南仁山低地雨林之物種組成及分佈類型

Abstract

為了瞭解熱帶亞洲之北界邊緣之森林結構及物種組成，研究中將南仁山區四個森林動態樣區、樣帶及蘭嶼樣區內所有胸高直徑大於1公分之木本植物均納入加以分析。總共包括109,060株植物，分屬於59科、141屬及255種。雙向指標種分析法(TWINSPAN)及降趨對應分析法(DCA)同時清楚的將樣區分成五個類型，其中蘭嶼樣區與南仁山區的四個樣區最先區分出來，主要是因為蘭嶼樣區中包含了許多馬來西亞植物區系的種類。之後切分出之植群型和海拔、坡向及風力影響有關。研究結果顯示植物組成與森林結構受到了植物地理區、各區域內的地形變化及其導致的風力梯度之影響甚深。在分佈類型分析上，本研究使用Ripley的K程序進行分析，分析對象為整個樣區中株數大於15株的植物種類。結果顯示大多數的種類在欖仁樣區及南仁湖樣區為聚集分佈，但在南仁山第一及第二樣區中則聚集分佈的比例降低。若只考慮大樹，每個樣區的聚集分佈比例都隨之降低，特別在南仁山第二樣區所有的植物都是隨機分佈，這些結果和先前棲地分析的結果類似。在不同的徑級下，樣區中有41.2%的植物種類其小樹的聚集程度較大樹為高，而有51.8%的種類則呈現相反結果，大樹的聚集程度較小樹為高。本研究顯示南仁山區大多數的樹種分布和棲地的異質性有關，而這棲地的異質性極可能受到季風的影響。

The lowland forests in southern Taiwan and on Lanyu Islet are parts of the remnants of tropical rainforests. Data from four plots and one transect in the Nanjenshan Reserve of southern Taiwan and one plot on the Lanyu Islet were used to understand the structures and compositions of the lowland rainforests at the northern margin of tropical southeastern Asia. All free-standing woody plants in these plots with DBH ≥ 1 cm were included in the analyses. A total of 109,060 individuals belonging to 255 vascular tree species in 141 genera and 59 families were recorded. To provide a quantitatively based classification of these assemblages, both two-way indicator species analysis (TWINSPAN) and detrended correspondence analysis (DCA) were performed. The forests of Nanjenshan and Lanyu were clearly separated in the initial TWINSPAN division and also along the first DCA axis, and this was attributed to the existence of a greater proportion of southern Malesian floristic elements in the Orchid Island forests. Further subdivisions of the dataset into five forest types were closely related to elevation, aspect and exposure. The results suggested that forest composition and structure of the study forests were strongly related to biogeography, regional topographical features and exposure. Spatial patterns of trees in the four lowland rainforests in Nanjenshan were evaluated by Ripley's K functions. Among the 256 species with more than 15 individuals in these four plots, most species were aggregated in Lanjenchi and Nanjen Lake plots but lower aggregated intensity in Nanjenshan plots I and II. Considering only larger trees, the proportion of aggregation were reduced in each plot, and all species were randomly in Nanjenshan plot II. About 41.2 % of the species shifted from highly aggregated patterns to a low level of aggregation or random distribution with an increase in tree size, and 58.8 % of the species had an inverse pattern. This study revealed that distributions of most species within the Nanjenshan forests were related to habitat heterogeneity and possibly the monsoon wind effect.