陡峻區域土地覆蓋變遷之分析－－以九九峰自然保留區為例

Analysis on Land-cover Change in Steep Area- An example of Jiou-Jiou Peaks Natural Reserve

九九峰地區因頭嵙山層地質，加上921地震干擾，形成陡峻的特殊地貌，為保留該地景，「九九峰自然保留區」於2000年5月22日成立，面積約1,198.4466 ha（南投處提供之GIS圖層計算面積為1,199.24 ha）。雖人為活動與擾動受到法律而禁止，但多時期颱風侵入仍不斷改變保留區地景。本研究利用多時期正射影像（1998年07月02日、1999年12月10日與2009年12月08日），以影像色調與組織為依據，將地覆判釋分類為森林、台灣蘆竹（Arundo formosana）草生地、河岸、裸露地、陰影區與其他地覆共六類，並繪製向量式（vector）土地覆蓋型圖（Land-cover map）與轉換成1 m × 1 m的網格（raster）資料，以套壘分析探討九九峰自然保留區地景現況與變遷。結果顯示，1998年時，森林為主要地覆，面積約861.18 ha（71.81 %），而台灣蘆竹草生地與裸露地分別為40.03 ha（3.34 %）、4.34 ha（0.36 %）。921地震後，1999年的主要地覆為森林356.34 ha（29.71 %）、台灣蘆竹草生地256.49 ha（21.39 %）、裸露地207.26 ha（17.28 %）等形式存在。2009時，隨植生自然恢復，土石堆積區域常由森林覆蓋，約366.05 ha（30.52 %），陡峭坡地則以台灣蘆竹草生地為主要地覆，共466.77 ha（38.92 %），而裸露地約13.09 ha（1.09 %）。變遷分析結果顯示，921地震產生的崩塌與植生自然恢復，於1999年時有，192.20 ha（16.03 %）與167.68 ha（13.98 %）的森林分別轉變成台灣蘆竹草生地與裸露地，且因為拍攝角度、時間與地形改變，共有212.66 ha（17.73 %）受陰影遮蔽效應無法準確分辨。可能因為鬆散地質，與連續性颱風干擾，至2009年時，有114.78 ha（9.57 %）從森林變裸露地，再發育成台灣蘆竹草生地，且有10.65 ha（0.89 %）變成河道的狀態。其他地覆類型的變化甚微。三個時期中，共126.60 ha（10.56 %）的森林與65.19 ha （5.44 %）的陰影區域保持不變，陰影常存在山谷、或是峰與峰間低處。研究已針對現況與三期變化進行描述，若要了解未來的植生演替趨勢與地景發展，則需將颱風雨量、地形、地勢等環境因子納入考量。 Jiou-Jiou Peaks, a gravel layer of Huoyanshan of Touke mountain formation, was caused a massive landslide and landscape change by the devastating disturbance, 921 earthquake. Jiou-Jiou Peaks Natural Reserve, around 1,198.4466 ha (1,199.24 ha was calculated with GIS), was established at 2000/05/22 to protect the unique topography. Although human disturbances were prohibited, the landscape and vegetation succession were still infl uenced by continuous typhoons. The aim of this study is to make land-cover maps and investigate landscape changes with multi-termporal ortho-aerial photos, taken in 1998/07/02, 1999/12/10 and 2009/12/08. The land-cover was separated into forest, Arundo formosana grasscovered land, river bank, bared soil, shadow and others areas. The land-cover maps were transformed into 1 m × 1 m raster data. We analyzed the landscape status and changes with overlapped analysis. The results showed that 861.18 ha (71.81 %) of forest area, A. formosana grass-covered land covered 40.03 ha (3.34 %) and bared soil covered 4.34 ha (0.36 %) before 921 earthquake in 1998. The reserve was covered by forest, 356.34 ha (29.71 %), A. formosana grass-covered land, 256.49 ha (21.39 %), and bared soil, 207.26 ha (17.28 %), after 921 earthquake in 1999, respectively. A steeper slopes of the reserve was covered by A. formosana grass-covered land, 466.77 ha (38.92 %), and forest, 366.05 ha (30.52 %), was distributed in foot of peaks at 2009. In the same time, bared soil only left 13.09 ha (1.09 %). Results of landscape change showed the 192.20 ha (16.03 %) of A. formosana grass-covered land and 167.68 ha (13.98 %) of bared soil were changed from forest in 1999. However, shadow effect made 212.66 ha (17.73 %) fail to be classifi ed. In 2009, 114.78 ha (9.57 %) from the forest became bared soil, and then developed into A. formosana grasscovered land because of unstable gravel geology and impact of continuous typhoons. Moreover, 10.65 ha (0.89 %) of rivers side was changed from forest from 1999 to 2009. Land-cover type of others almost didn't change. We also found that the shadow effect, 65.19 ha (5.44 %) shadow areas existed in all periods, was inaccurate the land-cover status and change analysis. The shadow often appeared in valley. Environmental factors should be considered, such as infl uence of continuous typhoons, slope and aspect, to recognize the tendency of vegetation succession and landscape change in the future.