Mountain Grasslands under Climate Stress: Drivers, Trends, and Future Projections

Mountain grasslands are crucial ecosystems that provide essential services such as carbon storage, water regulation, and biodiversity conservation. However, these ecosystems are increasingly under threat from changing climatic conditions and human activities. This study explores the historical and future dynamics of vegetation in mountain grasslands worldwide, using a combination of diverse datasets and machine learning tools. For historical trends, spanning the years 2000 to 2021, we analyzed ERA5 climate reanalysis data and global Human Modification (gHM) indices to evaluate the combined impacts of climate variability and human pressures. Future scenarios were developed using climate model projections from CMIP6 and vegetation coverage data, giving us a better understanding of potential changes under different Shared Socioeconomic Pathways (SSPs). We used machine learning techniques, such as Random Forest, XGBoost, and LSTM, to identify key drivers of vegetation changes. SHapley Additive exPlanations (SHAP) helped interpret the contributions of these factors. Our findings reveal that factors like near-surface temperature, evaporation, and human influence play a significant role in shaping vegetation patterns. Over the past two decades, while many grasslands have remained stable, substantial degradation was observed in regions such as South Africa, North America, and Western Asia due to water stress and expanding land use. On the other hand, recovery was seen in areas like Central Europe and Asia, where efforts like reforestation and improved land management have made a positive impact. Looking ahead, future trends vary across scenarios. Under SSP126, vegetation remains mostly stable, whereas SSP245 predicts more variability and localized stress. SSP585 presents a mixed picture: while some regions benefit from longer growing seasons and higher CO₂ levels, others face significant degradation due to extreme climatic events and water scarcity. In areas heavily influenced by human activity, tipping-point dynamics could lead to irreversible losses in vegetation and ecosystem function. This study underscores the complex interplay of climate and human activities in shaping mountain grasslands. It emphasizes the urgent need for sustainable land management and climate adaptation strategies to mitigate risks, protect these ecosystems, and ensure their continued provision of critical services.