Impact of climate change on potential productivity and phenological phase of forage in the Qinghai-Tibet Plateau in the past 50 years

The Qinghai-Tibet Plateau is considered to be ideal region for studying the response of natural ecosystems to climate change because its’ mountainous environments is one of the most fragile of the global ecosystems. The impacts of the changes in temperature and precipitation on the phenology varied among different grasslands. After experiencing a distinct warming in recent decades, some studies noted that remarkable variations in vegetation in the Qinghai-Tibet Plateau were potentially due to climate change. In order to determine the impacts of climate change on vegetation phenology and potential productivity, this paper used meteorological data during 1965–2013 in the Qinghai-Tibet Plateau (e.g., monthly temperature, precipitation and sunshine duration) of 107 meteorological stations, and extracted vegetation phenological indices using MODIS-derived normalized difference vegetation index data during 2000–2013, and used the Thornthwaite Memorial model and GIS techniques to analyze the spatial and temporal trends of potential climate-driven forage productivity in the Qinghai-Tibet Plateau. Then by analyzing 22 years of continuous observation data of growth stages of forage in the Qinghai-Tibet Plateau, the relationship between meteorological factors and major growth stages of forage was determined. Also the driving factors of the dynamics of potential climate productivity in the Qinghai-Tibet Plateau were determined. Furthermore, the relationship between temperature or precipitation and sunshine duration during forage growth period was determined based on regression analysis. The results showed that the potential climate productivity of forage in the Qinghai-Tibet Plateau was consistently varied with geographical region and spatial temperature distribution. Average temperature in the Qinghai-Tibet Plateau rose during the nearly 50-year period, increasing by 0.53 ℃(10a)1. Precipitation generally increased at the rate of 7.81 mm(10a)1, while sunshine duration decreased by 16.94 h(10a)1. Potential climate productivity of forage in the Qinghai-Tibet Plateau presented an increasing trend from 1965 to 2013, and spatial changes of the productivity, in turn, increased from northwest to southeast. Then potential climate productivity of forage in the north and south in the plateau significantly increased and there was less variation in the east of the plateau. Furthermore, the regreening, heading and blossoming of forages advanced, while yellowing and withering delayed year after year, which extended the forages phenological phases. Regreening stage of forage delayed from southeast to northwest, although withering stage showed no obvious change. Under drier and warmer conditions, phenological periods of grassland vegetation in the region became closely related to climate change. Then precipitation and sunshine duration were negatively correlated with phenological period of the grassland vegetation. Temperature was the dominant constraint on phenological phases of grassland vegetation in the study area. The study formed a relevant reference and basis for the protection of grassland ecosystems and enhancing potential climate productivity in Qinghai-Tibet Plateau.