考慮價格波動與碳給付機制下地主土地利用決策之研究──以臺灣杉木為例

A Study on the Effect of Price Uncertainty and Carbon Payment Schemes on Landowners' Land Use Decisions-A Case of Cunnignhania lancelata

本研究主要分析價格不確定情形下，政府提供碳給付政策對地主土地利用決策之影響。本研究根據過去文獻設計四種可能的給付方式，包括一次給付、碳流量給付、碳存量給付以及事後給付方式，造林地主之土地利用決策選項包括維持成林、砍伐林木後轉作農用，及砍伐林木後重新造林。地主追求土地現值極大來進行決策，站在政府立場則是希望地主繼續維持成林。本研究之主要結論如下：（1）若木材價格存在不確定因素，則農業收入及折現率影響私有地主土地利用決策之幅度最大。當農業收入或折現率減少時，私有地主參與造林之木材價格區間會增加，轉為農業用途之木材價格門檻會降低，而砍伐林木後重新造林之木材價格門檻會增加，也會延長維持造林之期間。（2）無論政府採行何種碳給付機制，實施碳給付政策都會降低造林地轉為農業用途之木材價格門檻，增加地主造林之木材價格區間。（3）在四種碳給付機制中，除了第二種機制之外，其他三種機制均會使得砍伐林木後重新造林之木材價格門檻降低，縮短維持造林之期間，亦即，碳給付政策之存在不一定會延長地主之輪伐期。除了第二種機制之外，其他三種機制均可能縮短地主之輪伐期。（4）在政府未執行碳給付政策時，地主選擇繼續造林之木材價格區間在第18年之後會越來越小。即使地主在第18年後繼續維持造林，最多也僅會種植到第32年。地主在第32年砍伐林木後是否會將農地轉作為農業用途或是重新造林，則視當時之木材價格而定。若每立方公尺之木材價格高於5,100元，農地地主會重新造林，低於5,100元，則會轉作為農業用途。（5）地主參與碳給付政策後，其木材收入現值會減少，且隨著每單位碳給付水準之增加，減少的幅度將擴大。另外，碳收入現值佔地主總收入現值之比例會隨著每單位碳給付水準之增加而增加，而其中以第二種機制之碳收入現值佔總收入現值的比例最小。（6）在相同政府支出之下，相較於其他三種給付機制，地主在第二種給付機制下繼續造林之價格區間最大，其輪伐期亦相對較長。整體而言，第二種給付機制之政策效果明顯優於其他三種機制。

This study analyzes the impacts of carbon payment mechanisms on landowners' land use decisions under timber price uncertainty. The carbon payment policies (or carbon subsidies mechanisms) considered in this study consist of four regimes, such as the lump-sum regime, flows regime, stocks regime, and ex-post lump-sum regime. The possible options for foresters' land use decisions are as follows: maintaining forests, harvesting forests and then switching to farming, or harvesting and then reforesting again. Under different carbon payment regimes, at each period of time the land owners will make land use decision in order to maximize the present value of land. The important decision made by foresters is the timing of harvesting timber and after that whether to reforest it again. Main conclusions of this study are as follows: (1) When there exists timber price uncertainty, the farm income and the discount rate contribute the most in influencing landowners' land use decisions. As the farm income or discount rate decreases, the timber price interval for the”maintaining forests”decision will become wider, i.e., the price upper bound for the”switching to farming”decision will fall and the price lower bound for the”harvesting and then reforesting”decision will increase. (2) No matter which carbon payment mechanism is implemented by the government, the timber price interval for the”maintaining forests”decision will become wider. (3) Among the four carbon payment regimes, except for the second one, the other three carbon payment regimes implemented by the government will decrease the forest rotation length. That is, when landowners participate in forest carbon payment mechanisms or carbon subsidy policies, they may not always lengthen their forest rotation period. (4) If the government does not implement any carbon payment mechanisms, the timing for harvesting timber will be around the 32nd year. The land use decision options after the 32nd year will be determined by the level of timber price. If the limber price is higher than 5,100/m^3, then landowners will choose to reforest; otherwise, landowners will choose to switch to farming. (5) When landowners participate in the carbon payment policies, the amount of profits generated by the harvested timber will decrease. The amount of reduction will increase with the increases of carbon price level. In addition, the ratio of the carbon profits to the total profits will increase along with the increases of the carbon price level. Among four mechanisms, the ratio for the second mechanism is the lowest. (6) Under the same governmental budget constraints, the timber price interval for the”maintaining forests”decision for the second mechanism is the widest. According to our analysis, when evaluated by policy effectiveness, among four mechanisms the second one is considered the best.