On the vulnerability of oasis forest to changing environmental conditions: perspectives from tree rings |
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Authors: | Qi-Bin Zhang Zongshan Li Puxing Liu Shengchun Xiao |
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Affiliation: | (1) State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, 20 Nanxincun, Xiangshan, Haidian District, 100093 Beijing, China;(2) Department of Geography, Northwest Normal University, 730070 Lanzhou, China;(3) Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, 730000 Lanzhou, China |
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Abstract: | In water-limited regions, oases are important localities for maintaining ecological biodiversity and supporting social and economic development. For oases situated by the side of rivers, variability of streamflow is often considered as a dominant factor influencing the vulnerability of oases forest, whereas other factors receive much less attention. Here we argue that ecological and hydrological processes creating spatial habitat heterogeneity and particularly the change of habitat structure through time are critical aspects when assessing vulnerability of oasis forest. This is demonstrated by dendroecological studies of a dynamic landscape in Ejina Oasis in the lower reach of Heihe River, the second largest inland river in China. Our results show that radial growth of euphrates poplar trees in Ejina Oasis did not follow the variation of streamflow coming from the middle reach, and the poplar tree-ring growth did not change in the same way from one site to the other. An index of multi-directional change (MDCi) is defined from tree-ring data to describe the change in spatial habitats through time. We propose that the decreasing trend of MDCi indices since the 1950s is related to persistently increasing human activities, whereas high-frequency variability in MDCi indices is related to frequent and strong local disturbances such as windstorms as well as human activities that directly cause changes in streamflow. The results obtained from this study have potentially broad implications for identifying dryland ecosystems that are at risk or susceptible to change, and for making spatially explicit decisions for rational utilization of water resources. |
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