Forest And Wetland Dynamic Change Research In Yuhang, Zhejiang Province Based On RS

Forest and wetland as two big ecological systems of the earth are regarded as "lung" and "kidneys" of the earth.They are closely related and interdependent and construct a powerful ecological security barrier for the earth.The dynamic changes of them have a certain relation, therefore,only researching one change is not comprehensive.It is an important responsibility of foestry department to Construct and protect forests and wetlands ecosystems, and the dynamic monitoring forests and wetlands is the important content of forest and the wetland protection.Using TM images data of 1994 and 2008, this paper aims at comparing different change detection techniques to assess their effectiveness for detecting changes of forests and wetlands from 1994 to 2008 inYuhang,Zhejiang provice. Following are the conclusions from this study:(1)This paper describes three change detection methods, including the post-classification comparison method,the multitemporal composition classification and the change detection techniques based on pixels.The detection accuracy of post-clsssification method depends on the choice of classification methods. Taking advantage of the approach of texture analysis,this study compares Maximum likelihood classification and decision tree classification and the result shows that the accuracy of the latter is better than the former. Finally, we get change category and change statistical results by overlay analysis. Compared to post-classification comparison method, multitemporal composition classification,which is more reasonable, only requires classification once and reduces the occurrence of the Unrealistic changes. But it is difficult to determinate the change category. Change detection techniques based on pixels mainly use the image difference method and the Change Vector Analysis(CVA), which is difficult to determine the appropriate changing threshold. In this paper, we choose Double Thresholding algorithm based on the Kappa and a new method named Double-Windows Flexible Pace Searching algorithm to determine image segmentation threshold, and select the most accurate change binary image,to classify(2)The changed results show that the area of forest and Wetland were 40146.66 hm2 and 4380.75hm2 in 1994 while there were 41618.97 hm2 and 9680.85 hm2 in 2008. From 1994 to 2008, forest cover was more stable,while wetland coverage area increased significantly. Part of the forest changed into farmland or building lands,changed from farmland. The increase of Wetland is mainly because of farmland transformation.(3) By Riitters Model, Compared to 1994, although the overall forest cover rate in Yuhang District has increased in 2008, forest fragmentation has accelerated due to a decreased proportion of interior forest and an increased proportion of perforated, patch and transitional forests. Perforated forest in 2008 was 7.32 times that of 1994, patch forest was 1.84 times that of 1994 and transitional forest was 1.27 times that of 1994. That human disturbance accelerates forest fragmentation from the 1980s to 2008.According to the analysis of Association Index, Rapid urbanization during 1994 to 2008 is considered to be the main driving force for this deterioration,while the interference of field is a gradual weakening trend.(4)From 1994 to 2008, artificial wetland increased obviously and natural wetland proportion dropped in yuhang district. Artificial wetland mainly includes reservoirs and aquaculture, and artificial wetland fragmentation dramatically rise, mainly due to the development of attention for aquaculture in yuhang district,and water aquaculture increase but lack of connectedness.