New methodological insights for the assessment of temporal changes in semi-natural dry grasslands plant species composition based on field data from Northern Apennines

In Europe, the management of semi-natural grasslands is changing steadily in extent and intensity. These changes represent a serious threat to one of the most species-rich habitats in Europe; therefore, the related shifts in species composition should be assessed by means of sound scientific. We describe a new methodology aimed at: (i) quantifying the temporal changes in vascular plant species composition of semi-natural grasslands; (ii) identifying the environmental and management variables that drive patterns of change. Our approach consists of a diachronic analysis based on historical phytosociological data associated with detailed vegetation maps. To describe and test our methodology, in 2013 we re-visited 24 historical plots of Bromus erectus grasslands that were first sampled in 1982. To designate the new sampling sites, we combined the topographic and typological information available for the historical plots with the spatial information of the associated map. The degree of change in species composition was calculated through ordination techniques; multivariate distances were used in a regression analysis to identify the environmental variables responsible for patterns of compositional change. Our worked example demonstrated that species composition has changed significantly in the last 30 years, with patterns that have been substantially influenced by topography and landscape structure.