Relationships among productivity, leaf phenology, and seasonal variation in moisture and light availability are poorly understood for evergreen broadleaved tropical/subtropical forests, which contribute 25% of terrestrial productivity. On the one hand, as moisture availability declines, trees shed leaves in order to reduce transpiration and the risk of hydraulic failure. On the other hand, increases in light availability promote the replacement of senescent leaves to increase productivity. Here, we provide a generalized and predictive framework that relates the seasonality of climate, leaf abscission and productivity across the entire evergreen broadleaved tropical/subtropical forest biome. The seasonal correlation between rainfall and light availability varies regionally from strongly negative to strongly positive across the Tropics and maps onto the seasonal correlation between litterfall mass and productivity for 68 forests. Where rainfall and light covary positively, litterfall and productivity are always greater in the wetter, sunnier season. Where rainfall and light covary negatively, litterfall is always greater in the drier, sunnier season while productivity is also greater in the drier, sunnier season if moisture supplies remain adequate and smaller otherwise. The pantropical distribution of these climate-phenology regimes is related to local and global climate drivers. This framework will improve the representation of tropical/subtropical forests in Earth system models and suggests how phenology and productivity will change as climate change alters the seasonality of cloud cover and rainfall across tropical/subtropical forests.

tropical forest, tropical phenology, leaf abscission, forest production, climate triggers, seasonality