Land-use legacies affect the composition and distribution of tree species and their belowground functions in a succession from old-field to mature temperate forest

Forests undergoing ecological succession following abandonment from agricultural use (i.e., old fields) are ubiquitous in temperate regions of the U.S. and Europe. Ecological succession in old fields involves changes in vegetation composition influenced by factors such as land-use history, soil conditions, and dispersal limitations. Species' behavioral, morphological, physiological and life-history attributes influence the outcomes of environmental and biotic filters on distribution and abundance. However, many studies have focused on aboveground attributes, while less attention has been placed on belowground species characteristics that influence community assembly and function. In this study, we used a trait-based approach to examine how aboveground plant composition and distribution vary with plant root functional traits (e.g., mycorrhizal association) that mediate access for nutrients such as nitrogen (N) and phosphorous (P). We inventoried every tree stem (n = 11,551) in a 10-ha forested area containing old-field and historical forests and matched every species with root functional traits (n = 33) from established databases. We found that land-use history influences community composition and distribution in old-field forests, which also varied with belowground root functional traits. Community composition in old-field forests, which were dominated by Acer saccharum and non-native species, were largely associated with arbuscular mycorrhizae (AM) and higher root nutrient concentrations. On the other hand, community composition in historical forests - largely dominated by Tsuga canadensis - were associated with ectomycorrhiza (EcM) and more variation of root length and depth. These results suggest that changes in aboveground communities have implications for belowground ecosystem services (e.g., nutrient cycling) which are important to forest ecosystem development. Trait-based approaches can elucidate mechanisms of community assembly, and understanding how traits influence species coexistence and interactions can inform management decisions related to biodiversity conservation and restoration efforts in disturbed or altered forests.