Drivers of plant functional traits in understory communities of Italian forests

The study of plant-environment relationships by trait-based approaches are fundamental to explore ecosystems functioning across space and time. However, studies on forest ecosystems using a large number of traits for different functions are lacking. Here we aim to assess the contribution of climate, soil and management variables in controlling community weighted mean (CWM) values of traits related to nutrient acquisition and use strategies, space occupancy and recovery after damage. We used the ICP Forests LI BD dataset for Italy. It contains 201 sampling sites representative of the Italian forests, across three biogeographic regions (Alpine, Continental, Mediterranean). Eleven plant traits were selected, including leaf, seed, whole-plant, clonal and bud bank traits, for the understory vegetation. We used i) redundancy analysis to assess traits-environmental variables relationships, ii) stepwise-forward-selection and variance partitioning to identify the relative role of single and groups of variables on single-trait CWM variation. Climate, alone and combined with other variables, explains the largest proportion of many traits variation (e.g. SLA, plant height, seed mass, clonality, large bud bank) due to temperature-related variables. Soil and management variables show a secondary, traitdependent effect. Management exerts a major role only for two clonal and bud bank traits (i.e. lateral spread and bud protection). In general, mesic, cold, and productive forests are characterized by understory communities with higher percentage of species having low plant height and seed mass, high SLA values, and both clonal and resprouting abilities. Mostly, this corresponds to forest specialist species, persistent under disturbance regimes. The opposite scenario can be linked to forest species living under stress conditions (e.g. drought). Plant traits approach along climatic gradients can reveal the adaptive ability of plant communities in face of climate changes.