Abstract
Alpine meadow and alpine steppe are the two most widely distributed nonzonal vegetation types in the Qinghai-Tibet Plateau. In the context of global climate change, the differences in spatial-temporal variation trends and their responses to climate change are discussed. It is of great significance to reveal the response of the Qinghai-Tibet Plateau to global climate change and the construction of ecological security barriers. This study takes alpine meadow, alpine steppe and the overall vegetation of the Qinghai-Tibet Plateau as the research objects. The normalized difference vegetation index (NDVI) data and meteorological data were used as the data sources between 2000 and 2018. By using the mean value method, threshold method, trend analysis method and correlation analysis method, the spatial and temporal variation trends in the alpine meadow, alpine steppe and the overall vegetation of the Qinghai-Tibet Plateau were compared and analyzed, and their differences in the responses to climate change were discussed. The results showed the following: (1) The growing season length of alpine meadow was 145~289 d, while that of alpine steppe and the overall vegetation of the Qinghai-Tibet Plateau was 161~273 d, and their growing season lengths were significantly shorter than that of alpine meadow. (2) The annual variation trends of the growing season NDVI for the alpine meadow, alpine steppe and the overall vegetation of the Qinghai-Tibet Plateau increased obviously, but their fluctuation range and change rate were significantly different. (3) The overall vegetation improvement in the Qinghai-Tibet Plateau was primarily dominated by alpine steppe and alpine meadow, while the degradation was primarily dominated by alpine meadow. (4) The responses between the growing season NDVI and climatic factors in the alpine meadow, alpine steppe and the overall vegetation of the Qinghai-Tibet Plateau had great spatial heterogeneity in the Qinghai-Tibet Plateau. These findings provide evidence towards understanding the characteristics of the different vegetation types in the Qinghai-Tibet Plateau and their spatial differences in response to climate change.
Highlights
VQTP all show parabolic shapes that are low on both sides and high in the middle, reflecting the changing rules of each normalized difference vegetation index (NDVI) curve over different periods of a year
Of the alpine steppe (AS) and VQTP was in late September (273 d), half a month earlier than that of the alpine meadow (AM), which was consistent with the field observation results
The length of the growing season (LGS) of the AS and VQTP were significantly shorter than that of the AM. It can be observed from the variation curves of the NDVI in the AM, AS and VQTP that the NDVI of VQTP was greater than that of AM in the non-growing season (Figure 3), while the NDVI of AM was greater than that of VQTP in the growing season
Summary
As an important part of the global terrestrial ecosystem, vegetation plays an important role in the global material and energy cycles, carbon balance regulation and maintenance of climate stability [1,2,3,4]. Vegetation is the natural link between soil, atmosphere and water, and is both affected by and positively responsive to climate change [5,6,7,8]. In the context of global climate change, vegetation change has attracted more attention. Vegetation dynamics affect global environmental evolution, and the study of surface vegetation cover has become a popular field of global change research. The vegetation-climate response is of great practical significance to studying the relationship
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