臺灣南部欖仁溪樣區之森林結構與物種組成

Species Composition and Structure of the Lowland Subtropical Rainforest at Lanjenchi, Southern Taiwan

南仁山區為臺灣南部保留之低地亞熱帶雨林。為了包含更多的地形變異及瞭解季風對森林結構及物種組成的影響，本研究將原先3公頃的欖仁溪樣區擴大至5.88公頃。樣區內所有胸高直徑大於1公分之木本植物均加以標定、鑑定、測量及記錄。整個樣區共記錄60,146株木本植物，分屬於42科83屬及136種。樣區中樹種累積底面積以殼斗科、茶科、五加科、冬青科、樟科及八角茴香科最為優勢。大多數的物種在徑級上呈現反J-型或L-型分佈，表示這些種類在樣區中皆能良好的更新。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四類型，其分佈與地形位置有關，此四型依照特徵種-優勢種（生育地類型）命名分別為：恆春石斑木-紅花八角林型（迎風型），小葉樟-紅花八角林型（緩風型），猴歡喜-革葉冬青林型（背風型）及石苓舅-山龍眼林型（溪谷型）。本研究之結果顯示植物組成與先前之3公頃樣區類似，且同時呈現出地形變化及其導致的風力梯度對此森林物種組成及結構之影響甚深。

The forest in Lanjenchi is a remnant patch of subtropical rainforests in southern Taiwan. In 1998, the previous Lanjenchi plot was enlarged from 3 ha to 5.88 ha in order to include more topographical variation and understand how the gradient of wind stress controls forest structure and species composition. All free-standing woody plants in these plots with diameter ≥ 1 cm were identified, measured, tagged and mapped. A total of 60,146 individuals belonging to 136 vascular tree species in 83 genera and 42 families was recorded. Families with the largest cumulative basal areas were Fagaceae, Theaceae, Araliaceae, Aquifollaceae, Lauraceae and Illiciaceae. The size-class distribution of all species showed that most species were in good recruitment patterns with the most stems in small size classes. The results of two-way indicator species analysis (TWINSPAN) classified the sampling plots into four forest and habitat types: 1. Rhaphiolepis indica var. hiiranensis - Illicium arborescens (Windward I) type; 2. Cinnamomum brevipedunculatum - Illicium arborescens (Windward II) type; 3. Sloanea formosana - Ilex cochinchinensis (Leeward) type; and 4. Glycosmis citrifolia - Helicia formosana (Creek) type. The forest composition changes formed a sequence on the topographic gradient from the most exposed windward ridges and north-east-facing slopes to more sheltered leeward footslopes and creeks. Further studies using detrended correspondence analysis (DCA) and canonical correspondence analysis (CCA) confirmed the results of TWINSPAN, and showed the important roles of the topographic variables in the distribution of most tree species.