Integration of Remote Sensing Vegetation Indices into a Structural Model for Sustainable Biomass Monitoring in Protected Mountain Areas: A Case Study in the Southern Carpathians (Romania)

Monitoring vegetation biomass dynamics is essential for assessing ecosystem functioning and biodiversity pressures in protected mountain areas, where reduced accessibility limits in situ data collection. This study investigates the multitemporal variation in vegetation biomass within the Cioclovina–Șura Mare–Piatra Roșie strictly protected area of the Grădiștea Muncelului–Cioclovina Natural Park (Southern Carpathians, Romania), using vegetation indices derived from Sentinel-2 imagery for the 2018–2022 period. Four complementary indices (NDVI, SAVI, MSAVI, and LAI) were computed and normalized, then integrated into an original synthetic indicator (BCIS—Biomass Change Integrated Score) for quantifying biomass changes. The results indicate an overall reduction in vegetation biomass, with 89.49% of the area classified under degradation trends, while 4.53% shows regeneration processes. Grasslands and mixed agricultural–natural lands are the most affected habitats, where degradation is linked to anthropogenic pressures and ecotonal vulnerability, whereas broadleaf forests display a high degree of resilience, maintaining substantial proportions of stable or regenerating surfaces. The multispectral integration through the BCIS indicator enabled a more robust detection of critical zones, supporting sustainable vegetation management and biodiversity monitoring in protected mountain ecosystems.