al 1980, Preston 1983). The species escaped cultivation and established populations throughout the eastern U.S.,

12 particularly in the Appalachian Mountains (Turner et al 1988, Innes 2009, National Plant

Data Team 2012). In these natural settings, most American land managers considered

Paulownia to be a “weedy” plant until 1973, when a Japanese customer of an American wood exporting company discovered that Paulownia tomentosa was growing naturally in the Blue Ridge Mountains of Virginia (Preston 1983). That find initiated the popularity of Paulownia plantations in the U.S., a cash crop which continues today (Preston 1983).

Plantations are commonly found in the south and southwest areas of the U.S., such as in

Kentucky, Georgia, and Texas (Preston 1983). In the 1970s-1980s, during the height of

Paulownia popularity, many educational institutions began researching best methods for

Paulownia cultivation, investigating preferred soil types, the impact of surrounding vegetation, and the effectiveness of herbicide use and coppicing (Beckjord and McIntosh

1983, Preston 1983, Arnold and Gertner 1988a, Johnson et al 2003). Today, there are

Paulownia groups, such as the American Paulownia Association, founded solely for the advancement of utilizing the tree in plantations and for providing information on

Paulownia nurseries, promoting the species as a cash crop (BJG Promotions 2012).

Worldwide, there are several forest regrowth initiatives, such as the Princess Project based in Panama, which plant Paulownia species across landscapes to help prevent soil erosion and offset carbon emissions from decades of agricultural activity (Silva Tree

2010).

Chapter 2 – The Response of Paulownia tomentosa to Disturbances and its Invasive Potential

Introduction

The characteristics of Paulownia tomentosa, a perennial deciduous tree native to

China, make it a likely species to escape cultivation: the tree is fast growing, has a short juvenile period, is a prolific seed producer, has tiny wind-dispersed seeds capable of traveling long distances, can sprout from adventitious buds on the trunk and roots, and can propagate asexually via cuttings (Hu 1961, Tang et al 1980, Beckjord and McIntosh

1983). These traits allow Paulownia to quickly establish in an area and subsequently spread beyond the initial site of germination.

In the 1840s, the tree was brought to America and planted in gardens, in city parks, and along roadways strictly as an ornamental species (Tang et al 1980, Preston

1983). Today, the tree has spread beyond its original role as an ornamental planting, growing throughout the eastern U.S., with a large population in the Appalachian

Mountains, and as far west as Missouri and Texas (Turner et al 1988, Innes 2009,

National Plant Data Team 2012). Additionally, Paulownia plantations and the use of the species for land reclamation have contributed to the widespread of the tree in the U.S. In

1973, upon learning of the large demand for high quality Paulownia wood in Japan,

Americans began growing it in plantations (Preston 1983). Exporting timber from the

14 exotic tree remains a steady cash crop, and plantations are still common in Kentucky,

Texas, North Carolina, and other parts of the Southeast (Beckjord and McIntosh 1983,

Preston 1983).

With a renewed interest in Paulownia in the 1970s-1980s, the tree was no longer considered a “weed,” but a plant with great potential. Around this time Paulownia was found growing naturally on old and recently strip-mined lands in the Appalachians

(Carpenter 1977, Tang et al 1980). Results from ensuing research indicated that

Paulownia seeds are able to germinate in acidic soils as low as pH 4.0, although there is some growth depression below pH 5.5 (Turner et al 1988). This find led to trial plantings of Paulownia in other strip-mined areas of Kentucky to reclaim the land (Tang et al

1980). It is clear that poor site conditions and proximity to a mature tree do not prevent

Paulownia from germinating in an area, but the intentional planting of the tree in plantations for timber exports and for land reclamation have aided in, perhaps increased the rate of, the spread of Paulownia across the U.S.

In its indigenous habitat of China, Paulownia is limited in geographical range by changes in temperature; the tree does not survive the colder environments of latitudes north of its current distribution around 30° N (Hu 1961). Research shows that Paulownia may be restricted in the U.S. by temperature gradients. In trial tree plantings in northern and southern Kansas, only Paulownia on the southern sites survived after ten years, and these stems had a low survival rate of 50-60% accompanied by poor health (Geyer 2000).

Within inhabitable regions of China, Paulownia is further restricted to isolated individuals across the landscape, described as “spontaneous. . . in the marginal areas of the forest” (Hu 1961 p.12). The species is but a minor component of Chinese deciduous

15 forests, often growing in open areas with moist, but well-drained soils; the tree can be found in dense clusters after vegetation-clearing human activity (Hu 1961). Although

Paulownia has escaped cultivation in the U.S., the tree is mostly found in recently disturbed areas, such as after a wildfire, hurricane, or anthropogenic activity – logging, building of roads and utility corridors, and mining (Tang et al 1980,Williams 1993b,

Langdon and Johnson 1994, Kuppinger et al 2010).

Paulownia appears to exhibit the same range restrictions within introduced habitats. However, there is limited research on the ability of Paulownia tomentosa to establish after a disturbance in nonindigenous environments. Almost all studies have focused on the establishment and growth of the tree in crop plantations; with few exceptions, knowledge of Paulownia growing in disturbed areas is lacking. It is unclear of the scale and intensity of disturbances that promote Paulownia colonization, if it is dependent upon disturbance for establishment in an area, and what factors impact the persistence of the species after establishment, such as native vegetation regrowth and habitat conditions.

The objective of this study was to determine which of the many disturbances at

Shawnee State Forest are contributing to the growth of Paulownia tomentosa throughout the region, and if the nonnative species can establish after both large and small-scale disturbances. I predicted that large-scale phenomena – wildfires and logging – would promote Paulownia colonization of an area. This research will also help with creating effective management plans for the future control of exotic woody species.

Study Area The study was conducted at Shawnee State Forest, located in the unglaciated hills of the Allegheny Plateau in southern Ohio. Shawnee covers over 25,000 ha in Adams and Scioto counties, characterized by highly dissected topography composed of narrow ridges, steep hillsides, and valleys (Appendix A). The ridges are dominated by Quercus spp., Carya spp., Sassafras albidum, and Pinus echinata. On the midslope, the dominant species are Nyssa sylvatica, Liriodendron tulipifera, Acer spp., Quercus spp., and Carya spp., while bottomland is commonly populated by Fagus grandifolia, Platanus occidentalis, and Prunus serotina juvenile trees (ODNR 2010a).

Shawnee State Forest was established in 1922 when the State of Ohio acquired over 2,000 ha of land from the Peebles Land Company (ODNR 2010a). The region had a history of agriculture, logging, mining, and uncontrolled wildfires (ODNR 2010a).

Consequently, the land and the little remaining forests were in poor condition (ODNR

2010a). In the following decades, the work of the Civilian Conservation Corps and the creation of the Ohio Department of Natural Resources led to an expansion in size of

Shawnee, reforestation efforts, and the building of the current access roads (ODNR

2010a). Today, Shawnee State Forest is a multi-use forest, with timber production a primary activity (ODNR 2010a). Only the approximately 3,200 ha wilderness area is protected from all logging and public motorized vehicles, based on a 1988 designation by the State of Ohio Department of Natural Resources (ODNR 2010a). Ten years later, the wilderness area was doubled in size with the addition of an adjacent back country management area (ODNR 2010a). Although limited anthropogenic activity is allowed, the purpose of this designation was to provide for the preservation and management of

17 particular flora and fauna, especially state-listed rare or threatened species (ODNR

2010a).

Throughout Shawnee’s history many disturbances have influenced the forest. As aforementioned, the entire region was farmed, logged, and mined for many decades

(ODNR 2010a). With the continuation of timber harvesting today, there is an extensive network of logging roads throughout the forest. Although logging has been ongoing in the region for decades, only geo-referenced data from harvests from 2005-2011 were available, with the majority occurring in 2008 and 2010 as clearcuts (Appendices A-B).

In 2003, an ice storm caused tree damage, resulting in large amounts of down woody debris and adding to the decline of Q. alba throughout the forest (ODNR 2009).

Trees were uprooted or snapped at the trunk, and many lost large limbs (ODNR 2009).

Q. alba, already in decline because of root disease, infestations by introduced insect species, and other stressors, experienced additional pressure, resulting in many standing dead trees in the overstory (ODNR 2009). The ice storm significantly stressed stands throughout Shawnee; areas experiencing at least 33% canopy mortality were mapped

(Appendix A; ODNR 2009).

From April 24-30, 2009, a large wildfire consumed approximately 1,200 ha at

Shawnee (ONDR 2009). Many areas of the forest experienced high and moderate fire intensities, and over 50 km of dozer lines were constructed to assist with containment

18 dozer lines were planted with native grass and legume seed in an effort to reduce the impact of the fire (ODNR 2009). High fire intensity was defined as a stand experiencing or expected to experience at least 95% canopy mortality within one growing season, moderate-high intensity at least 75%, moderate intensity at least 50%, and low fire intensity less than 50% canopy mortality (ODNR 2009). Additionally, the amount of black, defined as burned vegetation and ash on the ground, contributed to determining the fire intensity; this information was obtained from an aerial survey conducted by the

ODNR Division of Forestry shortly after complete containment of the fire (Bowden

2012). Because of the wildfire severity and the extent of the damage to trees, the ODNR

Division of Forestry created the “Shawnee State Forest Wildfire 2009 Forest

Management/Timber Salvage Plan” to manage and rehabilitate the post-fire stands

(ODNR 2009). Cruise plots were established within the burn in September 2009, followed by a timber regeneration harvest (clearcut) of the areas that experienced moderate to high fire intensities (Appendix A).

Nonnative invasive species are an issue of concern at Shawnee State Forest, and there have been control measures implemented for some woody species (ODNR 2010a).

In October – December of 2009, triclopyr and imazapyr herbicides were applied to the targeted species Paulownia tomentosa and Ailanthus altissima (ODNR 2010a). For stems with diameter less than 0.5 cm, triclopyr was applied using a cut and spray method, and for stems between 0.5-1.6 cm in diameter, triclopyr was applied via basal bark spray

(ODNR 2010b). Large trees, over 1.6 cm in diameter, had stems injected with imazapyr

(ODNR 2010b). In May and September – October 2010, follow-up herbicide treatments were applied to Paulownia using the same methods (ODNR 2010b). Treatments were

19 most often implemented along roadways, with herbicide applied only to stems within

30.5 m on either side of the road, although earlier mapping of Paulownia and A. altissima by Shawnee State Forest employees indicated that populations likely extended further into the forest interior (Appendix A; ODNR 2010b). Mapping of Paulownia by the

ODNR Division of Forestry was not comprehensive throughout Shawnee State Forest, and the species was not controlled for in all mapped locations (Appendix A).

Methods Vegetation was sampled at Shawnee State Forest in late June – September 2011.

A ground survey of the entire accessible 1,200 ha impacted by the fire was initially conducted to map the areas of Paulownia; some areas were not accessible because of current logging or the highly dissected topography (Appendix A). Clumps of Paulownia

(20-30 m2 area) and individual stems – at least 30 m from the next nearest Paulownia stem – were mapped as one point. The same procedure was conducted in the vicinity surrounding the fire perimeter, extending approximately 2 km outward from the fire boundary. From this larger area of mapped Paulownia, 61 points were randomly chosen with the species present, and a sample plot was established at each point; 28 plots (FP – fire, Paulownia) were located within the area impacted by the fire and 33 plots (NFP – no fire, Paulownia) beyond the fire perimeter. The minimum possible density of Paulownia within a plot was one stem. Each of the 61 plots had a matched plot (FNP – fire, no

20 established elsewhere in Shawnee where Paulownia was absent, but with similar topography. All plots were within approximately 100 m of a logging road or created dozer line.

Each of the 122 sample plots was 10x4 m in size. Percent slope, aspect

(transformed using the method of Beers et al 1966), elevation, latitude and longitude

(using a Garmin GPS 76 hand-held GPS unit, accuracy 15 m), and canopy closure (using a densiometer) were collected for each plot. Soil type (soil series) was determined from the latitude and longitude using the U.S. Department of Agriculture Web Soil Survey.

Within each plot, total percent cover of vegetation for the entire plot and average vegetation height were estimated. Total percent cover was defined as the percent of the plot covered by grasses, herbs, vines, and woody shrubs less than 1m in height. Average vegetation height was determined by taking the average of four random readings of the understory vegetation (herbs, vines, and woody shrubs), one reading in the center of each of four equal quadrats established within a plot. Stem counts of all identified herbaceous species and woody species were collected within the entire 10x4 m plot; plants were identified to the species level whenever possible. For the plots with Paulownia present

(FP and NFP), a circular area with a 15 m radius extending from the 10x4 m plot center was created; all Paulownia tomentosa stems within this area were counted, their height and d.b.h. were recorded, and whether the tree had seeded. Each Paulownia stem, in multiples or clumps, was counted and recorded separately, not dependent on origin (root or trunk sprout).

