The Dynamic Change Of Soil Erosion And Its Driving Mechanism In North Fujian Province

Taking north Fujian as the study area, by the application of GIS spatial analysis and run-off plots, the assay analyzes the spatial distributing and dynamic change of soil loss in north Fujian Province, probes into the driving mechanism, which will provide decision-making basis for soil conservation activities in north Fujian and ecological security in the upper reaches of Min River.Covering the largest area, with the features of northest latitude, and highest elevation in Fujian province, north Fujian locates in the north part of Fujian province, adjacent to Zhejiang and Jiangxi Provinces, between 117°02'～119°17'E and 26°14'～28°20'N, governing ten cities /districts/counties, that is Yanping, Shaowu, Wuyishan, Jian'ou, Jianyang, Pucheng, Shunchang, Guangze, Songxi, and Zhenhe, with the total area of 26299.42 square kilometer, and total population of 3,040,800. It belongs to medium sub-tropical monsoon climate, with the mountain and hill as main topography. The surface of this area descends from northwest and northeast to southeast, and its water system presents a string of beads densely distribution. Enjoying the features of abundant forest resources, it is one of main forest area in Fujian province, dominated by the manual trees and secondary forest. Red soil holds the trump card in all soil types.By the application of method on the GIS spatial analysis, the assay analyzes the data of soil and water loss of the RS investigations in 1985, 1995, and 2000. The result shows that:①Soil and water loss in north Fujian presents assembling spatial distribution pattern, comparatively concentrating in the resident area located in the upper reaches of streams of Napu, Chongyang, Futun and Songxi;②The main intensity of soil and water loss is listed in the light class;③The soil erosion area descended slowly during 15 years from 1985 to 2000, and the descending range in the later 5 years was larger than the former 10 years;④The soil erosion intensity increases as a whole, increasing during the former 10 years and decreasing in the later 5 years.⑤The dynamic change of soil erosion differs in the different areas of ten counties/cities, of which, soil erosion areas increases in 3 counties/cities (Zhenghe, Shunchang & Jianyang), while decreases in the other 7 counties/cities. Jian'ou City has the largest reduced soil erosion area and Guangze County has the largest decreasing amplitude of soil erosion rate. Among 129 townships, there are 82 townships with the reduced soil erosion area, with the totally reduced area of 48779.60 hm2,1.85% reduced. The other 47 townships have the increased soil erosion area, covering the land area of 19281.60 hm2,0.73% increased.By the application of methods on GIS spatial analysis and run-off plots actual measurement, the assay discusses the driving mechanism of soil and water loss in north Fujian. The result shows that the topography factor with features of high mountain and steep slope will easily result in the soil and water loss in north Fujian, large variable ratio, intensive rainfall, grid-shape runoff with powerful scouring force increase potential force on the soil loss. As one of the main forest area, north Fujian enjoys the advantage of high vegetation coverage rate, which effectively prevents and reduces the soil loss. Among various land use types, forestland has the lowest soil loss rate, of which, broad-leaf forest is listed at the bottom and cash forest on the top for soil loss. Unfortunately, the forest in north Fujian has the degraded trend, lots of natural forest are destroyed and substituted by manual and secondary forest, which has low capacity on soil and water conservation, resulting in the continually extension the soil erosion area followed by the degradation of vegetation system. Moreover, unreasonable mankind activities, such as agricultural exploration in mountainous region and development & construction projects without valid measure of soil and water conservation, will result in the constructive soil and water loss. However, actively taking the reasonable soil and water conservation measures will prevent and decrease soil and water loss.