Greening Implication Inferred from Vegetation Dynamics Interacted with Climate Change and Human Activities over the Southeast Qinghai–Tibet Plateau

Li Li,Xu Xu,Liu Liu

doi:10.3390/rs11202421

Abstract

Vegetation dynamics are sensitive to climate change and human activities, as vegetation interacts with the hydrosphere, atmosphere, and biosphere. The Yarlung Zangbo River (YZR) basin, with the vulnerable ecological environment, has experienced a series of natural disasters since the new millennium. Therefore, in this study, the vegetation dynamic variations and their associated responses to environmental changes in the YZR basin were investigated based on Normalized Difference Vegetation Index (NDVI) and Global Land Data Assimilation System (GLDAS) data from 2000 to 2016. Results showed that (1) the YZR basin showed an obvious vegetation greening process with a significant increase of the growing season NDVI (Zc = 2.31, p < 0.05), which was mainly attributed to the wide greening tendency of the downstream region that accounted for over 50% area of the YZR basin. (2) Regions with significant greening accounted for 25.4% of the basin and were mainly concentrated in the Nyang River and Parlung Tsangpo River sub-basins. On the contrary, the browning regions accounted for <25% of the basin and were mostly distributed in the urbanized cities of the midstream, implying a significant influence of human activities on vegetation greening. (3) The elevation dependency of the vegetation in the YZR basin was significant, showing that the vegetation of the low-altitude regions was better than that of the high-altitude regions. The greening rate exhibited a significantly more complicated relationship with the elevation, which increased with elevated altitude (above 3500 m) and decreased with elevated altitude (below 3500 m). (4) Significantly positive correlations between the growing season NDVI and surface air temperature were detected, which were mainly distributed in the snow-dominated sub-basins, indicating that glaciers and snow melting processes induced by global warming play an important role in vegetation growth. Although basin-wide non-significant negative correlations were found between precipitation and growing season NDVI, positive influences of precipitation on vegetation greening occurred in the arid and semi-arid upstream region. These findings could provide important information for ecological environment protection in the YZR basin and other high mountain regions.

Highlights

Vegetation is an important component in terrestrial ecosystems that reflects the land surface condition and interacts with the hydrosphere, atmosphere and biosphere [1]
The greening rate exhibited a significantly more complicated relationship with the elevation, which increased with elevated altitude and decreased with elevated altitude. (4) Significantly positive correlations between the growing season Normalized Difference Vegetation Index (NDVI) and surface air temperature were detected, which were mainly distributed in the snow-dominated sub-basins, indicating that glaciers and snow melting processes induced by global warming play an important role in vegetation growth
Basin-wide non-significant negative correlations were found between precipitation and growing season NDVI, positive influences of precipitation on vegetation greening occurred in the arid and semi-arid upstream region

Summary

Introduction

Vegetation is an important component in terrestrial ecosystems that reflects the land surface condition and interacts with the hydrosphere, atmosphere and biosphere [1]. Vegetation is often regarded as a good indicator of environmental changes [2] and can be used to describe interactive impacts between environmental changes and terrestrial ecosystems [3]. Zhu et al used the Leaf Area Index (LAI) to study vegetation dynamics and found that the globe experienced an obviously greening process, with CO2 fertilization effects playing an important role in this greening trend [4]. Lu et al considered that human activities in China were the most significant factors for vegetation dynamics, and the implementation of large-scale natural conservation measurements was more effective for vegetation recovery [11]. The increasing sensitivity of vegetation to climate change and human activities along an elevational gradient in high-altitude regions raises a great challenge to the understanding of the interaction between vegetation dynamics and environmental changes

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Discussion

Conclusion