| 其他摘要 | Guizhou province is located in the center of a widespread karst region in southwest of China, which is the largest one in the world. The province is undergoing the process of rocky desertification, which is apparent and deteriorating in recent years, and furthermore becomes an obstacle to the development of local economy and improvement of local citizen's living standards. It is well known that detailed study on the mechanism of rocky desertification lays the bases to harness it, however, the present study is mainly focused on qualitative study and is obviously lacking in quantitative and spatial one. Due to the various physiognomy in this province, the extent and leading factors of rocky desertification are different from one district to another, and the differences should be taken into consideration when dealt with rocky desertification related problems. This paper studied various effect factors including lithology, types of physiognomy, gradient, precipitation and soil type, in rocky desertification process in Guizhou by using geographic information systems (GIS) as an instrument. Detailed analysis is made by spatially superimposing above-mentioned factors as a layer onto the map of rocky desertification within the GIS method, further analysis also made on the spatial distribution of those factors and main driving forces in different districts. The following conclusions are drawn from the analysis. I .The correlation of rocky desertification and lithology is obvious in reason that lithology in the karst region is mainly of limestone and the extent of desertification is higher than that of dolomite. Rocky desertification occurred more frequently in limestone-continuously-distributed area than that of others, and mostly in moderate and severe degree; this is also true to dolomite-continuously-distributed area. It can be drawn that usually pure carbonate lays bases for the occurrence of rocky desertification. II. The incised depth of- physiognomy has made a great impact on the progressing of rocky desertification, which is a conclusion from the analysis of the correlation between physiognomy types and the extent of desertification. The deeper the physiognomy is incised, the more frequently desertification occurs; the more the relative height is, the more serious impact of incised depth on the desertification is made. Therefore, the highest possibility of the occurrence of rocky desertification is in those areas combined of conic hills and depressions. As to the impact of gradient on rock desertification, it is evident that when the gradient of a slope is bigger than 25 degree, the occurrence possibilities of the desertification at low or moderate or strong intensity are all very high. Meanwhile, it is mainly at low or moderate intensity when the gradient is smaller than 18 degree. The precipitation of an area also plays a role in rocky desertification, especially when it is more than 1200mm. Over that amount, the more the precipitation there is, the more severe desertification there will be. The intensity is mainly low or moderate when the amount is less than 1100mm. The rocky desertification of three levels of intensity is most likely to occur in rocky soil and limestone soil among all different soil types, while the low or moderate intensity ones occur in yellow soil and regosol. The moderate or severe rocky desertification is also very likely to occur in yellow-blown soil; at the same time, the occurrence possibility of moderate desertification in the area with alpine meadow soil is high. III. When analyzed the main leading forces in the progress of rocky desertification in different types of physiognomy in karst regions, it can be concluded that the formation of rocky desertification is based on the fragile geological environments, which are intensively disturbed by human activities. On the one hand, a large-scale continuously distributed carbonate is dominant in the progress of desertification, which also decides the soil depth and distribution of soil type; on the other hand, the gravity potential energy determined by physiognomy type and the hydrodynamic condition determined by precipitation are dominating initial force in rocky desertification, meanwhile it is also accelerated and magnified by human activities. IV. As a conclusion drawn from analyzing those dominating factors in the process in each district of the province, lithology and human activities are the most important factors in the desertification process. The carbonate's continuous distribution in lithology, especially limestone, makes an evident impact on desertification; the scale of desertification proportionate positively to a large scale distribution of limestone and an area of steep slope cultivation, such as Dafang and Panxian county and southern and south-west part of the province. Meanwhile, the extent of desertification is relatively low in an area of limestone-distributed (but serious compared to other districts), when affected by weak human activities, such as plateau region of Weining county; contrarily, an area with small distribution even disturbed by insensitive human activities is of low or moderate extent in desertification, such as those middle and northern part mountainous region in the province. As to an area mainly of dolomite distribution, the impact of lithology on the desertification is also evident, but to a milder or moderate,desertification, such as in middle part and eastern hilly regions of the province. On the other hand, in an area mainly of carbonate interbedded with clastic rock, take northern part of the province as an example, the desertification hardly progressed to a severe extent, which is mostly affected by human activities. V. Desertification at low extent is obviously affected by many integrated factors, while a severe one is by a few factors. Seen from the impact of territorial differences on desertification, in Weining plateau, Dafang county and Panxian county, the areas of the first terrace, also the largest continuous-limestone-distributed areas, desertification process at various extents is mainly controlled by the lithology and slightly by human activities; as to the second terrace areas such as the south and west-south part of the province, the desertification is collectively controlled by the both factors, but human activities play a more obvious role in the process. At the same time, in the middle part and the third terrace such as those eastern hilly areas of the province, which is widely distributed by continuous dolomite, the desertification is greatly affected by the lithology; but rarely developed to the severe extent. |
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