No description available.

O objetivo geral desta tese foi examinar diferentes 1 questões associadas ao 2 processo de invasão de plantas para investigar os mecanismos, impactos e 3 medidas de recuperação da comunidade vegetal, abordando diferentes estratégias 4 metodológicas que incluem estudos observacionais, experimentos de remoção e 5 uma revisão metodológica. Os resultados do Capítulo 1 mostraram como as 6 relações entre condições climáticas e estrutura da paisagem podem determinar o 7 grau de invasão de plantas na escala regional. Observou-se que os padrões de 8 invasão dos campos sulinos estão principalmente relacionados com maior 9 densidade de estradas, menor cobertura de campo nativo e com o aumento do 10 déficit hídrico. Além disso, constatou-se que a gramínea Eragrostis plana é a 11 planta invasora mais abundante dos campos sulinos. No entanto, os resultados do 12 experimento do Capítulo 2 mostraram que sua invasão não pode ser explicada 13 pela riqueza de espécies ou composição dos grupos funcionais de plantas da 14 comunidade residente. A invasão de E. plana foi principalmente associada ao 15 distúrbio causado pela remoção de biomassa na comunidade. Neste sentido, as 16 comunidades campestres poderiam ser resistentes à invasão de E. plana até que 17 algum distúrbio aumente sua vulnerabilidade. Por outro lado, através da 18 comparação entre comunidades invadidas, removidas e não-invadidas, os 19 resultados do experimento do Capítulo 3 contribuíram no entendimento do 20 impacto real da invasão de E. plana, em termos de redução da riqueza e cobertura 21 de plantas nativas na comunidade. No entanto, embora os métodos de remoção 22 utilizados reduziram a cobertura da invasora, não foram suficientes para conseguir 23 sua erradicação local. Além disso, após três anos de remoção de E. plana, as comunidades se tornaram distintas às invadidas mas não 1 foram semelhantes às 2 comunidades não invadias, o qual poderia indicar que outras medidas de 3 restauração são ainda necessárias. Embora os experimentos de remoção de 4 espécies sejam úteis para investigar questões associadas ao processo de 5 invasão, existem limitações importantes a considerar, como foi evidenciado nos 6 Capítulos 2 e 3. Neste sentido, oferecemos a revisão bibliográfica sistemática do 7 Capítulo 4, onde se discute o potencial dos métodos de remoção utilizados para 8 estudar a resistência e a recuperação da comunidade à invasão, apontando 9 algumas limitações. Como resultado, o Capítulo 4 mostrou que a maioria dos 10 trabalhos não propõem controles adequados nos experimentos, o que pode dar 11 lugar a confundimento de efeitos. Desta forma, foram desenvolvidas algumas 12 sugestões para serem consideradas nos experimentos de remoção de espécies, 13 com o objetivo de continuar avançando nesta temática. As informações geradas 14 nesta tese podem contribuir para o entendimento do processo de invasão de 15 plantas nos ecossistemas campestres, com vistas ao manejo, à conservação e à 16 restauração das comunidades invadidas, adquirindo um senso crítico no 17 planejamento de desenhos experimentas. / The general aim of this thesis was to investigate different 1 issues associated 2 with plant invasion process to understand the mechanisms, impacts and 3 community recovery, by employing different methodological strategies such as 4 observational studies, removal experiments and a literature review. The results 5 from Chapter 1 showed how the interactions between climate and landscape 6 structure can determine the level of invasion of South Brazilian grasslands, 7 highlighting that invasion is mainly related to high road density, less native 8 grassland cover and increased aridity. Furthermore, it was confirmed that 9 Eragrostis plana is the most important invasive species in the South Brazilian 10 grasslands. However, the results from the experiment of Chapter 2 showed that its 11 invasion could not be explained by the species richness or functional group 12 composition in the community. Eragrostis plana invasion was associated with the 13 disturbance effect caused by the amount of removed biomass. Thus, grassland 14 communities may be resistant to E. plana invasion until some disturbance 15 increases their vulnerability. Moreover, by comparing invaded, removed and non16 invaded communities, the experimental results of Chapter 3 highlighted the 17 ecological impact of E. plana invasion, in terms of richness reduction and native 18 species cover. However, although removals methods reduced the cover of the 19 invasive species, they were not enough to locally extinct it. Moreover, after three 20 years of the invasive removal, communities became different from invaded ones 21 but not resembling non-invaded references, which suggest that community 22 recovery may require restoration strategies. Although removal experiments have 23 been useful to investigate certain issues associated with invasion process, there are important limitations to consider, as was shown in Chapter 1 2 and 3. For this 2 purpose, our systematic review presented in Chapter 4 discussed the potential of 3 removal methods for assessing community resistance and recovery from invasion. 4 There, we showed that most of the studies did not use adequate controls in 5 removal experiments, which can lead to confounding effects. Thus, we developed 6 suggestions to be considered in experimental designs to advance the 7 methodological technique of removals. The information generated in this thesis can 8 contribute to the understanding of plant invasion process in South Brazilian 9 grasslands and, consequently, aid to management, conservation and restoration of 10 invaded communities by acquiring a critical sense in experimental designs.

