Monitoring spatio-temporal change of rangeland vegetation in Bhutan to inform sustainable rangeland management

Rangelands play a critical role in delivering ecosystem services, including biodiversity conservation, livestock production, and ecological stability in Bhutan’s high-altitude landscapes. However, these rangelands are increasingly threatened by climate change, overgrazing, shrub encroachment, invasive species, and the absence of structured management. This study presents the first nationwide, high-resolution, multi-temporal assessment of rangeland extent and condition in Bhutan using Google Earth Engine (GEE)-based multi-sensor data integration. Rangeland dynamics were assessed using Landsat 8, Sentinel-2, and Climate Hazards Group InfraRed Precipitation with Station (CHIRPS) data by comparing reference conditions (2013–2015) with recent observations (2022–2024). Participatory field data were collected through the engagement of local herders using smartphone applications, generating1,548 training points and 2,624 validation points to support ground truthing. The overall classification accuracy achieved was 65.09% with a Kappa coefficient of 0.53, reflecting moderate mapping reliability. Sentinel-2 imagery and a Random Forest classification algorithm based on FAO’s Land Cover Classification System (LCCS 3) helped delineate three major rangeland types: 3,451 km² of herbaceous rangeland, 3,546 km² of shrub and bush rangeland, and 2,310 km² of mixed rangeland. Relative to the baseline period (2013–2015), shrub and bush rangelands exhibited the most pronounced greening trends, while herbaceous and mixed rangelands showed spatially clustered areas of vegetation decline, indicating class-specific land-use and condition change across Bhutan. Vegetation index analysis showed that 1,425 km² of rangelands had increased vegetation index values, while 442 km² exhibited declining trends, and 7,159 km² remained stable. The results provide a spatially explicit and scalable geospatial infrastructure to inform rangeland monitoring, sustainable grazing, and rangeland restoration in Bhutan.