合歡山臺灣冷杉林截留作用之研究

Abstract

當雨水進入林木受到冠層的攔截，使得部分水分留存在冠層中，將改變降水到地面在時間或在空間上的分佈。本研究於合歡山台 14 甲線 35.5km，靠近小風口處，對臺灣冷杉進行一整年的研究。研究期間（2011.3~2012.2）合歡山臺灣冷杉樣區的林外年降水為3,560±110 mm（總和±標準差），穿落水為 3,070±90 mm（86%），幹流水為 200±10 mm（6%），若以截留量＝林外降水量－穿落水量－幹流水量計算，則截留量為 290 mm（8%），而穿落水與降水量有一良好的線性關係（y=0.85x+1.76，R2=0.97，n=28，13≦x≦363，x為林外降水，y為穿落水），而在降雨延時較長的時段，總降水量與穿落水的變異有增加，且幹流水的比例有上升的趨勢，另外，樹冠冠幅隨林木胸高直徑（DBH）的上升而增加，使臺灣冷杉能收集到更多的幹流水量。 本研究藉由分析 LAI(Leaf area index)、樹木密度、林木平均 DBH、林木最大DBH 與年平均穿落水水量的關係，得到在穿落水收集器範圍 6 公尺左右時，樹木密度與平均 DBH 會影響穿落水的水量，但影響效果有限。 此外，臺灣冷杉林在夏秋季時的冠層較為乾燥，因此截留能力較強；冬春季時的冠層較為濕潤，因此截留能力較差。

When canopy intercepts the rainfall, some water can be kept in the canopy. This can change the time or redistribution when rainfall dropped down. This research was conducted at 35.5km near Shao-feng-kou service tourist center at Mt. Hehuan. This study was on Taiwanese fir stand from Mar-2011 to Feb-2011. Results showed that annual rainfall was 3,560±90 mm (sum±SD), throughfall was 3,070±110 mm (86%), and stemflow was 200±10 mm (6%) for the studied year. According to water balance (the interception = rainfall - throughfall – stemflow), the interception was calculated to be 290 mm (8%). A good linear relationship was found between throughfall and rainfall (y=0.85x+1.76，R 2 =0.97, n=28, 13≦x≦363, x=rainfall, y=throughfall). The canopy also showed increased as DBH increased so that stemflow increased. This research found significant correction between throughfall and forest structural parameters such as LAI, tree density, average DBH, and maximum DBH. The most important factors were the tree density and average DBH within 6 m of the measurement points, which had better relationship with throughfall. Since the canopy of Taiwanese fir was drier during Summer and Fall, so it could intercept more rainfall. On the contrary, it was wetter during Winter and Spring, so it intercept less rainfall than the drier seasons.