Mire pools – shallow water-bodies in peat-forming wetlands – are a characteristic feature of New Zealand’s subalpine and alpine landscapes (>1000 m a.s.l.), yet have been the subject of few biological studies to date, particularly of their algal communities. This research focuses on these subalpine systems, and on their diatom communities. Despite the established paradigm of ubiquitous dispersal in micro-organisms, recent taxonomic studies have confirmed a distinctive endemic component in the freshwater diatom flora of the New Zealand / Tasmania / East Australian region. In this study, I examined benthic diatom communities from >320 freshwater sites throughout New Zealand and showed that over 20% of species may be confined to this region. The endemic diatom species had highest densities in stable, unproductive environments, particularly in high-altitude mire pools and tarns. In most cases, non-endemic taxa coexisted with endemic species. This raised questions about (1) the special characteristics of mire pools and tarns (since endemism might be expected in areas that have unique environmental characteristics), and (2) the mechanisms that have allowed existing endemic taxa to withstand displacement by common cosmopolitan taxa, which, by definition, are successful colonisers. I addressed these questions using two years of data from four subalpine mire pools (Bealey Spur wetland, near Arthur’s Pass, South Island). Physico-chemical data showed that water chemistry of these pools may differ from that of many Northern Hemisphere mire systems with respect to the relationship between pH and dissolved ions (especially calcium). This may be due to a combination of high pH rainfall, high rainfall quantities that limit the acidification effects of humic substances, and possibly vegetation differences. Therefore, some endemic taxa may be confined to these habitats because of the characteristic properties of the pools. I investigated the effects of disturbances in these stable environments. In the largest pool endemic species were shown to decline as wind-induced substrate disturbance increased. Endemic species also declined in two pools following small-scale experimental substrate disturbances. In all cases, non-endemic species remained unchanged. The distinctive species Eunophora cf. oberonica was responsible for much of the observed decline in endemic species abundances, which was evidently due to destruction of their specialised habitat within the cyanobacterial mats that made up the pool substrates. I explained pool-specific responses of diatom communities to disturbances by drawing on recent theory of invasibility as an intrinsic environmental property. I further investigated species coexistence by examining several general patterns of interspecific coexistence described for macroscopic organisms (e.g., abundance – occupancy, abundance – persistence). Patterns in mire-pool diatom communities were generally similar to those in larger organisms, and did not differ with respect to geographical range size (endemics vs. non-endemics), except at the scale of single pools. At this scale, endemic taxa, in particular E. cf. oberonica, can persist as dominant species. All the community analyses were underpinned by detailed taxonomic studies, from which I assessed over 40% of the more common species in the pools to be either endemic or likely to be endemic. Two species occurring in the study area are formally described as new species. Overall, this work highlights the vulnerability of this hidden component of New Zealand’s biodiversity to disturbances and environmental changes.

