Study On Dynamic Changes Of The Vegetation Cover Of The Three Gorges Reservoir Area In 1988～2007

Land use/land cover change (LUCC) play an important role in the study of global environment change and sustainable development. Remote sensing (RS) has become the main technology in monitoring land use/cover change, due to its quick, dynamic and various advantages. The vegetation cover is the most main part of the land covers, and now it has become the hot that the general experts study. In Basing on remote sensing images, we extracted the information of vegetation cover change and analysed the dynamic change in the Three Gorges Reservoir Area from 1988 to 2007. In this paper, the Unsupervised Classfication was used to classify the vegetation cover types, and some mathematic models were applied to study the spatio-temporal changes of vegetation cover during the 20 years in the Three Gorges Reservoir Area, such as vegetation cover type transferring matrix model, land use dynamic model and land use degree model. At last, the driving forces were analyzed based on the vegetation cover change. The main results showed:1. By using the Unsupervised Classfication method to extract the information of vegetation cover change in the Three Gorges Reservoir Area from 1988 to 2007, the result showed that the overall accuracy is only about 85%. It is not fit for strict study.2. The area of the vegetation cover decreased continuously during the past 20 years in the Three Gorges Reservoir Area, but the rate had a slower decrease. The area of the arbor forset (including conifer forest, broadleaved forest and conifer broadleaved forest) had reduced and the change quantity was very large, however, the area of the shrubbery had increased constantly. It was indicated that the vegetation in the Three Gorges Reservoir Area had been destroyed, especially the arbor forest, and the ecological environment declined. So the duty to the forest protection and the vegetation restore was still arduous.3. With the help of area transfer matrix of vegetation cover change, the interactive transfer relation of four types vegetation cover was also analyzed. The results showed that the main transfer direction during the period of 1988-2000 was the mutual transfer in various vegetations cover type and between the vegetation cover types and the farming land. Conifer forest transferred mainly into farming land and shrubbery, broadleaved forest into conifer forest mainly, conifer broadleaved forest into farming land mainly, and shrubbery into farming land mainly. The main tendency during 2000-2007 was the mutual transfer only between the vegetation cover types and the farming land. The rate of the transfer of conifer forest,broadleaved forest,conifer broadleaved forest and shrubbery into farming land were 8.27%, 60.33%, 47.2% and 29.11% respectively; and the rate of contribution were 3.92%, 10.15%, 1.04% and 13.18% respectively. And it was also found that the transfer rate and contribution rate of the vegetation cover type turning into the residential land in 2000-2007 had been higher than in 1988-2000.4. By using the land cover indexes of land use dynamic,trend and state of land use change to analyse the rate and trend of the vegetation cover change, the results showed that the single vegetation cover type transformed frequently and the variation rate was quick during 2000-2007 years in the Three Gorges Reservoir Area. In totally, the vegetation cover change had remained the balance state because of the mutual transfer between the different vegetation cover types.5. Through calculating the land use degree index in 1988, 2000 and 2007 of the Three Gorges Reservoir Area, it was discovered that the total land use degree index of Three Gorges Reservoir Area was above the medium level and higher than the national average level. At the same time, the study showed that the tendency of the land use degree in the Three Gorges Reservoir Area increased obviously. Then four forces driving the vegetation cover change in the Three Gorges Reservoir Area had been qualitatively described. They were the Three Gorges Project, national policy, economic development and urbanized construction and population perssure respectively.