蓮華池森林動態樣區之地形與土壤性質對於林木豐富度及生質量之影響

Abstract

森林為地球上物種豐富度最高的地方，且支持各種不同生態系統的相互運作，其中植物物種的森林多樣性，更是扮演著重要的角色。因此，藉由瞭解與維護植物多樣性，可達到森林保育管理和森林永續經營之目標。樹木標籤和樹木地上部之生質量常用來鑑定森林狀態，藉由樹木標籤可瞭解不同樹種的分佈，而樹木地上部之生質量則是可作為森林碳循環的指標。本試驗地點位於台灣南投縣蓮華池25公頃森林動態園區，於625個20 x 20 m的網格中隨機選取102個採樣點，採集0-5 cm和5-15 cm之土壤各500 g，分析項目為pH、導電度、有機物含量、氯化鉀溶液可萃取銨態氮和硝酸態氮、有效性磷和鉀、陽離子交換容量、可交換性鈣、鎂、鉀和土壤保水度。以每個採樣點為中心，計算半徑10 m範圍內總物種數為物種豐富度 (species richness)，計算樹木數目為立木數 (tree abundance)，並計算每公頃內所有樹木之地上部生質量，以主成分分析 (principle component analysis)、多元線性回歸 (multiple linear regression)和冗餘分析 (redundancy analysis) 探討園區內各項地型與土壤因子與林木豐富度及生質量之關聯。多元線性回歸的結果顯示，5-15 cm土壤因子對樹木物種豐富度和立木數中的變異較有影響力，而0-5 cm土壤則對樹木地上部生質量的變異較有影響力。進一步利用冗餘分析，以同時探討土壤和地形對樹木物種豐富度、立木數和樹木之地上部生質量的影響，結果顯示5-15 cm較0-5 cm的土壤可以解釋較多的總變異。5-15 cm土壤因子中以陽離子交換容量和導電度之影響力最大，而0-5 cm的土壤因子中有以機質含量和平均海拔之影響力最大。藉以推論，蓮華池森林動態園區 0-5 cm土壤的養分含量主要和有機質含量有關，並直接影響樹木的地上部生質量，而其5-15 cm土壤的養分含量和其陽離子交換容量的高低有關，而不同的養分含量有利於某些樹木物種的生長，因此，5-15 cm土壤的陽離子交換容量影響樹木物種的分佈並有助於樹木和土壤間的穩定關係。

Forest plant diversity is the basis of many ecological services. Thus understanding forest plant diversity for the purpose of conservation, management, and sustainable use becomes an important topic for many ecologists. Tree tagging and tree aboveground biomass are often used as indicators to examine the quality of a forest. Tree tagging shows the overall distribution of the tree species, while aboveground biomass is an important carbon pool in the forest ecosystem. In this study, 102 sampling sites were randomly chosen in the Lienhuachih Forest Dynamic Plot in Nanto, Taiwan. In each sampling site, 0-5 and 5-15 cm soil were collected, and soil pH, soil organic matter (SOM), electrical conductivity (EC), cation exchange capacity (CEC), available potassium and phosphorous, ammonium nitrogen (NH4-N), nitrate nitrogen (NO3-N), exchangeable calcium, magnesium and potassium, and water holding capacity (WHC) were measured. Species richness, abundance, and aboveground biomass were calculated within the circle of 10 m radius around the sampling site to study the effect of soil properties of different soil layers and topography on tree distribution. The results of multiple regression showed that 0-5 cm soil explained more variation in aboveground biomass, while 5-15 cm soil explained more variation in tree species richness and abundance. Redundancy analysis showed that 5-15 cm soil exerted a greater overall influence on species distribution and aboveground biomass. The influence of 0-5 cm soil was mostly associated with SOM, while the influence of 5-15 cm soil was mostly associated with CEC and EC. Overall, SOM contributes to the nutrient availability of 0-5 cm soil, and the available nutrient contents directly affect aboveground biomass. The CEC of 5-15 cm soil becomes an important factor in determining the availability of certain nutrients leached from 0-5 cm soil. Thus the presence and absence of certain nutrients in 5-15 cm soil might favor the growth of certain tree species, and CEC subsequently shapes the overall species distribution and contribute to the stability of soil-tree species relationship.