Mire pools – shallow water-bodies in peat-forming wetlands – are a characteristic feature of New Zealand’s subalpine and alpine landscapes (>1000 m a.s.l.), yet have been the subject of few biological studies to date, particularly of their algal communities. This research focuses on these subalpine systems, and on their diatom communities. Despite the established paradigm of ubiquitous dispersal in micro-organisms, recent taxonomic studies have confirmed a distinctive endemic component in the freshwater diatom flora of the New Zealand / Tasmania / East Australian region. In this study, I examined benthic diatom communities from >320 freshwater sites throughout New Zealand and showed that over 20% of species may be confined to this region. The endemic diatom species had highest densities in stable, unproductive environments, particularly in high-altitude mire pools and tarns. In most cases, non-endemic taxa coexisted with endemic species. This raised questions about (1) the special characteristics of mire pools and tarns (since endemism might be expected in areas that have unique environmental characteristics), and (2) the mechanisms that have allowed existing endemic taxa to withstand displacement by common cosmopolitan taxa, which, by definition, are successful colonisers. I addressed these questions using two years of data from four subalpine mire pools (Bealey Spur wetland, near Arthur’s Pass, South Island). Physico-chemical data showed that water chemistry of these pools may differ from that of many Northern Hemisphere mire systems with respect to the relationship between pH and dissolved ions (especially calcium). This may be due to a combination of high pH rainfall, high rainfall quantities that limit the acidification effects of humic substances, and possibly vegetation differences. Therefore, some endemic taxa may be confined to these habitats because of the characteristic properties of the pools. I investigated the effects of disturbances in these stable environments. In the largest pool endemic species were shown to decline as wind-induced substrate disturbance increased. Endemic species also declined in two pools following small-scale experimental substrate disturbances. In all cases, non-endemic species remained unchanged. The distinctive species Eunophora cf. oberonica was responsible for much of the observed decline in endemic species abundances, which was evidently due to destruction of their specialised habitat within the cyanobacterial mats that made up the pool substrates. I explained pool-specific responses of diatom communities to disturbances by drawing on recent theory of invasibility as an intrinsic environmental property. I further investigated species coexistence by examining several general patterns of interspecific coexistence described for macroscopic organisms (e.g., abundance – occupancy, abundance – persistence). Patterns in mire-pool diatom communities were generally similar to those in larger organisms, and did not differ with respect to geographical range size (endemics vs. non-endemics), except at the scale of single pools. At this scale, endemic taxa, in particular E. cf. oberonica, can persist as dominant species. All the community analyses were underpinned by detailed taxonomic studies, from which I assessed over 40% of the more common species in the pools to be either endemic or likely to be endemic. Two species occurring in the study area are formally described as new species. Overall, this work highlights the vulnerability of this hidden component of New Zealand’s biodiversity to disturbances and environmental changes.

Invasive species are cited as a major threat to native community composition and biodiversity throughout the world. Some recent studies have focused on whether invasive species are the drivers or passengers of change in degraded systems. A strongly-interactive community is supposed to resist invasion by all but the most strong invasive competitors (`drivers') which can establish there without the aid of disturbance and actively reduce the abundance of natives. A weakly-interactive community, impaired by some anthropogenic disruption, is invasible by weaker exotics which are merely `passengers' of the habitat degradation that is more constraining to natives. Though competitive and disturbance-adapted species fit into this model, there is no correlate for species with superior toleration of stress. Systems with high degrees of natural abiotic stress are weakly-interactive and as a result may be invasible by an exotic `tolerator' in the same way that anthropogenically-weak systems are invasible by passengers. Dolomite prairie, differentiated from typic tallgrass prairie by its shallow soils, represents a relatively stressful system. A study of its plant community composition and relationships to environmental variables was done to get a better understanding of the natural abiotic drivers of composition. Compositional patterns were most closely associated with the soil depth gradient. Exotic Poa species were by far the most frequent invaders, a finding more typical of Great Lakes alvars than of typic tallgrass prairie of which the dolomite prairie is a subset. I hypothesized that Poa species dominated dolomite prairie via the tolerator model. In a series of removal treatments, I determined that Poa is neither a driver nor a tolerator, but a passenger of environmental degradation. My results suggest that historic anthropogenic degradation rather than specific competitive ability is a common explanation for exotic dominance on the landscape today. More empirical work needs to be conducted in other stressful (particularly relatively undisturbed) systems to further investigate the tolerator model.

