Latitudinal and elevation gradient differently drives species understory coexistence in beech forests of Apennine chain (Italy)

The research aim was to understand whether and to what extent the latitudinal range affects the functional structure of the herbaceous layer of calcareous beech forests in Apennines, managed as high‐forest. We selected 163 plots (20 x 20 m), ranging from central to southern Italy, using a random stratified sampling design. We chose plant traits related to clonal strategies, storage organ, leaf phenology and reproductive strategies. We correlated the effect sizes of traits’ CWM, and functional diversity (calculated as FDis and Rao’s Q), with the main axes of variation in species composition, linked to the latitudinal range and elevation. Despite the weak variation in species composition along geographic range, functional diversity of storage organs and vegetative spread resulted negative correlated with the latitudinal range. Functional diversity of pollen/spore dispersal system was negatively related to elevation. Our study suggested that different environmental conditions filter different strategies across large‐spatial scales (Grime et al. 2006). Increasing of winter cold stress towards central Italy seems act as a climatic filter on clonal strategies, suggesting that persistence of species is guaranteed by the presence of particular clonal strategies (increasing rhizome and bulbs, decreasing runner and root with adventitious bud) and storage organs (secondary storage root) rather than leaf or reproductive strategies. Contrary, the persistence in higher elevation was ensured by the presence of reproductive strategies shared by the species (i.e., decreasing of wind pollination and increase of insect pollination). Finally, we provide an evidence that FDis and Rao’s Q are equivalent metrics in detecting the assembly rules.