民勤绿洲边缘柽柳荒漠林的时空变化及其驱动因素

Spatial-Temporal Variation and its Driving Factors of Tamarix Forestry at Edge of Minqin Oasis

柽柳属植物不仅是耐盐碱、耐干旱植物，同时也是最优良的防风固沙植物之一，曾在改善和维持民勤沙区生态环境中发挥了重要作用。在近40多年来，伴随民勤环境旱化，绿洲边缘柽柳荒漠林呈现出退化过程，并表现出旱生、超旱生植物增加，林带变窄，柽柳高度降低，柽柳种群及其群落盖度降低和防风固沙功能减弱等特征。目前，坝区、泉山区和湖区柽柳荒漠林均出现退化，其中坝区退化最为严重，残余宽度仅有30～75m，依靠农田灌溉外溢水生存，是民勤绿洲边缘柽柳荒漠林发展的最终阶段。分析柽柳荒漠林时空变化的驱动因素，认为地表水消失是时空变化的诱导因素，地下水位下降和林地土壤水分减少是时空变化的主导因素，在地下水位下降到10m的临界水位以下之前，地下水位起到主导作用；而下降到10m以下之后，土壤水分起到主导作用。

Tamarix is not only a salt-resisting and drought-tolerating tree, but also a excellent wind-breaking and sand-fixing plant, which has ever played significant role in rehabilitating and improving the desert ecological environment of Minqin county. Tamarix ramosissima Ledeb forestry is the main Tamarix forestry at edge of Minqin oasis, which has occurred degradation along with the environment getting drought in recent 40 years. In Tamarix ramosissima Ledeb forestry, the number of xerophytes and super-xerophytes increased, the width of forestry decreased and the coverage of Tamarix ramosissima Ledeb and its community all reduced. At present, even the Tamarix ramosissima Ledeb forestry in Dam area, Spring area and Lake area all took place certain degradation. Especially, the remained width of Tamarix ramosissima Ledeb forestry in Dam area are 30-75 meters, and the forestry only live on the seeping water from farmland. As for the driving factors for spatial-temporal variation of Tamarix ramosissima Ledeb forestry, we found out that surface water vanishing is the inducing factor, groundwater table lowering and soil moisture reducing are the dominant factors.