Application Of RS, GIS And GPS In Survey Of Returning Farmland To Forest Or Grass Land And In The Making Decision In The Dry Valleys Of The Western Sichuan, China

This paper focused on the key problems and mainly difficulties of returning farmland to forest or grass land which arose from crucial and significant region in the dry valleys of the west of Sichuan province. It was introduced that how to use the "3S" (RS,GIS & GPS) technology to survey returning farmland to forest or grass land and how to make decision of returning farmland to forest or grass land with "3S" technology and forest ecology principle. It was shown that the "3S" technology and ecology principle were suitable to survey and making decision of returning farmland to forest or grass land in studied region. Some methods were developed that how to use remote sensing image processing and information extraction to survey returning farmland to forest or grass land in the dry valley region where farmland is of a small percentage (about 0.6%) and cracked. It was get the conclusion that returning farmland to forest or grass land is a longtime and dynamic process and should be done step by step according to the farmland's different roles in ecology environment. It was not only a spatial decision but also a temporal decision in that all the elements such as terrain, ecology, soil fertility, forest and so on, are considered. It was introduced that how to use "3S" to making decision on Forest Site Condition and how to return farmland to forest according to the ecology principle. Some important points of the studied result as followed as:(1) The methods were developed that how to use remote sensing imaging technology to survey the result of returning farmland to forest or grass land in the dry valley region where farmland is of a small percentage (about 0.6%) and cracked. In the studied region, area of cultivated land and the proportions of cultivated land area were relative smallest to other that. Because the area of the cultivated lands is squeal to 48000 pixels in Landsat-6 TM image, the area of cultivated land to be used to return to forest is only a small part of cultivated land. What's more, the reforest lands are cracked and only distribute along the river, and the most area of the reforest lands are smaller than one hectare. Another reason is that the atmospheric drought of dry valleys leads to the reforest tree shorter than 40 centimeter. Because of the small, cracked reforest lands and the short reforest trees; it is very difficult to survey the situation of the reforest. On the base of investigation on the spot and remote sensing image processing as well as making use of different kinds of4vector graph, the author puts forward a method which is suitable to survey and making decision of returning farmland to forest or grass land in the complicated situation of dry valleys region.(2) The author supposed that the reforest former land is a systematic engineering with a longtime, and is complicated process which should be performed step by step. This viewpoint breaks the tradition ways which only used a rule of ground slope degree bigger than 25 or using difference soil erosion level to make decision. The author suggested that the processes of reforest farm land are a long-time, complicated and dynamic, and it should be considered what the most important things in the reforest processes are. The proportion and position of reforest land should be quantitative analyzed according to the soil fertility, ecological significance and soil erosion level. All of these may help us to determine the rate and distribution of the economic forest and the ecological forest, and the time sequence of returning cultivated land to forest land should be considered too.(3) The applications of ecology rebuilt supported by the "3S" technology were studied based on the knowledge of forestry and ecology. In the paper, it was introduced that how to use the "3S" technology to classify forest site condition, to chose different kinds of tree according to corresponding ecological environment and to attain the rational models of reforest in accordance with the concrete condition. It was put forward that all of us should pay more atte...