Spatio-temporal variation of alpine grassland spring phenological and its response to environment factors northeastern of Qinghai-Tibetan Plateau during 2000-2016

摘要

Vulnerable alpine grassland ecosystem is highly sensitive to climate change, and its response and feedback to climate change have been intensely studied by the scientific community. In this study, the alpine grassland ecosystem in the Qinghai Lake watershed of the northeastern Qinghai-Tibet Plateau was selected as the research subject, and MODIS time series data and field sampling data were used to analyze the characteristics of the beginning of the growing season (BGS) pattern and the spatio-temporal variation and responded to environmental factors. The results show that under the combined influence of elevation, land surface temperature (LST), and soil moisture, the multi-year alpine grassland BGS pattern presents zonal horizontal characteristics with increasing delays from the southeast to the northwest and also exhibits non-zonal vertical characteristics in the western mountainous area. Alpine grassland BGS shows significant negative correlations with elevation and the 0-10 cm soil moisture content but a significant positive correlation with the mean spring LST. The relationships among BGS, elevation, and LST change when the elevation is over 4200 m, but the relationship between BGS and soil moisture continues to be a significant negative correlation. In the period 2000-2016, the BGS of the alpine grassland in the watershed generally advanced at the rate of 1.4 days/10 years and in local areas showed spatially heterogeneous trends. Spring soil moisture plays a key role in controlling spatio-temporal variations of BGS in the arid and semi-arid areas of the alpine zone relative to LST. Grassland degradation also affects the BGS spatio-temporal pattern and shows grassland degradation result of BGS in advance. The findings would provide a scientific reference for further understanding the mechanism of alpine vegetation phenology.