Climatic conditions and local neighborhood have been described as important filters that select a subset of species with the appropriate traits to adapt to a site. Evidence for these filters comes from quantifying how trait values in a local neighborhood influence an individual’s performance. The relative influence of climate and biotic neighborhoods varies across a species range and this should be considered when describing trait neighborhood - performance relationships; however this has not been the case. In light of future shifts in the range of several plant species as a result of climate change, it is imperative to understand the effects of biotic and abiotic conditions on the trait neighborhood - performance relationships. Here we explore the impact of climate and biotic interactions on the relationship between trait values of neighboring individuals and performance, using data from long-term forest plots from three LTER sites (Luquillo, Harvard Forest and Hubbard Brook) and using USDA Forest Inventory and Analysis data to include species range.
We use spatially-explicit neighborhood models that include both the location of the individual and the processes affecting individual performance. We include functional traits related to tree performance: leaf nitrogen, carbon and phosphorus contents, leaf area (LA), specific leaf area (SLA), seed mass, wood density and maximum height (Hmax). We use Bayesian analyses to estimate performance of individual trees (survival and growth) based on (1) plant functional traits, (2) climate (habitat suitability index) and (3) crowding by neighboring trees. Trees with high LA and Hmax values had greater relative growth rates and survival than individuals with low LA and Hmax in Luquillo. Small trees grew faster than taller individuals in Hubbard Brook. Species at Harvard Forest with great seed mass had high relative growth rates. Tree survival at Luquillo and growth at Hubbard Brook were negatively affected by neighborhood crowding. Competitive interactions were mediated by a trait hierarchy and by the absolute trait differences between neighbors. At a larger scale, Hmax was positively associated to survival for Puerto Rico and SLA was positively correlated to growth in the North East of the US, while growth was negatively affected by neighborhood crowding. Finally, survival and growth were positively associated to climate in Puerto Rico. These findings will help to understand the mechanisms shaping plant communities to assess potential changes in community dynamics relevant for future management strategies.