Academic literature on the topic 'Tropical dry-forest community'

ABSTRACTSmall mammal live-trapping was carried out in a dry tropical forest mosaic in Huai Kha Khaeng Wildlife Sanctuary, central Thailand. Trapping was done in two forest types in three seasons.Maxomys surijerwas the dominant species in both plots. The three most abundant species in each plot accounted for > 90% of all captures. Community structure, density, relative abundance, biomass, age structure of populations, and habitat usage of some small mammal species varied by forest type and season. The dry evergreen/mixed deciduous forest type supported a greater abundance and biomass of small mammals than the mixed deciduous/dry dipterocarp forest type in all seasons, although species richness was the same. The greatest density, biomass, and home-range size forMaxomys surijeroccurred in the rainy season in both forest types. Seasonal changes in ratios of adults and subadulls of several species suggested a breeding peak at the end of the dry season or beginning of the rainy season. The mixed deciduous/dry dipterocarp forest showed a drastic drop in numbers, density, and biomass of small mammals six weeks after a fire burned through it.

SUMMARYAmong the most endangered tropical ecosystems, tropical dry forests are threatened by degradation that includes edge effects arising from perturbations such as the creation and maintenance of roads and other clearings. While much is known about these adverse effects on tree communities in tropical moist forests, similar effects in tropical dry forests are little understood. This paper examines the relationship between roads, road-related exotic plant invasion and tree community change in a tropical dry forest in southern India. Forty pairs of roadside and interior plots across four factorial combinations of road width (wide and narrow) and understorey type (native and exotic) were sampled. Tree death and extant tree community composition were compared using generalized linear models and similarity analyses. Tree death near roads was more than double that away from them, suggesting that roads may increase tree death in these forests. The interactive effect of understorey type (exotic or native) and road width on tree death was significant, with highest tree death near wide roads bordered by exotic understorey. Conversely, tree community composition was influenced by road width and understorey type, but not by proximity to roads. Creation and maintenance of roads for forest management may have serious implications for tree communities in tropical dry forests and should thus be minimized. Exotic plants may also be important contributors to increasing tree death, and further research on their impacts, particularly into underlying mechanisms, is critical to the long-term conservation of tropical dry forest communities.

Most studies on Seasonally Dry Tropical Forests (SDTFs) investigate phytogeographic patterns and floristic connections of this disjunct biome. However, little is known about the structural characteristics of SDTFs. We aimed to describe the structure of a SDTF in an ecotonal area between the Cerrado and Caatinga domains. In total, 79 tree species were recorded, and high values of Shannon diversity index (3.6 nats/individual) and equability (0.83) were observed. The diameter distribution for the species with higher cover values and for the entire community did not exhibit a reverse-J shaped distribution, which indicates the occurrence of different growth strategies and ecological adaptations to water stress. The results did not indicate the formation of floristic groups, as the high soil fertility in the study area results in a homogeneous environment. The structural characteristics of the study area associated with the soil composition highlight its importance for conservation and emphasize the need for community structure studies in SDTFs.

Deforestation and changes in land use have reduced the tropical dry forest to isolated forest patches in northwestern Costa Rica. We examined the effect of patch area and length of the dry season on nestedness of the entire avian community, forest fragment assemblages, and species occupancy across fragments for the entire native avifauna, and for a subset of forest dependent species. Species richness was independent of both fragment area and distance between fragments. Similarity in bird community composition between patches was related to habitat structure; fragments with similar forest structure have more similar avian assemblages. Size of forest patches influenced nestedness of the bird community and species occupancy, but not nestedness of assemblages across patches in northwestern Costa Rican avifauna. Forest dependent species (species that require large tracts of mature forest) and assemblages of these species were nested within patches ordered by a gradient of seasonality, and only occupancy of species was nested by area of patches. Thus, forest patches with a shorter dry season include more forest dependent species.

