古尔班通古特沙漠生物结皮的分布特征

新疆古尔班通古特沙漠是我国最大的固定和半固定沙漠，其间广泛发育着以地衣植物为主的生物结皮，是除种子植物以外的固定沙面的重要生物因子。研究表明，选择适当的时段，应用遥感技术并结合地面调查来研究沙漠生物结皮的空间分布格局是可行的，遥感制图与地面调查的结果基本一致。该沙漠南部是生物结皮最为丰富的区域，各种类型的生物结皮均有充分发育，呈连续分布，但其分布模式向北、向西和向东变得破碎。通过统计生物结皮像元的面积，得到生物结皮覆盖率超过33％的像元面积占研究区总面积的28．7％。生物结皮的分布对地貌部位有较强的选择性，生物结皮的不同发育阶段种类组成亦有较大的差别。

A comparison between different ecological de-farming modes in the loess hilly-gully region in China

The biological soil crust, especially lichen crust, was developed well in Gurbantunggut Desert, the largest fixed and semi-fixed sandy desert in China. Together with vascular plant, biological soil crust becomes an important factors relating to sandy surface fixation. In this study, the reflectance of lichen-dominated biological soil crust was measured and used to develop a new index for detecting and mapping the crust distribution. We examined the feasibility of the index for Landsat ETM sensor by using radiative transfer model (6S) to simulate different coverage of the crust under different atmospheric conditions. Then, we applied the new index to Landsat ETM data of the Gurbantunggut desert to map the spatial distribution patterns of biological soil crust in Gurbantunggut Desert. The results, combined with field investigations, showed that the biological soil crust was mainly distributed in southern part of this desert, but became gradually sparse toward northern, western and eastern parts of this desert. The coverage of biological soil crust was estimated up to 28.7%. The species composition of biological soil crust varies according to different positions of sand dunes and different developmental stages of biological crust.