Grazing legacy shapes biodiversity: Impacts on plant and butterfly communities across successional stages in subalpine ecosystems

Grazing influences the spatial and temporal dynamics of vegetation heterogeneity and structure. Whether due to intensification or abandonment, changes in grazing dynamics may cause a variety of habitat responses at different spatio-temporal scales that significantly influence ecological communities. Despite extensive knowledge on the effects of grazing on mountain ecosystems, there is still a limited understanding of how different grazing histories and their legacy (i.e. past long-term effects) interact to shape biodiversity across broad spatial gradients. We aimed to identify the optimal stage of vegetation conditions resulting from particular grazing dynamics and their legacy effects that would maximise butterfly and plant biodiversity across a large geographical range in the Pyrenees. We sought to assess how grazing (either through legacies or immediate effects) influences the richness, abundance, community composition and functional group structure of both plant and butterfly species. We conducted butterfly and plant surveys in 60-x-60m plots in 12 valleys in the Catalan Pyrenees (western Mediterranean) under four different grazing legacy regimes representing different vegetation conditions, ranging from heavily grazed grasslands to densely scrub-encroached areas. We also conducted participatory mapping with local cattle-herders to gain insights into the spatial-temporal dynamics of the grazing legacy regimes. Intermediate grazing stages exhibited significantly higher plant and butterfly richness and abundance, and also harboured species of greater conservation concern. Grazing legacy was the main driver for butterfly and plant diversity, community composition and functionality. Maintaining low to medium grazing intensity is essential for preserving vegetation heterogeneity and enhancing both butterfly and plant richness and abundance.