Key role of small woodlots outside forest in a mediterranean fragmented landscape.
Even if the ecological role of trees outside forests (TOF) is acknowledged, few studies provide an exhaustive census and define their principal characteristics, considering not only the patch size but also the effect of the surrounding land-use type on TOF biodiversity. Using a multiphase sampling design, we provided a map showing the spatial distribution of small woodlots outside forest (SWOF), a type of TOF, embedded in different land-use types in Sardinia, a Mediterranean hotspot of biodiversity conservation. Once located and mapped, we investigated the differences among SWOFs enclosed in different land-use types, in terms of vegetation structure and plant species richness (native and alien), searching for indicator species able to characterize SWOFs located in different land-use types. Hence, we explored the effect of environmental factors and vegetation structure on native and alien contingent in SWOF's plant communities. Our findings indicated that SWOFs were widely spread along the land-use intensification gradient, both in natural and human-modified land-use types. The area covered by SWOFs increased following the gradient of land-use intensification, reaching the highest value in urban zones (0.85%), and the lower in agricultural and natural and semi-natural areas (0.31% and 0.23%, respectively). We found dissimilarities between SWOFs located in different land-use types in terms of species richness, composition and indicator species, both native and alien. Notably, the contribution of alien species to the overall diversity was low both in natural and human-modified land-uses. Nevertheless, alien and native taxa showed different responses to environmental drivers: alien taxa were not affected by landscape variables, while the native ones were significantly influenced by all investigated environmental drivers and by the structural complexity of vegetation. SWOFs embedded in human-altered areas, in particularly in agricultural land-use, show good levels of naturalness: these results indicate that SWOFs represent an opportunity for natural conversion and rewilding of altered ecosystems. Small woodlands outside the forest can be the pillars to build and extend the green infrastructure network in both natural and modified land-uses, delivering important benefits for ecosystem services, and offering nature-based solutions to pamper fragmentation effects.