Tropical forests concentrate most of the world’s biodiversity. In the Northeast of Brazil it is possible to record mosaics of tropical dry and moist forests growing nearby but with completely different biotic and abiotic characteristics. These forests are constantly threatened by intense environmental devastation that affect not only above-ground communities but also those hidden below-ground, such as arbuscular mycorrhizal fungi (AMF), which act in maintaining ecosystem balance. This work aimed to determine the composition of native AMF communities in areas of humid forest (HF) and dry forest (DF) in northeastern Brazil. A total of 70 taxa of AMF were identified in the study areas, with Acaulospora (17) and Glomus (16) being the most representative genera. The sampling effort allowed the evaluation of 70%–73% of the species estimated for the areas. AMF communities differed between HF and DF areas. Species of the genus Glomus occurred predominantly in humid forest areas, whereas representatives of the order Gigasporales were associated more specifically with the dry forest area. Four soil attributes showed approximately 50% correlation with the composition of the AMF community (silt, clay, K, and CEC). Humid and dry forest areas presented a high diversity of AMF, and the soil properties were an important factor for the community composition of these fungi.

AbstractTropical dry forests are an intricate ecosystem with special adaptations to periods of drought. Arbuscular mycorrhizal fungi (AMF) are essential for plant survival in all terrestrial ecosystems but might be of even greater importance in dry forests as plant growth is limited due to nutrient and water deficiency during the dry season. Tropical dry forests in Ecuador are highly endangered, but studies about AMF communities are scarce. We investigated the AMF community of a premontane semi-deciduous dry forest in South Ecuador during the dry season. We estimated AMF diversity, distribution, and composition of the study site based on operational taxonomic units (OTUs) and compared the results to those from the tropical montane rainforest and páramo in South Ecuador. OTU delimitation was based on part of the small ribosomal subunit obtained by cloning and Sanger sequencing. Nearly all OTUs were Glomeraceae. The four frequent OTUs were Glomus, and comparison with the MaarjAM database revealed these to be globally distributed with a wide range of ecological adaptations. Several OTUs are shared with virtual taxa from dry forests in Africa. Ordination analysis of AMF communities from the tropical dry and montane rainforests in South Ecuador revealed a unique AMF community in the dry forest with only few overlapping OTUs. Most OTUs that were found in both dry and rainforests and on the two continents were globally distributed Glomus.

We analyzed phytosociological characteristics of a tropical dry deciduous forest located in an urban environment of Indian Institute of Forest Management (IIFM) Campus in the capital city of Bhopal of Madhya Pradesh state, Central India. A Comparison has been made among the tree community characteristics during the years 1988, 2002 and 2020 in terms of tree species composition, stem density, basal area and Importance Value Index (IVI). At the time of establishment of the institute in 1988, the forest area resembleda degraded dry scrubland. Due to continuous care/protection, plantation activities, degraded forest recovered remarkably, ecological processes evolved favorably with canopy cover reaching over 60% in some patches and about 50% in general over most part of the campus. During last two decades, tree density increased from 319 to 525 stem ha-1 indicating an increase of 64% whereas basal area increased from 18470.79 cm2 ha-1 to 29782.31 cm2 ha-1,an increase of about 61%. Leguminaceae family represented 26.4% of the tree community followed by Combretaceae (11.76%). Shannon-Weiner index (1.31), Simpson index (0.93) and evenness index (0.85) are within the reported ranges for similar forest type of dry deciduous nature in India. Theresults of the presentstudy will help forest managers in conservation planning of urban tropical forest ecosystem of central India.

1. A longstanding goal of ecology and conservation biology is to understand the environmental and biological controls of forest succession. However, the patterns and mechanisms that guide successional trajectories, especially within tropical forests, remain unclear. 2. We collected leaf functional trait and abiotic data across a 110-year chronosequence within a tropical dry forest in Costa Rica. Focusing on six key leaf functional traits related to resource acquisition and competition, along with measures of forest stand structure, we propose a mechanistic framework to link species composition, community trait distributions and forest structure. We quantified the community-weighted trait distributions for specific leaf area, leaf dry matter concentration, leaf phosphorus concentration, leaf carbon to nitrogen ratio and leaf stable isotopic carbon and nitrogen. We assessed several prominent hypotheses for how these functional measures shift in response to changing environmental variables (soil water content, bulk density and pH) across the chronosequence. 3. Increasingly, older forests differed significantly from younger forests in species composition, above-ground biomass and shifted trait distributions. Early stages of succession were uniformly characterized by lower values of community-weighted mean specific leaf area, leaf stable nitrogen isotope and leaf phosphorus concentration. Leaf dry matter concentration and leaf carbon to nitrogen ratio were lower during earlier stages of succession, and each trait reached an optimum during intermediate stages of succession. The leaf carbon isotope ratio was the only trait to decrease linearly with increasing stand age indicating reduced water use efficiency in older forests. However, in contrast with expectations, community-weighted trait variances did not generally change through succession, and when compared to null expectations were lower than expected. 4. The observed directional shift in community-weighted mean trait values is consistent with the 'productivity filtering' hypothesis where a directional shift in water and light availability shifts physiological strategies from 'slow' to 'fast'. In contrast with expectations arising from niche based ecology, none of the community trait distributions were over-dispersed. Instead, patterns of trait dispersion are consistent with the abiotic filtering and/or competitive hierarchy hypotheses.

