考慮碳效益與輻射能量收支下森林最適輪伐期與林地期望值之實證分析

Forest Optimal Rotation and Land Expectation Values under Carbon Sequestration and Radiation Budget

由於過量的人造溫室氣體排放，全球正積極制訂法規希望減緩氣候變遷的速率，其中森林扮演著相當重要的角色，對森林所提供的碳吸存貢獻，給予碳價格給付為一重要的政策方向。若僅考慮森林固碳作用的效益，而忽略地表反照率的影響，可能明顯高估森林碳吸存的效果，因比起已開墾的土地，森林的低地表反照率特性可能使地球吸收更多熱能，不過，森林所吸收的能量有部份會轉存為化學能，並不完全以熱能型式散失。因此，本研究模擬在考慮森林的碳效益下，額外納入輻射能量收支等值碳量的影響，來探究杉木的最適輪伐期與林地期望值之變化。據本研究之實證結果，若存在碳價格機制，隨著碳價格的增加，最適輪伐期會延長，林地期望值也會上升，若再加上輻射能量收支等值碳量的影響，則最適輪伐期會稍微縮短，抵減森林部份的固碳作用，針對「僅有木材收益」、「木材及碳效益」、「木材、碳效益及輻射能量收支等值碳量」三種情境下之最適輪伐期（T、Tcs、Ttecs）做比較，其關係為Tcs 大於等於Ttecs，而Ttecs 大於等於T。

International efforts strive to mitigate the rate of climate changecaused by man-made greenhouse gas emissions. Attributing aneconomical value to forest carbon sequestration might represent animportant strategy to achieve such goals. Such a policy is likely to impactoptimal rotation periods in forestry management. However, accounting forcarbon sequestration alone is not sufficient; the lower surface albedo offorests, compared to converted land, causes a higher grade of heatabsorption, which negatively affects the policy value of forests. Yet due tophotosynthesis, not all of the absorbed energy is converted to heat, butpartially used as chemical energy.Thus, this paper discusses the optimum rotation periods and landexpectation values of Cunninghamia lanceolata under the impact ofcarbon sequestration and the mentioned radiation budget. The findingssuggest that in the presence carbon sequestration pricing, the optimalrotation periods and land expectation values ought to increaseproportionally to carbon prices. The optimal rotation periods of threedifferent scenarios is compared: “just a timber (T),” “timber and carbonbenefits (Tcs),” and “timber、carbon and carbon equivalent of radiationbudget (Ttecs )”. The relation between them is: Tcs is greater than or equalto Ttecs; Ttecs is greater than or equal to T.