櫸木人工林造林木碳貯存量和吸存量之估算

櫸木(Zelkova serrata (Thunb.))為台灣最重要的闊葉樹造林樹種之一。本研究以苗栗約46年生和台東約25年生兩林人工林為對象，估算其造林木之生物量和生長量，建立根莖比和擴展係數等參數和迴歸式，以估算其碳貯存量和吸存量。結果顯示，櫸木根莖比苗栗為0.240，台東為0.250，兩林分相近，且與熱帶闊葉林平均值相似。地上部擴展係數台東為1.528 Mg m-3，只略高於苗栗的1.328 Mg m-3。兩林分地上部生物量連年生長和平均生長皆隨年齡呈上升趨勢，在24年生後上升趨勢才減緩。苗栗林分櫸木生物量為252.3 Mg ha-1，高於亞洲熱帶地區闊葉林的平均值，台東林分為108.4 Mg ha-1，則偏低。櫸木植體的地上部碳平均濃度，苗栗為49.0%，台東為49.6%。以此換算成林分櫸木碳吸存量，苗栗地上部平均量為1.95 Mg ha-1 yr-1，全株平均量為2.40 Mg ha-1 yr-1；台東地上部為1.81 Mg ha-1 yr-1，全株為2.25 Mg ha-1 yr-1。櫸木能長期貯存大量的碳，可減緩溫室效應。
關鍵詞：人工林、碳貯存量、碳吸存量、根莖比、擴展係數

Japanese zelkova (Zelkova serrata (Thunb.)) is one of the most important broadleaf afforestation tree species in Taiwan. This study targeted two planted forest stands: a ~46-year-old stand in Miaoli and a ~25-year-old stand in Taitung. We estimated the biomass and stand increment of the afforested trees, developed parameters including root-to-shoot ratio and expansion factor, as well as regression equations, to calculate their carbon storage and carbon sequestration. The results showed that the root-to-shoot ratios of Japanese zelkova were 0.240 in the Miaoli stand and 0.250 in the Taitung stand, which were highly similar between the two stands and consistent with the average value of tropical broadleaf forests. The aboveground expansion factor of the Taitung stand was 1.528 Mg m-3, slightly higher than the 1.328 Mg m-3 of the Miaoli stand. The annual and mean aboveground biomass growth of both stands increased with stand age, with the growth rate slowing down only after 24 years. The biomass of Japanese zelkova in the Miaoli stand reached 252.3 Mg ha-1, higher than the average value of broadleaf forests in Asian tropical regions, while that in the Taitung stand was 108.4 Mg ha-1, relatively lower. The average aboveground carbon concentration of Japanese zelkova was 49.0% in Miaoli and 49.6% in Taitung. Using these data, we calculated the average carbon sequestration of the two stands: 1.95 Mg ha-1 yr-1 for aboveground parts and 2.40 Mg ha-1 yr-1 for whole plants in Miaoli; versus 1.81 Mg ha-1 yr-1 for aboveground parts and 2.25 Mg ha-1 yr-1 for whole plants in Taitung. Japanese zelkova can sequester and store large amounts of carbon over the long term, contributing to the mitigation of the greenhouse effect. Keywords: planted forest, carbon storage, carbon sequestration, root-to-shoot ratio, expansion factor