O presente estudo tem como objetivo descrever a dinâmica recente de três trechos de Floresta Estacional Semidecidual estudados entre 1994/1995, em função das mudanças estruturais e dos mosaicos de manchas em diferentes fases do ciclo de crescimento florestal. Esse estudo foi desenvolvido em três áreas situadas na Reserva Municipal de Santa Genebra, localizada no distrito de Barão Geraldo, município de Campinas-SP. Foram remedidas todas as plantas anteriormente marcadas em 35 parcelas permanentes de 100m² presentes em cada uma das áreas, nos anos 2000 (área A) e 2010 (áreas A, B e C). Todos os indivíduos ingressantes, com perímetro a altura do peito (PAP) maior ou igual a 15 cm (DAP aproximadamente 5 cm) e maiores de 1,3 m de altura, foram marcados e plaqueados. As espécies amostradas foram classificadas quanto ao grupo sucessional, síndrome de dispersão e deciduidade. As clareiras foram novamente medidas e demarcadas. De acordo com os resultados obtidos, foi possível observar a influência dos distúrbios, de forma diferenciada, na mudança estrutural e da dinâmica dos trechos florestais estudados. O dossel, sub-bosque e as clareiras analisados apresentaram modificações no número de indivíduos, composição de espécies e grupos sucessionais. As avaliações feitas nas manchas do mosaico mostraram que na área A as modificações ocorridas seguiram o que é descrito pela dinâmica de clareiras para Floresta Tropical Úmida, porém para as demais áreas (B e C), esse modelo de dinâmica não se aplicou, não seguindo, portanto, um padrão de substituição de manchas, grupos ecológicos e espécies nestes trechos de Floresta Estacional Semidecidual. As espécies pertencentes aos diferentes grupos sucessionais foram registrados em todos os regimes de luz, mas as espécies clímaces predominaram, principalmente, nas áreas de clareira. O ingresso dos indivíduos de todos os grupos sucessionais ocorreu preponderantemente através das clareiras, o que indica que novos indivíduos, bem como novas espécies, são incorporados por esse local. / This study aims to describe the recent dynamics of three plots of Semideciduous Forest studied between 1994/1995, in function of their structural changes and their mosaics of patches at different stages of growth. This study was conducted in three areas located in Santa Geneva Municipal Reserve, located in the district of Barão Geraldo, Campinas-SP. All previously marked plants in 35 permanent plots of 100m ² present in each of the areas in the 2000s (area A) and 2010 (areas A, B and C) were remeasured. All entering individuals, with perimeter at breast height (PAP) heighter than 15 cm (dbh nearly 5 cm) and height greater than 1.3 m, were marked and plated. The sampled species were classified according to their successional group, dispersal syndrome and deciduousness. The gaps were again measured and marked. According to the results obtained, it was possible to observe the influence of disturbances, differently in each area, the structural change and the dynamics of the studied forest areas. The analyzed canopy, understory and gaps showed changes in the number of individuals, species composition and successional groups. The evaluations made in mosaic patches in the area A showed that the changes occurred followed what is described by the dynamics of gaps for Tropical Moist Forest, but for the other areas (B and C), this dynamic model cannot applied, not following therefore, a standard replacement patches, ecological groups and species in these stretches from Semideciduous Forest. The species belonging to different successional groups were observed in all levels of light, but the climaxes occurred mainly in the gaps.

Forests are a critical biome but are under threat from unprecedented global change. The need to understand forest dynamics across spatial, temporal and biological scales has never been greater. Critical to this will be understanding how the demographic rates of individuals translate into patterns of species diversity, biomass and carbon turnover at much larger scales. In this thesis, I present a modelling framework focussed on demography. In Chapter 2, I introduce methods for translating forest inventory data into population models that account for the size-dependency of vital rates and persistent differences in individual performance. Outbreaks of forest pest and pathogens are increasing in frequency and severity, with consequences for biodiversity and forest structure. In Chapter 3, I explore the impact of ash dieback on the community dynamics of a British woodland, describing a spatially explicit individual based model that captures the effect of an opening of the canopy on local competitive interactions. Chapter 4 introduces methods to infer the impact of historical deer herbivory on the juvenile survival of forest trees. The approach is generalisable and could be applied to any forest in which patterns of regeneration and community structure have been impacted by periodic disturbance (e.g. forest fires). Finding meaningful ways of incorporating species diversity into global vegetation models is increasingly recognised as a research priority. In Chapter 5, I explore the diversity of demographic rates in a tropical forest community and identify groups of species with similar life history strategies. I discuss the potential of integrating demographic and physiological traits as a way to aggregate species for inclusion in global models. In summary, translating measurements of individuals into population dynamics provides opportunities to both explore small-scale community responses to disturbance events, and to feed into much larger scale vegetation models.

