宁夏盐池植被盖度变化及影响因子

Research on change of vegetation fraction and its effect factors in Yanchi county,Ningxia Hui Autonomous Region

选取1989、1999和2003年8月的TM遥感影像3景,基于归一化植被指数NDVI和植被覆盖度遥感定量模型,提取了植被覆盖等级图。通过对3时段不同植被盖度类型比较分析得出:盐池县植被盖度变化趋势明显,尤其是低盖度植被和中高盖度植被,2003年较1989年变化幅度分别为64.62%和72.04%。出现植被好转的原因主要有2个方面,一是气候因素中的降雨和蒸发,二是荒漠化治理措施如退耕还林、全县禁牧封育等,而这些影响因素中尤其以降水和蒸发为主导。相关分析结果表明:盐池县植被覆盖度同降水、蒸发之间表现出较高的相关性;中等盖度主要以半固定沙地、退化土地、退化草场为主,2003年占全县总面积的70.65%,是盐池县的主要植被覆盖类型,该类型面积大,生态脆弱,是未来荒漠化治理的重点区域。

Selecting 3 sceneries of Landsat TM image shot in Aug 1989, Aug 1999 and Aug 2003 in Yanchi County, Ningxia Hui Autonomous and basing on NDVI and the quantificational model of remote sensing, the grade maps of vegetation fraction were extracted. Through contrasting and analyzing the vegetation fraction of different grade in 3 phases, the result show that the variable tendency of the vegetation fraction is obvious, especially the vegetation of low and medium-high coverage. From 1989 to 2003 the area of the low and medium-high coverage vegetation increasing sharply 64.62% and 72.04%. From another angle, the change show that the reverse motion of desertification occurred in the period from 1989 to 2003 in Yanchi County. There are two reasons for vegetation improvement in Yanchi County, one is climate factor such as rainfall and evaporation, and another is artificial factor such as converting cropland to forests, closing and fencing and discontinuing farming and letting go out of cultivation, but the most important effect factors are rainfall and evaporation. The results of correlation analysis show that the correlation coefficient between the vegetation fraction and rainfall, evaporation are very high in Yanchi. The land use types of medium vegetation fraction mainly include semi-fixed sand land, deteriorated land and deteriorated grassland, it is the main types of vegetation fraction, and area of this type was 70.65 % of total area in Yanchi in 2003. The area of medium vegetation fraction is large, its ecological structure is very fragile and it is the stress area of desertification prevention and cure in the future.