Valutazione della funzionalità dei boschi planiziali relitti della pianura veneta orientale per la conservazione delle specie nemorali erbacee.

The effects of fragmentation as a driver affecting environmental condition, habitat integrity and, consequently, the possibility of a long-term persistence of ancient forest species populations were evaluated. A check list of the flora was compiled for each forest. Repeated samplings have been surveyed in spring and in late summer-autumn following a stratified random design. 80 permanent plot (25m x 25m) were fixed, randomly and proportionately to the correspondent surface, on the two woodland habitat types: 1) the “edge habitat”, that is the concentric zone up to 50 meters from woods boundary and 2) the “core area”, the interior and protected zone. Species were clustered in 7 ecological groups, on the basis of similar ecology and similar role inside the community. The group assignment was based on phytosociological affinity. Binary data on occurrence of species in the 80 plots were used to perform Principal Coordinates Analysis (Sörensen Index). For each woods we defined richness, structure (on the basis of ecological groups) and an index of floristic quality (FQAI). Species richness and FQAI have been related to environmental variables (area and age, that is time from last fragmentation event) using a linear regression approach. Data analysis pointed out that three main indipendent variables affect habitat quality: surface, surrounding matrix and age. Our data confirm woodlands patches are experiencing the “relaxation time”, namely the time taken for a community to reach a new equilibrium after an environmental disturbance. After fragmentation, woodlands have lost their typical structure and, at present, they seem unable to assure a long-term conservation of herbaceous nemoral species.