Forecasted Afrotropical Forest Responses to Climate Change Diverge from Neotropical Predictions with Consequences for Biodiversity Conservation and Carbon Storage

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.