O presente estudo tem como objetivo descrever a dinâmica recente de três trechos de Floresta Estacional Semidecidual estudados entre 1994/1995, em função das mudanças estruturais e dos mosaicos de manchas em diferentes fases do ciclo de crescimento florestal. Esse estudo foi desenvolvido em três áreas situadas na Reserva Municipal de Santa Genebra, localizada no distrito de Barão Geraldo, município de Campinas-SP. Foram remedidas todas as plantas anteriormente marcadas em 35 parcelas permanentes de 100m² presentes em cada uma das áreas, nos anos 2000 (área A) e 2010 (áreas A, B e C). Todos os indivíduos ingressantes, com perímetro a altura do peito (PAP) maior ou igual a 15 cm (DAP aproximadamente 5 cm) e maiores de 1,3 m de altura, foram marcados e plaqueados. As espécies amostradas foram classificadas quanto ao grupo sucessional, síndrome de dispersão e deciduidade. As clareiras foram novamente medidas e demarcadas. De acordo com os resultados obtidos, foi possível observar a influência dos distúrbios, de forma diferenciada, na mudança estrutural e da dinâmica dos trechos florestais estudados. O dossel, sub-bosque e as clareiras analisados apresentaram modificações no número de indivíduos, composição de espécies e grupos sucessionais. As avaliações feitas nas manchas do mosaico mostraram que na área A as modificações ocorridas seguiram o que é descrito pela dinâmica de clareiras para Floresta Tropical Úmida, porém para as demais áreas (B e C), esse modelo de dinâmica não se aplicou, não seguindo, portanto, um padrão de substituição de manchas, grupos ecológicos e espécies nestes trechos de Floresta Estacional Semidecidual. As espécies pertencentes aos diferentes grupos sucessionais foram registrados em todos os regimes de luz, mas as espécies clímaces predominaram, principalmente, nas áreas de clareira. O ingresso dos indivíduos de todos os grupos sucessionais ocorreu preponderantemente através das clareiras, o que indica que novos indivíduos, bem como novas espécies, são incorporados por esse local. / This study aims to describe the recent dynamics of three plots of Semideciduous Forest studied between 1994/1995, in function of their structural changes and their mosaics of patches at different stages of growth. This study was conducted in three areas located in Santa Geneva Municipal Reserve, located in the district of Barão Geraldo, Campinas-SP. All previously marked plants in 35 permanent plots of 100m ² present in each of the areas in the 2000s (area A) and 2010 (areas A, B and C) were remeasured. All entering individuals, with perimeter at breast height (PAP) heighter than 15 cm (dbh nearly 5 cm) and height greater than 1.3 m, were marked and plated. The sampled species were classified according to their successional group, dispersal syndrome and deciduousness. The gaps were again measured and marked. According to the results obtained, it was possible to observe the influence of disturbances, differently in each area, the structural change and the dynamics of the studied forest areas. The analyzed canopy, understory and gaps showed changes in the number of individuals, species composition and successional groups. The evaluations made in mosaic patches in the area A showed that the changes occurred followed what is described by the dynamics of gaps for Tropical Moist Forest, but for the other areas (B and C), this dynamic model cannot applied, not following therefore, a standard replacement patches, ecological groups and species in these stretches from Semideciduous Forest. The species belonging to different successional groups were observed in all levels of light, but the climaxes occurred mainly in the gaps.

An ecologically based model of forest succession is presented. In the model, trees compete for a share of limited growth resources available from their environment. Competition is reflected by each tree's effect on the resource pool and is not explicitly modeled. Model parameters were fit to field data from subalpine forests of the Rocky Mountains. A technique for estimating model parameters from understory-tolerance rankings and silvical characteristics of each species is also presented. The model's output was consistent with our current understanding of forest dynamics. Emergent properties of the model also mimicked natural processes such as self-thinning, release, and maximum stand basal area as a function of species present and site quality.

