Abstract
The Tibetan Plateau, the highest plateau in the world, has experienced strong climate warming during the last few decades. The greater increase of temperature at higher elevations may have strong impacts on the vertical movement of vegetation activities on the plateau. Although satellite-based observations have explored this issue, these observations were normally provided by the coarse satellite data with a spatial resolution of more than hundreds of meters (e.g., GIMMS and MODIS), which could lead to serious mixed-pixel effects in the analyses. In this study, we employed the medium-spatial-resolution Landsat NDVI data (30 m) during 1990–2019 and investigated the relationship between temperature and the elevation-dependent vegetation changes in six mountainous regions on the Tibetan Plateau. Particularly, we focused on the elevational movement of the vegetation greenness isoline to clarify whether the vegetation greenness isoline moves upward during the past three decades because of climate warming. Results show that vegetation greening occurred in all six mountainous regions during the last three decades. Increasing temperatures caused the upward movement of greenness isoline at the middle and high elevations (>4000 m) but led to the downward movement at lower elevations for the six mountainous regions except for Nyainqentanglha. Furthermore, the temperature sensitivity of greenness isoline movement changes from the positive value to negative value by decreasing elevations, suggesting that vegetation growth on the plateau is strongly regulated by other factors such as water availability. As a result, the greenness isoline showed upward movement with the increase of temperature for about 59% pixels. Moreover, the greenness isoline movement increased with the slope angles over the six mountainous regions, suggesting the influence of terrain effects on the vegetation activities. Our analyses improve understandings of the diverse response of elevation-dependent vegetation activities on the Tibetan Plateau.
Highlights
Climate warming has been observed around the globe, and the increase of air temperature has been greater at high elevations than that at low elevations during the last few decades [1]
We reported the relationship between temperature and the elevation-dependent vegetation activities for six mountainous regions on the Tibetan Plateau by using the mediumspatial-resolution Landsat normalized difference vegetation index (NDVI) data (30 m) from 1990 to 2019
We found a general trend of vegetation greening during the past three decades in all the six mountainous regions, and there was a greater greening trend in the lower elevation bins between 4000 and 5000 m
Summary
Climate warming has been observed around the globe, and the increase of air temperature has been greater at high elevations than that at low elevations during the last few decades [1]. Temperature has been recognized as a principal factor determining species’ distribution [2], community compositions [3], and vegetation greenness [4]. Under the background of global warming, the phenomenon of vegetation greening has been found in Europe [5,6], China [7], and India [8], whereas vegetation browning has been observed in northern North America [9] and Southeast Asia [10]. It is important to understand the diverse responses of vegetation greenness to climate warming. Such investigations are more important in mountain areas because elevation-dependent warming may lead to elevation-dependent vegetation changes and further affect the shifts in species ranges and the composition of plant communities [2,3]
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