The trait based approach has been proposed as a way to reconcile community ecology. Despite recent advances in trait based ecology, such as the development of global trait databases and standardized methodology for trait collections, it remains unclear to what degree traits vary across individuals, species, and communities. In addition, the drivers of trait variation may shed light on the underlying processes that maintain species diversity and community assembly at local to continental scales yet these have been poorly studied. In this study, I examine both the magnitude of trait variation as well as the patterns of trait variation at local to continental scales in order to understand the drivers of diversity patterns across environmental gradients. First, I quantified the magnitude of trait variation at local scales in a dry tropical forest and determined that intraspecific variation is not negligible and can be quite large for compound-leaved species. However, I showed that the sample sizes necessary for quantifying trait variation are tractable and should encourage the adoption of trait variation in trait based ecology. Second, I tested whether climatic variables are predominantly responsible for observed trait variation across dry tropical forests in the Americas. I showed that climatic variability, specifically variability in precipitation, explained a large degree of observed trait variation across dry tropical forests and may provide a unique approach for classifying dry tropical forests based on their inherent degree of climatic seasonality. Third, I quantified patterns of trait variation at continental scales across elevational gradients at high to low latitudes. I showed that climatic variables largely drive patterns of trait variation at high latitudes while biotic factors largely drive patterns of trait variation at low, tropical latitudes. This finding has implications for understanding large-scale patterns of species diversity across elevational and latitudinal gradients. Finally, I apply trait variation to life history theory by quantifying variation in two life history traits (growth and reproduction) in a tropical tree species using a legacy dataset. I showed that variation in these two life history traits is due to both resource availability and allometric related effects on both traits. In sum, this study advances our understanding of the magnitude and underlying drivers of trait variation at local to continental scales.

The development of human societies rests on functioning ecosystems. This thesis builds on integrated theories of linked social-ecological systems and complex adaptive systems to increase the understanding of how to strengthen the capacity of ecosystems to generate services that sustain human well-being. In this work, I analyze such capacity in human-dominated production ecosystems in Tanzania and Madagascar, and how this capacity is related to local management practices. Resilience of social-ecological systems refers to the capacity to buffer change, to re-organize following disruption, and for adaptation and learning. In Papers I and II, qualitative interview methods are used for mapping and analyses of management practices in the agroecosystem of the Mbulu highlands, Northern Tanzania. Practices such as soil and water conservation, maintenance of habitats for pollinators and predators of pests, intercropping, and landscape diversification, act to buffer food production in a variable environment and sustain underlying ecological processes. The practices are embedded in a decentralized but nested system of institutions, such as communal land rights and social networks, that can buffer for localized disturbances such as temporary droughts. Paper II compares these findings with practices in a farming system in Sweden, and suggests that similar mechanisms for dealing with uncertainty and change can exist in spite of different biophysical conditions. In Papers III and IV, interviews are combined with GIS tools and vegetation sampling to study characteristics and dynamics of the dry forests of Androy, southern Madagascar. Paper III reports on a previously underestimated capacity of the dry forest of southern Madagascar to regenerate, showing areas of regeneration roughly equal areas of degenerated forest (18 700 ha). The pattern of forest regeneration, degradation, and stable cover during the period 1986-2000 was related to the enforcement of customary property rights (Paper III). Paper IV reports on a network of locally protected forest patches in Androy that is embedded in a landscape managed for agricultural or livestock production and contributes to the generation of ecosystem services and ecosystem resilience at a landscape scale. Forest protection is secured by local taboos that provide a well-functioning and legitimate sanctioning system related to religious beliefs. In Paper V, two spatial modeling tools are used to assess the generation of two services, crop pollination and seed dispersal, by the protected forest patches in southern Androy. The functioning of these services is dependent on the spatial configuration of protected patches in the fragmented landscape and can be highly vulnerable to even small changes in landscape forest cover. In conclusion, many of the identified practices are found to make ecological sense in the context of complex systems and contribute to the resilience of social-ecological systems. The thesis illustrates that the capacity of human-dominated production ecosystems to sustain a flow of desired ecosystem services is strongly associated with local management practices and the governance system that they are embedded in, and that, contrary to what is often assumed, local management can and does add resilience for desired ecosystem services. These findings have substantial policy implications, as insufficient recognition of the dynamics of social-ecological interactions is likely to lead to failure of schemes for human development and biodiversity conservation.

