二氧化碳通量長期生態監測試驗地林分構成主要為柳杉人工林，在系統取樣範圍中有臺灣杉人工林、紅檜人工林、臺灣杉柳杉混合林、山櫻花景觀林、孟宗竹林以及草坪區。經統計，柳杉人工林齡級跨度50至86年生，總平均胸徑與樹高值為36.3 cm、22.2 m，臺灣杉人工林齡級集中於43與46年生，總平均胸徑與樹高值為34.1 cm、23.6 m，紅檜人工林齡83年生，平均胸徑與樹高為46.2 cm、25.8 m。林下植物分布最多且最廣泛者為紫苧麻、牛奶榕、山香圓與闊葉樓梯草。所有樣區木本植物種類記錄共21科28屬31種，尤其樟科植物佔總種數的28%，地被植物共記錄43種，包括蕨類植物3種，雙子葉植物29種，單子葉植物11種，分屬於25科，41屬。不同的林分構成與底下的林下植物，在立體結構上能觀察到差異性，臺灣杉人工林林下植物多樣性最高，而柳杉人工林、紅檜人工林與臺灣杉柳杉混合林所記錄到的林下植物並無明顯不同之處。山櫻花景觀林主要地被植物為巴西水竹葉，次要地被植物為咬人貓。孟宗竹林林下地被覆蓋度稀疏，唯臺灣天南星是只出現在竹林下的特有種。草坪區地被植物為假儉草，在邊緣破碎處仍有其他植物發生。雖受到系統取樣的影響，植物種類與數量的記錄尚不及過去文獻紀載，透過背景調查資料的建立與文獻相佐，能作為生物量分布、碳儲存量、碳匯、二氧化碳貢獻來源等有效的推估依據。

The stand composition in carbon dioxide flux long-term ecosystem research site is mainly Cryptomeria plantation. In which, this study has systematically sampled Taiwania plantation, Red cypress plantation, Taiwania fir and Cryptomeria fir mixed stand, Cherry blossoms landscape forest, Moso bamboo forest and lawn area. The results have showed that age range of Cryptomeria plantation from 50 to 86 years old, and average DBH and H are 36.3 cm and 22.2 m, respectively. Taiwania plantation age-class focus on 43 and 46 years old and average DBH and H are 34.1 cm and 23.6 m. Red cypress plantation is 83 years old and average DBH and H are 46.2 cm and 25.8 m. The widely distributed understory plants are Oreoenide pedunculata, Ficus erecta, Turpinia Montana and Elatostema platyphylloides . In the sample area, the 31species of 28 genera of 21 families understory woody plants have been recorded. Additionally, lauraceae has shared 28% of the total number of species and there are 43 species groundcovers including 3 species of pteridophytes, 29 dicotyledonous, and 11 monocotyledonous belonging to 41 genera of 25 families. For three-dimensional structure, the differences of understory plants are found according to their stand compositions. Taiwania plantation has been recorded highest plant diversity, but limited differences are found among Cryptomeria plantation, Red cypress plantation, Taiwania fir and Cryptomeria fir mixed stand. The major ground cover of Cherry blossoms landscape forest is Tradescantia fluminensis , and the second one is Urtica thunbergiana . Arisaema formosanum is an endemic species and is sparse under Moso bamboo forest. The major ground cover in Lawn area is Eremochloa ophiuroides , and other plants are found at the edge and gap. The recorded species of this investigation is less than the past literature that might be due to systematically sampling approach. By establishing background investigation and further comparing to literature, it could be an effective baseline investigation for estimating distribution of biomass, carbon stocks, carbon sequestration, and carbon dioxide contribution sources.