No upward shift of alpine grassland distribution on the Qinghai-Tibetan Plateau despite rapid climate warming from 2000 to 2014.

The distributions of many species show climate-driven shifts towards higher elevations, but evidence for elevational shifts is scarce for the alpine grasslands on the Qinghai-Tibetan Plateau. The upward shift of alpine grassland distribution from 2000 to 2014 was assessed with field measurements and satellite remote sensing data obtained across six elevational transects on the Qinghai-Tibetan Plateau. The aboveground biomass (AGB) of alpine grasslands varied with altitude and its data produced a bell-shaped curve. This was mainly due to the elevational dependency of climate change at the surface (i.e., producing drier climate at low elevations and wetter climate at middle elevations). The normalized difference vegetation index (NDVI) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) exhibited a positive exponential relationship with the AGB of alpine grasslands. Overall, MODIS NDVI initially increased, then peaked at median altitude sites, then decreased with altitude on each elevational transect. MODIS NDVI at the upper limit of alpine grassland distribution did not show a significant increasing trend from 2000 to 2014, even though land surface temperature increased and precipitation remained approximately constant. High spatial resolution Landsat data supported this result. Further analyses of MODIS NDVI at all other sites found no general increase in AGB towards higher elevations. The results suggest that the distribution of alpine grasslands on the Qinghai-Tibetan Plateau did not show an upward shift despite rapid climate warming having occurred from 2000 to 2014.