Climate-ecosystem interactions on East Asian steppes: An analysis of vegetation responses to climate variability with remote sensing data.

摘要

The Mongolian steppes are known for their variable climatic patterns and diverse land use practices. Recent studies show that northeast Asia has had one of the highest warming signals on the planet over the past 20 years. The center of the warming zone appears to lie just southeast of Lake Baikal, putting the dryland of the Mongolian steppe near the center of this hotspot. A question that this study investigates is whether the ecosystems residing in this region responded to these changes? If so, does the response to this warming vary across different land cover type? How does the boundary of the Gobi desert in central Asia shift annually over the study period? Does variation in the land use intensity and practice affect the response to the climate changes?; In this study, I present evidence for a changing onset of green-up of the grasslands of eastern Mongolian steppes between 1982–1990, based on analyses of satellited-sensed normalized difference vegetation index (NDVI) and ground-based climate data. To accurately estimate the onset date from time-series NDVI data, an enhanced simple approach is developed to investigate the relationship between climate and onset of green-up over the study period. The results of this research show that timing of onset of green-up varies greatly across the ecosystems in the Mongolian steppe, corresponding to the climatic gradient in this region. During the study period, significant change in date of onset were observed with trend toward an earlier trend for the taiga forest beginning appropriately 50°N, while late trend of onset date was observed for areas of the desert steppe along the boundary of the Gobi Desert. Statistical analyses show that water availability is the major factor controlling the onset date in the grasslands of the eastern Mongolian Steppe. Analysis of the ecosystem variability based on the onset changes indicates that the typical steppe bear the desert steppe ecotone was undergoing ecosystem change over the study period. Annual shifts of the Gobi Desert boundary varies with different land use practices. The results of this research suggest that a climate induced decrease in growing season for the drylands of central Asia.