再议绿洲－沙漠过渡带——以策勒绿洲－沙漠过渡带为例

 被长期质疑的绿洲－荒漠过渡带在不断观测和丰富积累的基础上让我们有了一个完整的认识。以策勒绿洲为例对其进行剖析，作为绿洲－荒漠过渡带的一种典型类型，绿洲－沙漠过渡带可以界定为自绿洲边缘（人工防护体系或天然稀疏灌木林边界）到植被盖度为20%～25%的固定－半固定沙地为外缘边界（绿洲与流动沙漠之间）的荒漠地带。过渡带的内缘边界为绿洲外缘的人工防护体系，包括防风阻沙林带或天然稀疏灌木林。过渡带形成是因为从绿洲到外部荒漠存在水热环境因子的梯度变化，导致植被、土壤、地貌等综合景观展现出过渡特征，其组成与结构模式为：由绿洲向沙漠方向，稀疏灌木林（或边缘防护林体系）地－缓起伏灌草沉沙地－起伏灌丛沙堆和高起伏灌丛沙堆地。过渡带是乡土动植物重要的保留与保护地，是绿洲与沙漠间能流物流输送交换的缓冲带、绿洲的天然生态屏障，对地貌、土壤以及植被具有保护功能，且具有重要的固碳作用。

A Discussion on the transitional zone from oasis to sandy desert:a case study at Cele Oasis

A complete understanding of the transitional zone from oasis to desert was achieved，which had been long-term disputed，based on the abundent accumulation from continuous observation．Cele oasis is chosed as an example to analysis the ecotone from oasis to desert．As a typical type of transitional zone from oasis to desert，the Transitional Zone from Oasis to Sandy Desert can be defined as the desert zone from the edge of oasis(border of artificial protection system or natural sparse shrubs ) to fixed or semi-fixed sandy ground with the vegatation cover between 20%～25% on the outer edge between oasis and mobile desert. The inner boundary of the transitional zone is the artificial protection system on the periphery of oasis，including shelterbelt defending wind and sand or natural sparse shrubbery. The formation of transitional zone is due to the gradient difference of environment factors such as water and temperature that exist from oasis to the outer desert，leading to the transitional feature of the integrated landscape that showed by vegetation，soil and geomorphology，etc. Its composition and structure pattern is sparse shrubs (or shelterbelt system on the edge)-gentle relief ground with bushes and herbs where sand settled-relief ground with bush-herb cones and high relief ground with bush-herb cones in the direction from oasis to desert. The transitional zone is an important region to be retained and protected for native flora and fauna，a buffer zone where energy and material can be transported and exchanged between oasis and desert，and a natural ecological barrier for oasis. It has a protective function on topography，soil and vegetation，and plays an important role in carbon sequestration．