| Summary: | 博士 === 國立屏東科技大學 === 生物資源研究所 === 106 === Taiwan is located on the Pacific seismic belt where the geological structure is more complex, and cause frequent landslides, debris flows and other sediment disasters, especially when earthquakes, typhoons and heavy rains occurs. Chishan and Lennon river working circle lays in the national forest land of Kaoping river basin, and was greatly damaged by 2009 Morakot typhoon, thus, the understanding of land cover change before and after typhoon were important tasks in watershed management. However, satellite images enables the monitoring of large-scale landslide distributions. In this study, down-scale precipitation data was collected from TCCIP. The variation of long-term precipitation trend and change points was obtained by Mann-kendall trend verification, Theil-sen slope estimation, Cumulative Deviations verification and Mann-Whitney-Pettitt verification. Landsat images from the year 2000-2015 were acquires as materials and the digitizing of landslide distribution was completed by Geographic Information Systems (GIS). Accordingly, four types of landslide were classified, namely are unchanged, recovery, appending and expanding. The variation of forest disturbance degree from 2000-2015 was obtained through Tasseled Cap Transformation. Landscape metrics was applied to analyze the variation of landscape structure in different landslide types over the years. The environmental variables were examined by Kolmogorov-Smirnov test, and estimating landslide susceptibility via Instability index and Logistic regression, and the accuracy was reviewed by comparing Error Matrix and Area-under Curve. Estimating the distribution of environmental vulnerability through Principal Components Analysis, reduces the number of environmental variables and determines the weight of principal components. Moreover, the historical vegetation restoration data and environmental variables were used for evaluation of the vegetation restoration possibility in the existing landslide area by Logistic regression. The results shows that precipitation of season, wet period, dry period and annual precipitation at Chishan and Lennon river working circle has increased. Additionally, the change point of precipitation trend falls within 1975-2000. Landslides has indeed disturbed Chishan and Lennon river working circle. The IDI of Chishan were 2.128, 2.751 and 2.670, respectively, which represents that some areas were damaged by Morakot typhoon were partially recovered after 2015. There were no significant change in the annual IDI of Lennon river working circle. However, differences between each DI level of sample plot was found. The results of landscape metrics showed that the unchanged-type tend to be fragmented and geologically unstable, which leads to frequent natural disasters and caused existing landslide area to expand. The appending-type was mostly triggered by the Morakot typhoon, where heavy rainfalls hits the ground surface, and made surface objects unable to stand firmly. The recovery-type recovers gradually; however, the area of landslide formation is significantly faster than the area of recovery. The landslide susceptibility results indicates the receiver-operating characteristic (ROC) curve and the ratio of area-under curve (AUC) in Chishan and Lennon were 0.702 and 0.750 under the Instability index, 0.819 and 0.808 under the Logistic regression model, that the Logistic regression model is more appropriate than the Instability index. The environment vulnerability in Chishan and Lennon River were classified as heavy and extreme level of environmental vulnerability accounts for 38% and 31% of the area, mostly are located in relatively high altitude and steep terrain, where vegetation renewal and restoration is unlikely to happen. Estimating potential vegetation restoration ability in existing landslide area by Logistic regression, shows an overall correctness of 72.59% in Chishan working circle, and 67.76% in Lennon River working circle. Facing extreme climate challenges, the management of forest watershed must be based on the principle of ecological management, forest structure consideration and ecological function, in order to maintain the balance of the ecosystem.
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