Long-term changes of Tamarix-vegetation in the oasis-desert ecotone and its driving factors: implication for dryland management

The Oasis-desert ecotone plays an important role in ensuring oasis ecological security. This study was to determine the main factors on the changes of desert vegetation in the oasis-desert ecotone, and to understand the mechanisms of the long-term changes. During past 50 years, the dominant plant species of Tamarix-vegetation in the Minqin oasis-desert ecotone changed from mesophytes to xerophytes and finally to super-xerophytes. The vegetative distribution area (belt width of Tamarix-vegetation between desert and oasis) markedly decreased from 1,000 m past to 30 m current. The coverage of Tamarix bushes reduced from 25 to 7%. The importance value (IV) of the bushes fell from 0.957 to 0.752, and Simpson index decreased from 0.702 in 1959-0.589 in 1992, and then increased to 0.712 in 2002. These changes in vegetation were closely related with the rapid decrease of groundwater table and the reduction of soil moisture due to unsustainable use of water resources for expanded agriculture development. These findings suggested that the change of Tamarix-vegetation in the oasis-desert ecotone was a process of vegetation degradation and concurrent desertification. The maintaining of stable groundwater and Tamarix-vegetation is a vital prerequisite for dryland management, especially, conserving ecological health of oasis-desert systems.