私有地主參與農地碳匯合約之決策分析

Decision-Making of Landowners' Participation in Agricultural Carbon Contract

近來世界各國開始重視以耕地管理之措施來增加碳匯量，以減緩溫室氣體暖化問題，包括在農地上進行混農林種植、耕地經營管理、土壤保育以及暫時休耕等。透過這些耕地管理措施將可增加土壤中之碳匯量，計入土地使用、土地使用變化和林業活動（land use, land-use change and forestry, LULUCF）碳匯項目中，亦包含在京都議定書之減量範圍內。其中之一為耕地管理，但大多文獻並未針對此部分進行討論與分析，我國目前尚未對農地碳匯管理進行碳給付，然而我國休耕面積已超越稻作面積，增進碳匯方式可視為是未來休耕農地之利用方式之一。本研究主要分析農民參與農地碳匯合約之最適合約期間，以及對於折現率、碳價格以及合約規定之耕作集約度上限進行比較靜態分析。根據本研究之理論推導，若農民可自行決定碳匯合約期間，則雖然降低耕作集約度會減少農業收入，但土壤碳量增加將增加未來的農業收入，而在碳存量逐漸趨近飽和下，增量將隨之遞減，因此私有地主不會選擇無限期參與農地碳匯合約。當折現率增加、碳價格增加或耕作集約度增加，都會使私有地主選擇較長之合約期間。當政府規定之耕作集約度上限增加或碳價格增加，農民總收入現值將會增加。當折現率增加，農民之總收入現值將會減少。本研究結果符合Culati and Vercammen（2005）結果，即政府增加農地碳匯合約之耕作集約度上限，農民更有誘因參與碳匯合約，因此合約期間會增加，然此僅是在特定參數設定下的模擬結果，根據本研究所建立之一般模型推導結果，當政府增加耕作集約度上限，即越接近無合約下之耕作集約度（亦即政府對於合約規定較為寬鬆），則農地地主之農業收入現值會增加，但由於土壤累積碳匯較少，碳匯收入現值會減少，故農地地主不一定會延長合約期間。 Many countries in the world have actively adopted various kinds of approaches to reduce greenhouse gas emissions, such as agroforestry projects, cropland management, soil carbon management, fallow management, etc. In order to reduce the negative impacts due to the climate change resulting from increasing greenhouse gases. The Kyoto Protocol allows developed countries to claim credits for carbon sequestered as a result of LULUCF (land use, land-use change and forestry) activities. Most literatures didn't address the discussion of these parts in Taiwan. However to enhance carbon sinks can be seen as one of the agricultural land use patterns because the total area of fallow lands exceed that of paddy fields in Taiwan. This study analyzes the optimal length of soil carbon contracts which non-industrial private farmers participate in, and conducts the comparative static analysis on discount rate, carbon price, and the upper bound of cultivation intensity in soil carbon contracts. According to the theoretical model derived from this study, if a farmer can determine the length of his carbon contract, then the decrease of cultivation intensity will reduce his present income, and the increase of the level of soil carbon sequestration will increase his future income. As the total amount of soil carbon sequestration increases, the marginal amount of soil carbon sequestration will decrease, so the rational farmer will not choose the unlimited carbon contract length. In addition, the factors affecting the length of the carbon contract which is determined by farmers include discount rate, carbon price and cultivation intensity. As the values of these factors increase, the length of the carbon contract determined by farmers will also increase. On the other side, as the cultivation intensity and carbon price increases, farmers' income will increase; however as the discount rate gets lower, the farmers' income will decrease. The result of this study is consistent with that of Culati and Vercammen (2005); it is that if the government raises the upper bound of cultivation intensity on soil carbon contract, then it will increase farmers' participation incentives in the soil carbon contract and the length of the carbon contract will increase.

Many countries in the world have actively adopted various kinds of approaches to reduce greenhouse gas emissions, such as agroforestry projects, cropland management, soil carbon management, fallow management, etc. In order to reduce the negative impacts due to the climate change resulting from increasing greenhouse gases. The Kyoto Protocol allows developed countries to claim credits for carbon sequestered as a result of LULUCF (land use, land-use change and forestry) activities. Most literatures didn't address the discussion of these parts in Taiwan. However to enhance carbon sinks can be seen as one of the agricultural land use patterns because the total area of fallow lands exceed that of paddy fields in Taiwan. This study analyzes the optimal length of soil carbon contracts which non-industrial private farmers participate in, and conducts the comparative static analysis on discount rate, carbon price, and the upper bound of cultivation intensity in soil carbon contracts. According to the theoretical model derived from this study, if a farmer can determine the length of his carbon contract, then the decrease of cultivation intensity will reduce his present income, and the increase of the level of soil carbon sequestration will increase his future income. As the total amount of soil carbon sequestration increases, the marginal amount of soil carbon sequestration will decrease, so the rational farmer will not choose the unlimited carbon contract length. In addition, the factors affecting the length of the carbon contract which is determined by farmers include discount rate, carbon price and cultivation intensity. As the values of these factors increase, the length of the carbon contract determined by farmers will also increase. On the other side, as the cultivation intensity and carbon price increases, farmers' income will increase; however as the discount rate gets lower, the farmers' income will decrease. The result of this study is consistent with that of Culati and Vercammen (2005); it is that if the government raises the upper bound of cultivation intensity on soil carbon contract, then it will increase farmers' participation incentives in the soil carbon contract and the length of the carbon contract will increase.