溪頭營林區潛在崩塌地坡面土壤特性之研究

Abstract

本研究於溪頭營林區選定遭土石流嚴重破壞的大學坑之台灣杉與柳杉各設置三個樣區。於2002年7月23日及2003年7月20日分別在每個樣區之上坡段、中坡段及下坡段各取五個樣點，每個樣點採集0~15 cm、15~30 cm及30~60 cm三層不同深度之土壤，進行土壤質地、陽離子交換容量（CEC）與碳氮比測定。結果：土壤質地、陽離子交換容量（CEC）與碳氮比測定在同一年均無顯著差異。自2002年5月至2004年3月，每兩個月在每個樣區之上坡段、中坡段及下坡段各取三個樣點，進行簡易貫入試驗。結果：台灣杉林地在上坡段及中坡段之Nc值相似，但下坡段之Nc值變動則均較大。連年貫入試驗調查結果，台灣杉林地下坡段變動最大。柳杉林之孔隙度皆較同坡段之台灣杉林為高；兩林地土壤容重隨土壤深度增加而增加，而孔隙度隨土壤深度增加而減少。除了少數樣區，Nc值均與容重、孔隙度與礫石比呈現顯著相關，亦即礫石比越高，Nc值也越高；而孔隙度越高Nc值則越低。台灣杉林地中礫石重量百分比以中坡段最多，而在不同坡段不同土壤深度中礫石重量百分比，在台灣杉林地不同深度皆無顯著差異，而在柳杉林地以15-30㎝ 中最多。

Two sampling sites with severe landslide damage in Chitou Compartment were selected for this study. They were Taiwania cryptomeria stand and Cryptomeria japonica stand from Da-Shuie moat. Five sampling points were selected from each of the upper slope, middle slope and lower slope for each sampling site at July 23 2002 and July 20 2003. There was no significant difference in terms of soil texture, CEC, and C/N ratio within the same year for the soil samples collected from 0-15 cm, 15-30 am and 30-60 cm.Three sampling points were selected from each slope to conduct standard penetration test (SPT) for each sampling site from May 2002 to March 2003. The Nc values at the upper and middle slopes were similar in Cryptomeria stand, but varied a lot at the lower slope. The Nc value varied the most at the lower slope in Taiwania and Cryptomeria stands from the continuous SPT. Porosity in Cryptomeria stands is more than in Taiwania stands. The bulk density increases with soil deeper but porosity decreases with soil deeper in both stands. The percentage of gravel weight was the most at the middle slope in Taiwania and Cryptomeria stands. In terms of the percentage of gravel weight in different soil depths at different slopes in each sampling site, there was no difference in Taiwania stand, but with the greatest in 15-30 cm in Cryptomeria stand.