The Science

Tree death is the result of interactions between various factors, including direct and indirect effects. Crown damage and previous growth mediates effects of tree size, wood density, soil fertility, and habitat suitability on mortality.

The Impact

Crown damage and individual growth (growing more/less than typical for the species) are critical. Habitat is also important because fertility/moisture influences individual growth, more than influencing the mortality of trees inside/outside their preferred habitat.

Summary

The causes of individual tree death in tropical forests remains a major gap in understanding the biology of tropical trees, and leads to significant uncertainty in predicting global carbon cycle dynamics. Scientists from the NGEE-Tropics study and the Smithsonian Tropical Research Institute measured individual characteristics (diameter at breast height, wood density, growth rate, crown illumination and crown form) and environmental conditions (soil fertility and habitat suitability) for 26,425 trees that were 10 cm diameter at breast height and belonging to 416 species in a 52-ha plot in Lambir Hills National Park, Malaysia. The scientists used structural equation models to investigate the relationships between different factors and tree mortality. Crown form (a proxy for mechanical damage and other stresses) and prior growth were the two most important factors related to mortality. The effect of all variables on mortality (except habitat suitability) was substantially greater than expected by chance. Tree death is the result of interactions between factors, including direct and indirect effects. Crown form/damage and prior growth mediated most of the effect of tree size, wood density, fertility and habitat suitability on mortality. Large-scale assessment of crown form or status may result in improved prediction of individual tree death at the landscape scale.

Principal Investigator

Stuart J. Davies
Smithsonian Institute
daviess@si.edu

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Funding

The Lambir 52-ha plot was established as a collaboration between the Forest Department of Sarawak, Malaysia, Harvard University (NSF awards DEB-9107247 and DEB-9629601) and Osaka City University (grants 06041094, 08NP0901 and 09NP0901). The research has been supported by the Asia program of the Arnold Arboretum (Harvard University), the Center for Tropical Forest Science-Forest Global Earth Observatory of the Smithsonian Tropical Research Institute, and NSF award DEB-1545761 to S.J.D. G.A. and S.J.D. were supported as part of the Next Generation Ecosystem Experiments-Tropics, funded by the US Department of Energy, Office of Science, Office of Biological and Environmental Research. The authors thank the Sarawak Forest Department for permission to conduct this research in Lambir Hills National Park.

References