This thesis is spurred by the overarching question “why is a plant where it is in space and time?”, which, when asked in different global communities over the last century or so, has contributed to the development of general theories of plant community ecology and has provided information relevant to understanding, managing, and predicting the future of those communities. The question is asked in the context of a seasonally dry tropical forest (SDTF) plant community in southern India, based on long-term research conducted in a permanent 50-ha sampling plot. We employ a layered approach to answering this question, wherein we deconstruct the structure and dynamics of the plant community by first establishing the spatial structure of soils, topography and lithology in the plot. Next we assess how this spatial structure, together with temporal variation in precipitation, affects plant abundances in space and time. Next we break up abundance variation into the components of recruitment, mortality and stem radial growth and assess how these respond to variation in environmental factors such as precipitation, temperature, soils, topography and fire, and biotic neighborhoods. In Chapter 2, we examine the roles of lithology, topography, vegetation and fire in generating local-scale (<1 km2) soil spatial variability in the 50-ha plot. For this, we mapped soil (available nutrients, Al, total C, pH, moisture and texture in the top 10cm), rock outcrops, topography, all native woody plants ≥1 cm diameter at breast height (DBH), and spatial variation in fire frequency (times burnt during the 17 years preceding soil sampling) in a permanent 50-ha plot. Unlike classic catenas, lower elevation soils had lesser moisture, plant-available Ca, Cu, Mn, Mg, Zn, B, clay and total C. The distribution of plant-available Ca, Cu, Mn and Mg appeared to largely be determined by the whole-rock chemical composition differences between amphibolites and hornblende-biotite gneisses. Amphibolites were associated with summit positions, while gneisses dominated lower elevations, an observation that concurs with other studies in the region which suggest that hillslope-scale topography has been shaped by differential weathering of lithologies. This “inverse catena” pattern is possibly reinforced by topography due to nutrient leaching and clay depletion in the drainage area. Neither NO3--N nor NH4+-N was explained by the basal area of trees belonging to Fabaceae, a family associated with N-fixing species, and no long-term effects of fire on soil parameters were detected. A strong SW-NE trending P pattern remained unexplained by any of the factors considered. Local-scale lithological variation is an important first-order control over soil variability at the hillslope scale in this SDTF, by both direct influence on nutrient stocks and indirect influence via control of local relief. The extent to which interspecific niche differences structure plant communities is highly debated, with extreme viewpoints ranging from fine-scaled niche partitioning, where every species in the community is specialized to a distinct niche, to neutrality, where species have no niche or fitness differences. However, there exists a default position wherein niches of species in a community are determined by their evolutionary and biogeographic histories, irrespective of other species within the community. According to this viewpoint, a broad range of pair-wise niche overlaps – from completely overlapping to completely distinct – are expected in any community without the need to invoke interspecific interactions. In Chapter 3, we develop a method that can test for both habitat associations and niche differences along an arbitrary number of spatial and temporal niche dimensions and apply it to a 24-year data set of the eight dominant woody-plant species (representing 84% and 76% of total community abundance and basal area, respectively) from the 50-ha plot, using edaphic, topographic and precipitation variables as niche axes. Species separated into two broad groups in niche space – one consisting of three canopy species and the other of a canopy species and four understory species – along axes that corresponded mainly to variation in soil P, Al and a topographic index of wetness (the second and fourth principal components (PCs) of soil and topographic variables). All three species from the former group and one understorey species from the latter group showed evidence of niche specialization along the same axes. Based on the landscape-scale distributions, local-scale habitat associations, and traits of the constituent species, we suggest that species in the former group have a more resource-conservative strategy compared to those in the latter group. Species within groups tended to have significantly greater niche overlap than expected by chance. Community-wide niche overlap in spatial and temporal niche axes was never smaller than expected by chance. Species-habitat associations were neither necessary nor sufficient preconditions for niche differences to be present. Our results suggest that this tropical dry-forest community consists of several tree species with broadly overlapping niches, and where significant niche differences do exist, they are not readily interpretable as evidence for niche differentiation. We argue, based on a survey of the literature, that many of the observed niche differences in tropical forests are more parsimoniously viewed as autecological differences between species that exist independently of interspecific interactions. In Chapter 4, we study the dynamics of the plant community in relation to environmental factors and biotic neighborhoods. We assess resources (precipitation, soil nutrients), environmental conditions (temperature), microhabitat conditions (topography), disturbances (fire) and conspecific and heterospecific plant neighborhoods to identify which of these best predicted mortality, recruitment and growth over a 24-yr study period. We fitted regression trees with recruitment, mortality or growth as the response variable and environmental and biotic neighborhood variables as predictors, with tree selection performed by a cross validation technique that accounted for the spatial and temporal autocorrelation present in the data. Niche specialists or species with abundances skewed towards particular habitats did not necessarily grow faster, recruit more or die less on “preferred” habitats. On the whole, spatial environmental factors were selected into models less frequently than either temporal environmental or neighborhood factors, and their effect sizes were also smaller. The first and second PCs of soil and topographic variables were selected into more models than the remaining PCs. While there was some evidence of conspecific negative density dependence, particularly on suppressing growth, density-dependent effects were on the whole weaker than temporal environmental factors and also decayed rapidly with distance. Positive density-dependence was prevalent, possibly resulting from dispersal limitation and facilitation. In some cases, initial increases in neighborhood density had positive effects that turned negative when densities further increased, suggesting non-linear responses. Precipitation increases largely had a positive, and minimum and maximum temperatures increases a negative, effect on recruitment, growth and survival, although responses were species-specific and, sometimes, non-linear. By far, the strongest and most consistent effects amongst all factors considered were that of fire, with recent fires having a strong and unidirectional, negative effect on all species for which fire was selected into a model. From a theoretical standpoint, there is limited support for the neutral perspective, given the strong and species-specific responses to spatial and temporal environmental variation and the presence of niche specificity at the local scale. Despite the evidence supporting the existence of niche specialization, it seems unlikely that this community is strongly stabilized by the presence of systematic niche differences. The net evidence on the structure and dynamics of this community point to what may be considered a null hypothesis, that is, species are responding individualistically – and independently of each other – to fluctuations in the environmental. It is hoped these results will provide information relevant to understanding, managing, and predicting the future of this ecosystem and contribute towards the development of general theories of plant community ecology.
Ministry of Environment, Forests and Climate Change, the Department of Science and Technology, the Department of Biotechnology

