Modern Distribution Changes In The Upper Boundary Of Alpine Meadow Belt In The Qilian Mountains With Climate Warming

Alpine meadow,as the typical type of the vertical vegetation spectrum of the Tibetan Plateau,is widely distributed in the high altitudes in the Qilian Mountains.It is more sensitive to climate change.Due to constraints of data and workload,the studies were mainly based on a coarse-resolution remote sensing monitoring at a large scale.And rare studies focused on changes of vegetation dynamic distribution and vegetation belt shifts based on high temporal and spatial resolution data.In this study,we focused on the dynamic changes and spatial differences of the upper boundary of alpine meadow in the Qilian Mountains with the warming climate from the1990s to the 2010s.The distribution changes in the upper boundary of alpine meadow belt in the Qilian Mountains during the past three decades were obtained from the thematic mapper and the operational land imager remote sensing digital images by using decision tree classification and artificial visual interpretation.The results indicated that the dynamic changes in the upper boundary of alpine meadow mainly distributed in the transitional zone between the alpine meadow belt and the alpine desert belt.The upper boundary of alpine meadow expanded gradually in the Qilian Mountains with climate warming in the past 30 years.Alpine meadow expanded with a rate of approximately 348.3 km~2/a in the transition zone,and the amplitude of expanded changes was increased in turn from the eastern section to the west section.However,it observed to shrank in some local sections.The above phenomenon lead to the upper boundary of alpine meadow moving upwards at a significant velocity of 15m/decade.The vertical zonal process modulated by topography-induced difference in local hydrothermal conditions.Thus,the distribution changes in the upper boundary of alpine meadow belt mainly concentrated in its lower part.Because of the spatial difference of hydrothermal background,it was greater in the sunny slope than that of the shady slope in the eastern and middle Qilian Mountains,while that was the opposite in the western Qilian Mountains.Annual maximum NDVI in the transition zone increased significantly and showed a positive correlation with significantly increasing temperature than weakly increasing precipitation during 1990-2015.The above results indicated the climate change affected the dynamic changes and spatial differences of the upper boundary of alpine meadow in the Qilian Mountains,and climate warming was the main factor,which facilitated the upper boundary of alpine meadow by releasing the low temperature limitation on the vegetation growth.