Spatiotemporal Patterns of Vegetation Greenness Change and Associated Climatic and Anthropogenic Drivers on the Tibetan Plateau during 2000–2015

Abstract

Alpine vegetation on the Tibetan Plateau (TP) is known to be sensitive to both climate change and anthropogenic disturbance. However, the magnitude and patterns of alpine vegetation dynamics and the driving mechanisms behind their variation on the TP remains under debate. In this study, we used updated MODIS Collection 6 Normalized Difference Vegetation Index (NDVI) from the Terra satellite combined with linear regression and the Break for Additive Season and Trend model to reanalyze the spatiotemporal patterns of vegetation change on the TP during 2000–2015. We then quantified the responses of vegetation variation to climatic and anthropogenic factors by coupling climatic and human footprint datasets. Results show that growing season NDVI (GNDVI) values increased significantly overall (0.0011 year−1, p < 0.01) during 2000–2015 and that 70.37% of vegetated area on the TP (23.47% significantly with p < 0.05) exhibited greening trends with the exception of the southwest TP. However, vegetation greenness experienced trend shifts from greening to browning in half of the ecosystem zones occurred around 2010, likely induced by spatially heterogeneous temporal trends of climate variables. The vegetation changes in the northeastern and southwestern TP were water limited, the mid-eastern TP exhibited strong temperature responses, and the south of TP was driven by a combination of temperature and solar radiation. Furthermore, we found that, to some extent, anthropogenic disturbances offset climate-driven vegetation greening and aggravated vegetation browning induced by water deficit. These findings suggest that the impact of anthropogenic activities on vegetation change might not overwhelm that of climate change at the region scale.

Quantifying the Impacts of Anthropogenic Activities and Climate Variations on Vegetation Productivity Changes in China from 1985 to 2015

“…Therefore, the results are not very different from Tian et al and Zhang et al [35,65]. Similarly, Huang et al [64] and Li et al [26] concluded that the vegetation dynamics of Qinghai-Tibet plateau are primarily driven by climate variations, and precipitation is the leading climatic factor of vegetation growth. However, human activities had a negative impact on vegetation growth in most of the areas.…”

“…Grassland productivity changes were mainly observed in Xinjiang, Qinghai-Tibet Plateau, and Inner Mongolia. Previous studies concluded that the grassland changes in Qinghai-Tibet plateau are mainly driven by climate change during both base and restoration periods [26,64]. Tian et al [65] concluded that both climate and human factors contributed equally to vegetation restoration in Inner Mongolia after 1999.…”

“…Recently, many studies have documented that the comparison of actual vegetation productivity and potential vegetation productivity determines the human appropriation of vegetation productivity. Therefore, it is assumed that the difference between potential and actual productivities of vegetation represents the anthropogenic impacts [26]. Several researchers have followed the vegetation productivity difference method to quantify and separate the contributions of human activities and climate factors.…”

Time Series of Landsat Imagery Shows Vegetation Recovery in Two Fragile Karst Watersheds in Southwest China from 1988 to 2016

“…Moreover, Fang et al [8] investigated the vegetation vulnerability to drought stress in arid and semi-arid ecosystems (the Loess Plateau in China) using a bivariate probabilistic framework. Additionally, numerous studies have addressed the vegetation change and associated influencing factors in the Qinghai-Tibetan Plateau, known as the "Earth's third pole" [9]. For example, Song et al [10] analyzed the trends in vegetation change and its relationships with climate change and human activities on the Qinghai-Tibet Plateau from 2000 to 2016 using a growing season integrated enhanced vegetation index (GSIEVI).…”

Optimum temperature for photosynthesis: from leaf- to ecosystem-scale

“…This low value is still higher than the mean daily maximum air temperature during the growing season of 11 ± 2°C, indicating the potential for the enhancement of gross primary productivity by climate warming in this biome. Nevertheless, it should be noted that the warming induced enhancement of alpine plant growth mainly occurs in the mid-eastern Tibetan Plateau, with vegetation growth being found to be water-limited in the northeastern and southwestern Tibetan Plateau during 2000-2015 [13]. In addition, the results of a multi-level nitrogen addition field experiment suggest that non-legume species growth is nitrogen-limited in Tibetan alpine steppe [14].…”