Tree growth influences forest community dynamics and responses to environmental variations, but currently is not well understood. Tree growth in highly diverse wet tropical forests have been well studied and characterised compared to the species-poor dry tropical forests. Thus, it is not clear if growth rates and community dynamics of dry forests are similar to those of wet forests, given the longer dry season, greater rainfall variability, more open canopy and lower number of species in dry forests. This thesis focuses on identifying important factors that influence tree diameter growth rates in the dry tropical forest at Mudumalai, southern India, and also compares growth patterns at this dry forest with those at moister forests. The thesis thus contributes towards closing the gap in understanding of tree growth patterns across the tropics. An initial analysis involving matrix-based population projections of four common canopy species at Mudumalai showed that variations in diameter growth have the potential to drastically modify population trajectories of dominant species. Thus the main focus of this thesis is aimed at identifying the important intrinsic and extrinsic factors affecting growth in this dry forest, as this information could be useful for future management of the forest. The second important aim of the thesis was to find out if growth rates are influenced by different sets of factors in tropical dry versus moist forests. A large permanent 50ha plot vegetation monitoring plot was set up in 1988-89 in the Mudumalai dry deciduous forest, and was subsequently monitored annually by staff of the Centre for Ecological Sciences. Data used in this thesis represent a 12-year interval between 1988 and 2000. Girth measurements were obtained from all woody tree stems ≥1cm in diameter every four years during this 12 year interval, which provided three census intervals of diameter increment data on >13,000 trees. For the comparison between dry and moist deciduous forests, data were obtained from a similar large plot maintained and monitored at the Barro Colorado Island (BCI) in Panama. Influences of the intrinsic factors, tree size, individual identity, species identity and growth form, were examined using t-tests, Wilcoxon signed ranks tests, linear regressions, analysis of variance (ANOVA), principal components analysis (PCA) and cluster analysis. Among the intrinsic factors tested, species identity explained approximately 20% of growth rates at the community level, while tree diameter explained less of growth variation, and growth form had a minor influence on growth. Growth rates also were examined for variations across the three census intervals, and for relationships with rainfall and survival from fire. Statistical tests included t-tests, Wilcoxon and other non-parametric sign tests, logistic regression and ANOVA. Most species and individuals showed significant reductions of growth in the second census interval (1992-1996), and growth rates of most trees were positively related to rainfall. Growth rate variations generally were not related to survival from fire, and few species were capable of escaping fire mortality by fast growth. Spatial environmental influences were tested in the commonest fifteen species, using five habitat categories, local elevation, slope, aspect, and the biotic neighbourhood variables of local conspecific and heterospecific density. Statistical tests included analysis of covariance, multiple linear regression and redundancy analysis. The tests were quadrat-based or individual-based, and species' growth responses were tested at different levels of distance and spatial scale. Topographic features and habitat categories had ephemeral effects on species growth. Only the most dominant species, Lagerstroemia microcarpa, showed consistent conspecific neighbour density effects. Redundancy analysis using a subset of common species and environmental factors did not reveal common growth responses to spatial environmental factors. Comparison of factors influencing growth at Mudumalai versus at BCI using multiple factor ANOVA and multiple linear regressions showed a similar influence of temporal variation at the two sites, but stronger and more widespread influence of tree size (diameter) at BCI. The greater influence of tree size at BCI may be related to greater light limitation in this dense moist forest. Spatial environmental factors had weak influences at both plots. Species were less differentiated from each other at the more diverse BCI plot compared to the relatively species-poor Mudumalai plot, suggesting that species' growth niches may be weakly related to diversity across tropical forests. Overall the results showed that among the factors tested species identity and census intervals were the most important influences on diameter growth at the Mudumalai dry deciduous forest. Tree diameter was less important and less consistent in affecting growth at the Mudumalai dry forest, contrary to expectations based on moist tropical forests where this relationship has been established previously. When comparing Mudumalai and BCI, the relative importance of different factors was different at the two sites, and the most important difference was a dominant influence of light limitation at the wetter forest in Panama. In terms of management applications, this study showed that fires at Mudumalai might be an inescapable source of mortality for many vulnerable species, and improved fire management is crucial for long term survival of species in this dry forest. At a larger scale, light and other environmental variables were found to influence growth differently at Mudumalai compared to BCI. This suggests that location-specific responses may be important for projections of tree biomass and carbon sequestration, especially under future climatic change scenarios.

