IMPACTS OF DROUGHT LEGACIES ON TREE DEMOGRAPHY AND SUCCESSIONAL TRAJECTORIES OF TROPICAL FORESTS

Abstract:

Regenerating tropical forests account for 70% of all remaining tropical forest cover and 50% of the terrestrial carbon sink. Despite the importance of successional vegetation in tropical regions for global climate, how inter-annual climate variability influences successional trajectories and biomass accumulation remains poorly understood. Lagged effects of climate extremes on tropical tree demography and successional trajectories represent one key uncertainty. We couple 15 years of climate records and tree growth and survival data with functional trait information for 172 tree species to parameterize Stochastic Antecedent Models (SAMs) of lagged effects of drought on tree demography in second-growth tropical forests in Costa Rica. We also quantify how these legacies influence successional trajectories and biomass accumulation. Drought legacies on tree growth were particularly marked for species with high Specific Leaf Area and low wood density. These legacies led to elevated rates of tree mortality, particularly for large (>10 cm in diameter) up to 4 years after the occurrence of extreme droughts. Simulations of successional trajectories using immediate and lagged drought effects demonstrate that lagged effects lead to shifts in successional trajectories and substantial losses in biomass accumulation.