Tipping Points of Biodiversity and Sustainability in Traditional Alpine Pastures (BIOPAS)

Alpine and subalpine pastures are semi-natural, high-biodiversity grassland ecosystems shaped over centuries of livestock grazing. In South Tyrol (Italy), socio-economic and technological factors over the past century have contributed to land abandonment in less-favoured areas. This has resulted in shrub and tree encroachment into meadows and pastures, leading to a decline in grassland biodiversity. A key challenge is to understand how grazing intensity affects soil biodiversity and whether clear thresholds exist beyond which such changes can substantially impact the ecosystem.

To investigate this, we selected four high-altitude sheep pastures (ranging from 2100 to 2500 m a.s.l.) under three distinct management regimes: intensive grazing, moderate grazing, and abandonment (defined as no grazing for three or more years). For each regime, we chose three plots and collected ten soil samples from each (5–10 cm depth). We measured soil physical and chemical parameters, including aggregate stability, total organic carbon, total nitrogen, dissolved organic carbon, pH, nitrate, and available phosphate. Additionally, we studied belowground biodiversity through environmental DNA metabarcoding targeting soil bacteria (16S rRNA gene), fungi (ITS2 region), and soil fauna (COI gene).

We expect that high grazing pressure will significantly influence microbial communities, especially fungi, thereby affecting carbon and nitrogen cycling. Indeed, previous studies show that grazing disturbance and repeated nutrient inputs from urine and faeces increase soil nitrogen availability and stimulate nitrification processes. Conversely, grazing abandonment causes successional vegetation shifts and low biomass removal, as shown in comparable subalpine grasslands, with cascading effects on soil microbial biodiversity. Moderate grazing, on the other hand, has historically fostered the highest biodiversity in semi-natural grasslands in the Alps by maintaining ecological heterogeneity, which prevents competitive exclusion among plant species. This aboveground heterogeneity is closely linked to soil microbial patterns and can therefore sustain higher biodiversity compared to both intensive grazing and abandonment. Considering all these elements together, we aim to identify indicators and thresholds that signal a tipping point toward grassland recovery or degradation. Such information can support sustainable grazing management practices to preserve biodiversity and maintain ecosystem functions in alpine meadows.