Grazing alters the phenology of alpine steppe by changing the surface physical environment on the northeast Qinghai-Tibet Plateau, China

The response of vegetation phenology to environmental changes is very complex. We used time-lapse digital cameras to monitor the phenology of an alpine steppe in four winter pastures with different grazing intensities during 2015-2017. The results showed that the beginning of the growing season (BGS) and the growing season length (GSL) of the alpine steppe separately presented advances or prolonged trends with the increase in grazing intensity. There was no regularity in the end of the growing season (EGS) under the change in grazing intensity gradient, but the EGS of the no grazing (NG) plot occurred 24 days ahead of the other plots disturbed by grazing. Different winter grazing intensities obviously had different influences on the surface litter, soil temperature (ST), and soil moisture (SM) during spring but not during autumn. The ST under different grazing intensities played a decisive role in controlling the BGS of alpine steppe, followed by surface litter and SM. The EGS showed a significant correlation with the surface litter in autumn but did not show correlations with ST and SM. These results could further help us understand the phenological mechanisms of the soil surface and guide the scientific management of grazing to adapt to climate change.