Aspect Matters: Unraveling Microclimate Impacts on Mountain Greenness and Greening

Mountains are vital ecosystems, yet predicting plant growth there is complex due to diverse microclimates on slopes. Equatorial-facing slopes (EFSs) are drier and warmer, and polar-facing slopes (PFSs) are wetter and colder, than their regional macroclimates. Analyzing Moderate Resolution Imaging Spectroradiometer normalized difference vegetation index from 2003 to 2021, we identified a clear geographic pattern of differences in greenness on the two opposite aspects: EFSs were greener than PFSs in cold areas and were browner in dry areas, mainly determined by the relative importance of limitations of temperature and water. PFSs had stronger greening trends than did EPSs, leading to a weakening difference in greenness between EPSs and PFSs in temperature-limited areas, and an intensifying difference in water-limited areas. This suggests the alleviation of temperature limitation and exacerbation of water limitation. Montane ecosystems constitute a "natural laboratory" for deepening our understanding of the temporal evolution of the climatic control of vegetation growth with a space-for-time substitution. Mountains are essential for Earth's greenery, but understanding plant growth in these landscapes is complex due to varied microclimates on slopes. Some slopes are drier and warmer, while others are wetter and colder than the surrounding areas. These micro-habitats influence how plants respond to changing climates. Using satellite data from 2003 to 2021, we found that slopes facing the equator are greener in cold areas but browner in dry zones. Slopes facing the poles have stronger greening trends than equatorial slopes. Our research reveals how mountain plants adapt to local conditions, offering insights into how they might respond to climate changes. Mountains act as nature's laboratories, guiding us in understanding how temperature and water shape plant growth over time. Microclimatic disparities between Equatorial-facing slopes (EFSs) and polar-facing slopes (PFSs) shape distinct vegetation dynamicsGlobal study reveals EFSs greener in colder regions, while PFSs show stronger greening trends, reflecting changing climate limitationsMontane ecosystems provide insights into climate-driven vegetation growth, indicating temperature and water play pivotal roles