| Summary: | Understanding the response characteristics and thresholds of grassland spring phenology (GSP) to different climatic factors in arid and semi-arid regions is of great significance to deal with global climate change. The Mongolian Plateau is one of the largest plateaus located in arid and semi-arid regions of eastern Asia, extremely sensitive to climate change. At present, the response characteristics and thresholds of the grassland spring phenology to climate factors in the Mongolian Plateau remain uncertain. Here, we used statistical analysis, random forest and geographical detector to explore these uncertainty. We found that 1) 76.67% of study area showed a significant advancing trend. GSP has significantly advanced by −0.656 days/decade (P < 0.05) over the past three decades. 2) The vapor pressure (VAP) shows a more important impact on the GSP than other climate factors both in strength and range. Especially when the VAP value was between 2 and 5 hPa, the GSP advanced as the VAP increased. The near-surface temperature minimum (TMN), near-surface temperature (TMP), near-surface temperature maximum (TMX) and diurnal temperature range (DTR) have the greatest impact on the GSP in June, and the six-month cumulative effects of precipitation (PRE), wet day frequency (WET) and cloud cover (CLD) are greater than those in a single month. The interaction between VAP and PRE could largely explain GSP changes (69.35%). 3) The GSP have different response threshold to climate factors. The GSP advances as the temperature increases when TMP < 0 °C, DTR < 14 °C, TMX > 10 °C and TMN > −5 °C, and it delays as the FRS, WET and CLD increase. This study is of great significance to reveal the impact characteristics and threshold of climate change on the GSP, which could do help in understanding climate change.
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