Effect of Mineral Fertilization on Vegetation of HNV Pastures in the Apuseni Mountains (Romania)

High-Nature-Value (HNV) grasslands in the Apuseni Mountains represent traditional semi-natural ecosystems with high biodiversity and major ecological value, but are constantly exposed to pressures generated by both agricultural intensification and abandonment. This study asses the effects of long-term mineral fertilization on floristic composition and grassland diversity within a permanent experiment initiated in 2001 in Gârda de Sus (Romania). Four variants of mineral fertilization were tested: control (N0), low-input (N₅₀P₂₅K₂₅), medium-input (N₁₀₀P₅₀K₅₀) and high-input (N₁₅₀P₇₅K₇₅). Floristic analyses were performed using the modified Braun-Blanquet method, and the data were interpreted using multivariate analyses and diversity indices. The results revealed a clear trophic gradient. Both the control and low-input variants maintained high diversity and the stability of communities dominated by <i>Festuca rubra</i> and its associated oligotrophic species. In contrast, medium and high fertilization produced a pronounced reduction in community components, with the dominance of nitrophilous species, especially <i>Agrostis capillaris</i>, a species which is consumed by animals. Multivariate analyses confirmed that the dominant effect on plant communities was the fertilization level, outweighing the interannual climatic variations. Low fertilization maintained biodiversity with minimal changes after 17 years, while higher inputs led to significant species losses and reduced stability of community. The results provide a scientific benchmark for creating specific sustainable management scenarios and highlight the need for accepted organic alternatives. This study is one of the few long-term experiments in the Carpathians that documents the impact of fertilization on HNV grasslands and provides essential benchmarks for adapting management strategies in the context of the Common Agricultural Policy.