O objetivo geral desta tese foi examinar diferentes 1 questões associadas ao 2 processo de invasão de plantas para investigar os mecanismos, impactos e 3 medidas de recuperação da comunidade vegetal, abordando diferentes estratégias 4 metodológicas que incluem estudos observacionais, experimentos de remoção e 5 uma revisão metodológica. Os resultados do Capítulo 1 mostraram como as 6 relações entre condições climáticas e estrutura da paisagem podem determinar o 7 grau de invasão de plantas na escala regional. Observou-se que os padrões de 8 invasão dos campos sulinos estão principalmente relacionados com maior 9 densidade de estradas, menor cobertura de campo nativo e com o aumento do 10 déficit hídrico. Além disso, constatou-se que a gramínea Eragrostis plana é a 11 planta invasora mais abundante dos campos sulinos. No entanto, os resultados do 12 experimento do Capítulo 2 mostraram que sua invasão não pode ser explicada 13 pela riqueza de espécies ou composição dos grupos funcionais de plantas da 14 comunidade residente. A invasão de E. plana foi principalmente associada ao 15 distúrbio causado pela remoção de biomassa na comunidade. Neste sentido, as 16 comunidades campestres poderiam ser resistentes à invasão de E. plana até que 17 algum distúrbio aumente sua vulnerabilidade. Por outro lado, através da 18 comparação entre comunidades invadidas, removidas e não-invadidas, os 19 resultados do experimento do Capítulo 3 contribuíram no entendimento do 20 impacto real da invasão de E. plana, em termos de redução da riqueza e cobertura 21 de plantas nativas na comunidade. No entanto, embora os métodos de remoção 22 utilizados reduziram a cobertura da invasora, não foram suficientes para conseguir 23 sua erradicação local. Além disso, após três anos de remoção de E. plana, as comunidades se tornaram distintas às invadidas mas não 1 foram semelhantes às 2 comunidades não invadias, o qual poderia indicar que outras medidas de 3 restauração são ainda necessárias. Embora os experimentos de remoção de 4 espécies sejam úteis para investigar questões associadas ao processo de 5 invasão, existem limitações importantes a considerar, como foi evidenciado nos 6 Capítulos 2 e 3. Neste sentido, oferecemos a revisão bibliográfica sistemática do 7 Capítulo 4, onde se discute o potencial dos métodos de remoção utilizados para 8 estudar a resistência e a recuperação da comunidade à invasão, apontando 9 algumas limitações. Como resultado, o Capítulo 4 mostrou que a maioria dos 10 trabalhos não propõem controles adequados nos experimentos, o que pode dar 11 lugar a confundimento de efeitos. Desta forma, foram desenvolvidas algumas 12 sugestões para serem consideradas nos experimentos de remoção de espécies, 13 com o objetivo de continuar avançando nesta temática. As informações geradas 14 nesta tese podem contribuir para o entendimento do processo de invasão de 15 plantas nos ecossistemas campestres, com vistas ao manejo, à conservação e à 16 restauração das comunidades invadidas, adquirindo um senso crítico no 17 planejamento de desenhos experimentas. / The general aim of this thesis was to investigate different 1 issues associated 2 with plant invasion process to understand the mechanisms, impacts and 3 community recovery, by employing different methodological strategies such as 4 observational studies, removal experiments and a literature review. The results 5 from Chapter 1 showed how the interactions between climate and landscape 6 structure can determine the level of invasion of South Brazilian grasslands, 7 highlighting that invasion is mainly related to high road density, less native 8 grassland cover and increased aridity. Furthermore, it was confirmed that 9 Eragrostis plana is the most important invasive species in the South Brazilian 10 grasslands. However, the results from the experiment of Chapter 2 showed that its 11 invasion could not be explained by the species richness or functional group 12 composition in the community. Eragrostis plana invasion was associated with the 13 disturbance effect caused by the amount of removed biomass. Thus, grassland 14 communities may be resistant to E. plana invasion until some disturbance 15 increases their vulnerability. Moreover, by comparing invaded, removed and non16 invaded communities, the experimental results of Chapter 3 highlighted the 17 ecological impact of E. plana invasion, in terms of richness reduction and native 18 species cover. However, although removals methods reduced the cover of the 19 invasive species, they were not enough to locally extinct it. Moreover, after three 20 years of the invasive removal, communities became different from invaded ones 21 but not resembling non-invaded references, which suggest that community 22 recovery may require restoration strategies. Although removal experiments have 23 been useful to investigate certain issues associated with invasion process, there are important limitations to consider, as was shown in Chapter 1 2 and 3. For this 2 purpose, our systematic review presented in Chapter 4 discussed the potential of 3 removal methods for assessing community resistance and recovery from invasion. 4 There, we showed that most of the studies did not use adequate controls in 5 removal experiments, which can lead to confounding effects. Thus, we developed 6 suggestions to be considered in experimental designs to advance the 7 methodological technique of removals. The information generated in this thesis can 8 contribute to the understanding of plant invasion process in South Brazilian 9 grasslands and, consequently, aid to management, conservation and restoration of 10 invaded communities by acquiring a critical sense in experimental designs.

