Cross-scale drivers of plant trait distributions in a fragmented forest landscape

During community assembly, plant functional traits are under selective pressure from processes operating at multiple spatial scales. However, in fragmented landscapes, there is little understanding of the relative importance of local-, patch- and landscape-scale processes in shaping trait distributions. Here, we investigate cross-scale influences of landscape change on traits that dictate plant life history strategies in re-assembling plant communities in a fragmented landscape in eastern China. Using forest dynamics plots (FDPs) on 29 land-bridge islands in which all woody plants have been georeferenced and identified to species, we characterized and derived two composite measures of trait variation, representing variation across the leaf economics spectrum and plant size. We then tested for trait shifts in response to local-, patch- and landscape-scale factors, and their potential cross-scale interactions. We found substantial community-wide trait changes along local-scale gradients (i.e. forest edge to interior): more acquisitive leaf economic traits and larger sized species occurred at edges, with a significant increase in trait means and trait range. Moreover, there were significant cross-scale interaction effects of patch and landscape variables on local-scale edge effects. Altered spatial arrangement of habitat in the surrounding landscape (i.e. declining habitat amount and increasing patch density), as well as decreasing area at the patch level, exacerbated edge effects on traits distributions. We suggest that synergistic interactions of landscape- and patch-scale processes, such as dispersal limitation, on local-scale environmental filtering at edges, together shape the spatial distributions of plant life history strategies in fragmented plant communities.