棲蘭霧林生態系統能量平衡年際與季節變化之研究

Abstract

雲霧作為一種天氣現象，其對於通量的量測造成很大的影響。除了降低入射到森林的輻射通量，也會使能量通量與二氧化碳通量受到低估。過去的研究會計算所有資料的平均能量平衡閉合度，並藉此校正二氧化碳通量，但能量平衡閉合度並非全年不變，其會受到環境因子的變化而有所改變。因此本研究透過臺灣棲蘭山雲霧森林長時間的觀測資料瞭解雲霧森林在不同年份以及不同季節的能量通量與能量平衡閉合度會受到哪些因子影響。 棲蘭山雲霧森林的平均能量平衡閉合度（0.86）與過去的研究相仿。但其能量平衡閉合度會受到雲霧的影響。當能見度越低，能量平衡閉合度也越低。此外，當風速低於2.0 m s-1 時，其與能量平衡閉合度呈正相關，但風速高於2.0m s-1，能量平衡閉合度便開始下降，這與過去的研究發現並不相同。除此之外，能量平衡閉合度在上午七點到十點大多大於1，主要與風向轉變帶來不同性質的空氣團塊有關。透過主成份分析發現，能見度為主要影響棲蘭山雲霧森林能量平衡閉合度的環境因子。

Cloud forest is usually covered by dense fog influencing measurement of flux severely. Energy balance closure (EBC) is a parameter to correct measurement of flux but it will change by environment. This study find out the relationship between environmental factors and energy balance closure in Chi-Lan Mountain cloud forest. The Chi-Lan Mountain cloud forest in northeastern Taiwan is a typical subtropical cloud forest. At this site, the average EBC is 0.86, similar as other needle forest site. EBC is strongly influenced by dense fog. While the visibility is under 100 m, the EBC is only 0.48. EBC increase when visibility increase. Wind speed is also an environment factor effecting EBC. EBC will increase when wind speed increase to 2.0 m s-1, but decrease when wind speed over 2.0 m s-1. The EBC is more than 1 in morning due to the different characteristics of air masses causing by winds. In short, the inter-annual and seasonal variations in energy balance closure over Chi-Lan Mountain forest is dominate by dense fog.