The effects of deforestation and biomass burning in tropical dry forests (TDF) remain a little studied phenomenon. We quantified total aboveground biomass (TAGB), carbon and nutrient (N,S,Ca,P,K) loss under two separate fire severity scenarios; one early when the fuels were higher in moisture content, one later when the slash fuels were drier and then compared the loss and the regrowth of the sites. The TAGB and nutrients were measured (1993-1995) after the forest was cut, after a forest slash fire, one year after pasture establishment and, two years after the slash fire, biomass was quantified before and after a pasture fire. The treatments were based upon time from slash to burn. The low severity fires (Baja) were burned 65 days and the higher severity fires (Alta) were burned 95 days after the initial slash of TDF on ��� 3.5 ha near the Chamela Biological Research Station on the Ejido San Mateo, Jalisco, Mexico. As a result of the 1993 slash fire, TAGB declined from 118.2 to 43.6 Mg ha����� (62%) in the Baja treatment and from 134.9 to 26.8 Mg ha����� (80%) in the Alta treatment. Nutrients pools declined 57-88% with ��� 10% higher combustion of the Alta pools. In 1995, after the pasture fires, TAGB declined from 40.3 to 14.8 Mg ha����� (63%) and from 29.0 to 7.6 Mg ha����� (75%) in the Alta treatment and nutrient pools declined 57-88%. Total aboveground biomass loss from 1993-1995 was 103.4 Mg ha����� (87%) in the Baja treatment and 127.3 Mg ha����� (94%) in the Alta treatment. Carbon and nutrient losses ranged from 87-96% over the three-year study. We found little ash retention after fire, no increase in nutrient soil concentrations and, highly volatized nutrients (i.e. Ca and P) were essentially lost due to wind and water erosion on 40 to 60% slopes. Wood decomposition between fires reduced TAGB and nutrient pools by 15% in the Baja treatment and 3% in the Alta treatment. / Graduation date: 2000

A pollen profile from varved lake sediments sampled at 10-year intervals and spanning the past 1000 years is analyzed to understand the effects of climate change and anthropogenic activity on forests in southwestern Quebec. The forests responded rapidly to changes in temperature and precipitation during the Medieval Warm Period and Little Ice Age as well as to land-use changes associated with the European Settlement of the area. The transition into the Little Ice Age was abrupt and had significant impact on the pollen production within a couple of decades. A synthesis of this record with other high-resolution and well-dated pollen data from the conifer-hardwood forest of eastern North America shows consistent results across the whole area, indicating that very-high resolution pollen data can provide insight into multi-decadal climate variability and its impact on forest vegetation. Tree-ring records from the region show inter-annual fluctuations not always consistent between sites, while high-resolution pollen data record multi-decadal to century changes which enable us to interpret climatic effects on plant communities.

Graduation date: 1995

<p>Fungal pathogens likely play an important role in regulating populations of tree seedlings and preserving forest diversity, due to their ubiquitous presence and differential effects on survival. Host-specific mortality from natural enemies is one of the most widely tested hypotheses in community ecology to explain the high biodiversity of forests. The effects of fungal pathogens on seedling survival are usually discussed under the framework of the Janzen-Connell (JC) hypothesis, which posits that seedlings are more likely to survive when dispersed far from the parent tree or at low densities due to pressure from host-specific pathogens (Janzen 1970, Connell 1971). One of the key challenges to assessing the importance of JC effects has been to identify and quantify the effects of the large numbers of potential pathogens required to maintain host diversity. The primary objectives of this research were to (1) characterize the fungi associated with seedling disease and mortality for a number of important southeastern US forest tree species; and (2) determine if these associations are consistent with the Janzen-Connell hypothesis in terms of differential effects on seedling survival.<br></p><p>Culture-based methods and ribosomal DNA (rDNA) sequencing were used to characterize the fungal community in recently dead and live seedlings of thirteen common tree species in a temperate mixed hardwood forest (North Carolina, USA), with the goal of identifying putative seedling pathogens. Cultures were initially classified and grouped into 130 operational taxonomic units (OTUs) using 96% internal transcribed spacer (ITS) sequence similarity; 46% of all OTUs were found only once. Using rarefaction, it was concluded that the richness of the system was not fully sampled and likely included over 200 taxa (based on non-parametric richness estimators). Species richness did not differ between sampling sites or among the five most common hosts sampled. The large ribosomal subunit (LSU) region of rDNA was then sequenced for representative samples of common OTUs and refined identifications using a constrained maximum likelihood phylogenetic analysis. Phylogenetic placement verified strong BLAST classifications, and allowed for placement of unknown taxa to the order level, with many of these unknowns placed in the Leotiomycetes and Xylariales (Sordariomycetes).<br> </p><p>Next, a hierarchical Bayesian model was developed to predict the effects of multiple putative fungal pathogens on individual seedling survival, without forcing the effects of multiple fungi to be additive. The process of disease was partitioned into a chain of events including incidence, infection, detection, and survival, and conditional probabilities were used to quantify each component individually, but in the context of one another. The use of this modeling approach was illustrated by examining the effects of two putative fungal pathogens, <italics>Colletotrichum acutatum</italics> and <italics>Cylindrocarpon</italics> sp. A, an undescribed species of <italics>Cylindrocarpon</italics>, on the survival of five seedling hosts in both a maximum likelihood and Bayesian framework.<br> </p><p>Finally, the model was used to assess the impacts of these fungi on seedling survival, alone and in combination, using data on five potential fungal pathogens and five hosts. Multi-host fungi had differential effects on seedling survival depending on host identity, and multiple infections may impact survival even when single infections do not. Evaluating these interactions among multiple plant and fungal species generates a set of targeted hypotheses of specific plant-fungal combinations that could help us better understand pathogen-driven diversity maintenance at larger scales than previously possible. Building on these results, some recommendations are provided as to how the Janzen-Connell hypothesis can be re-evaluated with respect to host specificity, pathogen distribution, and environmental context.</p> / Dissertation

