COS 99-3 - Functional drivers of tropical forest resistance to hurricane disturbances

Abstract: Extreme weather events in the tropics, such as hurricanes and droughts, are projected to increase in frequency and intensity with global environmental change. During extreme droughts and hurricanes, there is an increase in mortality rates and an overall change in forest structure, highlighting their role as major disturbances in plant community assembly processes. At the same time, increases in the disturbance regime threaten tropical forests’ role as major carbon sinks. Therefore, it is crucial to understand what structural and functional properties mediate tropical forest resistance and resilience to extreme weather events across environmental gradients. However, the lack of data across forest types and contrasting results from different tropical regions hinder our ability to predict the impacts of such weather events. To fill this knowledge gap, in this study we leverage a trait database of 410 tree species, remote sensing metrics of canopy structure, and a long-term forest plot network that spans four tropical life zones (dry, moist, wet, and lower montane) to investigate whether the successional and climatic drivers that shape forest function modulate the impacts of a category 4 hurricane. Across all forest types, older stands with tall trees experienced large negative changes in canopy height, which explained a decrease in canopy cover. High functional and species diversity enhanced resistance to hurricane disturbances; more diverse forests showed smaller alterations of canopy structure than less diverse forests. Changes in canopy height did not translate into increased mortality rates, yet large reductions in canopy cover were linked to a spike in tree mortality after the hurricane. Dense-short forests dominated by drought-tolerant species in more arid regions showed greater resistance to hurricane disturbances than taller forests located in wetter environments. Our results provide support for the hypothesis that drought tolerance enhances resistance to hurricane disturbances and that the subsequent successional trajectories might differ greatly along gradients of water availability.