溪頭柳杉人工林能量收支特性之研究

Characteristics of Energy Budget in a Japanese Ceder (Cryptomeria Japonica ) Plantation at Xitou Area

洪志遠(Chih-Yuan Hung) ； 林宜蓁(I-Chen Lin) ； 陳明杰(Ming-Chieh Chen)

《國立臺灣大學生物資源暨農學院實驗林研究報告》 28卷1期 (2014/03) Pp. 1-15

https://doi.org/10.6542/EFNTU.201403_28(1).0001

摘要

本研究為探討人工林林分不同高度能量收支的特性，試驗地位於臺灣大學實驗林管理處溪頭營林區第3林班63年生柳杉人工林，蒐集2011年7月21日至2013年12月31日期間通量塔的淨輻射能、土壤熱能、氣壓、氣溫、濕度等觀測資料，利用包溫比能量平衡法計算顯熱通量與潛熱通量，並比較樹冠層上方（高度28～32m）及樹冠層下方（高度10～14m）顯熱通量與潛熱通量的分配。經計算結果，資料蒐集期間樹冠層上方之平均淨輻射通量為58.81W/m^2、顯熱通量為19.11W/m^2、潛熱通量為41.06W/m^2、土壤熱通量為-1.37W/m^2，亦即顯熱通量為淨輻射通量之32.49%、潛熱通量為69.83%、土壤熱通量為-2.32%。由於受到樹冠層對輻射吸收、反射等的影響，樹冠層下方的淨輻射通量僅為樹冠層上方的7.07%，並且，樹冠層下方顯熱通量為淨輻射通量之3.77%、潛熱通量為129.06%、土壤熱通量為-32.83%。顯示柳杉人工林的淨輻射通量主要分配於潛熱通量，提供蒸發散作用所需。相較而言，樹冠層下方潛熱通量僅為樹冠層上方的13.08%，乃因樹冠層下方空間的濕度高、氣溫及風速的變化較為緩和等因素，故蒸發散量消耗的能量較少。另外，四個季節之土壤熱通量的平均為-3.98～1.56W/m^2，於春、夏兩季，由於到達地面之太陽輻射能較多，以及氣溫高於地表溫度等，故土壤為吸熱的正值；反之，於秋、冬兩季，因為氣溫較低且地表溫度高於氣溫，故土壤為放熱的負值。尤其是冬季時，樹冠層下方土壤熱通量為淨輻射通量的二倍，此時大部分的土壤熱能可提供近地表植被蒸發散作用所需。

關鍵字

包溫比能量平衡法 ； 淨輻射通量 ； 顯熱通量 ； 潛熱通量 ； 土壤熱通量

並列摘要

This study is to investigate the characteristics of energy budget of different heights in plantation stand. Experimental site is the 63-years Japanese cedar plantation at Xitou tract, NTU Experimental Forest. Daily data of Flux tower, including net radiation, soil heat, air pressure, air temperature and air humidity, were collected from 21 July 2011 to 31 December 2013 that was used to calculate the sensible heat flux and latent heat flux by Bowen ratio energy balance method. Additionally, sensible heat flux and latent heat flux above the canopy (28 to 32m) and below the canopy (10 to 14m) were compared. The results showed that the average net radiation flux was 58.81W/m^2, sensible heat flux was 19.11W/m^2, latent heat flux was 41.06W/m^2 and soil heat flux was -1.37W/m^2 above the canopy during study period. It means that sensible heat flux, latent heat flux and soil heat flux are 32.49%, 69.83% and -2.32% respectively to net radiation flux above the canopy. Since solar radiation could be absorbed and reflected by canopy, the net radiation flux below the canopy is only 7.07% comparing to the measure above the canopy. Meanwhile, the sensible heat flux, latent heat flux and soil heat flux were 3.77%, 129.06% and -32.83% respectively to net radiation flux below the canopy. The results further revealed higher latent heat flux ratio above and below the canopy that explains the energy depletion for evapotranspiration. In comparison, humidity was higher and the change of air temperature and wind speed were also moderate below the canopy that causes a fewer energy depletion for evapotranspiration. The latent heat flux below the canopy was only 13.08% of above the canopy. Besides, the average soil heat flux was from -3.98 W/m^2 to 1.56W/m^2 across seasons. In spring and summer, the air temperature was higher than the surface temperature and the solar radiation incidence to ground surface was more, that in turn the soil was endothermic and the soil heat flux was positive. Conversely, the soil was exothermic and the soil heat flux was negative in autumn and winter. Below the canopy, the soil heat flux was twofold to net radiation particularly in winter. The most soil energy emits onto the near ground could provide for vegetation evapotranspiration.

並列關鍵字

Bowen ratio energy balance method ； net radiation flux ； sensible heat flux ； latent heat flux ； soil heat flux