From current to potential distribution: the case of Taxus baccata L. (Taxaceae, Pinales) on the island of Sardinia (Italy)

Taxus baccata is a relic declining species, especially at the southern margins of its natural distribution, such as the Mediterranean and Irano-Turanian biogeographic regions. On the Island of Sardinia, it is still present in many mountain sites. This study identified 232 locations where yews grow. The species is indifferent to substrates, but prefers moist sites with northern aspects, and has elevation range is 695-1225 m a.s.l. To predict yew’s potential distribution in Sardinia, we collected data from the literature and field observations and applied the Maximum Entropy algorithm (MaxEnt). We used 202 field-based sites and 19 bioclimatic variables to model the potential distribution area under current climatic conditions. Annual precipitation, mean temperature of the warmest month and isothermality were the key drivers for the distribution of T. baccata in Sardinia. In terms of permutation importance, mean diurnal range and precipitation of the warmest quarter were the main environmental variables. The response curves showed that T. baccata prefers annual mean temperatures ranging from 8.65 to 12.55°C and annual mean precipitation from 770 to 1085 mm. Most potential suitable conditions were found in northern and central Sardinia. Using the Global Circulation Model, we also modelled future habitat suitability for T. baccata under two different scenarios, highlighting a substantial reduction of the habitat suitability for the species by the end of this century. This reduction is associated with climate change and poses an increasing concern about the future of the species and the priority habitat described in many parts of Sardinia.