Local interactions can contribute to the maintenance of species diversity if they generate what is known as negative frequency dependence, a stabilizing force that should prevent common species from excluding others, allow rare species to recover from low abundances, and maintain higher species diversity. However, whether demographic consequences of local interactions are strong enough to contribute to patterns of diversity at larger scales remains unclear. Recent evidence indicates that differences in climate can alter the strength of frequency dependence at landscape to regional scales, representing a potential mechanism by which the consequences of local interactions can scale up to influence the maintenance of species diversity at larger scales. However, few studies have used long-term demographic data to evaluate if differences in climate at broad spatial scales influence frequency dependence and patterns of species diversity. Here, we use over over 40 years of tree demographic data from 23 old-growth forest stands (0.25 – 1 ha in size) that span a 1,100 m elevational gradient characterized by stark differences in temperature and precipitation in the H. J. Andrews Experimental Forest LTER site. We evaluate if differences in climate along the elevational gradient are associated with differences in frequency dependence and tree species diversity.
Results/Conclusions
We found that negative frequency dependence in growth and survival of small trees (5-15 cm DBH) was stronger with increases in temperature and precipitation across the elevational gradient. Moreover, stronger negative frequency dependence was associated with higher stand-level tree species diversity across forest stands. These results based on long-term demographic data support the hypothesis that increases in temperature and precipitation at broad spatial scales can influence the demographic consequences of local species interactions in a way that generates stronger negative frequency dependence and contributes to regional-scale patterns of tree species diversity.