考慮碳吸存價格下最適輪伐期與土地期望價之實證分析

An Analysis of Optimal Rotation and Expected Land Values under Carbon Pricing in Taiwan

在京都議定書的規範下，採用經濟誘因方式鼓勵造林來增加森林碳吸存，一般被認為是達到減量標準的有效方式。本研究分析私有林在最適管理策略下之碳吸存誘因效果， 其理論模型修正自Hoen（1994）與Murray（2003）之最適輪伐期模型，藉由碳吸存價格下森林最適輪伐期理論之引入，除修正原木價格與造林成本隨林齡變動外，亦考量砍伐成本，並考慮台灣現況以追求林地期望價值極大化，模擬分析杉木在不同碳價格對最適輪伐期、碳吸存效果、土地期望價與碳吸存機會成本之影響，以及分析碳價格是否對已成林地有縮短輪伐期之效果。根據本研究以杉木為例之模擬結果，若為裸露林地，考慮碳價格為每公噸1,400 元以上時，地主將會延長輪伐期為28 年以上（不存在碳價格時之輪伐期為20 年），林地期望價值提升為每公頃3,845,261.01 元，碳吸存量每公頃將增加為2,192.20 公噸。其次，對於開始給予獎勵給付時林齡為10 年之杉木已林地，若碳價格為每公噸1,000 元以上時，則地主之最佳決策為立即砍伐林木，再予以重新造林，以提早進入領取碳價格之階段，故林齡為10 年以下之林地將會被立即砍伐，造成森林外部效益之減損。台灣目前並沒有碳價格，但為了因應國際溫室氣體減量，未來無論是進行課徵碳稅、建立碳排放交易或碳價格給付等機制，都會對現存低林齡之已成林產生提早砍伐之誘因。若政府同時對新植造林與已成林之碳吸存提供碳價格給付，也可減輕已成林地提早砍伐的問題，其減輕程度則視對已成林之給付水準而定。

Economic incentives for sequestering atmospheric carbon dioxide(CO2) in forests may be an effective way to meet greenhouse gasreduction commitments under the Kyoto Protocol. Based on the modeldeveloped by Hoen (1994) and Murray (2003), this paper combines ananalytical model of the optimal forest rotation with both timber and carbonas priced outputs. A simulation is conducted by using cunnignhanialancelata as an example to determine the optimal forest rotation, theamount of carbon stock, and forest land values. It is found that for thebare forest land the carbon prices of $1,400 per metric ton – the highestprice evaluated– can considerably lengthen forest rotations from 20 to 28years, raise the forest land values to the level of $3,845,261.01 perhectare, and increase the amount of carbon sequestered up to 2,192.20metric tons per hectare, relative to the base case of no carboncompensation. If the carbon payments are only made for the regeneratedstand only, it will create an incentive for the forest owners to harvest theexisting forest earlier. When the level of payment is high enough, theforest owners might harvest the existing forest immediately after theenforcement of the carbon payment. Based on our simulation results, it isoptimal for forest owners to immediately harvest an 5-year-old stand and10-year-old stand at carbon prices as low as $600 and $1,000 per metricton, respectively. If carbon compensation were extended to existingstands, the incentives for prematurely harvesting existing stands wouldbe lessened.