臺灣中海拔霧林帶三種林相的降雨再分配和水質變化

為瞭解高山霧林帶生態系的降雨在通過樹冠層後，水量再分配和水質變化，本研究於臺灣北部觀霧地區之原始樟殼林、次生林與人工針葉林等三種不同林相下，蒐集林內之幹流雨量、穿落雨量及林外雨量，並量測其化學組成。於2012年3月至2013年7月期間，共紀錄54場降雨事件。研究結果顯示，在不同降雨量下，霧林帶森林的樹冠截留能力的變化。在雨量小（＜98mm）時，樹冠截留與降雨量呈顯著的線性正相關；在雨量高（＞98mm）時，樹冠截留與降雨量反成為負相關之關係，其歸因於霧水額外的輸入所致。在三種林相中，以原始林的樹冠截留率為最高（11.1％），人工林次之（8.1％），次生林的樹冠截留率最低（7.3％），而樹冠穿落率最高（91.2％）。研究期間所收集的雨水之pH容積加權平均值為5.01，在流經原始林和次生林後，穿落水和幹流的pH值均顯著提高，而流經人工林的穿落水pH顯著增加，但其幹流水pH則顯著降低呈現酸化。以林內雨H^+淨輸入量為負值來看，三種林相均能部分中和大氣的酸沉降，並且以原始林與次生林的緩衝能力高於人工林。研究結果指出，觀霧地區的霧林帶生態系中，無機氮和SO_4^(2-)的年沉降量高，分別達21.2 kg N ha^(-1) yr^(-1)和15.1 kg S ha^(-1) yr^(-1)，未來待進一步研究釐清酸沉降對於棲息於此的環境敏感物種之可能影響。

關鍵字

穿落雨量；幹留雨量；樹冠截留；霧；酸沉降

並列摘要

To improve our understanding of rainfall redistribution and associated chemical alterations through the canopy and bark in montane cloud forests, we measured rainfall and ionic concentrations in open areas, in throughfall, and in stemflow in stands of primitive and secondary forests, and a coniferous plantation in the Guanwu area of north-central Taiwan. During the study period from March 2012 to July 2013, 54 rainfall events in total were sampled. Apparent rainfall interception by canopies exhibited a linear positive relation with rainfall size in sampled events with ＜ 98 mm of rainfall. However, during heavy rainfall events (＞ 98 mm), negative correlations between apparent interception and rainfall amounts was found, probably resulting from additional hydrological inputs from fog precipitation producing low and negative apparent rainfall interception. Among the 3 forest types examined, the primitive forest had the largest interception loss (11.1%), followed by the coniferous plantation (8.1%), and the lowest interception loss (7.3%) and the largest throughfall ratio (91.2%) were in the secondary forest. The volume-weighted mean pH of gross precipitation was 5.01, and it increased as the rain passed through the tree canopy and bark as throughfall and stemflow in primitive and secondary forests. In the plantation, throughfall had a significantly higher pH value, but stemflow had a significantly lower pH value than precipitation. The annual net flux of H^+ was negative in the 3 types of forest, indicating that they could neutralize the incoming acids from the atmosphere, and the buffering capacity was larger in the primitive and secondary forests than in the plantation. Our study presents evidence that the high level of annual input of inorganic N (21.2 kg N ha^(-1) yr^(-1)) and sulfate (15.1 kg S ha^(-1) yr^(-1)) in montane cloud forest ecosystems, and shows the need to clarify its potential impacts on environmentally sensitive species living in these habitats.

並列關鍵字

throughfall ； stemflow ； canopy interception ； fog ； acid deposition

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