Detecting the response characteristics and thresholds of grassland spring phenology to climatic factors in the Mongolian Plateau

•GSP of the grassland in MP showed the trend of −0.656 day/decade in 1982–2015.•Vapor Pressure (VAP) is the key climatic factor affecting the GSP.•The interaction effect between VAP and PRE could explain 69.35% GSP changes.•The temperature and VAP showed a nonlinear relationship with GSP.