Divergent changes in the elevational gradient of vegetation activities over the last 30 years.

The reported progressive change of vegetation activity along elevational gradients has important aesthetic and conservation values. With climate change, cooler locations are suggested to warm faster than warmer ones, raising concerns of a more homogenized landscape along the elevation. Here, we use global satellite data to investigate the spatio-temporal dynamics of the elevational gradient (EG) in vegetation greenness (NDVImax3), spring (SOS) and autumn phenology (EOS) during 1982-2015. Although we find clear geographical patterns of the EG in NDVImax3 and SOS, there are no prevalent trends of vegetation homogenization or phenology synchronization along elevational gradients. Possible mechanisms, including spatially heterogeneous temperature lapse rate changes, different vegetation sensitivities to climate change, and human disturbances, may play diverse roles across different regions. Our finding of mixed EG trends and no general rules controlling EG dynamics poses challenges for mitigating possible adverse impacts of climate change on mountainous biological diversity and ecosystem services.