Paulownia Density Statistical Analysis

To determine the influence of disturbance types on the density of Paulownia, redundancy analysis (RDA) was used with CANOCO software Version 4.56 (Biometris-

Plant Research International, Wageningen, The Netherlands). RDA is a direct linear ordination method that redefines the sample units as linear combinations of the explanatory variables; thus, samples are distributed in the space defined by the explanatory matrix (Leps and Smilauer 2003, McCune and Grace 2002). The significant axes represent actual variation in the species data, as opposed to noise, and allow identification of the most influential environmental variables sampled (ter Braak and

Smilauer 2002). RDA was chosen after conducting detrended canonical correspondence analysis (DCA), which suggested a short gradient length, indicating more homogenous species data which are better fit by a linear than unimodal model (Leps and Smilauer

2003).

The environmental matrix factors consisted of the following continuous variables: slope, transformed aspect (Beers et al 1966), elevation, percent ground cover of vegetation, average height of vegetation, canopy closure, and the amount of time (years) since the last logging activity in the area, using the available data from 2005-2011. There were the following categorical variables: soil series (Berks channery silt loam or

Shelocta-Brownsville association), fire intensity (outside the fire boundary, low intensity, moderate to moderate-high intensity, and high), herbicide application (binary), and ice damage resulting in overstory mortality (binary).

Paulownia stems were divided into three categories: seedlings, saplings, and trees. Seedlings were defined as less than 137cm in height, saplings as 137cm or taller and 3cm d.b.h. or less, and trees as 137cm or taller and greater than 3cm d.b.h. Density was defined as the number of Paulownia stems per hectare.

Results Results of the RDA show a significant relationship between the species data

(Paulownia stem density) and the environmental variables (Monte Carlo Test, P = 0.002).

Together, the first two canonical axes explain 48.5% of the variation. The first canonical axis is also significant (Monte Carlo Test, P = 0.002), explaining 36.7% of the variation in the stem density data. The most important environmental gradients contributing to the first and second axes were canopy closure, ground cover, and average vegetation height

(Table 2.1). Fire intensity levels and ice damage to the overstory were variables with strong correlation coefficients, but because they are nominal variables bear little information (ter Braak and Smilauer 2002).

In Figure 2.1 the species arrow points in the direction of the greatest rate of increase of abundance. Quantitative environmental variables are represented by vectors, with lengths relating to a variable’s importance to the ordination. The direction of an environmental variable vector indicates its correlation with each of the canonical axes; vectors can be considered to pass backwards through the origin as well. Nominal environmental variables are represented by their centroid. The environmental variables elevation and soil type (Berks channery silt loam and Shelocta Brownsville association) are not included in Figure 2.1 because of the proximity of their value to the origin, indicating little importance to the ordination.

Sample plots impacted by the 2009 fire are generally restricted to the left of the ordination and have experienced other disturbances, such as logging and targeted herbicide application, as well as ice storm damage to certain plots. These areas have more gradual slopes facing southwest. There is more understory vegetation, measured by percent ground cover and average vegetation height (Figure 2.1).

Sample plots not impacted by the 2009 fire are generally restricted to the right of the ordination. Most plots have not been impacted by recent large disturbances, though some have canopy damage from the 2003 ice storm. The plots are on steeper slopes facing northeast and have more canopy closure (Figure 2.1, Table 2.2).

Maximum Paulownia seedlings densities seem to be restricted to plots within the burn area; Paulownia saplings and trees are found in high densities in plots both impacted by the 2009 fire and in areas not impacted. High stem density of Paulownia seedlings appear to be in areas that experienced high fire intensities and herbicide treatment.

Seedlings on southwest slopes seem to increase in abundance as the time from the last logging activity increases. Paulownia saplings are growing in greater density in areas that experienced medium fire intensities and greater ice storm damage. Sapling density is greatest as ground cover and vegetation height increases and slope decreases. Paulownia trees reach maximum stem density on northeast slopes in areas not impacted by the 2009 fire. Tree density increased as canopy closure increased (Figures 2.1-2.2).

Discussion

Seedlings

The areas with the highest density of Paulownia seedlings experienced several large disturbances in the past decade: a widespread wildfire in spring of 2009, pre and post-fire clearcut logging, and targeted herbicide application to Paulownia tomentosa stems and other invasive species. Paulownia tomentosa is known to easily colonize recently disturbed areas for several reasons. First is a light-dependency for seeds to germinate; studies have found only Paulownia seeds in high light levels germinate, one of the factors cited for the restriction of the species in its native range of China (Hu 1961,

Longbrake 2001). Additionally, increased photoperiods have resulted in a faster growth rate and longer duration of seed growth, resulting in greater overall growth height and biomass production (Carpenter et al 1983). This allows Paulownia to rapidly shoot above any competing vegetation, a necessity to survival as the species does not survive over-topping by other plants (Beckjord and McIntosh 1983, Carpenter et al 1983, Keeley

2006). The small, delicate seeds produce a weak primary root with sparse root hairs limited near the soil surface, making growth in areas with any leaf litter difficult

(Millsaps 1936, Carpenter et al 1983, Kuppinger 2008). Fire helps clear the forest floor and thin vegetation, the degree of which is dependent upon the fire severity (Ryan and

Noste 1985, Keeley 2009). The salvaging efforts post-fire also created an open canopy at

Shawnee State Forest. The recent high density of Paulownia seedlings and saplings in areas of Shawnee is thus likely a result of the fire in 2009. The open areas after the wildfire likely allowed Paulownia to establish as a seedling, and its rapid growth has kept the exotic tree above native vegetation, reaching sapling-size (Hu 1961, Beckjord and

McIntosh 1983). Studies have recorded Paulownia juvenile stems growing about 1 m in a year and sprouts more than 5 m, of particular relevance to Shawnee since Paulownia can root sprout after fire, with enough leaf area to successfully shade out any vegetation undergrowth (Beckjord and McIntosh 1983). This allows the exotic tree to successfully compete with natural vegetation regrowth.

Although clear-cutting produces open areas conducive to Paulownia germination, the relationship between seedling density and years since logging (2-7 year range) is positive; Paulownia seedling density reached its maximum as years since last logging increased. There are several possible explanations for this result, related to sampling technique, the 2009 fire, and the characteristics of Paulownia.

In September 2009, the ODNR Division of Forestry established 433, 2.2 m radius cruise plots within the entire burn area (Appendix A). All woody stems over 0.3 m tall and with a d.b.h. less than 2.1 cm were inventoried, and no Paulownia stems were found.

It is possible Paulownia was growing at the time of the cruise plot sampling and not inventoried; early seedlings are often only a few centimeters tall after several weeks of growth, and the sampling crews may have been focusing on common woody species to the forest (Millsap 1936). However, given the high shade-intolerance of Paulownia, it is unlikely seeds germinated years earlier, after logging activity, and have been suppressed until after the fire in 2009 (Beckjord et al 1985, Arnold and Gertner 1988a, Young and

Young 1992). Additionally, if Paulownia seedlings were growing in response to the previous logging activity in the area, they likely did not survive the fire of 2009.

Paulownia is not considered to be fire resistant – branches are brittle with thin bark,

26 making it likely stems were killed by fire (Hu 1961, Innes 2009, National Plant Data

Team 2012).

The seed source for the high density of Paulownia seedlings found after the fire is not certain. Germination could be from seeds stored within the soil, as Paulownia produces a large seed bank (Young and Young 1992, Hyatt and Casper 2000). However, in one of few studies conducted in situ, Hyatt and Casper (2000) found little build-up of the seed bank between years and seed bank viability was contested. Results from Hyatt and Casper (2000) showed Paulownia seed mortality exceeded 70% over a two year period, and only two individuals germinated from this seed source. The low viability of the species’ seed bank indicates this is probably not a significant source for new germination (Hyatt and Casper 2000). Conversely, Longbrake (2001) found low mortality of Paulownia field-sown seeds, and predicted that seeds could remain viable in the soil for up to fifteen years (Longbrake 2001). Longbrake’s study, however, used

Paulownia seeds that had been previously dry stored, a factor that could have influenced viability. Additionally, conclusions were based on extrapolation of data, a method some consider less reliable (Palmer 1990). It is more likely the seed source for the high density of Paulownia seedlings at Shawnee observed in 2011 are any mature Paulownia trees that survived the 2009 fire or mature Paulownia stems outside the burn area (Appendix

C). Paulownia seeds are produced in masses and travel great distances; field investigations have commonly discovered Paulownia seedlings 4 km from the parent plant (Hu 1961, Langdon and Johnson 1994). Thus, it is possible that the parent source for seedlings within the burn is a mature Paulownia kilometers away, especially considering the clumped distribution of sample plots with the species present. Kuppinger

(2008) found that Paulownia invaded a previously uninhabited area following a major wildfire because seeds are able to travel long distances. There has been little research on the direct effects of fire on exotic species, including Paulownia tomentosa – more work is necessary to elucidate the interactions between forest disturbances and seed dispersal and viability.

The third disturbance to areas with the highest Paulownia seedling density was herbicide application, made to Paulownia and A. altissima in 2009 and 2010 post-fire.

The two methods employed, stem injection and basal bark spray, are known to result in stump and root sprouts after main stems of Paulownia are deadened (Miller 2007). Field observations showed that many targeted Paulownia stems (visible hack marks) had sprouts, likely a result of the ineffective herbicide application (Chongpinitchai, personal observation). Treatment was conducted by a different crew of students each season, and application was not thorough even in targeted treatment areas (ODNR 2010b;

Chongpinitchai, personal observation). Multiple sprouts could thus be contributing to the high density of Paulownia seedlings found. The root sprouts, however, may also be a result of the 2009 fire. As aforementioned, fire likely top-kills Paulownia stems, but buried root systems can survive, giving rise to tall stems off adventitious buds (Hu 1961,

Kuppinger 2008, Innes 2009). Although no Paulownia stems were aged, it still cannot be determined if the high density of seedlings is a result of the wildfire or the herbicide application, as both occurred in the same year. It is likely that root sprouts from both disturbances led to the high density of seedlings, but the 2009 fire the greater contributor, as this was the more influential factor in the RDA model.

Saplings

The highest densities of Paulownia saplings occurred in both burned and unburned areas. With a fast growth rate, it is likely many stems that germinated post-fire within the 2009 wildfire area have already reached sapling-size. Outside the burn area, it is probable that the 2003 ice storm created forest canopy openings that favored

Paulownia colonization (Appendix A). Ice storms are common sources of disturbance in mesic forests of the Eastern United States, occurring on a large scale in fairly regular intervals – in the Appalachians, landscape-level ice storms occur about every twenty years (Boerner et al 1988). Ice storms result in overstory mortality, advancing, if not accelerating, forest succession (Lemon 1961, Boerner et al 1988). Glaze, a clear layer of ice that forms on the surface of objects, is the major cause of direct mortality, causing breaking, snapping, and bending of branches and tree tops (Lemon 1961, Bruederle and

Stearns 1985, Boerner et al 1988). The extent of direct mortality depends upon the specific species, crown form, slope, and aspect, as well as context specifics (Lemon 1961,

Bruederle and Stearns 1985, Boerner et al 1988). Such species as L. tulipifera, A. rubrum, Q. rubra, and Fagus grandifolia are a few of the many trees listed with varying susceptibility to severe ice damage, all species common to Shawnee State Forest (Lemon

1961, Boerner et al 1988). Secondary damage must also be considered; severely damaged trees often fall or lose significant limbs, toppling surrounding trees and enlarging the subsequent canopy gap (Boerner et al 1988).

Whether it is direct or secondary damage, ice storms cause disturbances that aide in forest succession. The openings to the canopy allow early or late successional species to grow in place of the damaged trees, depending on which suppressed understory species

29 are released (Lemon 1961, Boerner et al 1988). The new canopy gaps can also allow seeds from distant trees to invade the open floor (Boerner et al 1988). The latter scenario is likely to have occurred at Shawnee after the ice storm in 2003. As aforementioned,

Paulownia seeds are very windborne, allowing them to travel great distances (Millsaps

1936, Hu 1961, Langdon and Johsnson 1994, Kuppinger 2008). The mature Paulownia already established at Shawnee State Forest are a possible seed source for colonization of the ice-damaged areas which, eight years later, are now dense with sapling-sized stems.

