The Science

Scientists investigated the controls over forest mortality in Costa Rica’s dry-tropical region using satellite remote sensing. Estimates of tree mortality using the Enhanced Vegetation Index (EVI). matched well with field measurements. Substantial fine-scale variability in forest mortality was related primarily to the cumulative water deficit during the drought, leaf traits, and topography.

The Impact

This work is important for improving the ability to understand, observe, and predict dry-tropical forest vegetation dynamics and their response to drought. This approach greatly improves the utility of satellite measurements for this purpose from local to regional scales, and these datasets can be used to benchmark predictive model performance.

Summary

Remote sensing provides a powerful approach to quantify changes in vegetation on the Earth’s surface. The Enhanced Vegetation Index (EVI), an indicator of vegetation function and resilience, was derived from Landsat 30x30m resolution imagery and used to quantify changes in vegetation biomass due to mortality during a severe drought in 2015 in Costa Rica’s dry-tropical forests. After strong validation with in-situ ground inventories of tree mortality, the approach was applied to examine local drivers of mortality. The degree of drought, represented by the cumulative water deficit, played a strong role in localized mortality. Ecosystems with a greater fraction of evergreen tree species experienced greater mortality than those with a greater abundance of deciduous species, demonstrating the influence of plant trait strategies on drought vulnerability. Topographic position also played a significant role, with sun-exposed and steep slopes having the greatest mortality. These findings highlight the potential of high-resolution remote sensing to “fingerprint” forest mortality and the significant role of ecosystem heterogeneity in forest biomass resistance to drought.

Principal Investigator

Xiangtao Xu
Cornell University
xx286@cornell.edu

Program Manager

Brian Benscoter
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
brian.benscoter@science.doe.gov

Funding

This research was supported by Cornell University’s College of Agriculture and Life Sciences (CALS) and the National Science Foundation’s Faculty Early Career Development (CAREER)  program (grant DEB-1053237). Field plots were funded by the Biological and Environmental Research (BER) Program’s Environmental System Science (ESS) program within the U.S. Department of Energy’s (DOE) Office of Science (award DE-SC0014363). Special thanks to Roger Blanco and Maria Marta Chavarria who provided logistical help in the field. This research was also supported by DOE’s Next Generation Ecosystem Experiment–Tropics (NGEE–Tropics) project and by the National Science and Engineering Research Council of Canada (NSERC)–Discovery Grant Program.

References