雪山翠池地區玉山圓柏植物社會群聚之研究

Abstract

玉山圓柏為臺灣高山林木界線重要物種，在形態上可以區分為喬木型及矮盤灌叢型，是臺灣高山森林生態及環境變遷議題中重要的指標物種，雪山翠池地區之玉山圓柏林為臺灣地區面積最大且最具代表性。本研究針對該區之玉山圓柏群落，進行植物社會組成物種及數量調查、再針對各類型玉山圓柏林進行林木性狀量測，將所得資料進行植群、林分結構、垂直結構、樹冠結構、空間分布及林木競爭等分析，綜合闡述本區域玉山圓柏林之族群結構特性。結果顯示：本區域內計有36科69屬85種(含種以下分類群)維管束植物，蕨類商數為4.11，生活型以半地中植物最優勢(48種, 56.47%)。可劃分為玉山圓柏林型及臺灣冷杉林型等2個優勢林型；喬木型玉山圓柏林木性狀值間，主要是以胸高直徑、樹高、枝下高及樹冠長間有較高的相關性。喬木型及交會帶之玉山圓柏林中，玉山圓柏與臺灣冷杉之胸高直徑分布，均符合負指數分布函數，顯示為反J型直徑分布；透過密度-胸高直徑半對數圖，簡單線性迴歸驗證玉山圓柏天然林三種生長階段林分密度中，以各生長階段之直徑階間的負斜率，說明各生長階段之遞減速率的不同，反映出老熟林不對稱U型死亡率之現象。 垂直結構方面，喬木型玉山圓柏林分成9層個森林層次；交會帶玉山圓柏林分為8個森林層次。樹冠結構方面，就雪山翠池地區整體玉山圓柏林而言，樹冠半徑擴張方向以東至南向為主，玉山圓柏上下層樹冠有著不同方向的擴展趨勢。 玉山圓柏之空間分布隨胸高直徑增大，而趨向於隨機分布。交會帶樣區在小尺度距離下，呈現出顯著聚集分布，而在其大尺度，而呈現隨機分布，矮盤灌叢各樣區整體而言，呈現隨機分布。空間分布關聯分析方面，玉山圓柏初期生長階段與中期生長階段之空間關聯性，呈現負相關，其中距離尺度小於18 m時，呈現顯著負相關。交會帶樣區之玉山圓柏與臺灣冷杉在任何距離尺度下，均呈現無相關之趨勢。 單木競爭方面，競爭半徑10 m為玉山圓柏合理的競爭半徑。以Hegyi單木競爭指數與胸高直徑大小進行迴歸分析，無論在喬木型玉山圓柏林樣區、交會帶玉山圓柏林樣區，顯示均符合冪函數關係。在不同胸高直徑階方面，小徑級植株的競爭強度較大，大徑級植株的競爭強度較小。玉山圓柏在依森林分層而言，平均競爭指數分成4群，以樹冠層之競爭強度較小，下層之競爭強度較高即所受的競爭壓力較大。從競爭指數的面向，可以反映出玉山圓柏達到第4層高度後，其所受的競爭壓力，可以推斷為林分發展中到達樹冠層的門檻。理論生長空間及林木樹冠面積二者在森林層次迴歸線趨勢顯示，由最上層Y1層至最下層Y9層理論生長空間及樹冠面積均有減小之趨勢，在不同胸高直徑階方面，理論生長空間及樹冠面積均随胸高直徑階增大而加的趨勢，上揭研究結果可供後續對玉山圓柏林分動態研究參考。

Juniperus morrisonicola (juniper tree) is one of the important species on the timber line in Taiwan. It is also an indicator species in the alpine ecosystem and issues about environment change. The most representative J. morrisonicola forest was in the Cuei-Chih area on Mt. Xue. The vegetation could be distinguished into 2 categories, arbor and krummholz, by physiognomy . My purpose of this study was to explore the synecology of J. morrisonicola forest in the Cuei-chih area on Mt. Xue. In this paper, the vegetation was surveyed via the contagious quadrat method and the tree characteristics of individual in the juniper forest, ecotone between J. morrisonicola and Abies kawakamii, and krummholz were measured. The data were analyzed to reveal the composition, stand structure, vertical sturture, crown sturture, spatial patterns, and individual competition. The results showed that a total of 85 species of vascular plants belonging to 36 families and 69 genera were recorded in our studied plots. The pteriodophyte-quotient was 4.11. According to Raunkiaer`s life-form system, all the species were determined into five major life-forms that exhibited dominance of hemicryptophytes (56.47%) in this community. The vegetation was classified into 2 types: (1) Juniperus morrisonicola forest type and (2) Abies kawakamii forest type. The high correlation between the tree characteristics of DBH、H、Hc and CL were showed. The diameter distributions of the trees, including J. morrisonicola and A. kawakamii, at the juniper forest and ecotone sites were exhibited as inverse J-shaped. According to the DBH, J. morrisonicola individuals could be divided into 3 growth stages which were early stage (ES), middle stage (MS) and late stage (LS) respectively. Here we could see a trend in diminished rate of these 3 growth stages, as the highest diminished rate in ES, followed by LS and MS. The slope of simple regression of the density-diameter distribution on the Semi-log graph revealed the decreasing rate at different growth stages. It reflected the phenomenon of asymmetric U-shaped mortality in the J. morrisonicola forest stand and also suggested that J. morrisonicola was the dominant species with long longevity in this area. There were 9 layers in the juniper forest and 8 layers in the ecotone forest. The main direction of crown displacement of the J. morrisonicola was eastward to southward. The different directions of crown displacements were showed on the different layers. The spatial pattern would become random distribution with increasing DBH. At the krummholz plots, the aggregative distribution was showed at the short distance scale and the random distribution was showed at the long distance scale. All individuals in the krummholz plots were showed in a random distribution. Negative spatial correlation was detected for trees of J. morrisonicola between ES and MS, especially a significant correlation for the distance scale under 18 m . There was non-correlation between J. morrisonicola and A. kawakamii trees in the ecotone. It was found that ten-meter was an available distance competition scale in this study. The relationship between the competition index and DBH of the objective tree expressed as a power function in all plots. The competition intensity of the objective tree reduced as the DBH increased. The competition indices in different layers of the juniper forest were divided into 4 groups by Duncan test. The results showed low competition intensity in the canopy layer and high competition intensity in the understory. According to the competition index, it reflected an environmental selection in the fourth layer for developing to the canopy layer. The regression line of theoretic growth area and crown area showed that both of them reduced, but they increased as the DBH of the objective tree increased. All of the results would be new information for the further forest dynamic researches in the future.