Spatio-temporal variation and driving forces in alpine grassland phenology in the Zoigê plateau from 2001–2013

Based on the HANTS and dynamic threshold method, the spatio-temporal changes of the alpine grassland phenology in the Zoigê plateau was analyzed by using MODIS EVI data from 2001 to 2013. The results were found as follows: (1) The spatial distribution of the average vegetation phenology from 2001 to 2013 is closely related to the water and heat conditions. Accompanying the deterioration in heat and water conditions from low altitude to high altitude and south to north, SOG(start of growing season) was delayed gradually, EOG(end of growing season) advanced slowly, and LOG(long of growing season) shortened gradually. Water played an important role in the regional differentiation of phenology (2) From 2001 to 2013, SOG came earlier by 0.6d/a, EOG was late by 0.2d/a, and LOG lengthened by 0.8d/a. The inter-annual phenology changes of the vegetation exhibited significant differences at different elevations and water condition. (3) Heat and moisture is the main ecological factor influencing the growth of plant. Temperature responses of phenology significantly became stronger with increasing cumulative preseason precipitation.