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