Do Small Changes in Topography Influence Tree Characteristics in an Amazon Forest?

The Science

Previous work in Amazon forests has shown significant variation in both tree species distribution and drought-induced tree mortality across small ridges and valleys. In this study, forest ecologists measured 18 branch, leaf, and stomatal traits on 1,077 trees of 72 dominant species to identify underlying functional traits driving such changes across topography while controlling for a highly documented source of trait variability within species—tree size. Researchers found large trait variability across trees within species (i.e., intraspecific) that was related to trees’ topographic location for leaf traits and tree size for branch and stomatal traits.

The Impact

This study demonstrates the importance of accounting for intraspecific trait variation when testing trait-environment relationships. The study suggests tree size is a critical source of variability to be included in mechanistic models aiming to predict forest dynamics. The next steps include quantifying physiological traits, functional rooting depths, and water table dynamics to comprehensively understand trees’ vulnerability to climatic drivers (e.g., droughts) and their implications for forest composition and ecosystem services.

Summary

Tropical forest responses to variation in water availability, which are critical for understanding and predicting climate change effects, depend on trait variation among trees. Forest Global Earth Observatory (ForestGEO) scientists quantified interspecific (among species) and intraspecific (across trees within species) variation in 18 branch, leaf, and stomatal traits for 72 dominant tree species along a local topographic gradient in an aseasonal Amazon terra firme forest. They used these sampling designs to test trait relationships with tree size, elevation, and species’ topographic associations as well as trait correlations. Intraspecific trait variation was substantial and exceeded interspecific variation in 10 of 18 traits. For leaf acquisition traits, intraspecific variation was mainly related to tree topographic elevation, while most branch, leaf, and stomatal trait variation was related to tree size. Interspecific variation showed no clear relationships with species’ habitat association. Although trait correlations and coordination were generally maintained among trees and species, bivariate relationships varied among trees within species, across habitat association classes, and across tree size classes. These results demonstrate the magnitude and importance of intraspecific trait variation in tropical trees, especially as related to tree size. Furthermore, these results indicate that previous findings relating interspecific variation with topographic association in seasonal forests do not necessarily generalize to aseasonal forests.

Principal Investigator

Daniel Zuleta
Forest Global Earth Observatory, Smithsonian Tropical Research Institute
[email protected]

Program Manager

Brian Benscoter
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Funding

This research was supported by the National Doctoral Scholarship Colciencias-Colombia (647, 2015-II), the Smithsonian Tropical Research Institute Short-Term Fellowships, and the Next Generation Ecosystem Experiments Tropics (NGEE Tropics), which is funded by the U.S. Department of Energy’s (DOE) Office of Science, Biological and Environmental Research (BER) program. Data collection was supported by the ForestGEO of the Smithsonian Institution and Universidad Nacional de Colombia.

Related Links

• Functional Ecologists Article
• NGEE Tropics

References