Despite numerous studies in ecology focusing on changes in community composition, a majority of them lack long-term data sets necessary to approximate trends and patterns that will allow us to understand past drivers of community change and generate future predictions. This is especially important in tropical forest ecosystems where biodiversity and global carbon and nutrient cycling are being threatened under current and projected climate regimes. Trait-based approaches are of great relevance given their ability to provide insight on mechanisms of community assembly, but few long-term studies contain functional trait data. The San Emilio forest (16-ha) – the longest running forest dynamics plot – provides an excellent opportunity to assess how environmental change can shape forest composition and influence ecosystem functioning. We used past (2006) and recently collected (2017) censuses and trait data to address the following questions: (1) How have leaf and wood traits changed over time? and (2) Can we use traits to infer possible mechanisms of community assembly? Data were collected from five subplots totaling 1-ha using standardized methodology. Here, we focus on leaf area, wood density, and specific leaf area (SLA) to preliminarily examine patterns of change. T-statistics were used to obtain trait variance ratios to explore community assembly.
Results/Conclusions
Earlier work has shown that the steady decline in long term precipitation has led to shifts from mesic to xeric species, from a more evergreen forest to a more deciduous forest, and from species with simple leaves to compound leaves (signals of a shift toward a more drought adapted forest). Shifts in leaf area, wood density, and SLA are consistent with expectations for selection under drought. Evidence of an increase in wood density is consistent with selection for individuals that are less prone to drought-induced embolism and slower radial growth. Shifts toward lower SLA are consistent with shifts from less productive to more drought prone species. Declines in leaf area are consistent with selection to minimize leaf temperatures and leaf water loss. These preliminary results indicate the importance of biotic and abiotic drivers in determining community assembly. Our results can be used to help support trait-based modeling efforts in light of future climate change.