Confronto tra indicatori di diversità floristica e strutturale nelle foreste europee.

Evidence-based policies are necessary to support the role of forests in the conservation of biodiversity and provisioning of ecosystem services. Assessing forest resources and their trends over time is required by many international agreements, and is a key step in developing policy strategies. In the context of National Forest Inventories, measures of tree species composition and structure are considered as possible biodiversity indices, despite ground vegetation usually having greater species richness than other forest strata. This study is aimed at evaluating relationships and connections between the overstory and understory by considering both stand structure and diversity indices, through a network analysis in which the system takes the form of a network or "graph". We used tree-related and ground vegetation data from 2789 plots collected as part of the BioSoil project through the ICP Forests Level I network and stored in the LI-BioDiv database. Additional information levels such as biogeographical region, forest management type and European Forest Type were also considered. The relationships among the structural and diversity measures showed few and weak correlations between overstory and understory diversity over the additional information levels. We demonstrated that at European level the overstory and understory indices are complementary, and they explain forest diversity components. Based on these results, overstory diversity cannot be considered as a proxy for the diversity of the entire forest plant community.