Tree growth influences forest community dynamics and responses to environmental variations, but currently is not well understood. Tree growth in highly diverse wet tropical forests have been well studied and characterised compared to the species-poor dry tropical forests. Thus, it is not clear if growth rates and community dynamics of dry forests are similar to those of wet forests, given the longer dry season, greater rainfall variability, more open canopy and lower number of species in dry forests. This thesis focuses on identifying important factors that influence tree diameter growth rates in the dry tropical forest at Mudumalai, southern India, and also compares growth patterns at this dry forest with those at moister forests. The thesis thus contributes towards closing the gap in understanding of tree growth patterns across the tropics. An initial analysis involving matrix-based population projections of four common canopy species at Mudumalai showed that variations in diameter growth have the potential to drastically modify population trajectories of dominant species. Thus the main focus of this thesis is aimed at identifying the important intrinsic and extrinsic factors affecting growth in this dry forest, as this information could be useful for future management of the forest. The second important aim of the thesis was to find out if growth rates are influenced by different sets of factors in tropical dry versus moist forests. A large permanent 50ha plot vegetation monitoring plot was set up in 1988-89 in the Mudumalai dry deciduous forest, and was subsequently monitored annually by staff of the Centre for Ecological Sciences. Data used in this thesis represent a 12-year interval between 1988 and 2000. Girth measurements were obtained from all woody tree stems ≥1cm in diameter every four years during this 12 year interval, which provided three census intervals of diameter increment data on >13,000 trees. For the comparison between dry and moist deciduous forests, data were obtained from a similar large plot maintained and monitored at the Barro Colorado Island (BCI) in Panama. Influences of the intrinsic factors, tree size, individual identity, species identity and growth form, were examined using t-tests, Wilcoxon signed ranks tests, linear regressions, analysis of variance (ANOVA), principal components analysis (PCA) and cluster analysis. Among the intrinsic factors tested, species identity explained approximately 20% of growth rates at the community level, while tree diameter explained less of growth variation, and growth form had a minor influence on growth. Growth rates also were examined for variations across the three census intervals, and for relationships with rainfall and survival from fire. Statistical tests included t-tests, Wilcoxon and other non-parametric sign tests, logistic regression and ANOVA. Most species and individuals showed significant reductions of growth in the second census interval (1992-1996), and growth rates of most trees were positively related to rainfall. Growth rate variations generally were not related to survival from fire, and few species were capable of escaping fire mortality by fast growth. Spatial environmental influences were tested in the commonest fifteen species, using five habitat categories, local elevation, slope, aspect, and the biotic neighbourhood variables of local conspecific and heterospecific density. Statistical tests included analysis of covariance, multiple linear regression and redundancy analysis. The tests were quadrat-based or individual-based, and species' growth responses were tested at different levels of distance and spatial scale. Topographic features and habitat categories had ephemeral effects on species growth. Only the most dominant species, Lagerstroemia microcarpa, showed consistent conspecific neighbour density effects. Redundancy analysis using a subset of common species and environmental factors did not reveal common growth responses to spatial environmental factors. Comparison of factors influencing growth at Mudumalai versus at BCI using multiple factor ANOVA and multiple linear regressions showed a similar influence of temporal variation at the two sites, but stronger and more widespread influence of tree size (diameter) at BCI. The greater influence of tree size at BCI may be related to greater light limitation in this dense moist forest. Spatial environmental factors had weak influences at both plots. Species were less differentiated from each other at the more diverse BCI plot compared to the relatively species-poor Mudumalai plot, suggesting that species' growth niches may be weakly related to diversity across tropical forests. Overall the results showed that among the factors tested species identity and census intervals were the most important influences on diameter growth at the Mudumalai dry deciduous forest. Tree diameter was less important and less consistent in affecting growth at the Mudumalai dry forest, contrary to expectations based on moist tropical forests where this relationship has been established previously. When comparing Mudumalai and BCI, the relative importance of different factors was different at the two sites, and the most important difference was a dominant influence of light limitation at the wetter forest in Panama. In terms of management applications, this study showed that fires at Mudumalai might be an inescapable source of mortality for many vulnerable species, and improved fire management is crucial for long term survival of species in this dry forest. At a larger scale, light and other environmental variables were found to influence growth differently at Mudumalai compared to BCI. This suggests that location-specific responses may be important for projections of tree biomass and carbon sequestration, especially under future climatic change scenarios.

