Response of Tree Recruitment to Climatic Variability in the Alpine Treeline Ecotone of the Qilian Mountains, Northwestern China

There is ample evidence of the ecological impacts of climate change, and treeline ecotones resulting from environmental gradients are a particularly sensitive indicator of climate change. However, the response of alpine treelines to climatic variability in semiarid mountain regions is not clearly understood. In this study, we analyzed the impacts of temperature and precipitation on tree recruitment in treeline ecotones in the Qilian Mountains of northwestern China from 1957 to 2007. The results showed that climate warming has increased tree recruitment. Tree recruitment was significantly positively correlated with the mean growing season temperature and with the mean minimum temperature in June and in winter. Treeline elevation shifted upward by 5.7 to 13.6 m from 1907 to 1957 and by 6.1 to 10.4 m from 1957 to 1980, but did not appear to change after 1980. Our results suggest that temperature controls treeline dynamics more strongly than precipitation in the Qilian Mountains, and support the hypothesis that treeline dynamics are strongly linked to growing season and winter temperatures. FOR. SCI. 59 (1):118-126.