Worldwide changes in tropical forest ecosystems

Background/Question/Methods Tropical forests comprise much of the world's biodiversity and forest carbon.  Even mature forests have been subject to an unprecedented degree of change in their baseline conditions, including both climate and atmospheric change as well as a host of more direct human processes.  Individual forests typically respond and change individualistically, but if widely sampled a wider picture should emerge, less contingent on local histories.  With collaborators working across continental-scale networks of several hundred permanent plots, we (1) review the evidence for recent changes within mature, moist, tropical forests, and (2) assess possible drivers of these changes. Results/Conclusions In South America and Africa, mature forests far from active zones of deforestation have clearly been changing since at least 1980.  In the Neotropics these forests have tended to gain tree biomass, gain lianas, grow faster, and experience faster mortality.  In Africa, forests have gained biomass over the same period.  These changes are generally consistent with model expectations of increased productivity.  While strong drought events such as the 2005 Amazon drought are capable of at least temporarily disrupting some of these trends they may not, as yet, be powerful enough to permanently reverse the old-growth carbon sink.  By contrast the evidence for recent biomass and growth changes within remaining South-East Asian mature forests is weak and uncertain.  We will assess the drought sensitivity of forests on different continents and briefly suggest what can be done to reduce the large uncertainties in the past and future trajectories of these systems.