Browsing by Subject "Logging"

Understanding how tropical forests respond to changes in the abiotic environment and human disturbance is critical for preserving biodiversity, mitigating climate change, and maintaining ecosystem services in the coming century. The lowland rainforests of Central Africa in particular are expected to lose 41% of present dense forest cover in the next 50 years to forest clearing, due in large part to forest loss resulting from the expansion of subsistence agriculture and logging. Deforestation also contributes a net increase in carbon dioxide to the atmosphere, exacerbating forest losses via increased tree mortality from drought, fire, and dispersal failure. Despite these grim circumstances, we know little about how Paleotropical tree communities are likely to respond to predicted changes in disturbance and climate.

To evaluate the unique response of Afrotropical forests to changes in the abiotic environment and disturbance, I employ diverse data including species inventories, seed rain, species traits, remotely sensed historic climatic data, future climate predictions, and soil nutrient data collected from 134 1-ha plots arrayed in two large-scale observational experiments spanning the central African countries of Gabon and the Republic of Congo (Brazzaville). I then combine these diverse data using novel modeling methods to 1) determine the relative roles of climate and human disturbance on tree community composition, 2) quantify the relative effects of human disturbance and the abiotic environment on tree fecundity and seed dispersal, and 3) forecast future tree community change given predicted changes in climate.

This work demonstrates that Afrotropical plant communities are more sensitive to human disturbance than to climate, with particular sensitivities to hunting and distance to village (a proxy for other human activities, including tree-cutting, gathering, etc.). These pressures have meaningful long-term effects on seed dispersal, increasing dispersal distances for animal dispersed seeds in disturbed forests. Finally, We forecast a 3 - 8% decrease in Afrotropical forest species richness by the end of the century, in contrast to the 30-50% loss of plant diversity predicted to occur with equivalent warming in the Neotropics.

This work reveals that community forecasts are not generalizable across regions, and more representative studies are needed in understudied biomes like the Afrotropics. Nascent data sets, increased availability of high quality remote sensing data, and new statistical techniques capable of synthesizing these various data will help in further resolving the fate of the world’s ecosystems. This study serves as an important counterpoint to work done in the Neotropics by providing contrasting predictions for Afrotropical forests with substantially different ecological, evolutionary, and anthropogenic histories.

Understanding how tropical forests respond to changes in the abiotic environment and human disturbance is critical for preserving biodiversity, mitigating climate change, and maintaining ecosystem services in the coming century. The lowland rainforests of Central Africa in particular are expected to lose 41% of present dense forest cover in the next 50 years to forest clearing, due in large part to forest loss resulting from the expansion of subsistence agriculture and logging. Deforestation also contributes a net increase in carbon dioxide to the atmosphere, exacerbating forest losses via increased tree mortality from drought, fire, and dispersal failure. Despite these grim circumstances, we know little about how Paleotropical tree communities are likely to respond to predicted changes in disturbance and climate.

To evaluate the unique response of Afrotropical forests to changes in the abiotic environment and disturbance, I employ diverse data including species inventories, seed rain, species traits, remotely sensed historic climatic data, future climate predictions, and soil nutrient data collected from 134 1-ha plots arrayed in two large-scale observational experiments spanning the central African countries of Gabon and the Republic of Congo (Brazzaville). I then combine these diverse data using novel modeling methods to 1) determine the relative roles of climate and human disturbance on tree community composition, 2) quantify the relative effects of human disturbance and the abiotic environment on tree fecundity and seed dispersal, and 3) forecast future tree community change given predicted changes in climate.

This work demonstrates that Afrotropical plant communities are more sensitive to human disturbance than to climate, with particular sensitivities to hunting and distance to village (a proxy for other human activities, including tree-cutting, gathering, etc.). These pressures have meaningful long-term effects on seed dispersal, increasing dispersal distances for animal dispersed seeds in disturbed forests. Finally, We forecast a 3 - 8% decrease in Afrotropical forest species richness by the end of the century, in contrast to the 30-50% loss of plant diversity predicted to occur with equivalent warming in the Neotropics.

This work reveals that community forecasts are not generalizable across regions, and more representative studies are needed in understudied biomes like the Afrotropics. Nascent data sets, increased availability of high quality remote sensing data, and new statistical techniques capable of synthesizing these various data will help in further resolving the fate of the world’s ecosystems. This study serves as an important counterpoint to work done in the Neotropics by providing contrasting predictions for Afrotropical forests with substantially different ecological, evolutionary, and anthropogenic histories.

The biotic forces that shape plant communities across ontogenetic stages drive patterns in survival, vegetation structure, and species diversity. In tropical forests, many of these forces are facilitated by interactions with animals, which can either promote or inhibit plant reproduction. Disruptions to these interactions – such as defaunation resulting from hunting and logging – can generate broad changes in tree recruitment, forest structure, and carbon storage, with demographic filtering at the seed and seedling stages responsible for many of the effects. Research to date has largely focused on a subset of prominent interactions (especially seed dispersal), while concurrent disruptions to other less-studied ecological processes may drive changes of opposite directionality for individual species or entire communities. With a limited understanding of seed predation, seedling establishment, and seedling physical damage and survival – particularly in Central African forests – it remains difficult to predict the outcomes of defaunation for tropical forest plant communities. In this dissertation, I use a combination of literature reviews, field-based experimental methods (including telemetric seed tags, seed and seedling exclosures, and artificial seedlings) and statistical analyses to assess 1) the role of plant-animal interactions and the influence of hunting on the regeneration of timber trees across tropical forests; 2) patterns of secondary dispersal and seed fate for two tree species in northeastern Gabon; 3) the role of seed traits and both seed density and distance from the parent tree in driving patterns of seed mortality and seedling establishment for ten tree species in northeastern Gabon; 4) the impacts of hunting on seed predation and seedling establishment for eight commercially important tree species across a defaunation gradient in northeastern Gabon; and 5) the role of physical damage by vertebrate trampling, rooting, and digging to artificial seedlings in intact and hunted and/or logged forests in Peru, Gabon, and Malaysian Borneo. I conclude that 1) hunting is likely to disrupt plant-animal interactions and tropical forest timber regeneration, but that these effects can be ameliorated given appropriate management; 2) seed fate is dependent on seed size and the identity of the seed predator, with evidence of scatterhoarding and secondary dispersal in northeastern Gabon; 3) seed traits, not density or distance from the parent tree, drive patterns in seed mortality and seedling establishment in northeastern Gabon, with vertebrate seed predation a stronger force than other mortality factors; 4) hunting-induced defaunation drives increased rodent seed predation and decreased seedling establishment of commercially-important tree species; and 5) vertebrate physical damage to seedlings is a consistent force in forests across the tropics, and hunting significantly reduces its strength. This dissertation highlights the important roles of wildlife in tropical forest ecological processes as well as the degree to which these interactions can be disrupted through hunting-induced defaunation, and emphasizes the value of appropriate management and continued comparative research across tropical forest regions.