O objetivo geral desta tese foi examinar diferentes 1 questões associadas ao 2 processo de invasão de plantas para investigar os mecanismos, impactos e 3 medidas de recuperação da comunidade vegetal, abordando diferentes estratégias 4 metodológicas que incluem estudos observacionais, experimentos de remoção e 5 uma revisão metodológica. Os resultados do Capítulo 1 mostraram como as 6 relações entre condições climáticas e estrutura da paisagem podem determinar o 7 grau de invasão de plantas na escala regional. Observou-se que os padrões de 8 invasão dos campos sulinos estão principalmente relacionados com maior 9 densidade de estradas, menor cobertura de campo nativo e com o aumento do 10 déficit hídrico. Além disso, constatou-se que a gramínea Eragrostis plana é a 11 planta invasora mais abundante dos campos sulinos. No entanto, os resultados do 12 experimento do Capítulo 2 mostraram que sua invasão não pode ser explicada 13 pela riqueza de espécies ou composição dos grupos funcionais de plantas da 14 comunidade residente. A invasão de E. plana foi principalmente associada ao 15 distúrbio causado pela remoção de biomassa na comunidade. Neste sentido, as 16 comunidades campestres poderiam ser resistentes à invasão de E. plana até que 17 algum distúrbio aumente sua vulnerabilidade. Por outro lado, através da 18 comparação entre comunidades invadidas, removidas e não-invadidas, os 19 resultados do experimento do Capítulo 3 contribuíram no entendimento do 20 impacto real da invasão de E. plana, em termos de redução da riqueza e cobertura 21 de plantas nativas na comunidade. No entanto, embora os métodos de remoção 22 utilizados reduziram a cobertura da invasora, não foram suficientes para conseguir 23 sua erradicação local. Além disso, após três anos de remoção de E. plana, as comunidades se tornaram distintas às invadidas mas não 1 foram semelhantes às 2 comunidades não invadias, o qual poderia indicar que outras medidas de 3 restauração são ainda necessárias. Embora os experimentos de remoção de 4 espécies sejam úteis para investigar questões associadas ao processo de 5 invasão, existem limitações importantes a considerar, como foi evidenciado nos 6 Capítulos 2 e 3. Neste sentido, oferecemos a revisão bibliográfica sistemática do 7 Capítulo 4, onde se discute o potencial dos métodos de remoção utilizados para 8 estudar a resistência e a recuperação da comunidade à invasão, apontando 9 algumas limitações. Como resultado, o Capítulo 4 mostrou que a maioria dos 10 trabalhos não propõem controles adequados nos experimentos, o que pode dar 11 lugar a confundimento de efeitos. Desta forma, foram desenvolvidas algumas 12 sugestões para serem consideradas nos experimentos de remoção de espécies, 13 com o objetivo de continuar avançando nesta temática. As informações geradas 14 nesta tese podem contribuir para o entendimento do processo de invasão de 15 plantas nos ecossistemas campestres, com vistas ao manejo, à conservação e à 16 restauração das comunidades invadidas, adquirindo um senso crítico no 17 planejamento de desenhos experimentas. / The general aim of this thesis was to investigate different 1 issues associated 2 with plant invasion process to understand the mechanisms, impacts and 3 community recovery, by employing different methodological strategies such as 4 observational studies, removal experiments and a literature review. The results 5 from Chapter 1 showed how the interactions between climate and landscape 6 structure can determine the level of invasion of South Brazilian grasslands, 7 highlighting that invasion is mainly related to high road density, less native 8 grassland cover and increased aridity. Furthermore, it was confirmed that 9 Eragrostis plana is the most important invasive species in the South Brazilian 10 grasslands. However, the results from the experiment of Chapter 2 showed that its 11 invasion could not be explained by the species richness or functional group 12 composition in the community. Eragrostis plana invasion was associated with the 13 disturbance effect caused by the amount of removed biomass. Thus, grassland 14 communities may be resistant to E. plana invasion until some disturbance 15 increases their vulnerability. Moreover, by comparing invaded, removed and non16 invaded communities, the experimental results of Chapter 3 highlighted the 17 ecological impact of E. plana invasion, in terms of richness reduction and native 18 species cover. However, although removals methods reduced the cover of the 19 invasive species, they were not enough to locally extinct it. Moreover, after three 20 years of the invasive removal, communities became different from invaded ones 21 but not resembling non-invaded references, which suggest that community 22 recovery may require restoration strategies. Although removal experiments have 23 been useful to investigate certain issues associated with invasion process, there are important limitations to consider, as was shown in Chapter 1 2 and 3. For this 2 purpose, our systematic review presented in Chapter 4 discussed the potential of 3 removal methods for assessing community resistance and recovery from invasion. 4 There, we showed that most of the studies did not use adequate controls in 5 removal experiments, which can lead to confounding effects. Thus, we developed 6 suggestions to be considered in experimental designs to advance the 7 methodological technique of removals. The information generated in this thesis can 8 contribute to the understanding of plant invasion process in South Brazilian 9 grasslands and, consequently, aid to management, conservation and restoration of 10 invaded communities by acquiring a critical sense in experimental designs.

