台東地區相思樹與楓香兩人工林碳累積量

相思樹(Acacia confusa Merr.)和楓香(Liquidamber formosana Hance)為台灣最重要的闊葉樹造林樹種之一。本研究以台東縣約30年生的相思樹和約25年生楓香兩林人工林為對象，伐取樣木，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，並估算其碳吸存量和林分碳貯存量。結果顯示，根莖比相思樹為0.296，楓香為0.216，相思樹較高，且與熱帶闊葉林平均值相近。地上部擴展係數相思樹為1.137 Mg m-3，高於楓香的0.855 Mg m-3。兩樹種胸徑生長20年生前楓香生長較快，20年生後相思樹生長較快。地上部生物量連年生長和平均生長皆隨年齡呈上升趨勢，兩曲線尚未相交。相思樹林造林木全株生物量為126.6 Mg ha-1，楓香林造林木則為186.3 Mg ha-1。植體的地上部碳平均濃度，相思樹為48.3%，楓香為48.8%。以此加上粗根碳濃度換算成林分造林木全株碳貯存量，相思樹為60.1 Mg ha-1，低於楓香的90.4 Mg ha-1。以此再換算成林分造林木年平均碳吸存量，相思樹單株碳吸存量為3.50 kg tree-1 yr-1，林分碳吸存量為1.85 Mg ha-1 yr-1；楓香單株碳吸存量為2.78 kg tree-1 yr-1，林分碳吸存量為3.03 Mg ha-1 yr-1。土壤碳貯存量兩林分相近，約為86.0-86.4 Mg ha-1。

Acacia confusa Merr. and Liquidambar formosana Hance are two of the most important broadleaf afforestation tree species in Taiwan. This study targeted two planted forests in Taitung County: a 30-year-old A. confusa stand and a 25-year-old L. formosana stand. Sample trees were felled to estimate the biomass and growth of the afforested trees, establish parameters including root-to-shoot ratio and expansion coefficient, as well as regression equations, and calculate their carbon sequestration amounts and stand carbon storages.

The results showed that the root-to-shoot ratio of A. confusa was 0.296, and that of L. formosana was 0.216; A. confusa had a higher ratio, which was close to the average value of tropical broadleaf forests. The aboveground expansion coefficient of A. confusa was 1.137 Mg m⁻³, which was higher than that of L. formosana (0.855 Mg m⁻³). For the diameter at breast height (DBH) growth of the two tree species, L. formosana grew faster before the 20th year, while A. confusa grew faster after the 20th year. Both the annual and mean aboveground biomass growth exhibited an upward trend with age, and the two curves had not yet intersected.

The total tree biomass of the A. confusa afforested stand was 126.6 Mg ha⁻¹, while that of the L. formosana stand was 186.3 Mg ha⁻¹. The average aboveground carbon concentration of plant tissues was 48.3% for A. confusa and 48.8% for L. formosana. Combined with the carbon concentration of coarse roots, this was converted to the total stand carbon storage of the afforested trees: 60.1 Mg ha⁻¹ for A. confusa, which was lower than the 90.4 Mg ha⁻¹ of L. formosana. This was further converted to the mean annual carbon sequestration of the afforested stands: the per-tree carbon sequestration of A. confusa was 3.50 kg tree⁻¹ yr⁻¹, with a stand-level carbon sequestration of 1.85 Mg ha⁻¹ yr⁻¹; for L. formosana, the per-tree carbon sequestration was 2.78 kg tree⁻¹ yr⁻¹, and the stand-level carbon sequestration was 3.03 Mg ha⁻¹ yr⁻¹. The soil carbon storage of the two stands was similar, ranging from approximately 86.0 to 86.4 Mg ha⁻¹.