The elaboration of conservation strategies at regional scale, dealing with the potential effects of climate change on the abundance and distribution of tree species, should be supported by models produced at the appropriate scale. We used a bioclimatic model aimed at analysing the large-scale effects of climate change on the abundance and distribution of tree species with respect to their chorological and ecological characteristics. Abundance data for 16 species, sampled in 912 plots, distributed on a 3x3 km grid were used. A climatic model provided high resolution current climatic surfaces and a climatic scenario for 2080 was obtained using the A1FI emission scenario of HadCM3 GCM. A determ inistic Regression Tree Analysis (RTA) and Multiple Linear Regression (MLR) were applied in order to define the realised niche of the species in relation to the chosen environmental variables. The comparison between RMSE values showed that RTA always outperforms MLR, in terms of predicting species distri bution. Zonal species were better predicted than rare species (extrazonal or with specific habitat requirements). Climate change is expected to determine a general increase of the average potential altitude. Only the Mediterranean spe cies are likely to be favoured by the predicted climate change, while for the two other chorological types (Sub-Mediterranean and Eurosiberian) the re sponse seems to be species-specific, depending on the ecological characteristic of each species: the more thermophilous and xerophilous species should bene fit from the predicted drought in terms of area and mean abundance, while mesophilous species should suffer a strong reduction.Keywords: Climate change, Tree species, Central Italy, Potential distribution maps, Regional scale, Regression tree analysis cording to the following formula:where x is one of the considered species, NS is the number of stems of a plot and BA is the basal area of the plot calculated using the diameter at breast height of each one of the stems. In monotypic stands, the IV could reach a maximum of 200. We analysed sixteen species that are the most abundant in the study area: (see Tab. 2 -Pignatti 1982). In order to explain the response of the species to climate change, Ellenberg's indicator val ues (Ellenberg et al. 1992), revised for Italy by Pignatti (2005), for temperature and moisture were used. These indicator values describe the ecological optima for the spe cies along ecological gradients using an or dinal scale, i.e., temperature: 1 (cold, alpine environment) to 12 (hot, subdesertic envir onment); moisture: 1 (dry environment, arid soil) to 12 (water environment).
Environmental variablesVery high resolution (30 arc-seconds) cur rent climatic surfaces were obtained by inter polating climatic data (average of the 1961-1991 period) from 210 stations for pre cipitation and 151 for temperature through universal kriging (i.e., simple kriging with trend function defined on the basis of a set of co-variates) that has been proven to produce reliable estimates at a regio...