No description available.

No description available.

For this dissertation, I measured how plant communities in Appalachian forests responded to disturbances caused by forest management activities. I had two primary objectives including (1) testing theories of biological diversity and invasions by nonnative species; and (2) providing empirical data that will help guide the sustainable use of forest resources. This work is part of the Southern Appalachian Silviculture and Biodiversity (SASAB) experiment that was established in the early 1990s to investigate ecosystem responses to a gradient of timber harvesting disturbances. Ranging from undisturbed controls to silvicultural clearcuts, the disturbance gradient is replicated at sites located throughout the Appalachian mountains of Virginia and West Virginia. The plant community was sampled across a wide range of spatial scales (2 hectares to 1 m2) using a nested sampling design and was also sampled at three times including pre-disturbance, one year post-disturbance, and ten year post-disturbance. For one element of the study I tested modern theories of biological invasions and investigated how the forest disturbance gradient interacted with species diversity to influence invasion by nonnative species (Chapter 2). Contrary to popular ecological theories of biotic resistance, the most diverse sites tended to be more easily invaded following intense canopy disturbance. Interestingly, none of the sites in this study were dominated by invasive plants, which led me to ask whether dominant tree species in forests provided resistance to nonnative plant establishment and growth through the quality of the litter they produce. I also asked how might animals that are known to alter litter layers interact with dominant tree species to influence plant invasions. Therefore, I conducted an experiment investigating how changes in litter from dominant tree species and invasions by nonnative earthworms might influence invasibility of forests using forest floor mesocosms (Chapter 3). I found that plant invasion was inhibited by native oak litter even when earthworms were present, suggesting that oak forests may resist plant invasions via oak tree litter. In contrast, plant invasion was greater under invasive tree litter and earthworm activity tended to facilitate invasive plant success only under invasive tree litter. I was also interested in understanding how disturbance might alter relationships between local and regional diversity. The long-term data of the forest disturbance experiment allowed me to investigate how local species richness is mediated by regional species richness after disturbance and during forest community development (Chapter 4). Local richness depended strongly on regional richness only after disturbance via colonization of species, but this relationship changed during forest aggradation. These results suggest that regional species pools are important to maintain local diversity following disturbance, but that local interactions (through canopy closure of dominant trees) exert control over species diversity during community reorganization. Lastly, I tested current theories on how diversity influences compositional stability after disturbance (Chapter 5). Disturbance consistently resulted in decreased compositional stability, but diversity was associated with stability in complex ways, which depended on how stability was measured and at what scale. Species-rich areas were in some instances less stable; in other instances areas with intermediate levels of diversity were more stable. These results suggest that disturbance causes shifts in species composition via colonization, but the ways in which diversity of sites influences compositional stability is complex and depends on methods used and the scales of observation. Taken together, these results suggest that disturbance influences invasibility, species saturation, and compositional stability of ecological communities. These properties change immediately following disturbance, and during forest development and canopy closure. Data from this project were useful in testing existing theories of community ecology, and may ultimately prove useful for forest managers as they decide how to protect biodiversity while planning for other uses of forest resources. Overall, these results suggest that colonization of species is the primary process driving plant community patterns in Appalachian forests following disturbance. / Ph. D.