2001—2010年策勒绿洲-沙漠过渡带的变化及其成因

Change of the Oasis-desert Ecotone and Its Causes in Qira County during the Period of 2001- 2010

通过分析多年的NDVI,探讨策勒绿洲-沙漠过渡带的空间结构变化,并结合同期自然环境和人为活动情况进行讨论。结果表明:①过渡带植被变化总体上受地下水位控制,植被由绿洲向沙漠梯度递减;其内部植被覆盖区域与裸沙地并存,植被分布呈斑块状。根据过渡带NDVI的变化,将过渡带分为单向渐变型、双向渐变型和突变型过渡带。②2001—2010年策勒绿洲-沙漠过渡带边界变化剧烈,过渡带内边界主要受控于人为活动;过渡带外边界主要受控于自然因素。③虽然绿洲地下水受到持续过度开采,绿洲-沙漠过渡带不断被开垦成为耕地,但是由于封育保护,2001—2010年过渡带植被略有改善,基本上保持其自身的稳定。④策勒绿洲-沙漠过渡带NDVI变化趋势与年降水量的变化趋势相一致,但变化幅度相差较大。

In this paper, the variation of the Normalized Difference Vegetation Index （NDVI） in the oasis-desert ecotone in Qira County, Xinjiang during the period from the year 2001 to 2010 was analyzed so as to understand the variation of spatial structure of the oasis-desert ecotone. Moreover, the effects of natural environment and human activities on the variation ofNDVlwere discussed. The results are as follows： （1） In general, the vegetation coverage decreased gradually from the oasis to the desert. Groundwater level was the most important factor affecting the varia- tion of vegetation in the oasis-desert ecotone in Qira County. The variation of vegetation near the oasis was higher than that far away from the oasis, because the zone near the oasis was affected by irrigation water, and such effect was decreased with the increase of distance away from the oasis. In the oasis-desert ecotone, the distribution of veg- etation is patchy. There were some mobile or semi-mobile dunes among the vegetation patches, and the vegetation coverage was extremely low. Based on the variation of vegetation coverage, the oasis-desert ecotone was divided into three types, i. e. , the unidirectional graded type, bidirectional graded type and mutant type; （2） There was a rapid shift of the oasis-desert boundary during the period from 2001 to 2010, and such shift was mainly affected by human activities. Boundaries of the desert and the oasis-desert ecotone were far away from the Qira Oasis, the impact of human activities on them was low, and the outer boundary was mainly affected by natural factors ; （3） Although there was the excessive exploitation of groundwater and land reclamation in the ecotone, vegetation in the ecotone was im- proved to some extent, its stability was basically maintained, and its coverage was slightly increased because of closing the hillsides for facilitating afforestation and grass planting; （4） Variation of vegetation coverage in the eco- tone was consistent with the change of annual precipitation. There was a poor correlation between annual tempera- ture and NDVI. Vegetation in the ecotone was also impacted by aeolian sand disasters.