Changes in Stipa austroitalica grassland communities over twenty years.

Endemic dry grasslands dominated by Stipa austroitalica are recognised for their conservation relevance, due to their narrow southern-Italian distribution and for being listed among EU habitats of community interest [1]. Although the occurrence and preservation of these semi-natural communities depend on a combination of anthropogenic and natural factors, little is known on their responses to recent and ongoing environmental changes [2]. While documenting community changes over two decades, this study aims to provide an updated depiction of the conservation status of S. austroitalica grasslands in the agro-pastoral systems of Alta Murgia and Murgia Materana, in southern Italy. In 2023, we resurveyed 20 vegetation plots that were originally sampled in 1995–2003 [3]. Species richness and diversity, and the proportion of ecological attributes (life forms, Ellenberg’s indicator values) were used to explore community variations. We used paired T-test and Non-metric multidimensional scaling to identify significant changes in vegetation parameters and species composition. For each plot, we grouped species according to their dominance (> 95th percentile of abundance distribution) and their affiliation to main syntaxonomic categories. Then, we calculated species turnover index to assess the proportion of increasing and declining species. Our study demonstrates that species composition and community parameters have changed significantly in the last 20 years. Recent surveys showed a significant increase in species richness and diversity, coupled with a lower cover of perennial grasses and an increase in short-lived plants and geophytes. Our findings indicated an increase in Ellenberg’s indicator values for light and temperature, and a decrease in continentality and pH. Multivariate ordination highlighted a consistent variation in the considered timeframe, indicating a shift of species composition towards more xero-thermic communities. Species turnover values underlined a marked decline of species that were dominant in the original samples, and for species that are typically associated with meso-xeric perennial grasslands, in turn replaced by those associated with more xero-thermic and synanthropic vegetation. By revisiting historical data, our study allows us to identify temporal dynamics and ecological processes in the studied ecosystems, indicating a recent and substantial decline of meso-xeric perennial communities, in favour of communities adapted to warmer and highly disturbed environments. Different anthropogenic and natural factors likely acted as drivers of community responses, e.g., an altered grazing regime, wild boar soil disturbance, and variations in climate conditions, in turn associated with an increase in the frequency of wildfires and local soil erosion processes. In view of preserving the biodiversity value of the studied semi-natural grasslands, restoration and management strategies should be tailored to address the ongoing trends of habitat transformation.