Recurrent Climate-Driven Dieback of Subalpine Grasslands in Central Europe: Detecting from Multi-Decadal Landsat and Sentinel-2 Time Series

Subalpine grasslands represent highly sensitive ecosystems that are increasingly exposed to climate extremes, yet their long-term disturbance dynamics remain poorly documented. This study investigates climate-driven dieback of subalpine grasslands in Central Europe using a harmonized, multi-decadal satellite time series. We analyzed Landsat (TM, ETM+, OLI, OLI-2) and Sentinel-2 imagery spanning 1984–2024 to detect changes in grassland condition, supported by field-based validation, climatic indices, and geomorphological analysis. Several spectral indices related to non-photosynthetic vegetation were evaluated, with the Normalized Burn Ratio (NBR) showing the highest ability to discriminate dead grassland biomass from live vegetation. Retrospective mapping revealed four distinct dieback events since 2000, comprising two short-term episodes with rapid within-season recovery and two long-term events characterized by persistent degradation and slow regeneration. Dieback timing corresponded closely with climatic extremes, particularly droughts of varying duration, while winter frost under shallow soil conditions likely contributed to long-term damage in some cases. Geomorphological analysis indicated that wind exposure, elevation, and terrain convexity strongly modulate dieback susceptibility, highlighting the importance of fine-scale environmental controls. Our results demonstrate the value of long-term, multi-sensor satellite observations for detecting and interpreting climate-driven disturbances in subalpine grasslands and provide a transferable framework to support monitoring and conservation of mountain ecosystems under ongoing climate change.