利用小型量水堰評估復育造林過程對土壤沖蝕影響之初探

Preliminary Assessment of Soil Erosion Impact During Forest Restoration Process Using Self-Designed Tiny Weirs

賴彥任(Yen-Jen Lai) ； 張振生(Cheng-Sheng Chang) ； 曹崇銘(Tsung-Ming Tsao) ； 魏聰輝(Tsong-Huei Wey) ； 江博能(Po-Neng Chiang) ； 王亞男(Ya-Nan Wang)

《國立臺灣大學生物資源暨農學院實驗林研究報告》 27卷4期 (2013/12) Pp. 273-284

https://doi.org/10.6542/EFNTU.201312_27(4).0003

摘要

臺灣地質脆弱、地形陡峭，歷經921地震、桃芝、莫拉克風災侵襲且居民對林地之開發利用，山區地貌遭受重大破壞，對臺灣山區生態系將有更嚴峻的挑戰。臺大實驗林2008－2010年執行國土保育計畫，收回之契約林地共約1500公頃，這些契約林地大部分以竹、茶、檳榔、果樹且蔬菜為主，目前已復育造林共約1298公頃。復育造林過程包括整地、新植、及六年的刈草，對土地將有相當的衝擊，亦可能在復育期間造成異常沖蝕。藉由此次林地回收造林機會，對復育造林過程在土壤沖蝕之影響加以探討，將有利於未來造林撫育實務操作。本研究還取一個2013年的新植造林地及其附近的29年生成熟林為實驗樣區及對照樣區。各放置一組研究所設計之小型量水堰於樣區之小集水區內，用以觀測流量及土砂流出量。根據2013年5月至8月雨季期間的結果顯示，現地的土壤質地為砂質壤土至砂土且含有許多礫石，反推洪峰逕流係數僅0.3～0.4，推知試驗地之地表入滲率應相當高，此現象大幅降低了逕流量，連帶土砂輸出量無預期來得大。蘇力及潭美颱風兩次暴雨案例分析顯示，僅成熟林於蘇力颱風後有淤積土砂濕重為233（kg），其餘均為懸移所造成濁度增高，新植林地樣區之逕流濁度則高於成熟林7－9倍。為能完整評估復育造林六年過程對土壤沖蝕的衝擊，選擇不同土壤質地剖面特性之地區進行長期觀測有其必要性。

關鍵字

復育造林 ； 土壤沖蝕

並列摘要

Taiwan has a fragile geology and steep landscape. The 921 earthquake, Typhoon Toraji, Typhoon Morakot, as well as the exploitation of local residents have severely damaged the landscape, and therefore the montane ecosystem faces a serious challenge. A land conservation project has been implemented by the Experimental Forest of National Taiwan University and reclaimed approximately 1,500 hectares of leased woodland during 2008 to 2010, primarily used to grow bamboo, tea trees, betel nut, fruit, and vegetable, in which about 1,298 hectares have been reforested. The process of forest restoration involves clear cutting, soil preparation, a six-year weeding and tending period that may affect the amount of soil erosion dynamically. This study aims to assess the soil erosion of forest restoration on the recovered land and this research could benefit practical implementations of reforestation. A new plantation set-up in early 2013 and a nearby 29-year-old mature forest were chosen as an experimental and a comparison sites respectively. Both study sites were set up a self-designed weir for measuring the runoff and sediment. The results during May to August 2013, a raining season in Taiwan, the coefficient of runoff and flood peak was in the range of 0.3 to 0.4 that indicates the runoff and erosion were not as high as expected. A possible reason might be that the soil texture of both sites is sandy with high percentage of coarse fragments that increases the infiltration. Comparing two rainstorm events (Typhoon Soulik and Typhoon Trami), around 233 kg of wet sand/soil was found in the weir of mature forest during Typhoon Soulik and suspended materials were measured at both sites. Additionally, the runoff turbidity in the weir of the new plantation site was 7 to 9 times higher than the one of the mature forest site. In order to have a comprehensive assessment of the influence of six-year weeding and tending period, a long term investigation of soil erosion within different soil texture profiles is needed.

並列關鍵字

forest restoration ； soil erosion