LTREB: Legacy effects of compounding disturbances in the Amazon: implications for ecosystem carbon and water cycling

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The carbon stored in the Amazon’s forests is equivalent to ten years of current global carbon fossil-fuel emissions. This large carbon reservoir has seemingly grown over the past few decades and mitigated some of the negative effects on the global climate system associated with greenhouse gas emissions. At the same time, Amazon forests transfer enough moisture to the atmosphere to influence regional precipitation patterns. Interactions between climate change, deforestation, logging, windstorms, and wildfires have threatened the carbon stocks and climate regulatory functions of Amazon forests. Growing concerns that ongoing climate change combined with human disturbances will change Amazon forests into open savannas across large regions. This long term experiment in environmental biology award focuses on a forest that lies at the edge between continuous neotropical forests and savannas. This is an area where native vegetation has been fragmented and is frequently subject to interactions between human and natural disturbances such as fires, droughts, and windstorms. This award evaluates forest resilience from seasonally dry evergreen tropical forests to multiple disturbances based on long- term ecological measurements of a highly threatened Amazon forest. The project’s outcomes could inform regional land and fire management, particularly the development of new strategies to avoid catastrophic wildfires that reduce the capacity of forests to provide ecosystem services. This award will also connect US-based research with researchers and institutions in Brazil, in the process helping to train a diverse group of US students. Finally, the award represents important benchmarks for land surface models and remote sensing techniques that have been widely used to understand potential trajectories of tropical forests This award tests the hypothesis that forests subjected to novel compounding disturbances use different pathways to recover climate services. Disturbed forests that experience minor, short-term reductions in climate functions such as ET and net carbon uptake, have high forest resilience and low probability of large-scale forest replacement by scrubland. However, repeated disturbances triggering long-term losses of forest climate functions would point to low forest resilience. This award will add a decade of ecological data to a long-term, large-scale experimental site in southeast Amazonia that has been degraded by edge effects, recurrent fires, two windthrow events, and multiple droughts. These extended data measurements will permit a comprehensive assessment of how potential future pathways of the experimentally disturbed forests affect ecosystem-level climatic functions across different successional forest pathways and as plant traits change. The experimental site is located in one of the most threatened regions of the Amazon, on the boundary between a dense evergreen rainforest and seasonally dry forests and where native vegetation has been fragmented and subjected to anthropogenic (fire, edge effects) and natural disturbances (droughts and windthrow events). How forests’ long-term climate functions change as a function of novel disturbances and climate change has direct implications for the future of the world’s largest tropical forest. This award will rely on long-term ecological measurements to build a clearer understanding of Amazon forest resilience to multiple disturbances. It will evaluate how interactions between fire legacies to trees (e.g., wounds to tree trunks) and extreme weather events (droughts, windstorms) affect forest climatic functions. In the next ten years, this award will lead to a new understanding of how forest successional pathways and plant traits influence ecosystem-level ET and carbon stocks following compounding disturbances. This award will provide new insights into the (as yet unquantified) thresholds that may lead to large-scale ecosystem change under future climate and land use changes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.