南仁山區亞熱帶雨林凋落物量及其養分含量之研究

Abstract

本研究於南仁山亞熱帶雨林三公頃永久樣區內，採用系統取樣法設立50個收集網，按月收集凋落物，分成葉、枝條、花、果和碎屑等部份，且依樹種分別記錄乾重量。並分析落葉中氮、磷、鉀、鈣和鎂等元素含量，以及收集地面落葉層以測定分解商數。 年凋落物總量1992年為5.16t/ha，1993年為5.81t/ha，與其他亞熱帶森林相比，本區凋落物量偏低。樣區中各生育地之凋落物量，以背風坡區高於迎風坡區。凋落高峰期出現在3、4月生長季和9-12月盛行東北季風時期，並受颱風和焚風影響而導致較高的落葉量。此外，各組成樹種在季節性變化的表現上有所不同，依高峰出現時間大致分為東北季風期、生長季和無明顯高峰期等三種類型。 經由RDA和變方分析的結果，落葉之養分含量在不同地形、植被類型和月份間皆有差異。營養元素中氮和磷含量較其他熱帶和亞熱帶森林為低；落葉分解商數為1.71，表示分解速率快。可見本區森林養分利用效率頗高，營養循環情況良好。 南仁山區在各項地形氣候因素共同作用下，形成了不同植物社會，而造成凋落物在質與量上的不同，進而影響營養元素之含量。

Fifty traps were placed in a systematic design within a 3-ha permanent plot established in Nanjenshan Subtropical Rain Forest. Litterfall was collected over a 2-year period. All sample were seperated into leaves, branches, flowers, fruits and miscellaneous fraction, each of which were then sorted into species level. Concentrations of nitrogen, phosphorus, potassium, calcium and magnesium in leaf-litter were analyzed, and decomposition quotient (KL) values were calculated from the amount of collected litterfall on the ground surface per unit area. Annual litterfall for 1992 and 1993 were 5.16t/ha and 5.81t/ha; respectively, less than the production observed in most subtropical forests. The results of ANOVA indicated that litter production was significantly higher in leeward region than in windward region within the permanent plot. There were two pronounced peaks of total litterfall which seemed to occurred in growing seasons (from March to April) and during the north-eastern monsoon periods (from September to December). Besides, typhoon and foehn might cause much leaf and branch fall as well. The patterns of leaf fall varied with tree species. Thay markedly fell into 3 different patterns. Results of RDA and ANOVA test indicated that there were significant differences in nutrient content between different topographic positions, vegetation types and seasons. The concentrations of nitrogen and phosphorus in leaf-litter were considerably lower in comparison to those estimated in other tropical and subtropical ecosystems. However, the average of decomposition quotient value, calculated as 1.71, showed a high decomposition rate. These suggested a high nutrient use efficiency and a fast nutrient cycling seemed to occur in the forest.