Effects of forest establishment on plant diversity: a retrogressive analysis.

Biodiversity conservation, in the face of increasing human impacts and global environmental changes, requires accurate analysis of multitemporal patterns and effective management actions at landscape scales. Historical ecological data are needed to calibrate predictions of future global change impacts on biodiversity; when historical ecological data are not vailable, one key lies in extrapolating them through the construction of ecological models that include the use of historical cartographic data. This work aims at developing an approach to estimate backward in time plant diversity shift in response to land use changes and analyzing the potential effect of afforestation, occurred in the last 60 years, on heterogeneity and plant species richness in a Mediterranean context. The field data from an extensive monitoring program (Mo.Bi.SIC) and a nearest neighbour selection were used to model the plant species diversity change and rebuild the past species pool matrix. Species based rarefaction curves were derived for the two dates (1954 and 2010) to estimate temporal changes in alpha and beta diversity. The results showed that the methodology developed for this work it may serve as an approximation in the analysis of the effects of the establishment of forest on forest plant species richness. This method, although aware of its weakness compared to direct multitemporal field studies in the analysis of ecological dynamics, could serve as support in the purely quantitative cartographic analysis. The estimation of species diversity change through our model represent a formalization of what could be expected analysing land use spatial pattern changes. From a nature conservation perspective, the process of abandonment of traditional management techniques in favour of agriculture intensification and deforestation is quickly producing an overall homogenization of the landscape.