光蠟樹人工林碳貯存量和吸存量之估算

光蠟樹(Fraxinus griffithii C. B. Clarke)是台灣原生種，為台灣最重要的闊葉樹造林樹種之一。本研究以林業試驗所轄區內，位於六龜和太麻里試驗林的兩處光蠟樹人工林為對象，估算其造林木之生物量和生長量，建立根莖比和材積生物量轉換係數等參數和迴歸式，並估算其碳貯存量和吸存量。光蠟樹材積地上部生物量轉換係數，六龜林分為1.14 Mg m-3，高於太麻里林分的0.89 Mg m-3；根莖比則分別為0.235和0.233，兩林分相近。兩林分材積連年生長和平均生長曲線皆隨年齡而呈上升趨勢，但尚未相交。經估算，六龜林分光蠟樹地上部生物量為121 Mg ha-1，高於太麻里林分的114 Mg ha-1。光蠟樹林分全部植物地上部生物量達163-199 Mg ha-1，不低於台灣年齡相近的闊葉樹人工林。經分析光蠟樹植體的碳濃度為48.3-50.9%。推估光蠟樹全株碳吸存量，六龜林分光蠟樹平均可吸存碳2.58 Mg ha-1 yr-1，即吸存9.47 Mg ha-1 yr-1 CO2；太麻里林分則為1.93 Mg ha-1 yr-1，即吸存7.08 Mg ha-1 yr-1 CO2，大致上與台灣主要闊葉樹造林樹種全株碳吸存量相近。但低於熱帶地區闊葉人工林如桉樹等的碳吸存量。以整個生態系而言，兩林分碳貯存量，六龜林分為175 Mg ha-1，太麻里林分為230 Mg ha-1，土壤分別佔生態系碳貯存量的44.7%和47.7%，在生態系碳貯存量上扮演主要角色。

Fraxinus griffithii C. B. Clarke, a native tree species in Taiwan, is one of the most important broad-leaved afforestation tree species in the region. This study selected two Fraxinus griffithii plantation stands located in the Liugui and Taimali experimental forests under the jurisdiction of the Taiwan Forestry Research Institute as research subjects. We estimated the biomass and growth of the planted trees, established parameters including root-to-shoot ratio and volume-to-biomass conversion factors along with corresponding regression equations, and calculated their carbon stocks and carbon sequestration rates.

For the above-ground biomass volume-to-biomass conversion factor, the Liugui stand measured 1.14 Mg m⁻³, which was higher than the 0.89 Mg m⁻³ of the Taimali stand; the root-to-shoot ratios were 0.235 and 0.233 respectively, with minimal difference between the two stands. The annual and average volume growth curves of both stands showed an upward trend with stand age, and had not yet intersected.

The estimated above-ground biomass of Fraxinus griffithii in the Liugui stand was 121 Mg ha⁻¹, higher than the 114 Mg ha⁻¹ of the Taimali stand. The total above-ground biomass of the two stands ranged from 163 to 199 Mg ha⁻¹, which was not lower than that of broad-leaved plantations of similar ages in Taiwan. Analysis showed that the carbon concentration of Fraxinus griffithii tissues ranged from 48.3% to 50.9%.

We estimated that the average whole-tree carbon sequestration rate of the Liugui stand was 2.58 Mg ha⁻¹ yr⁻¹, equivalent to sequestering 9.47 Mg ha⁻¹ yr⁻¹ of CO₂; the Taimali stand had a rate of 1.93 Mg ha⁻¹ yr⁻¹, equivalent to 7.08 Mg ha⁻¹ yr⁻¹ of CO₂. These rates were generally comparable to those of major broad-leaved afforestation tree species in Taiwan, but lower than those of tropical broad-leaved plantations such as eucalyptus.

For the entire ecosystem, the total carbon stocks of the two stands were 175 Mg ha⁻¹ (Liugui) and 230 Mg ha⁻¹ (Taimali) respectively. Soil accounted for 44.7% and 47.7% of the ecosystem carbon stocks, playing a dominant role in the total ecosystem carbon storage.