At Shawnee, the highest densities of Paulownia saplings occur in areas where taller vegetation and more ground cover exist. Some studies have shown that Paulownia has the ability to successfully outgrow other vegetation in certain circumstances, indicating that native vegetation regrowth is not necessarily an impediment to the species’ survival (Beckjord and McIntosh 1983). In contrast, Kuppinger et al (2010) found that after initial establishment of seedlings post-fire, Paulownia stems were reduced the most in areas with native vegetation regrowth of at least 1 m in height.

Paulownia persisted only on steep, xeric outcroppings where native vegetation was sparse ten years post-fire (Kuppinger et al 2010). Paulownia survival from seedlings to saplings seems to be dependent on multiple factors. First, if Paulownia can gain the competitive edge over native vegetation initially, it appears the species will keep the advantage. This is likely what occurred at Shawnee State Forest – after the fire,

Paulownia seedlings germinated immediately in the post-fire conditions. Coupled with its rapid growth rate, Paulownia was able to establish as saplings before the surrounding vegetation outcompeted it, the results Kuppinger et al (2010) found in their study. In this

30 way, the shade-intolerant Paulownia has established in high densities of saplings though the areas now have tall vegetation and more ground cover than immediately post-fire.

Second, ensuring that Paulownia survives to sapling size may depend upon the species of native vegetation present and the growing conditions. Some native species can out-compete invasive species, but only in certain conditions. In a pair-wise comparison of co-occurring native and nonnative species, Daehler (2003) found that native plants consistently performed better when there was low resource availability – light, water, or nutrients. However, there were exceptions, such as invaders better capturing and photosynthesizing light in disturbed Hawaiian forests, similar to what Paulownia appears capable of doing, especially given its large leaf area (Daehler 2003). These findings led

Daehler (2003) to conclude that at some life stage under some combination of growing conditions, native species will have a survival advantage over exotic species. Growing conditions are directly related to topography, and these two factors in the areas of

Shawnee with the highest density of Paulownia saplings may be contributing to the success of other vegetation regrowth. In the areas of significant vegetation regrowth, slopes are more gradual, which can produce differences in soil drainage, litter distribution and decomposition (Hicks and Frank 1984, Desta et al 2004). Such conditions can be favorable to native vegetation success. However, other research, such as the exception

Daehler (2003) found in disturbed Hawaiian forests, has stated that nonindigenous species have the advantage over native vegetation, which are commonly less aggressive and more shade tolerant species (Keeley 2006). Such studies have concluded that nonnative plants out-compete native vegetation because the introduced species are more adept at utilizing resources in the local habitat, for example the ability to grow in higher

31 density on drier sites (Sakai et al 2001, McDonald and Urban 2006). The competitive ability of native versus nonnative species growing together remains a topic of contention and requires further study.

At Shawnee State Forest, Paulownia saplings successfully established in high density in areas with high amounts of ground cover and tall vegetation. Although native vegetation regrowth out-competed Paulownia over time in previous studies, this is currently not the case at Shawnee (Kuppinger et al 2010). The combination of surrounding vegetative species, topography, growing conditions, disturbance influences, and the fast-growth of Paulownia have resulted in the persistence of the nonnative to advance to sapling-size.

Trees

The highest densities of Paulownia trees, both juvenile and seed-bearing, at

Shawnee State Forest occur in areas not impacted by the 2009 fire. There is a notable absence of any large disturbance outside of the burn area in recent years, further evidenced by the high amount of canopy closure. Paulownia establishment is disturbance-dependent to some degree, as the seedlings need sunlight and cleared soil in order to germinate (Hu 1961, Williams 1993b, Langdon and Johnson 1994). Although the RDA model did not identify any recent disturbance, there are two possibilities in these areas, neither of which was included in the analysis. First is the presence of canopy gaps. Although no empirical data was collected on the size and frequency of the canopy gaps in the stands at Shawnee, field observations show Paulownia growing in overstory openings (Figure 2.3). Many Paulownia stems are growing on root mounds, suggesting a

32 single tree fall as the disturbance producing the canopy opening (Chongpinitchai, personal observation). It is known that tree falls are a common source of disturbance in

Eastern deciduous forests, with most tree falls creating small gaps (Whitmore 1989).

Still, the varying sizes of gaps, even those that are smaller, influence the species composition (Billups and Burke 1999). Typically shade-intolerant species, which require full sunlight for at least part of the day, are termed pioneer species (Whitmore 1989).

Shade-intolerant species are often restricted to large canopy gaps, due not only to their need for high sunlight to germinate, but also because if a gap is not large enough, it will close laterally before the pioneer species is able to reach the canopy and become shaded by another species (Canham 1989, Whitmore 1989). Paulownia, requiring bare soil and high light for seed germination, is considered a pioneer species. However, the small tree gaps at Shawnee do not seem to present a hindrance to Paulownia colonizing these places, given some full sunlight penetrates the opening. Paulownia likely was successful because of its immediate germination after dispersal, as opposed to delayed germination of other species (Connell 1989). Coupled with fast-growth, Paulownia had an advantage over other species attempting to colonize the small canopy gap, allowing the exotic to reach canopy level before the gap closed laterally (Connell 1989, Knapp and Canham

2000). Additionally, it is probable Paulownia has the capacity for greater physiological plasticity than many native species because it is a shade-intolerant subjected to greater environmental fluctuation; Paulownia has had to adapt to environmental gradients in its indigenous habitat and uses this feature to its advantage in introduced habitats (Canham

1989). Although small canopy gaps produce only a minimal change in the microclimate, as long as full sunlight is able to reach the forest floor for some time during the day,

Paulownia seems equipped with advantages over native vegetation to colonize such small openings (Billups and Burke 1999, Knapp and Canham 2000). Betula alleghaniensis and

Tsuga heterophylla are known for germinating on soil mounds, so it is likely Paulownia may have the ability to do the same, although no studies have looked at this factor

(Lorimer 1985).

Logging roads are the second source of disturbance to the stands where

Paulownia trees were found growing in high densities. Shawnee State Forest is a working and actively managed forest, with approximately 3,200 ha designated as wilderness area. The working forest is logged and is open to other anthropogenic activities, such as hiking, biking, horseback riding, and research. Prior to the wilderness designation, the region was a high resource-extraction area, with a history of heavy mining and logging. Some of the logging roads are still in use, while others are visibly older with various stages of vegetation regrowth. The extensive network of logging roads throughout Shawnee is not mapped, but almost all sample plots were located within 100 m of a logging road or dozer line from the 2009 wildfire. Paulownia has been documented growing densely near roads, trails, and utility corridors – in general, areas disturbed by anthropogenic activities are considered more prone to colonization by the species (Williams 1993a, Langdon and Johnson 1994, Innes 2009). This is an issue common with most nonnative invasive species: areas impacted by human activities, particularly those that result in loss of canopy cover and increased bare ground, have the potential to be suitable sites for nonnative invasive plants (Gelbard and Belnap 2003,

Watkins et al 2003, Keeley 2006). Roads, both primitive and paved, are especially known to have an increased frequency and density of exotic species in proximity

(Gelbard and Belnap 2003, Watkins et al 2003). Reduced leaf litter and depth, increased sunlight, compacted soil, potentially damaged seed banks of native species, and reduced competition from native vegetation are a few of the reasons that roads are favorable to exotic species (Gelbard and Belnap 2003, Watkins et al 2003). Thus, it is likely that the logging roads and dozer lines throughout Shawnee are serving as vectors for the spread of

Paulownia even to mature stands in the forest.

The densest areas of Paulownia trees at Shawnee show a strong positive correlation with northeast aspects. North and east aspects are generally more productive than west and southwest aspects (Trimble and Weitzman 1956, Hicks and Frank 1984,

Desta et al 2004). West and southwest facing slopes are sunnier and drier due to the angle of the sun’s rays (Hicks and Frank 1984, Desta et al 2004). Research has found this can lead to slower rates of decomposition of leaf litter, a possible reason for the lower productivity on these aspects, as nutrient cycles are less dynamic (Hicks and Frank

1984, Desta et al 2004). These factors influence the vegetative composition on slopes, and studies show that some tree species have a strong association with certain aspects.

For example, Quercus species are more common on southwest slopes, while L. tulipifera on north-facing slopes (Desta et al 2004). Juvenile and mature Paulownia stems appear to have a strong association with northeast slopes, but seedlings the opposite, with highest densities facing southwest. This finding may only be temporary; while research has shown Paulownia seedlings prefer cleared, drier sites for the first year, it is not known whether seedlings at least two years old can survive the drier southwest slopes

(Arnold and Gertner 1988b). Paulownia seedlings may need bare soil and high sunlight to germinate, but it seems the species is also able to persist on moister, shadier sites; this

35 may be related to the species’ greater physiological plasticity than its competitors at

Shawnee. Most plants exhibit some physiological plasticity in simple ways, such as the dropping of leaves, but certain species have more specialized adaptations to their environments (Bradshaw 1965). Photosynthesis is a process plastic in many species; different rates of photosynthesis have been measured across environmental ranges as plants respond to light intensity changes (Bradshaw 1965, Delagrange et al 2004,

Davidson et al 2011). Specifically, shade-intolerant species and woody species in the understory show more dependence on light-physiological plasticity (Delagrange et al

2004). Additionally, invasives are more plastic than non-invading native plants, including, but not limited to, exhibiting responses to environmental changes via photosynthesis, leaf area, and root biomass both when resource availability increased and decreased (Davidson et al 2011). These capabilities allow the plant to adapt to new environments, often different from their indigenous habitat, and may be a factor contributing to invasive plants’ wider range distribution (Schlichting and Levin 1986,

Pohlman et al 2005, Davidson et al 2011). In her studies, Longbrake (2001) found

Paulownia exhibited phenotypic plasticity when exposed to low versus high light. While no data was collected on the rate and efficiency of photosynthesis in Paulownia tomentosa in more closed stands at Shawnee State Forest, it is possible the tree exhibits plasticity of this trait; the species’ large leaves, known to reach sizes around a meter in length, may be an example of how Paulownia has adapted to competition for sunlight from neighboring plants. With high plasticity, Paulownia would not be restricted to more open and sunnier south and southwest aspects, where the tree is known to be more

36 common, but would also be able to grow on shadier northeast slopes with more canopy closure (Hu 1961, Tang et al 1980).

Further, many native tree species become infected by diseases or pathogens which reduce their health and vigor (USDA Forest Service 2012). Paulownia, with no known natural predators outside its native China, has a competitive advantage, facing fewer habitat pressures (Innes 2009). This could be another factor in the ability of the exotic tree to persist in sites outside its known ecological niche, what appears to be occurring at

Shawnee.

Conclusion

Across Shawnee State Forest, there have been multiple disturbances in the past decade – ice storm damage, a large wildfire, logging, and herbicide treatments – that are interacting to influence the structure and composition of the forested landscape. All of these disturbances have created conditions conducive to Paulownia growth, verifying that the exotic species is disturbance-dependent. Some studies further suggest that Paulownia requires large-scale disturbances to colonize an area, but this may not be necessary (Hu

1961, Williams 1993b, Longbrake 2001). Paulownia is growing in small canopy gaps at

Shawnee, often caused by a single tree fall. In this way, the growing habits of Paulownia at Shawnee State Forest seem different than in the tree’s native habitat where it is restrained by the occurrence of large-scale disturbances. The key to successful growth after small-scale disturbances in Shawnee may reside in the species’ plasticity, after its wind-dispersed seeds germinate in a small, but cleared area. It has been established that

Paulownia tomentosa is a shade-intolerant and thus capable of greater light-dependent

37 plasticity (Longbrake 2001, Delagrange et al 2004). However, it remains to be seen if

Paulownia populations will persist in these areas as the small canopy gaps continue to close and no new disturbances occur. It is also possible the Paulownia growing in openings from single tree falls are ramets from a parent tree established elsewhere; however, there has been no direct research on the contribution clonal growth makes to the survival of the species in shadier habitats.

Returning to Shawnee State Forest in 8-10 years will determine if Paulownia has regenerated in the mature closed stands or has been replaced by native woody species, and if density of the species has decreased in the areas impacted by the 2009 wildfire.

Long term research is necessary to determine if Paulownia tomentosa can persist after colonizing a recently disturbed area, or if the exotic tree is dependent upon continual disturbances for a self-sustaining population. Similarly, more work is needed to determine if Paulownia can expand its range in introduced habitats without the aid of disturbances, a key stage of an invasion by any species (Allendorf and Lundquist 2003).

Table 2.1 Redundancy analysis of Paulownia stem density data – correlations of species ordination axes with environmental variables.

