Structural stability and compositional reorganization of high-mountain grasslands under anthropogenic load in the Ukrainian Carpathians

Anthropogenic pressure can alter plant communities without immediately causing changes in total species richness or broad vegetation structure. We assessed the response of high-mountain grasslands to anthropogenic load across five mountain regions of the Ukrainian Carpathians using 30 vegetation relevés, including 15 pairs of control and anthropogenically loaded plots. Vegetation responses to anthropogenic load were examined comprehensively across different structural levels. Total species richness and broad vegetation structure remained highly similar between control and loaded plots. In contrast, reaction to the anthropogenic load was associated with changes in the distribution of species richness among dominant plant families and functional groups, particularly after accounting for regional heterogeneity. Loaded plots showed higher grass richness and lower forb richness, while their overall functional-group cover remained largely unchanged. Differences between paired control and loaded plots were predominantly attributable to species turnover rather than nested species loss, although turnover did not exceed the high background beta diversity of the studied grasslands. The community ecological specialization (cover-weighted) was significantly higher in loaded plots, mainly reflecting reduced dominance of species-generalists, whereas species evenness remained unchanged. Overall, the results indicate that anthropogenic load is associated with compositional reorganization of high-mountain grasslands within a broadly persistent vegetation structure, rather than with straightforward species- and biodiversity-level loss. Species functional identity, within-group species richness structure, and abundance-weighted community properties may therefore provide more sensitive indicators of anthropogenic change than evaluation of species richness or vegetation cover alone.