Understanding whether land use intensification causes regime shifts is of key importance for management, particularly if these shifts are associated with thresholds separating different ecosystem states and with hysteretic dynamics. Here we use a unique, long-term grassland database to identify thresholds in the response of 16 ecosystem functions and the diversities of 21 taxa to land use intensity. We show that aboveground diversity (5 of 10 taxa), shoot biomass and soil N retention showed threshold responses to land use intensity, i.e., abrupt changes between extensively and intensively managed grasslands. Time-series analysis revealed that ecosystem functions showed hysteresis around the threshold, while diversity did not. Shifting back to the functioning seen in extensively managed grasslands may therefore require larger reductions in land use intensity than shifting to the high intensity state. Identifying such thresholds along land use gradients is critical to prevent ecosystem degradation and conserve biodiversity and ecosystem functions.

Experimental evidence shows that grassland plant diversity enhances ecosystem functioning. Yet, the transfer of results from controlled biodiversity experiments to naturally assembled ‘real world’ ecosystems remains challenging. Here, we address this issue by experimentally sowing locally absent plant species in 73 agricultural grasslands along a land-use intensity gradient, to test how ecosystem functions related to productivity and nutrient cycling respond to species enrichment. We found that only one of 12 ecosystem functions responded to changes in species richness. In fact, ecosystem functioning was rather driven by environmental conditions and land-use intensity. This suggests that the functionally-relevant niche space is saturated in naturally assembled grasslands, and that competitive, high-functioning species are already present. While nature conservation and cultural ecosystem services certainly benefit from species enrichment, our study indicates that plant species enrichment may deliver only weak increases in ecosystem functioning in both moderately intensive and traditionally managed agricultural grasslands.