Community diversity has been shown to positively influence forest resilience to disturbances such as fire, flooding, and drought, but we still do not fully understand the role that species interactions play in this framework. Species richness within forest stands may not accurately reflect competition and facilitation that occur on the level of an individual tree, where interactions with immediate neighbors can be the most important factor affecting resource acquisition. These interaction effects are particularly important to understand within the context of climate change, where novel climatic conditions and novel species assemblages are predicted to occur. As part of a long-term monitoring study, we analyzed tree-ring chronologies from 423 adult trees in a temperate broad-leaved forest. All individuals within a 1 ha grid were measured for DBH and mapped to sub-meter accuracy. We then paired nearest-neighbor data (neighboring adult trees within 10 meters of focal tree) with climate records to evaluate the effects of two extreme weather events: an extreme drought event in 1964 and a year of exceptionally high rainfall in 2009. Using yearly radial increments we calculated a resilience index to quantify the impacts of neighbors on focal trees for each event.
Results/Conclusions
Results suggest a biologically significant response to extreme events for multiple species. While community radial growth was lower on average during the drought event of 1964, the magnitude of this decrease depended on focal tree species and size relative to neighbors’ species and size. High neighborhood diversity and larger size prior to disturbance translated to greater individual resilience to the extreme drought event. Conversely, excess precipitation in 2009 resulted in the radial growth of focal trees being negatively affected by their neighbors, supporting our hypothesis that competitive effects will be more pronounced in years of high resource availability. These results suggest that extremes on either end of the precipitation spectrum can significantly affect radial growth of mature trees in temperate forests. With warming climate trends and increased frequency of severe weather events, comparing forest neighborhood effects under two extremes will help contextualize future species interactions.