Thesis (M.S.)--Oregon State University, 2003. / Typescript (photocopy). Includes bibliographical references. Also available on the World Wide Web.

Forest assemblage composition is determined by local ecological (e.g. patch area, species interactions), landscape (e.g. patch connectivity) and regional (e.g. historical change in forest distribution) processes. I investigated the relative effect of these processes on bird and frog assemblage composition in two isolated archipelagos of Afrotemperate forest in the Limpopo Province. The linear relationship between local and regional species diversity suggests that forest bird assemblages in the Limpopo Province are unsaturated. In addition, 66% of bird species and 42% of frog species in southern African forests are generalist species (i.e., forest associated as opposed to forest dependent), suggesting that matrix species have invaded forest assemblages. I thus argue that forest bird and frog assemblage composition is primarily determined by regional (historical) processes and that local ecological processes play a relatively minor role. Forests in the Limpopo Province were eliminated by major climatic changes during the Quaternary with major forest expansion only in the last 6000 years. Limpopo Province forest assemblages have thus established fairly recently. No forest dependent frogs and one forest dependent bird have established in the Limpopo Province forests from the relatively proximate forests in eastern Zimbabwe. This suggests that the Limpopo River catchment has acted as a significant barrier to the dispersal of forest vertebrate faunas. Cluster analyses showed that the forest bird and frog assemblages are essentially Afrotemperate and South African in origin with all forest dependent frogs and 97% of forest dependent birds occurring in the KwaZulu-Natal scarp forests. In addition the most important environmental gradient of change in the southern African forest bird faunas was the geographical distance from northern KwaZulu-Natal. This gradient is congruent with a major northward radiation of faunas from the KwaZulu-Natal scarp into the Limpopo Province. As a result the Limpopo Province forests have low biodiversity values compared to the KwaZulu-Natal scarp because forest frog and bird faunas are largely derived from the latter region. However, the importance of the Limpopo Province forests lies in their protection of threatened vertebrates as well as in providing landscape heterogeneity and ecological services to the surrounding matrix. Soutpansberg forest bird assemblages appear to be more robust and resilient and comprise a significantly greater proportion of forest associated species than those of the Limpopo Province Drakensberg. This is likely to be a consequence of more severe climatic extinction filtering of these faunas caused primarily by the proximity of the Soutpansberg forests to the arid Limpopo valley during the development of these forests. Consequently, regional and historical processes have played a relatively greater role in determining forest bird assemblages in the Soutpansberg than in the Limpopo Province Drakensberg and species richness in the former region was not significantly affected by local ecological processes (including forest area, isolation and habitat heterogeneity). Forest area and habitat heterogeneity did, however, affect forest bird species richness and abundance in the Limpopo Province Drakensberg where the relatively lower importance of regional processes (compared to the Soutpansberg) has combined with anthropogenic disturbance of smaller forests to increase the influence of local ecological processes. However, the role of local processes in determining local species richness is likely to increase in both archipelagos if the current rates of anthropogenic change and disturbance to forests are sustained. Forests greater than 138 ha (minimum critical patch size) are needed to avoid an island effect on bird species richness in the Limpopo Province Drakensberg. However, the long-term conservation of vertebrate assemblages in Limpopo province forests depends upon the successful conservation of evolutionary and landscape processes. This can best be achieved by maximising forest connectivity and landscape heterogeneity through the protection of both riparian corridors and forests of all sizes. The maintenance of historical dispersal routes, in particular connectivity along the escarpment with the scarp forests of KwaZulu-Natal, is important. This would require the protection of forests on the KwaZulu-Natal scarp and along the entire northern Drakensberg escarpment. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2003.