Response of Orthoptera assemblages to environmental change in a low-mountain range differs among grassland types

Grasslands are among the most species-rich ecosystems in Europe. However, their biodiversity has become increasingly threatened by land-use and climate change. Here, we analyze Orthoptera assemblage shifts between 1996 and 2017 across three grassland types in the Black Forest (SW Germany) (N = 63): (i) formerly managed wet grasslands which have been frequently abandoned in recent decades (WET) (N = 15); (ii) common pastures which are still traditionally managed by rough grazing (COMMON) (N = 29), and (iii) mesic grasslands which have recently suffered from land-use intensification (MESIC) (N = 19). Both annual and summer temperatures increased during the study period. Orthoptera assemblages strongly responded to the altered environmental conditions in the grasslands. However, effects differed clearly among grassland types. Despite a strong increase in overall species richness in common pastures, neither the Community Farmland Index (CFI) nor the Community Temperature Index (CTI) had changed. In the two other grassland types, the CFI decreased and the CTI increased. The CFI - established here for Orthoptera - helped to disentangle the effects of climate and land-use change on Orthoptera assemblage composition. Based on our study, climate warming has led to biotic homogenization of the Orthoptera assemblages of wet grasslands affected by abandonment, and mesic grasslands affected by land-use intensification towards a dominance of more widespread species. In contrast, common pastures characterized by a high heterogeneity and low-intensity management were more resilient to the effects of climate warming.