台灣國有林地森林碳吸存估算方法之探討

Abstract

上個世紀末起，全球暖化現象成為舉世注目的焦點。世界各國為解決此問題，於1992年通過氣候變化綱要公約。而後又通過具法律約束力的京都議定書，並於2005年生效。氣候變化綱要公約與京都議定書中皆肯定森林碳吸存可減緩氣候變遷，並規定各締約國每年需依IPCC溫室氣體統計指南估算並提交溫室氣體國家清冊。然而，台灣地區的森林調查資料與IPCC規定不全然相符，無法套用IPCC的模式估算台灣森林碳吸存。不過，自京都議定書通過後，國內仍有不少學者曾估算台灣的森林碳吸存，其結果約每年4.56至9.62百萬公噸。個別樹種也陸續有學者進行研究。本研究藉由森林調查簿主、副檔、檢定調查圖層、森林永久樣區資料、氣候區圖層，建立符合溫室氣體國家清冊要求的國有林碳吸存估算系統，並估算2006年一年國有林地各林型碳吸存量。研究結果，利用調查簿原有資料重新劃分71種樹種林型。依IPCC規範，本島則可區分8類生態區。此外，本研究還利用永久樣區資料推估各林型單位面積蓄積量、林木生長率與枯死率。藉此，配合調查簿，估算2006年全島國有林總蓄積量達617,699千立方公尺。再加上生態區圖層以及IPCC的轉換係數與估算模式，估算2006年國有林地碳貯存量137.27百萬公噸，碳吸存一年約4.70百萬公噸；單位面積平均碳貯存每公頃99.52公噸，碳吸存每年每公頃3.41公噸。不過，永久樣區設置與資料仍有許多不足，用來估算國有林地蓄積量與碳吸存量容易有高估的情況發生。另外，各樹種的本土轉換係數尚未建立，台灣的調查技術雖好，仍舊只能依賴IPCC建議的轉換係數。以上這些碳吸存估算的相關問題都有待解決。

Global climate change has become an important subject since the end of the 20th century. In attempt to resolve the issues, nations worldwide accepted “The United Nations Framework Convention on Climate Chang” in 1992 and also the “Kyoto Protocol” in 2005. Both the UNFCCC and KP agreed that forest carbon sequestration will reduce climate change, and thus participating nations are required to estimate their greenhouse gases and provide a national greenhouse gas inventory report. But forest inventory data in Taiwan does not accord to the IPCC guidelines for National Greenhouse Gas Inventories; hence, these data cannot be used to estimate the forest carbon sequestration using the IPCC guidelines. After the KP was accepted, many scholars have tried to approximate the forest carbon sequestration in Taiwan. The result is between 4.72 and 9.62. million tons per year. There are still many experts studying carbon sequestrated by other trees. This study uses the forest inventory data book, date in permanent sample plot, forest map and eco-zone GIS layers to build an estimative system of forest carbon sequestration for national forest land, according to the guidelines for national greenhouse gas inventory report. This system will then estimate Taiwan’s national forest carbon sequestration of different forest types in 2006. There are 71 forest types divided from the original forest inventory data book and eight eco-zones are recognized following the IPCC Ruler. Forest stocks in uni-area, growth rate and death rate are estimated by using the permanent plot database. The national forest stock in Taiwan in 2006 is 617,699 thousand cubic meter. The forest carbon stock is 137.27 million tons and the carbon sequestration is 4.70 million tons per year. There are still some problems in the permanent sample plot database, so using the database for carbon sequestration approximations often result in overestimation. Furthermore, local factors for the individual species have not yet been established, so we can only rely on the factors suggested by the 2006 IPCC Guidelines. The issues mentioned above are still to be solved.