Abrupt boundaries between mountain meadows and forests separate ground-dwelling invertebrate communities: a case study from South Tyrol, Italy

In mountain regions, available agricultural land is often limited by the rugged topography and therefore an efficient and small-scale land use is needed to ensure food and fodder security. In the European Alps, mountain meadows at mid-elevations were created in medieval times by clearing and are therefore often still embedded in forest areas. The transition between these two habitats is mostly smooth due to the presence of a shrub strip, but sometimes sharp, as it is the case in our study. It is not well known whether such abrupt shrub-free habitat shifts affect the exchange of ground-dwelling macro-invertebrates between habitats and whether this may affect local biodiversity. We set up nine straight transects with five pitfall traps each, running from montane open extensive meadows through the sharp ecotone lines to mixed forest plots in South Tyrol, Northern Italy. Invertebrate activity densities, distribution, and biodiversity patterns were assessed. We found well separated invertebrate communities for the meadows and forests, with the ecotone communities being similar to those of the forests and not forming a distinct intermediate cluster. Araneae were significantly more abundant in the meadows and decreased towards the meadow edges and forests. In contrast, Diplopoda and Isopoda were significantly more abundant in the ecotone and forest plots. The meadow plots and partly the edge plots were inhabited by threatened Red List species. In heterogeneous mountain regions such as South Tyrol, where agricultural land is scarce and therefore must be used efficiently, sharp shifts between habitat types result in distinct invertebrate communities impeding species exchange. Maintaining the extensive management of grasslands and the establishment of buffering shrub strips are therefore desirable measures to support the local soil invertebrate biodiversity, as species may not be able to spill over the abrupt ecotone borders and seek shelter during management activities.