關刀溪不同林分二氧化碳濃度之變化

Abstract

本試驗之目的在探討森林生態系中二氧化碳濃度的空間變化。以及不同林分組成對於林內二氧化碳濃度的影響。樣區設於惠蓀林場關刀溪長期生態研究區，選擇其中之天然闊葉林及人工杉木林進行採樣，兩個林分內各設有三個樣點，每個樣點以冠層為中心設置三個採樣高度進行採樣，同時在兩林分外的開闊地各設一對照樣點。採樣期間為2003年6月，共取得7個採樣週期之二氧化碳濃度資料。採樣時利用儀器持續監測，採樣週期為24小時。 試驗期間，兩林分夜間的二氧化碳濃度均較日間為高，天然闊葉林夜間的二氧化碳濃度(412.4±12.5 ppm)略高於人工杉木林(399.2±15.3 ppm)，日間則是人工杉木林(395.6±15.3 ppm) 略高於天然闊葉林 (391.0±9.0 ppm)。兩林分的二氧化碳濃度在垂直高度上有不同的變化趨勢，天然闊葉林以冠層下方之二氧化碳濃度最高(406.9±14.3 ppm)，人工杉木林則以冠層處的二氧化碳濃度最高(407.4±13.1 ppm)。 影響二氧化碳濃度最重要的因子為光度及二氧化碳本身之日變化，二氧化碳濃度與光度常呈負相關，亦即二氧化碳濃度會隨光度上升而下降。試驗期間，光度最大值通常出現在早上10點到正午間，二氧化碳濃度最小值出現的時間則稍晚，約在正午到下午3點間。

CO2 concentrations within a China-fir plantation and a natural hardwood stand were measured to explore the distribution of CO2 and the effect of stand composition in forest ecosystem. The experiment site locates in Guandaushi Long Term Ecological Research site in Nantou. We chose three sampling plots in each stand, three sampling heights were set in each plot. Contrast plots were set at three sampling heights outside each stand. LI-COR 6252 was used to offer 24-hour continuous sampling, each sampling period sustained 24 hours at least. During the experiment period, nighttime CO2 concentrations were higher than daytime CO2 concentrations in each stand. Nighttime CO2 concentrations in natural stand(412.412.5 ppm) were higher than China-fir plantation(399.215.3 ppm). But daytime CO2 concentrations in China-fir plantation (395.615.3 ppm) were higher than natural stand(391.09.0 ppm). CO2 concentration showed different trends in different stands. The highest CO2 concentrations appeared below canopy in nature hardwood stand(406.914.3 ppm), but appeared within canopy in China-fir plantation(407.413.1 ppm). The most important factors that influence CO2 concentrations were diurnal CO2 concentration variance and light intensity. CO2 concentrations usually increase while light intensity decreases. During experiment period, the maximum light intensity values appeared between AM 10:00 and noon, but the minimum CO2 concentration values appeared between noon and PM 15:00.