同時考慮碳價格與木材價格不確定下最適輪伐期之決定

Measuring the Optimal Rotation Period under Carbon Price and Timber Price Uncertainty

世界各國開始重視以森林碳吸存作為二氧化碳排放減量之政策工具，將部份農地轉為造林地來增加碳吸存之方式，成為世界各國控制溫室氣體排放之趨勢。以政府而言，社會期待造林地主延長輪伐期，以增加森林之碳吸存量。大部分的文獻僅考慮價格確定下之模型，然現實市場存在諸多不確定性因素，因此本研究同時考慮木材價格與碳價格兩變數不確定下之最適輪伐期，並以我國地主種植杉木為例進行實證模擬分析，分析台灣私有地主面對木材價格與二氧化碳價格隨機波動下之最適輪伐期，本研究亦考慮林木砍伐之後碳釋放比率不同對輪伐期之影響。本研究之主要研究結果如下：（1）杉木價格與二氧化碳價格固定時，則我國地主在存在有碳價格時之輪伐期比不存在碳價格時之輪伐期短，主要是因為二氧化碳價格過低所致。（2）杉木價格與二氧化碳價格固定時，則我國杉木之最適輪伐期為21 年，而考慮任一變數隨機變動時，其輪伐期均會比價格固定下之輪伐期長，其中以杉木價格變動造成輪伐期增加之影響較為顯著。（3）當考慮折現率變動下，則無論杉木價格與二氧化碳價格變動與否，折現率越高，則輪伐期均會愈短。（4）當杉木價格隨機變動而二氧化碳價格固定時，則當折現率為3％以上時，碳釋放比例愈小，則輪伐期愈短。其次，當杉木價格與二氧化碳價格均隨機變動時，則隨著碳釋放比例愈小，輪伐期亦愈短。

Countries around the world start to focus on forest carbon sequestrationas a policy instrument of CO2 emission reduction. It becomes a trend ofcontrolling GHG emission that changing some parts of agricultural land intoforest land to increase carbon sequestration. This research considers howdifferent carbon release proportion affects the rotation length. Theempirical results are summarized as follows: (1) When the prices ofcunnignhania lancelata and carbon dioxide are fixed, while the price ofcarbon dioxide is existed, the optimal rotation becomes shorter, it isbecause that the price of carbon dioxide is too low. (2) When the prices ofcunnignhania lancelata and carbon dioxide are fixed, the optimal rotationperiod of cunnignhania lancelata in Taiwan is 21 years. When either theprices of timber or carbon dioxide fluctuates randomly, the optimal rotationperiod will become longer than that of fixed price one. (3) If the discountrate increases, the optimal rotation period will become shorter, whether theprices of cunnignhania lancelata and carbon fluctuate randomly or not. (4)When the price of cunnignhania lancelata fluctuates randomly and theprice of carbon dioxide is fixed, while the discount rate is above 3%, if thecarbon release proportion becomes lower, the optimal rotation period willbecome shorter. Then, when both the prices of cunnignhania lancelata andcarbon dioxide fluctuate randomly, the optimal rotation period will becomeshorter if the carbon release proportion becomes lower.