南仁山區亞熱帶雨林海拔梯度與植被組成、結構、歧異度及分佈類型的關係

Abstract

本研究的目的在瞭解南仁山亞熱帶雨林（subtropical rain forest）之梯度性歧異度（β-diversity）及海拔梯度上的分佈類型。在南仁山西北側稜線上設立一長500公尺，寬20?40公尺，海拔高度200?467公尺，面積約1公頃的長形樣帶。紀錄樣帶內DBH?1公分的木本植物種類及其株高、生長狀況等，並加以編號。 樣帶內共紀錄49科91屬139種植物，其中喬木有99種，灌木30種，籐本10種。以革葉冬青為最大優勢，重要位佔7.41％，共有植株533株。其次為細脈赤楠，重要值6.02％，植株200株。前十種優勢種即佔43.55％，優勢度非常集中。 由降趨對應分析法（Detrended-corresponding analysis）可將此樣帶沿海拔梯度區分成三群植被帶。第I群位於溪穀附近海拔330公尺以下，以白榕、紅果椌木及南仁鐵色為最大優勢。第II群位於海拔330-390公尺之間，以草葉冬青、江某、南仁鐵色為優勢。第III群位於海拔390公尺以上，以細脈赤楠、草葉冬青及錐果櫟為優勢。 將種的優勢度沿海拔梯度排列，可以分成四種主要分佈類型。一、溪穀優勢型：以咬人狗、茄冬、白榕為典型種類；二、稜線中段優勢型：以倒卵葉山龍眼為典型種類；三、山頂優勢型：以嶺南椆、錐果櫟、金平氏冬青為典型種類；四、廣泛分佈種：以九節木、南仁鐵色、石苓舅及水同木為典型種類。 科的優勢度也有沿海拔梯度改變的趨勢。其中桑科、大戟科、茜草科、楝科隨海拔增高而減少；樟科、冬青科、殼鬥科則相反的在較高海拔形成優勢。此種改變的趨勢反應出南仁山區在海拔梯度上由熱帶到溫帶的植群帶改變。 樣帶的調查共發現6屬15種在海拔梯度上有分化的現象。分別是楨楠屬、瓊楠屬、山龍眼屬、冬青屬、栲屬、及椆屬。 以樣區間的社會性係數（community coefficient）及海拔高度差作圖，求出迴歸線方程式：Y＝-0.0019x＋0.5925，其斜率即為梯度性歧異度指數。此結果顯示：1．在同一海拔高度重覆取樣，則相似性指數僅達0.6，顯示社會性歧異度（α-diversity）高。2．若海拔相差300公尺，則植物社會完全改變。本區高β-歧異度的原因可能是由於強烈東北季風造成生育地異質性及恆春半島特殊地理位置所致。

The purpose of this study is to understand the β—diversity and spatial pattern of the Nanjenshan forests along an altitudinal gradient. A one-hectare transect, which is 500 m long and 20-40 m wide at altitudes of 220-467 m, was established on the northwestern ridge of Nanjenshan, Kenting National Park. Inventory of woody plants in the transect was conducted, and DBH, height and growth condition for each individual were recorded. A total of 139 woody species, belonging to 49 families and 91 genera, were recorded. Among them 99 were trees, 30 shrubs and 10 lianas. The most dominant species is Ilex cochinchinensis with an important value (IV) of 7.61% and 533 individuals; the second dominant one is Syzygium euphlebium with an important value of 6.02% and 200 individuals. In general, the forest shows a strong dominance, that is, 43.55% of the dominancewere shared by the first ten species. The result of Detrended-Corresponding Analysis (DCA) shows that the transect can be divided into three vegetation zones along the altitudinal gradient. Zone I is located near river valley with elevations between 220 m and 330 m, and dominated by Ficus benjamina, Dysoxylum kuskuensis, Drypetes hieranensis. Zone II is located at elevation 330-390 m, and dominated by Ilex cochinchinensis, Schefflera octophylla, Drypetes hieranensis. In Zone III between 390 m to 470 m, Syzygium euphlebium, Ilex cochinchinensis, and Cyclobalanopsis longinux are dominant species. Four types of species distribution pattern were classified based on the peak of dominance along the altitudinal gradient: 1) lower elevation type, examplified by Laportea pterostigma, Bischofia javanica, Ficus Benjamina; 2) middle elevation type, examplified by Helicia rengetiensis; 3) high elevation type, examplified by Cyclobalanopsis championii, Cyclobalanopsis longinux; 4) wide distribution type, examplified by Psychotria rubra, Drypetes hieranensis, Glycosmis citrifolia and Ficus fistulosa. Dominance at the family level also tends to change along the altitudinal gradient. Dominance of Moraceae, Euphorbiaceae, Rubiaceae and Meliaceae decreases with increasing altitude. In contrast, that of Lauraceae, Aquifoliaceae and Fagaceaee increases along with altitude. This pattern indicates that a sharp transition from semi-tropical to temperate forest type is evidence. In this study, 15 species of six genera, Machilus, Beilschmiedia, Helicia, Ilex, Castanopsis and Cyclobalanopsis, are found with such niche differentiation along the altitudinal gradient. The slope of regression formula, Y= —0.0019x+0.5925, which is plotted by community coefficient to altitudinal differences, is β—diversity. This result indicates that: 1) when repeated samplings are done at the same elevation, the community coefficient is only 0.6, indicating high α—diversity; 2) when the altitude varies over the range of 300 m, the plant community completely changes. These result agree with the conclusion of previous studies that high β—diversity is resulted from the heterogeneous habitats under a strong influence of northeast seasonal wind, and from the geographically special location of the Hengchun Peninsula.