The Development Laws Of The Shelterbelt Network And Its Rational Distribution In Coastal Area Of Western Hainan In The Last Hundred Years

The coastal area of western Hainan takes plain, tableland and low mound as its core topography, whose climate is tropical and half arid, soil is barren and ecological environment is fragile. The unreasonable human activity of this area is extremely apt to cause the changes of the ecological environment. The desertification of the southern Dongfang County and the littoral zone of Changjiang county has already become a serious ecological environmental problem. These two areas have been the focal areas manipulated by the Hainan Island coast shelter forest project for many years. Thus, a deep understanding of the characteristics and changing laws of the geographical environment of this district can offer a scientific basis for the regional development and ecological environmental optimization. Regarding the basic principles of disciplines such as geography and ecology as the theoretical foundation, through modern scientific and technical means such as the remote sensing (RS) and geographical information system (GIS), using big scale topographic maps in the rate of 1:50000 of the thirties, 1:25000 of the fifties, 1:50000 of the seventies and materials based on 3 TM image pictures of 1986, 1996, 2003, and with the combination of the field investigation, this dissertation studies the changing characteristics and interactions of the shelterbelt, desertificated land and the cultivated land of the western coastal region of Hainan in the past one hundred years; furthermore, it works on the ecological environment characteristics of the western region of Hainan at the beginning of last century. The result of study shows:1) In the initial stage of last century, the climate of the western region of Hainan was almost similar to the present situation, and the annual precipitation was about 800 mm to 1000 mm. No large stretches of sand ground or flowing sand ground appeared, but when there was strong wind, great danger would be caused. It was covered with more vegetation than nowadays, and there were small patches of forest in the lowland hills where the precipitation condition was slightly better, there were also sporadic trees scattered in other places and near the villages as well. The soil was white and thin with young sand. By means of transformation such as constructing the compost plant ash, the soil would be fit for crops. In the early 20th century, the population of Gan'en county (Dongfang) is 40,000 and Changjiang county around 45,000, so it was the kind of vast and sparsely populated area, and also the district with minimum density of population in Hainan. In this district only little land was utilized and the rate of the cultivated land was low.2) In the recent hundred years, the land for garden plots and building sites has been in a tendency of increasing all the time; Fields spread extremely fast after the 1980s; the change of the shelter forest is in an undulate growing trend on the whole, and a trough appeared in the 1980s.The cultivated land had tended to increase all the time before the 1980s, and the large increase range came to 107.50km~2 in total. Since then, it has been reduced year by year. The whole change course was presented in the shape of an inverted"V".The desertificated land has been reducing since the 1980s. By the year 2000, it has already been reduced to only 35.08km~2 , the minimum level of the history.3) The change of shelter forest and desertification are the main environmental changes of the western region of Hainan. The development laws of shelter forest and the desertification indicate that human activity is the main cause of the change.In the local areas, the danger of desertification has not been dispelled at all. Therefore, greatattention has to be paid to the construction of the shelter forest all the time. The construction of shelter forest should agree with the local conditions. A new shelterbelt pattern with the characteristics of the western Hainan should be set up in accordance with factors such as topography, river, wind condition, the sand condition on the earth's s...