PS 25-59 - Tropical forest plant communities show resistance to drought, hurricanes, and warming in Puerto Rico

Background/Question/Methods

Tropical forests are projected to experience more frequent and intense disturbance events atop significant changes in temperature and precipitation due to anthropogenic climate change. These changes in climate and disturbance regimes can have non-additive effects on plant communities and result in complicated disturbance legacies, which limits our understanding of how tropical forests might fare in the future. The Tropical Responses to Altered Climate Experiment (TRACE) in Puerto Rico offers an unprecedented opportunity to address this knowledge gap. In less than five years, the TRACE understory vegetation was exposed to a severe drought (2015), two years of experimental warming (4°C above ambient in half of the plots, 2016-2017 and 2018-2019), and two major hurricanes (Irma and María, September 2017). Using data from yearly censuses of woody seedlings and saplings (2015-2019), we evaluated disturbance-driven changes in species richness, diversity, and composition across ontogeny. We then used Bayesian predictive trait modeling to assess how species responded to disturbance and how this might influence the functional structure of the plant community.

Results/Conclusions

In stark contrast to our expectations, we observed only a slight reduction in seedling richness after hurricane disturbance, while drought and experimental warming increased sapling diversity. We also found a shift in species composition through time for both seedlings and saplings, yet the individual effects of each disturbance were not significant. Several species showed significant changes in abundance in response to the various stressors, leading to predicted changes in functional composition of the community in favor of a mixture of fast-growing and drought-tolerant species. Overall, we found that both the seedling and sapling communities exhibited strong resistance to a wide range of climatic stressors in this forest, highlighting their potential to continue supporting critical ecosystem functions and services in the face of a changing climate. However, early signs of changes in species composition might suggest lagged responses that take longer to emerge. Longer-term monitoring of seedling and sapling dynamics in this forest might be needed to understand the long-term implications of repeated disturbances in a warmer world.