Abstract
The Three-River Source Region (TRSR) is an important area for the ecological security of China. Vegetation growth has been affected by the climate change, topography, and human activities in this area. However, few studies have focused on analyzing time series tendencies of vegetation change in various terrain conditions. To address this issue in the TRSR, this study explored vegetation stability, tendency, and sustainability with multiple methods (e.g., coefficient of variation, Theil-Sen median trend analysis, Mann-Kendall test, and Hurst index) based on the 2000–2017 Global LAnd Surface Satellite Leaf Area Index (GLASS LAI) product. The differentiation patterns of LAI variations and multiyear mean LAI value under different topographic factors were also investigated in combination with digital elevation model (DEM). The results showed that (1) the mean LAI value in the study area increased, with a linear tendency of 0.013·10 a−1; (2) LAI values decreased from southeast to northwest in terms of spatial distribution and the CV indicated LAI variations were relatively stable; (3) the trend analysis revealed that the improved area of LAI accounted for 62.72% which was larger than the degraded area (37.28%), and hurst index revealed a weak anti-sustaining effect of the current tendencies; and (4) the increasing trend was found in multiyear mean LAI value as relief amplitude and slope increased, while LAI stability improved with increasing slope. They exhibited a clear regular pattern. Moreover, significant improvement in LAI generally occurred in low-altitude and flat areas. Finally, the overall improvement and sustainability of LAI improved when moving from sunny aspects to shady aspects, but the LAI stability decreased. Note that vegetation degradation was observed in some high slope areas and was further aggravated. This study is beneficial for revealing the spatial and temporal changes of LAI and their changing rules as a function of different topographic factors in the TRSR. Meanwhile, the results of this study provide theoretical support for sustainable development of this area.
Highlights
As an important part of terrestrial ecosystems, vegetation is the main component of land cover, is a key factor when considering the process of land-use changes and plays an essential role in interactions between the biosphere and atmosphere [1]
Annual mean leaf area index (LAI) values were obtained from the 2000–2017 GLASS LAI data at 1 km pixel levels during the vegetation growing season, and DOY 129–289 data were selected as annual growing season data according to the literature [9]
The temporal and spatial variations in interannual LAI values and their relationships with topographic factors in the Three-River Source Region (TRSR) were analyzed using GLASS LAI data and a digital elevation model (DEM) supplemented with Theil–Sen trend analysis, coefficients of variation, and the
Summary
As an important part of terrestrial ecosystems, vegetation is the main component of land cover, is a key factor when considering the process of land-use changes and plays an essential role in interactions between the biosphere and atmosphere [1]. In the past few decades, the TRSR has experienced major climatic changes, such as significant increases in temperature [2,3,4,5,6], rainfall [7], solar radiation [8]. The coupling of these factors has greatly influenced the vegetation growth [9,10,11,12,13], which is constrained by different climatic factors in different regions [14]. Some studies have shown that in some parts of the TRSR, grasslands are fragmented, and swamps have dried out [15,16]
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