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Assessing evidence for a pervasive alteration in tropical tree communities
Jérôme Chave1, Richard Condit, Helene C Muller-Landau
1Laboratoire Evolution et Diversité Biologique CNRS/Université Paul Sabatier, Toulouse, France. chave@cict.fr
Plos Biology
|March 6, 2008
Summary
Global environmental change impacts tropical forests, but findings on biomass and species shifts are not universal. This study suggests recovery from past disturbances and resource changes may be more influential than previously thought.
Area of Science:
- Ecology
- Forest Science
- Global Change Biology
Background:
- Recent studies indicate tropical forests are experiencing increased aboveground biomass and productivity, with shifts favoring fast-growing species.
- These alterations in mature tropical forests are often attributed to global environmental changes like increased atmospheric CO2, nutrient deposition, and altered climate patterns.
Purpose of the Study:
- To evaluate the generality of observed changes in tropical forests across multiple continents.
- To assess trends in aboveground biomass, tree species composition, and growth rates in response to global environmental change.
Main Methods:
- Standardized, repeated measurements of over 2 million trees across ten large forest plots (16-52 ha each) on three continents.
- Analysis of aboveground biomass changes, carbon accumulation rates, and species-specific growth dynamics over multiple census intervals.
Main Results:
- Aboveground biomass increased at seven of ten plots, with significant increases at four; one plot showed a significant decrease.
- Pooled carbon accumulation was significant (+0.24 MgC ha(-1) y(-1)), but lower than previously reported for Amazonia.
- No consistent increase in biomass gain was observed across multiple census intervals at three sites, contradicting the increased productivity hypothesis. Fast-growing species did not consistently increase in dominance; slow-growing species biomass increased across all plots.
Conclusions:
- The hypothesis of consistently increasing dominance by fast-growing species in tropical tree communities is not supported by this study.
- Observed changes may reflect simultaneous recovery from past disturbances and alterations in resource availability.
- Long-term studies are crucial to fully understand the contribution of global change to tropical forest functioning.
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