五十年代以来毛乌素沙地荒漠化扩展及其原因

THE DEVELOPING SITUATI0N AND EXPANDING CAUSES OF DESERTIFICATION IN MU US SANDY LAND SINCE TIIE 1950s

本文在毛乌素沙地景观分类、制图及景观动态研究的基础上，分析了50年代以来毛乌素沙地荒漠化发展状况及其时空特征，并对其扩展原因进行了分析和探讨。结果表明，50年代以来，该地区荒漠化整体上处于迅速扩展之中，只是某些局部地方植被得到一定程度的恢复；荒漠化扩展存在明显的空间和时间差异：西北部纯牧区扩展速度远远高于东部和南部半农半牧地区，70年代末至90年代初扩展速度远远低于50年代末至70年代末；荒漠化的迅速扩展主要是由于不合理的人类活动造成的，气候波动也有一定影响。

As a key area on desertification researeh in China, the Mu Us Sandy Land is located in the transihon zone of the Ordos Plateau and the Loess Plateau, with an area of abou 4 ×104Km2. The sand land is situated in the west of the ecotone of faedng and grazing in northem China, having a grazing area in the northwest and a transihon area of agriculture and ndning industry in the east and the southast. Based on the landscape classification and cartography and the researeh on landscape dynamics, the situation, the spatial and temporal characterishcs of the desertification development and the expanding causes of desertification after the 1950s in the Mu Us Sandy Land were analyzed. (1) From the 1950s t0 the 1990s, desenification expanded raPidly as a whole,while the vegetation in some local regions was restored in the Mu Us Sandy Land.The shifting and semi-fixing sandy land made a total extension of 94O 217.4hm2, which takes up 24.84% of the area of the Mu Us Sand Lan, at a growth rate of 60.37%and a increasing velocity of 26 863.4hm2 per year As the fastest spreedng one, the shifting sandy land had develoPed at a velocity of 15 454. 7hm2 per year, the semi-fixing sandy land had increased at a velocity of 11 408.6hm2 per year and the flxing sandy land had decreased at a velocity of l6 346.6hm per year. (2) The obvious spatial and temporal variations in the development of desertification from the 1950s were discovered. Spatially, the regions where the fixing sandy land consideraby decreased, and the send-fixing and shifting sandy land obviously increased are mainly located in the west and the north, while the regionswhere the fixing sandy land increased, and the send-fixing and shifting sandy land increased are dispersed in the east and the south. The developing speed of desertification in the middle and the northwest pure grazing land is much higher than that in the east and the south where there are partially farming and grazing areas.Temporally, the developing speed of desertification from the fare 1970s is apparently lower than that from the fare 1950s to the fare 1970s, and desenified lands in some regions show a negative growth. (3) Desertification seems to result from natural and artificial processes. The Mu Us Sandy Land is located in the send-arid area and the ecotone of farming and grazing, thus the fragility of ecosystem and the aridity of climate are the prerequisite of the occurrence and development of desertification in mis area. In the ecotone of farming and grazing, human activities play an important role in the modem process of desertification because of the very high population density and the backward mode of production. The rapid developing of desertification of the Mu Us Sandy Land since the 1950s is mainly provoked by excessive and unreasonable human activities, while the climate fluctuation is responsible to a certain degree for the development of desertification. The large-scale reclamation and the serious overgrazing produced by rapid increasing in livestock and so on are the main causes of the rapid spreading of desertification in the middle and the northwest of the Mu Us Sandy Land, as well as the principal reasons for the fast expanding of desertification of the Mu Us Sandy Land from the late 1950s to the late 1970s. (4) Working out a reasonable land use planning is a basic measure to combat desertification. According to natural conditions, the heat can satisfy the needs of the growth of crops in this area, but the aridity is frequent. and the output of crops is very unsteady because of a small amount of precipitation. In addition, the land is covered with sand, the soil is mainly sandy and the wind erosion and desenization is very serious, and the majority of mis area is good for grazing but not farming.Grazing should be stressed on in the middle and the northwest of this area, and grazing and firing should all be paid attention to in the east and the south of it. As a whole, the comprehensive development of agriculture, forestry and animal husbandry is the guiding principle of economy in the M