Abstract
Changes in global climate patterns and human activity have the potential to alter key components of terrestrial ecosystems, such as the productivity of grasslands. The Qinghai–Tibetan Plateau is one of the most sensitive regions and is affected by substantial climatic changes and intensive human activities. In this study, the spatial distribution and temporal variation in grassland productivity from 1980 to 2015 were examined using the proxy net primary productivity (NPP). Trend and redundancy analyses were used to determine the contributions of driving indicators (climate change and human interventions) to the changes in NPP. During the past 35 years, the trend in grassland productivity across the Qinghai–Tibetan Plateau was one of significant increasing trend (increase of 1.08 g C/m2/year). A trend of increase of NPP was observed for approximately 82.79% of the total grassland area, with most of this area distributed in the central region. However, a trend of degradation was observed in the northwestern region of the plateau. The primary reason for the complex spatial pattern and distribution of vegetation productivity was unsynchronized changes in temperature and precipitation. Therefore, temperature and water content (precipitation and melting water) were not good indicators for trends in NPP in this area. Moreover, although variation in rainfall and temperature explained 9.75% of the variation in grassland productivity, the effects of human interventions were greater (23.48%). According to the redundancy analysis, the positive contribution of ecological restoration projects (reducing the negative effects of humans) was the most important indicator in the entire study area, followed by temperature (conducive to vegetation growth and acceleration of melting glaciers). Most conservation policies produced significant positive effects on the restoration of grasslands and prevented or reversed the degradation of grasslands on the plateau. Under increases in temperature and moisture on the Qinghai–Tibetan Plateau, the ecological restoration policies in conservation areas demonstrate an “increasing trend in grassland productivity.”
Highlights
Grassland, as one of the most common vegetation types worldwide, accounts for 20% of the global land surface (Squires et al, 2018)
The main questions that this study addressed were as follows: (1) Did the Qinghai–Tibetan Plateau expe rience a trend of increasing net primary productivity (NPP) from 1980 to 2015?(2) Which factors explained the most variation in the NPP trends observed on the plateau? (3) Can ecological restoration management be an indicator of grassland degra dation on the plateau?
The interannual variations in NPP were analyzed to reveal the trend in vegetation growth on the Qinghai–Tibetan Plateau over the past 35 years (Fig. 2f)
Summary
As one of the most common vegetation types worldwide, accounts for 20% of the global land surface (Squires et al, 2018). Grasslands are the largest terrestrial ecosystem type by area in China, covering 3.93 million km, accounting for approximately 40% of China’s total land area and 6%–8% of the global total grassland area (Ni, 2002). More than half of the grasslands in China have been degraded to some extent because of climate change, land use patterns, human population growth, and socioeconomic development (Nan, 2005). The Qinghai–Tibetan Plateau, as the highest and largest plateau on Earth, has a unique set of terrestrial ecosystems, and the vegetation on the plateau is highly sensitive to climate change (Shen et al, 2015; Liu et al, 2018; Dakhil et al, 2019). Monitoring the spatial and temporal variations in grassland vegetation and understanding their causes have been a crucial focus during the past few decades and are expected to be so in the future (Xu et al, 2016; Xiong et al, 2019)
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