Tropical forests represent major uncertainties in climate models and have the potential to act as both net carbon sources and sinks in the future. Projections that hurricanes will be an increasingly powerful disturbance in many tropical forests further complicate our ability to predict how these ecosystems will respond to climate change. By understanding how environmental variation at small spatial scales affects ecosystem processes shaping present-day forests, it may be possible to improve our predictions for how these forests will change in the future. This dissertation consists of three chapters examining the spatial patterns of tree species and soil greenhouse gas fluxes in a tropical forest in the Luquillo Experimental Forest, Puerto Rico. Disentangling the forces that drive the spatial distribution of tree species has been a foundational question in ecology and determining the relative importance of these forces is central to understanding spatial variation in soil biogeochemistry. In chapter 1, I use percolation threshold analysis to examine the clustering patterns of simulated and real tree spatial point patterns to understand the role that environmental filtering and density dependent processes play in shaping tree species distributions. I demonstrate that percolation threshold analysis successfully distinguishes thinning by random, environmental filtering, and density dependent processes. Additionally, the relative importance of these thinning processes varies by species’ traits; fast growing species with low LMA and shade intolerance have stronger evidence of density dependent processes compared to species with high LMA and shade tolerance. In chapter 2, I examine the spatial relationships between soil greenhouse gas fluxes and two proximal drivers of soil environmental variation: tree species and topography. I also examine how incorporating small-scale variation in greenhouse fluxes affects our scaled-up estimates of ecosystem greenhouse gas emissions. I show that including species effects improves estimates of soil CO2 fluxes, and including measures of topography improve estimates of CH4 and N2O fluxes. Incorporating spatial variation in GHG fluxes related to tree species and topography into our estimates of ecosystem GHG emissions decreased estimates of the total CO2-equivalent emissions in this forest by 5%. Finally, in chapter 3 I examine how the GHG fluxes in this forest change after an intense hurricane. I demonstrate that GHG emissions shift following a hurricane; this shift is primarily driven by a 176% increase in N2O emissions that represent a significant net loss of gaseous nitrogen from this forest. N2O fluxes accounted for 4.2% of the post-hurricane GHG-induced radiative forcing (compared to 1.8% pre-hurricane) and the combined increase in CO2, CH4, and N2O emissions observed translates to a 25% increase in CO2-equivalent emissions compared to pre-hurricane conditions. This dissertation focuses on the role of small-scale environmental variation in shaping forest communities and spatial patterns of GHG fluxes and aims to highlight how this variation can help us to better understand the role tropical forests play in the biosphere.