Variable Axis 1 Axis 2 Canopy Closure 0.71 -0.13 No Fire 0.53 -0.05 Ground Cover -0.51 -0.26 High Fire Intensity -0.40 0.06 Aspect 0.38 -0.08 Slope 0.36 0.21 Last Logging (years) -0.28 0.03 Low Fire Intensity -0.19 0.08 Herbicide Application -0.19 0.18 No Herbicide Application 0.19 -0.18 Medium Fire Intensity -0.18 -0.14 Average Vegetation Height -0.14 -0.42 Shelocta Brownsville Assoc. -0.10 0.09 Berks channery silt loam 0.10 -0.09 Ice Damage to Overstory -0.08 -0.35 No Ice Damage to Overstory 0.08 0.35 Elevation 0.01 -0.06

Table 2.2 Percent canopy closure for all sample plots (N = 122) from densiometer readings at Shawnee State Forest, Ohio

Plot Location Average % Canopy Closure Range of % Canopy Closure Within 2009 Burn Area 21 0-89.5

Outside 2009 Burn Area 81 15.5-100

Figure 2.1. Redundancy analysis triplot of Paulownia tomentosa stem density and environmental variables. HighFire = high fire intensity, LowFire = low fire intensity, MedFire = moderate fire intensity, NoFire = outside the burn area, Logging = years since last logging activity, IceDmge = 2003 canopy ice damage, No IceDm = no canopy mortality, GroundCo = percent ground cover, AvgVegHt = average vegetation height, NoHerb = no herbicide application, CanopyCl = canopy closure

100

50 2009 Burn Area

no. ofstems no. 40 Outside 2009 Burn Area 30

0 Seedlings 0-3.0 cm 3.0+ cm d.b.h. class

Figure 2.2 Distribution of Paulownia stem d.b.h. classes at Shawnee State Forest, Ohio in 2011

Figure 2.3 Paulownia tomentosa growing in a canopy gap in a mature stand not impacted by the 2009 wildfire at Shawnee State Forest, Ohio.

Chapter 3 – Effects of Paulownia tomentosa on Natural Vegetation

Introduction

Exotic species are an increasing concern in the management of native biodiversity and ecological processes. There is a continuous influx of nonindigenous species to the

U.S., including plants, many of which have become invasive (Allendorf and Lundquist

2003). Both the U.S. National Park Service and the U.S. Department of Agriculture

Forest Service state invasives as significant threats to forests and native species (Keeley

2006). Most managers faced with control of exotic plant species are lacking in sustainable environmental and economic plans of approach, as solutions prove to be costly in terms of funds, labor, collaboration efforts, and time (Larson et al. 2011).

However, nonindigenous plant species change the dynamics of native ecosystems in numerous ways, making sound management crucial.

Nonnative species can greatly alter the fire regime of an ecosystem. Exotic plants can increase the fuel-bed flammability, making fires more frequent; increase the likelihood of crown fires by changing the structure of a forest; and promote fire spread by increasing rates of plant tissue decomposition or adding more flammable chemical compounds via plant tissues (Brooks et al 2004). Paulownia tomentosa, which has very brittle branches and large leaves, likely adds to the amount of coarse woody debris and leaf litter buildup on a forest floor (Hu 1961). As fuel density, type, and arrangement are integral parts of a fire regime, Paulownia, and other nonnative plants, can easily alter the

44 intensity, frequency, and periodicity of fire regimes by changing the fuel characteristics of a habitat (Brooks et al 2004). After years of fire suppression, there is an increase in prescribed burns and manipulation of fire severity to return ecosystems to their historical regime (Keeley 2006). However, this leaves cleared gaps that are susceptible to exotic plant invasions by species that were not present in the historical landscape (Brooks et al

2004, Keeley 2006). Additionally, many invasive species benefit from fire by subsequently sprouting, adding to their spread in introduced habitats (Keeley 2006).

Nonnative plants can alter soil characteristics in multiple ways. Because of their tissue composition, plant morphology, and phenology, nonindigenous plants often produce more leaf litter and have faster rates of litter decomposition, which in turn can change the dynamics of nutrient cycling in a soil community (Ehrenfeld 2003, Brooks et al 2004). Many invasive species increase the biomass and net primary production of their introduced habitat, which can lead to an increase in nitrogen and other nutrient availability, as well as change the soil pH (Ehrenfeld 2003). If an exotic plant is capable of clonal reproduction, ramet growth can alter the rhizosphere composition (Ehrenfeld

2003). Mycorrhizal associations with nonnative species may change the soil in a similar manner (Ehrenfeld 2003).

Ecological processes can be altered by the presence of nonnative plants. In the dominant shrubland ecosystem of South Africa, an invasion by exotic woody species has led to a decrease in annual runoff, ultimately reducing the stream-flow of the entire region (Le Maitre et al 1996). The habitat has become less favorable for native plant species, and the drier climate has increased the frequency and intensity of fires, which in turn has increased soil erosion (Le Maitre et al 1996).

In many cases, exotic plants have an advantage over native species, which leads to reduced biodiversity of an area when the latter are out-competed; this is common in areas invaded by garlic mustard (Alliaria petiolata), which monopolizes resources in its introduced habitat (Schwartz and Heim 1996, Brooks et al 2004). Exotic species may be able to out-compete native plants because they evolved advantageous adaptations in their natural habitat or exhibit greater plasticity, allowing them to thrive in new ecosystems

(Canham 1989, Allendorf and Lundquist 2003). There is also often a lack of natural predators for exotic plants in introduced habitats, whether insects, herbivorous species, or diseases (Allendorf and Lundquist 2003). In its native China, Paulownia is often ravaged by a disease referred to as witches’ broom, a specialized bacterial disease (phytoplasma) that is transmitted by insects (Hiruki 1999, Yue et al 2008). Witches’ broom causes yellowing, stunted growth, and reduced vigor, ultimately leading to premature death of a tree (Hiruki 1999, Yue et al 2008). Although this phytoplasma has been affecting

Paulownia in China for decades, neither the bacteria nor the vector are in the U.S. (Yue et al 2008). With no known predators in introduced habitats, Paulownia and other exotic species can have an edge over native plants which are faced with multiple stressors

(Sakai et al 2001).

Nonindigenous species can affect native plants indirectly by changing habitat conditions and ecological processes, or directly by competing with native species for resources and space (Call and Nilsen 2003). In both ways, introduced species can have a negative effect on the vegetation composition, which can lead to a decrease in biodiversity; as areas lower in species richness are considered more susceptible to invasions, this becomes a self-perpetuating cycle of reduced biodiversity (Sakai et al

2001, Martin et al 2009). For most exotic species, there is little information on the interaction of the invader with the native vegetation of the targeted habitat, but this is critical to understanding what makes a species a successful invader (Knapp and Canham

2000). Paulownia tomentosa is no exception; there is a lack of knowledge on the role of the nonnative tree in introduced habitats. Most research has focused on establishing the species in plantations as a crop, and little work has been conducted in natural settings since Paulownia escaped from cultivation in the U.S. My objective was to determine if

Paulownia is negatively affecting the vegetation composition at Shawnee State Forest, specifically changing the native species composition and lowering species richness. I predicted that the presence of Paulownia is changing the understory composition of the forested landscape by acting as an early successional species in an introduced habitat.

Consequently, the land and the little remaining forests were in poor condition (ODNR

2010a). In the following decades, the work of the Civilian Conservation Corps and the creation of the Ohio Department of Natural Resources led to an expansion in size of

Shawnee, reforestation efforts, and the building of the current access roads (ODNR

2010a).

Throughout Shawnee’s history many disturbances have influenced the forest. As aforementioned, the entire region was farmed, logged, and mined for many decades

In 2003, an ice storm caused tree damage, resulting in large amounts of down woody debris and adding to the decline of Q. alba throughout the forest (ODNR 2009).

Trees were uprooted or snapped at the trunk, and many lost large limbs (ODNR 2009).

Q. alba, already in decline because of root disease, infestations by introduced insect

48 species, and other stressors, experienced additional environmental pressure, resulting in many standing dead trees in the overstory (ODNR 2009). The ice storm significantly stressed stands throughout Shawnee; areas experiencing at least 33% canopy mortality were mapped (Appendix A; ODNR 2009).

From April 24-30, 2009, a large wildfire consumed approximately 1,200 ha at

Shawnee (ONDR 2009). Many areas of the forest experienced high and moderate fire intensities, and over 50 km of dozer lines were constructed to assist with containment

(Appendix A; ODNR 2009). Large standing dead oaks from the 2003 ice storm contributed to the high fire intensities and canopy mortality (ODNR 2009). The forest is still recovering in areas that suffered higher burn intensities, and some of the constructed dozer lines were planted with native grass and legume seed in an effort to reduce the impact of the fire (ODNR 2009). High fire intensity was defined as a stand experiencing or expected to experience at least 95% canopy mortality within one growing season, moderate-high intensity at least 75%, moderate intensity at least 50%, and low fire intensity less than 50% canopy mortality (ODNR 2009). Additionally, the amount of black, defined as burned vegetation and ash on the ground, contributed to determining the fire intensity; this information was obtained from an aerial survey conducted by the

ODNR Division of Forestry shortly after complete containment of the fire (Bowden

2012). Because of the wildfire severity and the extent of the damage to trees, the ODNR

Division of Forestry created the “Shawnee State Forest Wildfire 2009 Forest

Management/Timber Salvage Plan” to manage and rehabilitate the post-fire stands

(ODNR 2009). Cruise plots were established within the burn in September 2009,

49 followed by a timber regeneration harvest (clearcut) of the areas that experienced moderate to high fire intensities (Appendix A).

Nonnative invasive species are an issue of concern at Shawnee State Forest, and there have been control measures implemented for some woody species (ODNR 2010a).

(ODNR 2010b). Large trees, over 1.6 cm in diameter, had stems injected with imazapyr

(ODNR 2010b). In May and September – October 2010, follow-up herbicide treatments were applied to Paulownia using the same methods (ODNR 2010b). Treatments were most often implemented along roadways, with herbicide applied only to stems within

ODNR Division of Forestry was not comprehensive throughout Shawnee State Forest, and the species was not controlled for in all mapped locations (Appendix A).

Methods

Vegetation was sampled at Shawnee State Forest in late June – September 2011.

Paulownia and NFNP – no fire, no Paulownia) where Paulownia was absent but with similar slope steepness, aspect, elevation, and soil type. Matched paired-plots were established within 75 m of each other with the exception of five plots where Paulownia was too abundant and the topography too dissected. For these five, its matched plot was established elsewhere in Shawnee where Paulownia was absent, but with similar topography. All plots were within approximately 100 m of a logging road or created dozer line.

Each of the 122 sample plots was 10x4 m in size. Percent slope, aspect

(transformed using the method of Beers et al 1966), elevation, latitude and longitude

51 vegetation height was determined by taking the average of four random readings of the understory vegetation (herbs, vines, and woody shrubs), one reading in the center of each of four equal quadrats established within a plot. Stem counts of all identified herbaceous species and woody species were collected within the entire 10x4 m plot; plants were identified to the species level whenever possible. Woody species were divided into the following groups: white oaks (Q. alba, Q. prinus), red oaks (Q. marilandica, Q. velutina,

Q. rubra), maples (A. rubrum, A. saccharum), Carya spp., Fraxinus spp., Rhus spp.,

Prunus spp., Ulmus spp., Pinus spp., L. tulipifera, N. sylvatica, S. albidum, A. altissima,

P. tomentosa, and other (all other woody species). The height and the diameter at breast height (d.b.h.) of all woody species over 137 cm were measured.

Paired Plots Statistical Analysis

To compare the similarity of environmental characteristics between matched pairs and among all 122 sample plots, principal components analysis (PCA) was used with

CANOCO software Version 4.56 (Biometris-Plant Research International, Wageningen,

The Netherlands). PCA is an indirect gradient analysis used to estimate similarity of sites by ordination axes that are theoretical gradients best explaining variation in the data set

(ter Braak and Smilauer 2002). The variables slope percent, aspect, and elevation were included in the model, and a correlation matrix was used because each of the three variables was measured in different units. Soil was not included in the analysis because results from the U.S. Department of Agriculture Web Soil Survey indicated only two main soil series present in the sample plots. With only two series identified, sample plots did not significantly differ in soils, and inclusion of this variable would not have added to the model.

Natural Vegetation Statistical Analysis

To determine the degree of similarity in vegetation composition among all plot types (FP, FNP, NFP, and NFNP), multi-response permutation procedure (MRPP) was used with PC-ORD software Version 5.0 (MjM Software, Gleneden Beach, Oregon,

U.S.A.). MRPP is a nonparametric method that determines if there is a significant difference between two or more groups; the method does not require normally distributed data or homogeneity of variance (McCune and Grace 2002). A Euclidean distance measure and a weighting factor were used; pair-wise comparisons were made between all possible treatment combinations to determine if they differed in vegetation composition.

