Abstract
Alpine grasslands on the Tibetan Plateau, being vulnerable to environmental and anthropogenic changes, have experienced dramatic climate change and intensive livestock grazing during the last half-century. Climate change, coupled with grazing activities, has profoundly altered alpine grassland function and structure and resulted in vast grassland degradation. To restore degraded grasslands, the Central Government of China has implemented the Ecological Security Barrier Protection and Construction Project since 2008 across the Tibetan Autonomous Region. However, the relative effect of climate change and grazing activities on the variation in alpine grassland productivity is still under debate. In this study, we quantified how aboveground net primary production (ANPP) varied before (2000–2008) and after (2009–2017) starting the project across different alpine grasslands and how much variance in ANPP could be attributed to climate change and grazing disturbance, in terms of temperature, precipitation, solar radiation, and grazing intensity. Our results revealed that Tibet’s climate got warmer and wetter, and grazing intensity decreased after starting the project. Mean ANPP increased at approximately 81% of the sites, on average from 27.0 g C m–2 during 2000–2008 to 28.4 g C m–2 during 2009–2017. The ANPP positively correlated with annual temperature and precipitation, but negatively with grazing intensity for both periods. Random forest modeling indicated that grazing intensity (14.5%) had a much lower influence in controlling the dynamics of grassland ANPP than precipitation (29.0%), suggesting that precipitation variability was the key factor for alpine grassland ANPP increase across Tibet.
Highlights
Climate change and human activities are primary drivers for changes in terrestrial ecosystems globally (Haberl et al, 2007; Chen et al, 2013; Tong et al, 2018), especially for unprecedented changes in ecosystem service and function (Knight and Harrison, 2012; Seiferling et al, 2014; Erb et al, 2018)
The results showed that both simulated Aboveground net primary production (ANPP) and AGBp matched well with observed records
mean annual temperature (MAT) trend was faster, but annual total precipitation (AP) trend was slower in 2000–2008, compared to those in 2009–2017 (Figures 3A,B)
Summary
Climate change and human activities are primary drivers for changes in terrestrial ecosystems globally (Haberl et al, 2007; Chen et al, 2013; Tong et al, 2018), especially for unprecedented changes in ecosystem service and function (Knight and Harrison, 2012; Seiferling et al, 2014; Erb et al, 2018). A considerable volume of literature tried to identify and quantify the relative influences of climate change and human activities on ecosystem productivity with various methods (Paudel and Andersen, 2010; Erb et al, 2018; Li L. et al, 2018), such as manipulative experiments, traditional statistical analysis, and residuals-trend modeling (Li L. et al, 2018). Scientists often recommended random forest models for processing high-dimensional and -correlated datasets (Breiman, 2001)
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