Responses of vegetation zones, in the Qinghai-Tibetan Plateau, to climate change and anthropogenic influences over the last 35 years

The types and growth statuses of vegetation are considered critical indicators that reflect climate regimes and have received much attention in ecology and climatology. However, studies focusing on climate warming influencing vegetation replacement toward high altitudes and latitudes, from the perspective of the redistribution of vegetation zones, are scarce. This study used AVHRR/GIMMS-NDVI as the indicator to represent the growth status of vegetation zones and chose the Qinghai-Tibetan Plateau (QTP) as the study area, because of its high sensitivity to climate change. The spatiotemporal dynamics of vegetation in the last 35 years, during 1981–2015, were analyzed. Additionally, the responses of vegetation to climate change and human activities were examined by analyzing the relationship between vegetation and climate/anthropogenic influences, using the temperature and precipitation data from 87 metrological stations, assimilated meteorological data, and economic statistical data on the QTP. The results show that ⅰ) on the whole, the growth status has been improving during the past 35 years. This trend was consistent with that of the temperature and precipitation data. However, it is difficult to explain the reasons behind the changes, when taking the QTP as a whole. By dividing the QTP into different sub-regions, from different zoning schemes, the spatiotemporal characteristics are clearly depicted and causes are reasonably explained. ⅱ) The vegetation in the middle and southwestern QTP, with high altitudes, was improving and the warm-humid climate trend was the main reason for this. That is, the frigid climatic conditions at high altitudes have been alleviated with global warming. With the treeline / timberline being lifted and vegetation zones expanding, the NDVI correspondingly increased. ⅲ) The degenerated regions are mainly in the northern and eastern QTP, which have high population/livestock densities. The slowly changing climate regime and anthropogenic influences, e.g., the rapid growth of livestock and population (urbanization), are the main reasons for the vegetation degradation.