MRPP was conducted separately for the understory (herbs, vines, and woody shrubs), seedlings (woody species less than 137cm in height), and sapling (woody species 137cm or taller) compositions of all four plot types. Multiple stems or root sprouts were not counted separately for the woody species in this analysis. All group comparisons with P- values less than 0.05 were considered significant.

A jackknife procedure was used to estimate the understory (herbs, vines, and woody shrubs) species richness for the plots of all four plot types (FP, FNP, NFP, and

NFNP) with PC-ORD software Version 5.0 (MjM Software, Gleneden Beach, Oregon,

U.S.A.). A first order jackknife procedure is appropriate for determining species richness when sub-sampling a larger area; the method is based on the observed frequency of rare species in a sample community (Palmer 1990). The calculated value is the number of species expected per unit area.

To determine which species were indicators of the four plot types (FP, FNP, NFP,

NFNP) indicator species analysis was used with PC-ORD software Version 5.0 (MjM

Software, Gleneden Beach, Oregon, U.S.A.). The method determines which species are indicative of a particular group of samples based on both the abundance and the frequency of a given species in that area (Dufrene and Legendre 1997). Thus, a good indicator species should be representative of only one particular group of sites and be present in the majority of samples in that group (Dufrene and Legendre 1997). Indicator species analysis was run for the understory, seedlings, and saplings data sets separately.

Multiple stems or root sprouts were not counted separately for the woody species in this analysis. Species with P-values less than 0.05 were considered significant for that plot type.

Results

Paired Plots

PCA revealed no major separation of the 122 sample plots based on the environmental variables slope percent, aspect, and elevation (Figure 3.1). The first two principal components combined explain 73.4% of the variation in the data set, with the variables slope percent and aspect contributing most to the first principal component. All four plot types (FP, FNP, NFP, and NFNP) are distributed along the first and second axes, showing no discernible pattern (Figure 3.1). All plots are similar in terms of slope, aspect, and elevation, and are either one of two soil series, Berks channery silt loam or

Shelocta-Brownsville association (Table 3.1).

MRPP

Results from the MRPP on the understory data show a significant difference in vegetation composition according to plot type (T = -12.3428, P = 0.00). Pair-wise comparisons between all plots were significant (P < 0.05) except FP and FNP (Table

3.2a). MRPP on the seedling stratum again show a significant difference in the composition by plot type (T = -9.0835, P = 4.45E-06). Pair-wise comparisons between all plots were significant (P < 0.05) except FP and FNP (Table 3.2b). The MRPP on the sapling data gives the same results – a significant difference in the vegetation composition according to plot type (T = -7.7520, P = 3.61E-06). Again, pair-wise comparisons between all plots were significant (P < 0.05) except FP and FNP (Table

3.2c).

Jackknife Species Richness

The first order jackknife estimates of understory species richness indicate the group FP has the highest estimated species richness per plot, followed by FNP, NFNP, and NFP (Table 3.3). The NFNP group has the greatest rate of increase of species richness, while FP the lowest (Table 3.3).

Indicator Species

Results from the indicator species analysis on the understory data reveal no species common across all four plot types (Table 3.4a). Sample plots impacted by the

2009 wildfire and with Paulownia present (FP) have the highest number of indicator species, including fireweed (Erechtites hieracifolia), common ragweed (Ambrosia artemisiifolia), and beggar ticks (Bidens frondosa). Plots that were impacted by the fire

55 with no Paulownia (FNP) have only two indicator species, Vaccinium spp. and

Lysimachia spp., both able to grow in drier waste places or moister open areas, depending on the specific species present. Outside the impact of the 2009 fire (NFP, NFNP) there are multiple indicator species which appear to have a high affinity for these generally shadier and moister woods, including clearweed (Pilea pumila), wild yam (Dioscorea villosa), and white snakeroot (Eupatorium rugosum).

Results from the indicator species analysis on the seedling data show Paulownia tomentosa as an indicator for the plots impacted by the 2009 fire where the exotic tree is present (Table 3.4b). Plots within the burn area with Paulownia absent (FNP) have several seedling indicator species – L. tulipifera, N. sylvatica, S. albidum, Rhus spp, and

Pinus spp. – all of which are either early successional species, or species that benefit from or are well-adapted to fire. In plots beyond the fire perimeter, those with Paulownia present (NFP) have Ulmus spp. in high abundance, while those with Paulownia absent

(NFNP) have the white oak group and various other species showing a high affinity.

At the sapling stratum, FP plots have Rhus spp. as an indicator species, while its matched pair, FNP, has no sapling indicator species (Table 3.4c). With these plots impacted by fire only two years before, it is not surprising there is a lack of abundance of sapling-sized woody species. In the plots not impacted by the 2009 wildfire (NFP),

Paulownia tomentosa and L. tulipifera are both indicator species, while Acer spp. is the sole indicator species in NFNP.

Discussion

Paired Plots

It is known that there is a correlation among site factors, environmental variables, and vegetation composition (Roberts and Christensen 1988, Goebel and Hix 1996,

Iverson et al 1997). Aspect, slope, and soil characteristic interactions are a few of the variables that influence herbaceous, seedling, and tree strata (Roberts and Christensen

1988, Goebel and Hix 1996, Iverson et al 1997). Although the degree of influence can differ among sites, there is a relationship between vegetation and environmental site variations; research has found this to be true of a mixed hardwood forest of southern

Ohio where aspect and slope change on a fine scale to influence the ecology of a microsite (Roberts and Christensen 1988, Iverson et al 1997). Since the topography at

Shawnee State Forest is highly dissected, the two sample plots within a pair were specifically chosen to have comparable gradients (slope, aspect, and elevation) to one another to minimize confounding of vegetation analyses by changes in environmental and site variables. The lack of a discernible pattern in separation of all 122 sample plots in the PCA demonstrates that all plots are similar in slope, aspect, and elevation.

Soil series was not included in the PCA since only two major types were present, as determined from the Web Soil Survey. There was no discernible pattern of soil and plot type; both identified soil series were spread among all four plot types. The Web Soil

Survey only maps to soil series, and the size of sample plots was finer than the detail of the maps referenced. Consequently, small areas of contrasting soils were not shown and interpretation of the lines of soil series may not have been wholly accurate. If a finer

57 scale of soil mapping had been available, more than two soil types may have been identified in the sample plots at Shawnee, leading to its inclusion in the PCA. A more detailed map may have revealed more subtle differences only visible on a finer scale, such as nutrient concentrations. Soil samples also could have been collected from each plot in order to estimate such characteristics, but was beyond the scope of this project.

Differences in the minerals present and their relative abundance are known to influence vegetation composition, especially woody species (Muller 1982, Roberts and Christensen

1988). Additionally, although the two identified soils, Berks channery silt loam and

Shelocta-Brownsville association, are both categorized as well drained soils, in the field it was obvious that sample plots not impacted by the 2009 fire were much moister than those plots within the burn area, likely due to differences in the amount of canopy closure. Even with all sample plots approximately comparable in terms of certain environmental site conditions, there were still multiple related factors not considered which may have caused site differences, such as nutrient concentration, soil drainage, and soil pH. Further, given the highly dissected topography of Shawnee State Forest, more complex interactions, beyond the few variables considered separately, are likely influencing vegetation composition (Iverson et al 1997).

MRPP - Understory

Vegetation composition is known to be affected by site factors, so while it is likely that fine-scaled topographical changes are influencing the composition of the plots at Shawnee State Forest, the differences in vegetation are probably due to other influences as well (Roberts and Christensen 1988, Iverson et al 1997). Stand age, natural disturbances, and anthropogenic activity all play a major role in determining stand

58 compositions, with the first often influenced by the latter two (Roberts and Christensen

1988). Successional sources of variation can differ among vegetation layers, as research shows that different strata may respond at varying rates to disturbances (Roberts and

Christensen 1988). A study by Cantlon (1953) in a deciduous forest of New Jersey found that the herbaceous layer showed the greatest variation in response, measured by both diversity and density. Although this find was context-dependent, it is clear that there is a range of response rates by vegetation layers to distinct disturbances, and this is likely leading to the dissimilarities of composition at Shawnee.

Fire is one disturbance driving the dynamics of herbaceous plants in a forest

(Royo et al 2010). It is estimated that herbaceous species constitute over 75% of the plant diversity in a temperate forest, by far the stratum with the highest species richness

(Gilliam 2007, Royo et al 2010). Today, numerous factors – fire suppression, anthropogenic activity, and introduction of exotic species – are leading to decreased herbaceous species richness (Gilliam 2007). Many believe that natural disturbances occurring in their historical pattern, which are usually intermediate in terms of frequency, support the greatest understory diversity, creating a patchwork mosaic of herbaceous plants that was once widespread in temperate forests (Crawley et al 1986, Beatty 2003,

Royo et al 2010).

Studies have found that post-fire the herbaceous stratum changes in several ways: herbaceous species cover and frequency increase, and different species germinate, leading to increased species richness (Hutchinson 2005, Royo et al 2010). A natural fire regime allows for variability in species composition by alternating between favoring species that benefit from fire and those that are fire sensitive (Royo et al 2010). The

59 increased herbaceous frequency and diversity after a fire are partly due to elevated soil temperatures and increased light levels, conditions which allow many seeds to break dormancy and for shade-intolerant species to germinate (Hutchinson 2005). Shrub frequency and richness often also increase in the understory because of seed bank recruitment and expansion via underground rhizomes surviving all but the hottest of fires

(Hutchinson 2005, Royo et al 2010). This is commonly seen in previously oak- dominated forests of southern Ohio, leading to an extensive spread of such shrubs as

Rubus spp. (Hutchinson 2005, Royo et al 2010).

The lack of a significant difference in understory composition between plots with and without Paulownia within the burn (FP and FNP) is likely because both are still responding to the effects of the fire and subsequent salvage logging from only two years previous. Regardless of whether or not Paulownia is present, similar shade-intolerant vegetation is probably growing in the burned plots, as the logging after the wildfire resulted in removal of almost the entire canopy in the majority of the burned area. The significant difference in understory composition between all fire and non-fire plot pairings (FP and NFP, FP and NFNP, FNP and NFP, FNP and NFNP) is also likely due to the different disturbances impacting the plot types. Since fire is known to change the herbaceous composition of forests in multiple ways, the plots within the burn are likely more similar to one another than they are to those outside the burn area. Additionally, the salvaging efforts in combination with the 2009 wildfire were large-scale disturbances to

FP and FNP. The plots outside the burn area (NFP and NFNP), although clear-cut in previous years, were not impacted by large-scale disturbances as recently as those plots within the fire. Rather, the most recent disturbances to these two areas included smaller-

60 scale tree damage from the 2003 ice storm, herbicide application to targeted species in certain areas, abandoned logging roads, and individual tree falls. All of these disturbances create small gaps of varying sizes, but not complete loss of canopy cover as seen in the burn and salvage area. Although disturbances typically increase plant density relative to undisturbed stands, studies show that canopy gaps are not typically conducive to an increase in herbaceous diversity, as changes in light levels alone are not sufficient and herbaceous species remain trapped underneath woody species (Ehrenfeld 1980,

Lorimer 1980, Royo et al 2010). Even if some of the created microclimates created from the small disturbances facilitated an increase in herbaceous richness, the species composition is likely different in these lower light areas than in the burn area with the completely open canopy.

