Effects of Management and Climatic Variability on Indicator Species and Biomass Production in Carpathian Mountain Grasslands

Carpathian mountain grasslands are increasingly affected by management intensification and climatic variability, with consequences for species composition and ecosystem functioning. This study assessed the long-term effects of a mineral fertilization gradient and interannual climatic variability on indicator species dynamics and biomass production in a semi-natural high-nature-value (HNV) grassland in the Apuseni Mountains, based on a 17-year field experiment. Increasing fertilization intensity promoted a clear shift from species-rich oligotrophic communities toward simplified mesotrophic and eutrophic grassland types, accompanied by a decline in indicator species richness and the increasing dominance of competitive grasses. Biomass production increased consistently along the fertilization gradient. Climate-driven effects were assessed using unfertilized control plots, allowing management effects to be disentangled from interannual climatic variability. Variations in temperature and precipitation influenced floristic composition and productivity across the years, highlighting the sensitivity of mountain grasslands to short-term climatic fluctuations. Multivariate analyses revealed increasing vegetation homogenization under high fertilization and distinct year-to-year shifts in species composition under unfertilized conditions. These results emphasize the vulnerability of Carpathian HNV grasslands to both nutrient enrichment and climatic variability, and underline the need for climate-adaptive, biodiversity-oriented management strategies.