Greening of the Qinghai–Tibet Plateau and Its Response to Climate Variations along Elevation Gradients

Zhaoqi Wang,Kai Zheng,Zhifang An,Guolong Cui,Zhiyuan Lu,Xiang Liu,Gaini Wang,Honglin Li

doi:10.3390/rs13183712

Abstract

The vegetation of the Qinghai–Tibet Plateau (QTP) is vital to the global climate change and ecological security of China. However, the impact of climate variation on the spatial pattern and zonal distribution of vegetation in the QTP remains unclear. Accordingly, we used multisource remote-sensing vegetation indices (GIMMS-LAI, GIMMS NDVI, GLOBMAP LAI, MODIS EVI, MODIS NDVI, and MODIS NIRv), climate data, a digital elevation model, and the moving window method to investigate the changes in vegetation greenness and its response to climate variations in the QTP from 2001 to 2016. Results showed that the vegetation was greening in the QTP, which might be attributed to the increases in temperature and radiation. By contrast, the browning of vegetation may be caused by drought. Notably, the spatial patterns of vegetation greenness and its variations were linearly correlated with climate at low altitudes, and vegetation greenness was non-linearly correlated with climate at high altitudes. The Northwestern QTP needs to be focused on in regard to positive and decreased VGEG (vegetation greenness along the elevation gradient). The significantly positive VGEG was up to (34.37 ± 2.21) % of the QTP, which indicated a homogenization of vegetation greenness on elevation. This study will help us to understand the spatial distribution of vegetation greenness and VGEG in the QTP under global warming, and it will benefit ecological environment management, policymaking, and future climate and carbon sink (source) prediction.

Highlights

Vegetation plays a crucial role in mitigation of global climate [6]; vegetation greenness generally decreases with the increased elevation, because the low temperature limits the growth of vegetation in high altitudes [7], which indicates a negative vegetation greenness along the elevation gradient (VGEG can be defined as the regression value between vegetation greenness and elevation gradient in a certain extent)
Even if we have found that the changes in vegetation greenness have large discrepancies by using multisource vegetation index (VI) in the hinterland of the Qinghai–Tibet Plateau (QTP)
We found clear spatial distribution patterns of VGEG based on GIMMS NDVI and Moderate Resolution Imaging Spectroradiometer (MODIS)-based VI

Summary

Introduction

The accelerating global warming and carbon dioxide (CO2 ) concentration have exerted widespread impacts on the terrestrial ecosystem in the past three decades [1,2,3], the impact of which on vegetation dynamics may be more pronounced in high mountainous areas [4,5]. Growing evidence demonstrated that the warming rate is intensified in mountain environments [5,8,9,10], and this is likely to cause a completely different distribution of vegetation greenness on the altitude gradient [11]. The vegetation changes in high mountainous areas have not been unanimously concluded yet. The elevation pattern of vegetation greenness may have changed in mountainous regions under the influence of global warming, because the warming rate in high-altitude areas is often greater than that in low-altitude areas [4,12]

Methods

Results

Discussion

Conclusion