The significant difference in the understory stratum between the two plot types not impacted by the 2009 wildfire (NFP and NFNP) may be due not only to the aforementioned reasons, but also to the presence of Paulownia. Studies have found that herbaceous species and canopy species are linked, with each layer influencing the other

(Gilliam et al 1995, Gilliam and Roberts 2003, Gilliam 2007). In a hardwood forest in

West Virginia, Gilliam et al (1995) found that overstory and herbaceous species were linked only in mature stands. Furthermore, linkage between the overstory and understory strata occurs when studied on a spatial scale smaller than the landscape level (Gilliam and

Roberts 2003). Studies show that disturbances to forest stands are potential mechanisms behind these linkages (Gilliam et al 1995, Gilliam 2007). Although not old-growth forests, the sample plots outside the fire area at Shawnee are mostly mature second- growth stands that have experienced disturbances, such as logging and mining, for

61 decades. Overstory species can influence herbaceous dynamics by changing the amount of light reaching the forest floor, altering soil fertility properties along spatial patterns, and competing with the understory stratum for resource uptake (Gilliam et al 1995,

Gilliam and Roberts 2003, Gilliam 2007). In Shawnee State Forest, outside the area impacted by the 2009 fire, most Paulownia stems are growing in the subcanopy or the canopy. With its extensive leaf area, Paulownia is definitely contributing to the amount of canopy closure in these stands, and the capacity for greater plasticity (see Chapter 2) may allow Paulownia to better compete for resources. Exotic plants in particular can increase soil pH, change the amount of available nitrogen, and alter levels of other nutrients, leading to patches of habitats more conducive to nonnative species (Ehrenfeld

2003, Gilliam 2007). Recent research has shown that increased nitrogen leads to a decrease in herbaceous species diversity (Gilliam 2007). Nonnative species can also influence soil fertility properties by changing the amount of plant debris contributing to forest floor litter. An increase or decrease in the amount of leaf litter, and the rate of litter decomposition, can modify the usual flux of nutrients in the soil, potentially creating patches of herbaceous variability (Ehrenfeld 2003). The brittle nature of Paulownia wood and the large, easily damageable leaves, add to the species’ potential to increase the amount of debris on the forest floor, in turn affecting the herbaceous composition of the area. Additionally, pits and mounds in mature stands, created from tree falls, are known to increase herbaceous diversity in the understory (Roberts and Gilliam 2003). In the no burn areas (NFP), Paulownia were often growing on these soil mounds. If Paulownia can out-compete native species, then this would decrease the amount of herbaceous richness usually associated with mound microclimates across the topography. One way

Paulownia may out-compete native herbaceous species is via root sprouts, a common method for the tree to form dense clusters (Innes 2009). Although there has been no direct research on the spread and efficacy of Paulownia root systems in forested settings, studies on other species that exhibit clonal growth indicate that physiological integration of ramets can provide multiple benefits (Shumway 1995, Brooker et al 1999). The interconnected underground network of clonal plants can efficiently recycle nutrients between ramets and increase nutrient uptake, particularly by rhizomatous growth, across gradients, even in resource poor areas (Shumway 1995, Brooker et al 1999). These benefits of linked ramets and their associated rhizomes may explain why vegetative spread is common when disturbances cause bare soil, where certain environmental gradients can cause depressed seedling recruitment for native species (Shumway 1995).

Although there is a lack of research on the nature of clonal root systems in Paulownia, the increased surface area from root sprouts alone may be enough to help the exotic species compete with natural vegetation for nutrients and other resources in an area.

MRPP - Seedlings and Saplings

The seedling and sapling strata had no significant differences in composition between the fire plots with and without Paulownia (FP and FNP). After a disturbance, the canopy usually becomes more open, both starting tree seedling germination and releasing suppressed seedlings from light competition (Ehrenfeld 1980). The combination of the 2009 wildfire and the subsequent salvaging effort resulted in the removal of the majority of the canopy at Shawnee State Forest. The sudden increase in light levels likely allowed shade-intolerants and pioneer trees to germinate, leading to similar seedling and sapling compositions within all the fire plots. Studies of mixed oak

63 forests, similar to Shawnee State Forest, have found that the composition and structure differ significantly between low and high fire intensity areas (Regelbrugge and Smith

1994). More specifically, total stand density of woody species stems decreases and species richness increases after high intensity fires only (Regelbrugge and Smith 1994).

However, both plot types impacted by the wildfire (FP and FNP) experienced a range of intensities (low, moderate, moderate-high, and high), making any subsequent heterogeneity in woody vegetation composition spread between the plot types. These factors are likely contributing to the similarity in structure and composition of the plots impacted by the fire in comparison to the plots beyond the burn. Future research should investigate the influence of different fire intensities on the specific species composition post-fire.

Seedling and sapling composition was significantly different between all fire and non-fire plot pairings (FP and NFP, FP and NFNP, FNP and NFP, FNP and NFNP).

After a fire or other disturbance, the establishment of seedlings is dependent upon species composition, seed availability and viability, and site characteristics (Reader et al 1995).

Seed availability is directly related to tree density in the canopy: a greater number of mature trees of a species hypothetically lead to a higher ratio of that specific species in the overall pool of available seeds (Reader et al 1995). For species with windborne seeds, such as Paulownia, parent sources can also be canopy trees several kilometers away, adding to their potential pool of seed availability (Langdon and Johnson 1994,

Kuppinger et al 2010). Seed availability, however, is not only dependent on tree density.

Heat from a fire usually kills all seeds in the litter layer, while those in the mineral soil underneath survive; acorns in the litter layer are commonly known to die after fire in

64 mixed oak forests (Hutchinson 2005). Seed position and subsequent survival thus play a part in determining which woody species germinate after a wildfire. For the comparisons with only one plot having Paulownia present, the structure of the exotic species’ seeds may be contributing to the dissimilarities in the woody composition. Paulownia seeds are very small and delicate, and will be killed by fire unless buried within the soil, and even then the seeds are not guaranteed to survive to successful germination. Although there are mixed results as to the exact fire temperature Paulownia seeds within the soil can survive – anywhere from 30-100° Celsius – it is clear that only the lowest intensity fires will not inhibit germination (Kuppinger 2008, Todorovic et al 2010). This statement, however, assumes that Paulownia seeds are able to survive in the seed bank, a topic still under contention. Additionally, some tree species have shown smoke-induced germination, including Paulownia seeds after light-induction, which would give these trees a greater chance at germination following the 2009 wildfire (Hutchinson 2005,

Todorovic et al 2010). Even with the variable survival and germination rates of

Paulownia seeds after a fire, wind-dispersal of the seeds to an area must be considered.

Direct effects of fire on woody stems can vary with species, size of stem, wood properties, and stand density (Regelbrugge and Smith 1994, Hutchinson et al 2005). An obvious dissimilarity between the fire and non-fire plots is that saplings are less common on recently burned stands, as the flames kill most small woody stems (Signell et al 2005).

Many hardwoods produce stump or root sprouts in response to a disturbance, with the top-killing of stems common after a wildfire; this characteristic can greatly increase the density of a species in patches or across a landscape (Hutchinson 2005). With the ability to prolifically root sprout, this characteristic is a great advantage to Paulownia, even if a

65 disturbance does not top-kill the tree (Innes 2009). Although oaks are one of several native species also able to sprout after damage, the fast growth rate of Paulownia gives the nonnative a competitive advantage. Furthermore, different species have various mortality rates to fire, depending partly on bark thickness and tree form (Hutchinson et al

2005). In studies of mixed deciduous forests of southern Ohio, Hutchinson et al (2005) found that post-fire, saplings significantly decreased in abundance, especially when the stand was mainly composed of shade-tolerant species. In similar studies, results showed a decrease in density of saplings less than 10cm at d.b.h., as well as a decrease in seedling richness after a fire in mixed oak forests (Crawford 1976, Regelbrugge and Smith 1994,

Hutchinson 2005). In contrast, in these same stands, woody species that were significant seed bankers, such as L. tulipifera, increased in richness after a fire (Hutchinson 2005). It is likely that the 2009 wildfire at Shawnee is the primary cause of differences in seedling and sapling composition among the plots within and beyond the burn area, and the presence of Paulownia contributes to the dissimilarities among the comparisons.

The significant difference in both the seedling and the sapling strata between plots with and without Paulownia in areas not impacted by the 2009 wildfire (NFP and NFNP) may be a combination of several factors. As aforementioned, woody species respond differently to fire and to other disturbances, especially when there are resulting gaps in the canopy (Reader et al 1995). Population dynamics of seedlings and saplings are site and species dependent (Good and Good 1972). The sample plots not impacted by the wildfire (NFP, NFNP) were previously subjected to tree damage from an ice storm, targeted herbicide application to invasive species, abandoned roads from decades of logging, and individual tree falls. The variability in these disturbances alone is enough to

66 create a patchwork of different sized canopy gaps and subsequent microclimates, leading to heterogeneity of woody composition across the stands (Good and Good 1972). For example, Quercus spp. have low to intermediate shade-tolerance, and research has found that disturbances resulting in minimal canopy openings are not sufficient to advance regeneration (Signell et al 2005). However, more shade-tolerant species, such as A. rubrum and N. sylvatica, would do well in these smaller openings with lower light levels

(Signell et al 2005). Although a shade-intolerant, L. tulipifera has a straight, upward growth pattern in which the tree loses smaller side branches as stand density increases, allowing the species to also successfully grow in smaller gaps (Poulson and Platt 1989).

Observation of Paulownia growing in these small canopy gaps in stands not impacted by the wildfire may be an additional variable in the determination of the woody species composition, as the nonnative is acting as another competitor for resources in the openings.

Population dynamics of mature stands can influence seedling and sapling composition. Seedling mortality in general is highest during the first few years of life, and sapling growth rate is usually twice as much as the seedling growth rate within a species (Good and Good 1972). These two factors enhance the variability of stand composition, especially after a disturbance, by selective survival of stems. Research shows an inverse relationship between the density of the canopy and the understory

(Ehrenfeld 1980). With the patchwork of canopy gaps at Shawnee due to previous disturbances, it is likely that seedling and sapling populations are influenced by the amount of overstory cover at specific microsites. N. sylvatica is a species able to grow in high abundance after heavy logging to an area, an advantage because of use of the land

67 that is now Shawnee State Forest (Crawford 1976). Q. prinus, the dominant species in the white oak group at Shawnee State Forest, has a low rate of growth as a seedling and experiences a “bottleneck effect” in which saplings die out after being over-shaded

(Signell et al 2005). Yet the species’ ability to grow on drier, lower quality sites, especially ridges with a lack of limestone in the parent layer, ensures the presence of Q. prinus in certain areas despite competition from the ubiquitous, more shade-tolerant Acer spp. (Good and Good 1972, Signell et al 2005). However, the ability of Paulownia to colonize dry outcroppings could be a direct hindrance on the regeneration of Quercus spp. on these sites; the exotic tree may be filling the ecological niche of native species.

Further research is necessary to understand the interaction of Paulownia and native

Quercus spp. competing for limited resources.

Jackknife Species Richness

The highest species richness in FP and FNP is most likely attributable to the 2009 wildfire at Shawnee. As aforementioned, there is usually higher herbaceous species richness and percent cover after a fire; the increased levels of light and nutrient availability break seed dormancy and allow for germination of more species (Roberts and

Gilliam 2003, Hutchinson 2005, Royo et al 2010). Although plots within the burn with

Paulownia present (FP) have the highest species richness, there does not seem to be any direct correlation between the presence of the exotic tree and this higher richness value.

The characteristics of Paulownia – fast growth, invasion of disturbed and marginal areas, and prolific seeding – lead to the conclusion that the exotic tree would actually be a competitor for native species and thus decrease herbaceous richness in areas where present. A possible explanation for the highest jackknife value in the FP plots could be

68 the small sample size. The species area curves and calculated regression coefficients indicate that the data collected were not complete samples of the herbaceous vegetation present in the plots – the species area curves do not level off at a constant value

(Appendix D). Even if more vegetation plots were sampled, there may not have been a measurable impact of Paulownia on the composition, as the area was still recovering from the large disturbances of fire and logging two years previous. However, future research should look at fire intensity within the burned plots to investigate if this variable is impacting species richness values or if Paulownia is.

The plots not impacted by the fire (NFP and NFNP) have the two lowest species richness values. More specifically, the plots with Paulownia present (NFP) have the lowest richness out of all four plot types (Table 3.2). The difference in richness values may be due to the presence of Paulownia. After fire or another disturbance damages any portion of the stem, Paulownia sprouts from adventitious buds; this trait allows the exotic tree to form patchy, yet dense, colonies (Hu 1961, Innes 2009). Gilliam (2007) showed that ferns influenced germinating tree seedling composition in deciduous forests, suggesting that herbaceous species may be better competitors than woody seedlings for soil nutrients. While ferns may be more efficient at extracting resources from the soil in the face of woody competition, this is not necessarily true for all herbaceous species of the forest floor; however, there has been no direct research on other specific understory species. Additionally, the potential for extensive root systems from clonal growth may give the exotic tree the advantage of increased surface area of roots and consequently more nutrient uptake within a stand (Shumway 1995, Brooker et al 1999). Although it is known that Paulownia seedlings possess a small and weak taproot, there is no literature

69 on the form and function of adult Paulownia root systems in natural settings, and with the tree’s fast growth, it is possible the efficacy of the mature roots fuel this ability (Millsaps

1936, Hu 1961, Tang et al 1980). Although no empirical data was collected, Kuppinger et al (2010) reported that Paulownia had a deep root system several years after establishment. A similar nonnative invasive tree that has clonal growth, A. altissima, is known to possess allelopathic properties, with high concentrations of the phytotoxin in the species’ roots and bark (Lawrence et al 1991, Heisey 1996). Ailanthone allows the invasive tree to inhibit growth of both herbaceous and woody species, aiding the exotic tree in out-competing native species to form almost pure stands (Heisey 1996, Small et al

2010). Small et al (2010) found no apparent negative effect from the phytoxin of A. altissima on a targeted nonnative invasive herb, only on a native herbaceous species.

