Disturbance-recovery cycles of tree growth after droughts in tropical forests

Tropical forests will be increasingly impacted by intensifying droughts under ongoing climate change. Droughts may have large implications for the capacity of tropical forests to store carbon in wood and act as long-term carbon sinks. To assess this possible implication, pantropical analyses of tree growth recovery from past droughts are needed. Here we use tree-ring data from 250 tropical forest sites (>5000 trees) in the tropical tree-ring network (tropicaltreeringnetwork.org) to evaluate the capacity for woody growth to recover after droughts. We assessed impacts on stem growth of the 10% and 5% driest years since 1930 and the extent to which stem growth recovered in the subsequent years. We selected years with the lowest rainfall, highest vapour pressure deficit, and largest climatic water deficit. We found that the pantropical impact of droughts on stem growth was a modest 2.8% reduction (CI95%: -3.0 to -2.4%) during the 10% driest years, and 2.9% (CI95%: -3.4 to -2.4%) during the 5% driest years. Yet, in a quarter of sites located predominantly in the drier tropical forest regions, growth was reduced by over 10%. Growth recovery was generally rapid: postdrought years exhibited significantly smaller negative growth anomalies, and anomalies often shifted to positive. Thus, this rapid recovery of stem growth to predrought levels suggests that no strong or long lag effects exist at the pantropical scale. We also analysed regional, taxonomic and seasonal differences in growth recovery, and compared the results to drought responses in photosynthesis. We conclude that stem growth of tropical forest trees has so far been able to recover from droughts, but that this capacity may diminish under aggravating climate change.