Plant communities of the dune complex are a result of interaction between tolerance of plant species and sandy substrate, high wind velocities, salt spray, sand accretion and environmental heterogeneity. Propagules of many plant species are dispersed by water currents and deposited on the driftline. Most of these species find ideal conditions for germination but seedling establishment, growth and reproduction is denied to all but a few species with ecological amplitude sufficient to withstand the physical stresses associated with sand accretion, erosion and sandblasting in the highly disturbed environment. The distinct differences between habitats from the water´s edge to the inland grass-forest ecotone leads eventually to the establishment of ecologically distinct communities consisting of both plants and animals. The distinction is caused by sharp differences in the physical environment that may create sharp zones with abrupt or gradual blending of the two community types. In some locations these zones are relatively stable for long periods before any visible change occurs in the community depending on the recession of the shoreline, availability of new bare areas and the advance of communities towards the sea coast. The occurrence of plant communities in zones has been documented along sea coasts worldwide. This chapter examines the plant communities of the sand dune complex along seashores of the world. The following information has been assembled from Doing (1985), Dry coastal ecosystems Vol. 2 A, B, C, edited by Eddy van der Maarel (1993), Doody (1991) and Thannheiser (1984). It presents data on plant communities and ecology of each zone from various parts of the world. The species complement in the ´foredune complex´ in tropical, temperate and other regions around the world may be different, but their response to the prevailing environmental stresses of foredunes is convergent. In different world regions the boundaries between vegetation zones of the sand dune complex may not be defined sharply because of climatic variability, geographic location, physiography of the dune system and other factors peculiar to each location. Usually three to six different plant assemblages have been identified on the dune complex along sea coasts and lakeshores. A brief description of vegetation and ecological traits of species in each zone are presented below.

This chapter encompasses a literature survey and strategic analysis to understand the elaboration and implementation of Participatory Forest Management (PFM) in Benin, with a focus on the case of the “Forêt des Trois Rivières”. By analyzing the historical background of forest management systems in Benin, we highlighted two major turning points. The first relates to the creation and autocratic management of protected forests, which took place from 1940 to 1990. The second change took place after the Rio conference in 1992, and this emphasized the importance of local communities in natural resources management. Moreover, the results of our strategic analysis of stakeholders involved in the specific case of Participatory Forest Management Plan (PFMP) of the “Forêt des Trois Rivières” showed that it is important to emphasize on active community participation while designing a participatory management plan and for decision making at the implementation stage. We also observed that alliances between foresters and timber loggers are likely to hinder the achievement of the PFM objectives.

This chapter encompasses a literature survey and strategic analysis to understand the elaboration and implementation of Participatory Forest Management (PFM) in Benin, with a focus on the case of the “Forêt des Trois Rivières”. By analyzing the historical background of forest management systems in Benin, we highlighted two major turning points. The first relates to the creation and autocratic management of protected forests, which took place from 1940 to 1990. The second change took place after the Rio conference in 1992, and this emphasized the importance of local communities in natural resources management. Moreover, the results of our strategic analysis of stakeholders involved in the specific case of Participatory Forest Management Plan (PFMP) of the “Forêt des Trois Rivières” showed that it is important to emphasize on active community participation while designing a participatory management plan and for decision making at the implementation stage. We also observed that alliances between foresters and timber loggers are likely to hinder the achievement of the PFM objectives.