Distribution, floristic and ecological characterization of Sardinian Gymnospermae communities

A complete analysis of the distribution, ecology and floristic composition of the natural pine woods of Sardinia, belonging to Pinus halepensis Mill., P. pinaster Ait. subsp. pinaster and P. pinea L., was for the first time produced in Sardinia by means of aerial photographs, literature, Local Ecological Knowledge (LEK) and phytosociological surveys carried out within the areas where the three pine species are considered native or putative native. The phytosociological work allowed the description of two new associations for P. halepensis woods, located in the south-western coastal area, as well as the confirmation of a previously described one on the island of San Pietro, which is currently in a more mature stage than its original description. A new association related to P. pinaster subsp. pinaster woods was described in north-eastern Sardinia, with two new sub-associations. Finally, a new association for P. pinea woods on coastal dunes of the south-western Sardinia. The diachronic study of pine woods’ decrease and subsequent recovery represents an important step in the analysis of how human impact and land use change can influence the vegetation dynamics of pioneer species with restricted distribution ranges in insular contexts. In this respect, the help of local people and toponymy was crucial for trying a reconstruction of the loss happened in recent times. The method here applied can be an example for further research on rare and declining species. We improved the knowledge of the distribution, ecology and threats of Taxus baccata L. populations in Sardinia as well, by analysing climatic factors, to define yew’s ecological niche and the species potential distribution in the island. In this study, we found 234 different localities were T. baccata grows or was known in recent times, then confirming how the potential distribution is similar to the real one. On the other hand, we highlighted that in many localities the presence of the species is today related to isolated to scattered old individuals. Many factors are driving this species to become more and more rare in the Mediterranean environments. We selected 40 sites, a part of which are characterised by the presence of T. baccata old-growth woods, then compared these woods with others where human impact and mean dimensions of the samples identify them as younger formations. This comparison was useful to understand which of the structural features are significantly differentiating old-growth stands with yew from younger ones, and can therefore have a methodological value. The places where the species still thrives today are subject to a long pressure by overgrazing and are often the remnants of wider populations reduced by practices such as wildfires, cuttings, and subsequent reforestations. This work increases the knowledge in relation to the health of the species and its distribution in Sardinia. Moreover, it represents a crucial point for its conservation since it shows how future conservation measures seem to be necessary to preserve the most endangered populations. In managed forests, silvicultural systems should be able to maintain, restore or develop structural attributes useful to a reprise of yews free of competition of alien naturalised taxa. Moreover, the application of protection protocols can represent an effective tool for the characterisation of the old growth stands with yews, in order to plan better management and conservation measures.