南仁山區低地雨林地被層植物之研究

Abstract

本研究於南仁山熱帶低地雨林永久樣區之重複樣區進行地被植物調查，以系統取樣方式調查樣區之地被植物組成與覆蓋度，研究目的為（1）瞭解南仁山低地雨林之地被層的組成；（2）探討地被組成與環境因數間的關係；（3）探討林隙對地被組成的影響，以及（4）探討小苗之更新情形是否受地被覆蓋度及林隙時期之影響。 對兩個已建立完成位於南仁山溪谷的永久樣區（2.1公頃及0.64公頃）之地被植物進行系統取樣，調查面積分別為960m2及324m2，共記錄210種植物，分屬於88科174屬。2.1公頃樣區之第一優勢種為莎勒竹（Schizostachyum diffusum (Blanco) Merr.），其次為冷清草（Elatostema lineolatum Forst. var. major Thwait.）及黃藤（Calamus quiquesetinervius Burret.）等；優勢科以禾本科（Poaceae）為最優勢，次為蕁麻科（Urticaceae）及棕櫚科（Areaceae）等。0.64公頃樣區之第一優勢種為冷清草，其次為莎勒竹及黃藤等；優勢科則為蕁麻科、禾本科及棕櫚科。兩樣區的相似性係數（ISMO）達77％，因此本研究結果對南仁山海拔300m以下近溪谷地區低地雨林之地被組成具一定的代表性。 將樣區之地被組成進行雙向列表分析法（TWINSPAN），可區分為三種類型。第一型以莎勒竹優勢度最高，特徵種為突尖小毛蕨（Christella acuminata (Houtt.) Lev. var. kuliangensis (Ching) Kuo），多分佈於林隙及林隙附近，應是與林隙相關之地被類型。第二型以莎勒竹為優勢，但其覆蓋度顯著低於第一型，特徵種為麥門冬（Liriope spicata Lour.），為樣區中較為普遍的地被類型。第三型以冷清草為優勢，特徵種為刺蕨（Egenolfia appendiculata (Willd.) J. Sm.），本型分佈於西南坡面的凹地中，為較濕潤環境的地被類型。 典型對應分析（Canonical Correspondance analysis，CCA）的結果說明地被植群的分佈受坡度（slope）、海拔（elevation）、樹冠破空率（canopy openness％）及葉面積指數五（LAI5 Ring）等五項環境因數影響；坡向朝東北方之樹冠破空率顯著較高，葉面積指數顯著較低，而地被植群分佈也隨之變化；地被類型的第一型多分佈於樹冠破空率較高及東北坡向的環境，第二型為廣泛分佈的地被類型，第三型則多位於西南坡向。植物種類分佈與林隙時期之相關以X2-test of goodness of fit檢定，分析的72種植物中有29種植物之覆蓋度多寡受林隙形成之影響。根據各植種生育地之差異可分為四種地被植物分佈類型，分別為廣泛分佈型（I）、廣泛分佈型（II）、西南坡向型及林隙型。 兩樣區之木本植物小苗共調查到6287棵，計35科56屬70種；依據高度與株數之分佈情形推測小苗高度在30 cm級以上之數量呈現較為穩定的狀況。小苗高度30cm級以上，數量較多的前三名依序為雞屎樹（Lasianthus obliquinervis Merr.）、九節木（Psychotria rubra (Lour.) Poir.）及大葉樹蘭（Aglaia elliptifolia Merr.），皆為灌木種類的小苗。典型對應分析結果顯示小苗的分佈受地形因數、樹冠特性因數及地被植群的影響。不同的地被組成影響小苗的建立，地被覆蓋度較高，則小苗高度30 cm級以上的株數較少。 整體而言，地被組成受地形因數影響下，有不同的地被類型及分佈區域，地被類型的第一型與林隙相關，多分佈於樹冠破空率較高及東北坡向的環境，第二型為廣泛分佈的地被類型，第三型則為潮濕環境的地被類型，多位於西南坡面的凹地中；不同的地被組成亦影響小苗的建立，地被覆蓋度較高，則小苗高度30 cm級以上的株數較少。林隙對地被亦有影響，但其影響程度因林隙大小而有所不同，大林隙可使地被組成產生變化，而小林隙則未改變地被組成。

This investigation was conducted at a lowland rain forest in Nanjenshen area to study understory vegetation distribution pattern, the relationship between species distribution and environmental gradient, and the role of understory vegetation affecting tree seedling bank. Study sites were located systematically along the transects in a 2.1-ha permanent plots and a 0.64-ha permanent plot (with total sampled areas of 960 m2 and 324 m2, respectively). All understory vascular plant species in each 1×1 m2 area were identified and the coverage for each species was recorded as well. The understory vegetation investigated was composed of 210 species, belonging to 174 genera and 88 families. In the 2.1-ha permanent plot, dominant species included Schizostachyum diffusum, Elatostema lineolatum var. major and Calamus quiquesetinervius, while dominant families are Poaceae, Urticaceae and Areaceae. The 0.64-ha plot was dominated by the species of Elatostema lineolatum var. major, Schizostachyum diffusum and Calamus quiquesetinervius, and by the families of Urticaceae, Poaceae and Areaceae. The Similarity index ISMO between these two permanent plots was 77%. According to TWINSPAN analysis, the understory communities in the study plots could be divided into three groups. The first group was identified as Gap Type with indicator species of Christella acuminata var. kuliangensis and dominated by Schizostachyum diffusum. The second group was Widespread Type dominated by Schizostachyum diffusum and its indicator species was Liriope spicata Lour. The third group was thought to be Creek type and dominated by Elatostema lineolatum var. major. and its indicator species was Egenolfia appendiculata. Canonical correspondence analysis (CCA) indicated that aspect, elevation, canopy openness, and LAI 5 Ring were the main environmental factors related to understory vegetation distribution. According to x2-test of goodness of fit analysis, the distribution of 29 species was related to the Gap or understory sites. A total of 6287 seedlings investigated included 70 species, belonging to 56 genera and 35 families. Survival rate of the seedlings above 30cm height was more stable than those under 30cm. Of those seedling above 30 cm, Lasianthus obliquinervis, Psychotria rubra, and Aglaia elliptifolia were the most dominant species. Canonical correspondence analysis (CCA) suggested that seedlings composition and distribution were influenced by topographic and light factors, and the understroy vegetation. Overall, the understory vegetation was influenced by topographic factors, while the variation of understory vegetation affected the seedlings bank. The effect of gap on understory vegetation depended on the gap size. The larger gaps could change the composition of understory vegetation.