Print PageTemperatures are projected to rise by 1.8-5.1°C in the Amazon rainforest this century. These forests are globally important as a carbon store and for precipitation cycling, and small changes in forest dynamics could have large feedbacks to global climate. Some models predict the transition of the Amazon rainforest to drier forest types; however experimental data relating to the mechanisms of forest responses, particularly at the plant community level is lacking.
Recent analysis of the Tapajos National Forest in the Brazilian Amazon showed a precipitous decline in net ecosystem exchange (NEE) above a temperature threshold of 28˚C. The Biosphere 2 (B2) tropical rainforest (TRF) mesocosm has experienced temperatures ~5-7˚C higher than lowland Amazonia for over 20 years, and thus provides a useful tool for understanding the responses of tropical forests to increased temperatures.
Thirty-six percent of tree species went extinct in the B2 TRF by the year 2000. We analyzed tree community changes over this time period in comparison to a random extinction model to assess whether high temperatures had exerted a selective pressure on particular species or clades. We also analyzed NEE data in the B2 TRF to compare the temperature threshold to that of the Tapajos.
Results/Conclusions
Analysis of NEE showed the B2 TRF to be substantially more temperature tolerant than the Tapajos National Forest in the Brazilian Amazon. Whereas in the Tapajos, NEE undergoes a sudden decline at 28˚C, whole ecosystem function is maintained to much higher temperatures (37.5˚C) in B2 TRF.
The higher temperature tolerance of the B2 TRF could have been caused by (i) selection of particular species via traits that confer thermal tolerance, and/or (ii) acclimation of individual plants to the increased temperatures. Analyses of within-community phylogenetic relatedness and taxonomic filtering were indistinguishable from random extinction of individual trees. Our results suggest that the ability to acclimate to high temperatures is independent of species-level traits, and may be more ubiquitous among plant species than current models project. Recent studies have demonstrated greater resilience of Amazon forests to climate change in the short term than assumed by models, but ours is the first to demonstrate long term resilience of a tropical forest to climate warming.