Although more research is necessary, preliminary results indicate that nonnative plants may facilitate further invasion by other nonnative species because of allelopathy (Small et al 2010). There is no research on the adult root system and allelopathic compounds produced by Paulownia, thus it is unclear whether these two properties aid in the nonnative species’ ability to out-compete other plants and decrease species richness.

Even if Paulownia does not possess either characteristic, the exotic may still be changing the soil composition to disfavor native species by altering the amount of nitrogen and other soil nutrients, and the amount and rate of litter decomposition in the understory

(Ehrenfeld 2003, Gilliam 2007). Furthermore, Paulownia can tolerate low soil pH, the reason for trial plantings of the species on previously mined lands (Tang et al 1980). Soil pH was not tested in the sample plots, but the presence of Paulownia in NFP could be

70 attributed to more acidic soils in these stands, and which could be limiting the number of herbaceous species growing in the areas.

Paulownia stems in the mature stands not impacted by the fire were often growing on soil mounds created by tree falls (Chongpinitchai, personal observation).

Mound microsites in mixed deciduous forests have high species richness, especially when compared to their pit counterparts, and are a main component of maintaining understory heterogeneity across a landscape (Beatty 2003). Beatty (2003) demonstrated that the continued species richness on soil mounds is promoted by the presence of a keystone plant, Aster divaricatus. This competitive aster can dominate the herbaceous understory, and its loss eliminates the coexistence of many species in the microsites, thus lowering species richness (Beatty 2003). At Shawnee State Forest, Aster species are abundant throughout, and although they were only identified to the genus during sampling, the range of A. divaricatus reaches the counties of southern Ohio (National Plant Team

2012). Paulownia growing on soil mounds may be filling the niche usually occupied by

A. divaricatus, or another aster species, removing the keystone competitor and changing herbaceous diversity. Furthermore, Paulownia’s fast growth rate might otherwise fill the canopy gaps created by tree falls – this could influence the dynamics of herbaceous species richness as well.

The presence of Paulownia tomentosa may be decreasing herbaceous richness in certain areas of Shawnee State Forest. However, plant growth is complex, influenced by multiple factors and interactions, some of which were not measured during sampling.

Although some site variables were kept similar among all sample plots – slope, aspect, elevation, and soil series – soil pH, drainage, soil compaction, and nutrient content and

71 availability were not sampled, although they are known to influence species growth and composition. The differences in richness values may simply be a result of varying site characteristics and their interactions, and not the presence or absence of Paulownia.

Further research, controlling for more variables, needs to be conducted in order to determine if Paulownia is having a detrimental effect on native species.

Indicator Species - Understory

The lack of a common herbaceous indicator species across all plot types indicates differences in site conditions, despite having controlled for slope percent, aspect, and elevation. The amount of canopy closure, soil moisture, and litter depth were obviously different between the plots impacted by the 2009 wildfire and subsequent logging, and those that were not (Chongpinitchai, personal observation). As aforementioned, herbaceous plant growth is greatly dependent upon light and soil gradients, as well as competition for such resources (Cantlon 1953, McCarthy et al 1987, Beatty 2003, Desta et al 2004, Hutchinson 2005, Gilliam 2007). Differences in site and environmental variables among all 122 sample plots influenced which species are indicative of certain areas in Shawnee.

In the FP plots, E. hieracifolia and Rubus spp. are two of the indicator species

(Table 3.3a). Both are prime examples of species known to spread extensively in forests of southern Ohio after a fire, the former because of its high intolerance to shade, and the latter due to its seed banking (Hutchinson 2005). Fire helps clear the forest floor and overstory, and with the removal of almost the entire canopy during the post-fire salvaging efforts at Shawnee, the areas within the burn were very dry, sunny, devoid of leaf litter,

72 and consequently nutrients. It is not surprising then, that plants such as A. artemisiifolia,

Taraxacum spp., Euphorbia corollata, Aster patens, Solidago bicolor, Lobelia spp.(L. inflata particularly) and B. frondosa showed an affinity for the recently disturbed areas, as these species are commonly inhabitants of dry places, such as roadsides and “waste places” (Newcomb 1977). There was also a high affinity of Phytolacca americana and

Helianthus spp. in the plots impacted by the fire; there has been documentation of a significant increase in both species following prescribed fires in southern Ohio, most likely due to seed bank recruitment (Hutchinson 2005, Royo et al 2010). Plots that were impacted by the wildfire but with no Paulownia (FNP) have only two indicator species,

Vaccinium spp. and Lysimachia spp. Fires have shown to increase shoot growth and stem density of other berry species in mixed deciduous forests, and several species of

Lysimachia are common on dry, open areas, such as the habitats found at Shawnee State

Forest following the wildfire (Arthur et al 1998, Hutchinson 2005). It is unclear why there are more indicator species in the plots with Paulownia than those with it absent; further research is necessary to determine if the nonnative tree is acting as a driver of species composition and abundance, or if perhaps differences are due to sampling methods or site conditions.

In the plots not impacted by the 2009 fire (NFP, NFNP) there are multiple indicator species, all of which have a high affinity for shadier, moister woods, common to the sites outside of the burn where mature stands are more prevalent (Newcomb 1977).

P. pumila, D. villosa, and E. rugosum are a few of these species. Other herbaceous species indicators of these unburned sites are Toxicodendron radicans (poison ivy) and

Parthenocissus quinquefolia (Virginia creeper), two plants ubiquitous in mature mixed deciduous forests of the eastern U.S.

Indicator Species – Seedlings and Saplings

In the fire plots with no Paulownia present (FNP), there are multiple seedling indicator species, including N. sylvatica, Sassafras albidum, and Pinus spp. These species are all either fire tolerant or benefit from fire, exhibiting enhanced germination from the more open canopy and cleared soil (Carey 1992, Sullivan 1993). N. sylvatica in particular is very fire resistant, especially because of its thicker, corky bark, with younger stems capable of surviving high fire intensities (Regelbrugge and Smith 1994, Signell et al 2005). As expected, there is an abundance of L. tulipifera seedlings, which is not only a high seed banker, but also a shade-intolerant and fast growing species (Brose and Van

Lear 1998, Hutchinson 2005, Royo et al 2010). Rhus spp. is another indicator seedling, and others have found a significant increase in this shrubby woody species following wildfires in southern Ohio forests, most likely attributable to the species’ branched rhizome system (Johnson 2000, Hutchinson 2005). Contrastingly, these same plots do not have any indicator saplings. With many areas of high intensity fire, most woody species were likely killed or significantly damaged, and the subsequent salvaging removed almost all standing trees (Signell et al 2005, ODNR 2009). As sampling was conducted only two years after the disturbances, only very fast growing species would have reached sapling height or taller.

In the plots impacted by the wildfire (FP), Paulownia is the only seedling indicator species. This is not surprising since it is known to rapidly colonize sunny, dry,

74 and recently disturbed areas (Tang et al 1980, Langdon and Johnson 1994, Kuppinger et al 2010). With the occurrence of the wildfire and salvaging efforts in spring and fall of

2009, the disturbed bare soil presented the ideal habitat for the germination of Paulownia seeds newly dispersed to the area, even those with a parent tree beyond the fire perimeter

(Hu 1961, Tang et al 1980, Langdon and Johnson 1994, Kuppinger 2008). The mass production of seeds, fast growth, and ability to sprout from adventitious buds even without top-kill, are characteristics that give Paulownia an advantage over native vegetation, allowing the tree to establish in high density in the recently cleared areas

(Innes 2009). FP plots have only one sapling indicator, Rhus spp., which is known to increase in number following fires in southern Ohio, mostly due to root sprouting; the tree also grows best on sunny sites found after large disturbances (Johnson 2000,

Hutchinson 2005).

Outside the fire area (NFP) Paulownia is also an indicator species as a sapling.

Although these stands generally have more canopy closure, and consequently lower light levels and moister soils, Paulownia seems able to grow on these sites. It is possible that

Paulownia exhibits greater phenotypic plasticity and uses its wind-dispersed seeds to invade distant sites different from habitats in its indigenous range. However, Paulownia is not an indicator species as a seedling in these same plots, indicating perhaps there is no new seedling recruitment and stems only reached sapling-size because of the fast growth of the species after an earlier disturbance. There are mature Paulownia growing both in and outside the area impacted by the 2009 wildfire, and with the large amounts of wind- dispersed seeds Paulownia produces, it seems likely some seeds would have reached the areas dense with saplings, but without a recent disturbance to the area, the changed

75 conditions may no longer be conducive to Paulownia germination (Appendix C).

Williams (1993b) found that in a mixed deciduous forest of central Virginia, twenty years after Paulownia invaded the area following a hurricane, the nonnative tree exhibited a convex d.b.h. and age distribution, while other native species a concave shape. Williams (1993b) concluded that while native tree species were germinating and increasing in number, Paulownia was not self-replacing because of the lack of any recent large disturbance to the area. Although no Paulownia stems in Shawnee were aged, the notable absence of seedling-size stems in mature stands may indicate that the population of this nonnative species is not self-sustaining, perhaps because there has not been a recent disturbance. The only other indicator species sapling in these plots is L. tulipifera, a tree comparable to Paulownia in its very fast growth and high shade-intolerance. If conditions become favorable again for early successional species, it may seem that the native L. tulipifera possesses an advantage by forming a viable seed bank, while this is still unclear for Paulownia. However, the exotic tree also can easily disperse its seeds long distances, which can increase its seed source. More research is needed to determine if Paulownia is out-competing L. tulipifera at Shawnee, occupying early successional niches, or if both species can coexist after a disturbance to the area. Additionally, it is unclear whether Paulownia can germinate with only small-scale disturbances.

In areas not impacted by the wildfire and with Paulownia absent (NFNP), the white oak group is a seedling indicator species. There is a lack of advancing regeneration of Quercus spp. in eastern deciduous forests, as years of fire suppression and other management techniques have put more shade-tolerant species in position to become dominant in the overstory (Hutchinson et al 2005, Signell et al 2005). Q. prinus and Q.

76 alba, representing the white oak group in this study, are known to benefit from fire, both increasing in number of stems and new germination (Regelbrugge and Smith 1994).

These unburned plots were subjected to other disturbances in the past decade, including logging and overstory mortality, leading to canopy gaps in stands. Studies in similar mixed-oak forests in eastern United States show that Quercus spp. exhibit episodic reproduction and mortality linked to small-scale disturbances (McCarthy et al 1987). The land use history of Shawnee State Forest is thus very fitting for the sustainability of

Quercus spp., and the abundance of white oak seedlings in the understory looks promising for new growth. However, current oak-dominated forests usually are characterized by Acer spp. in the understory, and this is also true of Shawnee (McCarthy et al 1987, Arthur et al 1998). These same plots have Acer spp. as an indicator species in the sapling size class. If the disturbance regime of Shawnee does not significantly change, it is likely that the more shade-tolerant maples will grow into the canopy and become the dominant species, eventually replacing oaks (McCarthy et al 1987, Arthur et al 1998). One possible solution to the problem is to conduct more prescribed burns, clearing the soil and opening the canopy, conditions conducive to Quercus spp. growth.

However, the situation at Shawnee shows that increased, large-scale disturbances, such as the 2003 ice storm and 2009 wildfire, are facilitating an invasion by Paulownia. There is the risk that in an attempt to foster Quercus spp. growth, the nonnative tree will spread; this seems highly likely as currently oaks only show any sign of regeneration in areas devoid of Paulownia.

Conclusion

Species diversity across all strata in eastern deciduous forests is influenced by a myriad of factors. Succession, whether impelled by natural disturbances or human activity, fosters a high level of species richness, creating a patchwork mosaic of various habitats across a landscape (Gilliam et al 1995). The ensuing seral stages differ in microsite characteristics – soil properties, litter depth, and light levels (Roberts and

Christensen 1988). Coupled with variations in topography, vegetation composition becomes heterogeneous, creating species diversity in all strata. At Shawnee State Forest, the dissimilarities in seral stages from numerous disturbances and the dissected topography of the region play a main role in shaping the vegetation, explaining some of the variance in both specific species growth and species richness values. There is also the possibility that the nonnative Paulownia tomentosa is influencing the vegetation composition; differences in species and diversity may be, in part, attributed to the presence of the exotic tree. Lower herbaceous species richness values and the lack of

Quercus spp. germination in certain stands could be due to Paulownia changing the microclimate and out-competing native species when present. There is uncertainty as to the extent of the invasiveness of Paulownia, but regardless, it is clear that the exotic tree alters the natural processes and structure in introduced habitats. It can be as simple as increasing litter debris, or as complex as changing nutrient availability in different ways.

