考量碳吸存效益之杉木造林獎勵金分析

An Analysis of Optimal Afforestation Subsidy for Cunnignhania lancelata

森林除了能提供木材價值之外，尚能提供涵養水源、國土保安、生物多樣性、調節微氣候等功能。為達到森林資源有效供給，政府獎勵造林有其必要性。政府獎勵方式應如何訂定為目前獎勵造林政策所面臨最關鍵的問題。台灣現行政策之獎勵額度決定乃單純由機會成本與造林成本之加總所決定，並沒有考慮森林碳吸存效益，獎勵期限主要是以常見樹種之平均輪伐期為原則，然本研究之分析結果顯示，若按此輪伐期施行，將無法達到造林總效益最大，也會增加政府的財政支出。有別於過去僅考慮造林之機會成本來決定獎勵金之文獻，本研究在追求森林碳吸存效益最大的前提下，建立最適造林獎勵金決定模式，此模式引入森林最適輪伐期之理論，將森林碳吸存效益納入土地期望價值，決定出造林總效益最大之輪伐期，作為獎勵造林政策之政策目標，另以地主土地利用決策模式為基礎，在私人透過獎勵而延長輪伐期至造林總效益最大之輪伐期的架構下，求出政府財政支出最小之獎勵金分配方式，換言之，使私人延長輪伐期至造林總效益最大之輪伐期的獎勵金分配有無限多組解，而最適獎勵金分配為可達到政策目標政府支出最小的一組解。根據所研擬的理論模式，本研究進一步以杉木為例，實證模擬分析在不同情形下之最適造林獎勵金分配，並在政策簡化原則下，估算各期獎勵金額固定下之最適獎勵金分配。本研究的造林獎勵給付模型之主要特色是能夠適用在不同土地區位與不同樹種之造林獎勵政策，並且能考慮森林的碳吸存效益。本研究藉由地主決策模型及森林最適輪伐期理論之引入，在追求造林總效益極大化，而政府支出極小化之下，建構最適造林獎勵給付模型，此模型之建立期能對政府制訂相關政策有所助益。

In addition to providing the commodity value of lumber, forests can also provide the function of conserving water and land resources, enrich biodiversity, and modulate micro-climate, etc. Under current afforestation program in Taiwan, the amount of afforestation payment covers the total cost of afforestation and opportunity cost of agricultural land. The social benefits of forests are not included in the consideration. The period of payment is determined by the forest rotation years of most common trees planted in Taiwan. It is 20 years for all kinds of trees over the whole country. Based on the model developed in this paper, it is found that the current system in Taiwan will not be able to achieve the socially optimal result; it will also cause higher government expenditure in subsidizing farmers. According to the present literature, most studies did not consider the effect of the penalty farmers have to pay if they harvest forest before the contract year. In this paper we develop a landowner's behavior model and analyze the effect of the penalty payment. Most studies also use the forest maintenance year to determine the subsidy duration without considering its proper justification. In this paper we develop a model to determine the optimal payment structure over the whole period. Based on the theoretical model developed in this paper, a simulation is conducted by using cunnignhania lancelata as an example to determine the optimal number of years of subsidy and optimal amount of subsidy in each year. It can be shown that the model developed in this paper can be applied to different kinds of trees over various kinds of situations.