Such changes in the habitat can lead to disastrous consequences for certain species, specifically in the understory. Herbaceous species naturally have higher extinction rates than vegetation in any other stratum, and there is documentation of the loss of rare plants due to anthropogenic activities – overexploitation and introduction of

78 exotic species – leading to both habitat fragmentation and loss (Gilliam et al 1995,

Gilliam 2007). Rare herbaceous plants can be used as indicators of biodiversity and forest health because of their smaller habitat and resource niche (Gilliam 2007). Thus, a loss of rare plants signifies a loss of biodiversity and lower site quality. Several studies have reported that even with increased human disturbances and fires in eastern mixed-oak forests, there has been no significant increase of invasion by nonnative species

(Hutchinson 2005). Even if this is true, the establishment of exotic plants in the understory leads to their altering of the microsite and potential to become the dominant species (Gilliam 2007). Additionally, Paulownia is known to colonize dry outcroppings, the preferred habitat of many rare herbaceous plants in eastern deciduous forests

(Langdon and Johnson 1994, Kuppinger et al 2010). These same rare species are often dependent on disturbance for habitat maintenance, but it is known that Paulownia thrives after a disturbance as well (Hu 1961, Williams 1993b, Langdon and Johnson 1994,

Kuppinger et al 2010). At Shawnee, Paulownia is established in areas of the forest along with several threatened or endangered plants of southern Ohio (ODNR 2012), suggesting the possibility of greater species diversity loss because of the exotic tree’s presence. In addition to rare herbaceous species, Paulownia may be exacerbating the demise of

Quercus spp., out-competing on the sunnier, drier areas where Q. prinus grows, and increasing the rate of canopy closure when gaps do occur with its fast growth and high foliar coverage. Whether or not Paulownia tomentosa will invade all parts of Shawnee

State Forest, it is clear that the nonnative tree holds the potential to change a forest ecosystem.

Future Implications

The complexity of the situation makes management of Paulownia tomentosa at

Shawnee State Forest difficult. The nonnative tree seems to benefit from fire, especially high intensity burns, subsequently increasing its distribution and germination by seed and vegetative growth. More research is necessary to determine how different fire intensities impact Paulownia colonization of an area, but in Shawnee, and other areas with highly dissected topography, it may not even be possible to ensure no fires reach higher intensity levels. The continual logging at Shawnee State Forest creates cleared areas conducive to invasion by Paulownia, a species with high numbers of wind-dispersed seeds, an affinity for full light, and a tolerance to dry conditions. Using chemical methods to control

Paulownia is a multi-step process, and ramifications of extensively using herbicide on a large scale must be considered, particularly in habitats with threatened or endangered species, although treating seed-bearing trees may help reduce long distance seed dispersal. Unless there is complete removal of Paulownia at Shawnee, even smaller scale disturbances, such as tree falls and abandoned logging roads, may serve as vectors for the spread of the species.

Currently, there is not a comprehensive mapping of Paulownia at Shawnee State

Forest, particularly in the designated wilderness area. There is a general lack of information about the presence and spread of nonnative invasive species in wilderness areas across the U.S., but this gap in knowledge may be the key for ecologists and managers alike (Marler 2000). Knowing the extent of spread of nonnative species in less disturbed wilderness areas may help us understand the role disturbances play in colonization of nonindigenous habitats by exotic species. Additionally, long-term

80 monitoring is necessary to fully comprehend the dynamics of nonnative species in introduced areas (Marler 2000). An active monitoring of Paulownia tomentosa both in and around the 2009 wildfire area at Shawnee State Forest needs to continue to determine its spread and establishment.

It is interesting to note that although Ailanthus altissima is present at Shawnee

State Forest, this species does not appear to be benefitting from the 2009 wildfire as

Paulownia is (Appendix A). Out of the 61 sample plots impacted by the fire, only one A. altissima stem was recorded in 2011, and the cruise plots within the burn sampled by

ODNR personnel in 2009 recorded only two A. altissima stems. Further research is necessary to determine if perhaps there is another factor facilitating the spread of

Paulownia within the burn area, or if Paulownia exhibits a negative effect on A. altissima growth. It is clear there is still much to be learned about the nonnative tree Paulownia tomentosa.

2.0 -1.5 -1.5 2.0

SAMPLES

FP FNP NFP NFNP

Figure 3.1 Principal components analysis of environmental variables (slope percent, aspect, elevation) for the four plot types (N = 122 plots).

Table 3.1 Mean slope percent, mean aspect, mean elevation, and soil type (series) for the four plot types (N = 122). FP = fire, Paulownia, FNP = fire, no Paulownia, NFP = no fire, Paulownia, NFNP = no fire, no Paulownia

Plot No. Plots with Soil Type Type Mean Slope Mean Aspect Mean Shelocta- Berks- Percent (degrees) Elevation (m) brownsville channery FP 36 190 350 17 11 FNP 33 189 349 16 12 NFP 40 133 338 21 12 NFNP 38 134 341 20 13

Table 3.2 Summary of multi response permutation procedure on the understory, seedling, and sapling strata relationships associated with Paulownia and fire (N = 122). Vegetation composition is significantly different at P < 0.05 for comparisons marked with an asterisk. FP = fire, Paulownia, FNP = fire, no Paulownia, NFP = no fire, Paulownia, NFNP = no fire, no Paulownia

Groups Compared P - value Groups Compared P - value

(a). Understory

FP vs FNP 0.3835 FNP vs NFP* 2.68E-05

FP vs NFP* 2.00E-08 FNP vs NFNP* 1.13E-05

FP vs NFNP* 1.00E-08 NFP vs NFNP* 0.0298

(b). Seedlings

FP vs FNP 0.3334 FNP vs NFP* 0.0003

FP vs NFP* 0.0124 FNP vs NFNP* 0.0003

FP vs NFNP* 0.0006 NFP vs NFNP* 0.0119

(c). Saplings

FP vs FNP 0.1237 FNP vs NFP* 1.5E-05

FP vs NFP* 0.0033 FNP vs NFNP* 0.0135

FP vs NFNP* 0.0031 NFP vs NFNP* 0.0045

Table 3.3 First order jackknife estimates of understory species richness (N = 122). Regression coefficients (c = expected number of species per unit area, z = rate of species richness increase) are calculated from the species area curve, fit with a power function. FP = fire, Paulownia, FNP = fire, no Paulownia, NFP = no fire, Paulownia, NFNP = no fire, no Paulownia

Group Jackknife Estimate Regression Coefficients

of Species Richness c z

FP 106 21.866 0.394

FNP 96 17.456 0.427

NFP 90.5 19.651 0.400

NFNP 93.3 15.737 0.441

Table 3.4 Indicator species for understory, seedling, and sapling plot data (N = 122). FP = fire, Paulownia, FNP = fire, no Paulownia, NFP = no fire, Paulownia, NFNP = no fire, no Paulownia

Species Group Species Group (a). Understory Rubus spp. FP Gnaphalium obtusifolium FP

Bidens frondosa FP Vaccinium spp. FNP

Ambrosia artemisiifolia FP Lysimachia spp. FNP

Erechtites hieracifolia FP Toxicodendron radicans NFP

Lobelia spp. FP Parthenocissus quinquefolia NFP

Helianthus spp. FP Pilea pumila NFP

Solidago bicolor FP Eupatorium rugosum NFP

Aster patens FP Polystichum acrostichoidis NFP

Eupatorium coelestinum FP Ipomoea spp. NFP

Taraxacum spp. FP Thalictrum dioicum NFP

Phytolacca americana FP Dioscorea villosa NFNP

Cassia nictitans FP Lindera benzoin NFNP

Euphorbia corollata FP Polygonatum spp. NFNP (b). Seedlings

Paulownia tomentosa FP Sassafras albidum FNP Pinus spp. FNP Ulmus spp. NFP Liriodendron tulipifera FNP White Oaks NFNP

Nyssa sylvatica FNP Other NFNP

Rhus spp. FNP (c). Saplings Rhus spp. FP Paulownia tomentosa NFP None FNP Liriodendron tulipifera NFP Acer spp. NFNP

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Appendix A: Maps of Shawnee State Forest, Ohio

Shawnee State Forest

Figure A.1 Location of Shawnee State Forest in Adams and Scioto Counties, Ohio.

Figure A.3 Areas experiencing 33-100% canopy mortality from the 2003 ice storm at Shawnee State Forest, Ohio (blue). Although tree damage was more widespread throughout Shawnee State Forest, only the areas where sample plots (pink squares) are located are shown. Access roads (black), hiking trails (green), and bridle trails (brown) are also shown.

Figure A.4 Intensity levels of the 2009 fire at Shawnee State Forest, Ohio. Shown are the perimeter of the approximately 1,200ha fire (red), high fire intensities (red shading), moderate-high intensities (purple shading), and moderate intensities (yellow shading). All other areas within the fire perimeter are considered low intensity. Sample plots (pink squares), created dozer lines (brown shading), and access roads (black) are also shown.

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Figure A.5 Mapped Paulownia tomentosa and Ailanthus altissima and areas of herbicide application to the two species at Shawnee State Forest, Ohio. Areas of implemented herbicide application to the two target species are shown (yellow stripe). Herbicide was applied in October – December 2009, May 2010, and September – October 2010. Mapped areas of Paulownia and A. altissima not targeted with herbicide are shown (green). The perimeter of the approximately 1,200ha fire of April 2009 (red), created dozer lines (brown shading), sample plots (pink squares), access roads (black), hiking trails (green), and bridle trails (brown) are also shown.

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Figure A.6 The 433 cruise plots within the 2009 fire perimeter at Shawnee State Forest, Ohio. Plots were 2.2m radius in size, established by Shawnee State Forest employees in September 2009. All woody stems over 0.3m tall and with a d.b.h. less than 2.1cm were inventoried within each plot radius.

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Appendix B: Harvest data of sample plots at Shawnee State Forest, Ohio 2005-2011

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Table B.1 Logging data for the sample plots (N = 45) established in areas that were harvested between 2005-2011 at Shawnee State Forest, Ohio.

Location Harvest Harvest Acres Volume Year Method 2009 Burn Area 2008 clearcut 100.6 141936 2009 Burn Area 2008 clearcut 100.6 102816 2009 Burn Area 2008 clearcut 100.6 127116 2009 Burn Area 2008 clearcut 100.6 119990 2009 Burn Area 2010 clearcut 54.9 -- 2009 Burn Area 2010 clearcut 124.3 -- 2009 Burn Area 2010 clearcut 91.7 -- Outside 2009 Burn 2007 Area clearcut 62.5 105270 Outside 2009 Burn 2005 single Area selection 129.9 107420 Outside 2009 Burn 2011 Area clearcut 105.5 --

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Appendix C: Seed-bearing Paulownia tomentosa stems at Shawnee State Forest, Ohio in 2011

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Table C.1 Seed-bearing Paulownia tomentosa stems from the sample plots (N = 61) with the species present in Shawnee State Forest, Ohio 2011.

Location No. Seed- No. Total No. Plots with No. Total Bearing Stems Seed-Bearing Plots Stems Stems 2009 Burn Area 1 129 1 28

Outside 2009 34 131 14 33 Burn Area

106

Appendix D: Species area curves for the understory stratum of the four plot types at Shawnee State Forest, Ohio in 2011

107

y = 21.866x0.3946 FP Plots R² = 0.9877 90

80 70 60 50 40

30 Avg. Number Avg. ofSpecies 20 10 0 0 5 10 15 20 25 30 Number of Plots

108

y = 17.456x0.4275 FNP Plots R² = 0.9859

70 60 50 40 30

Avg. Number Avg. ofSpecies 20 10 0 0 5 10 15 20 25 30 Number of Plots

109

y = 19.651x0.4001 NFP Plots R² = 0.9725 90 80 70 60 50 40 30

Avg. Number Avg. ofSpecies 20 10 0 0 5 10 15 20 25 30 35 Number of Plots

110

NFNP Plots y = 15.737x0.4417 R² = 0.9834

80 70 60 50 40 30

Avg. Number Species of Avg. 20 10 0 0 5 10 15 20 25 30 35 Number of Plots

111