臺灣山毛櫸森林之組成與結構

Structure and Floristic Composition of the Beech Forest in Taiwan

臺灣山毛櫸森林為拉拉山保護區最具特色之生態體系，屬落葉林。其分佈北起逐鹿山海拔1,350公尺之稜線，向西南延綿經喀博山、羅培山、塔開山、至盧平山，再朝南延伸至拉拉山。一般多生長於稜線上，數量上以塔開山以北為多。為了解山毛櫸森林立組成結構，於其分佈區之北、中、南三處設置32樣區，每一樣區為100平方公尺。分別調查各樣區內之植物種類、植株數目、胸高直徑及百分比覆蓋度，並鑽取材心以測定年齡。所得資料經分析後顯示山毛櫸森林是由172種所組成其中以山毛櫸佔絕對優勢，其他較常出現的種類有臺灣杜鵑、日本吊鐘花、尾葉灰木、紅星杜鵑、錐果櫟及異葉木犀。林下植物以玉山矢竹及臺灣瘤足蕨之覆蓋度最大。各樣區出現之種數自19～59 種，喬木株數自8～25株。Shannon-Wiener Index介於1.74與2.93之間，平均為2. 32。Simpson's Index介於0.05與0.28之間，平均為0.12。對應分析（Averaging reciprocal analysis）的結果顯示海拔高度是影響山毛櫸森林組成之最重要環境因子。最小變異分析法（Minimum variance analysis）的結果可將32樣區劃分為二主要社會類型。第一類型以塔開山及拉拉山之樣區為主，另一類型以羅培山之樣區為主。山毛櫸樹幹大小結構隨區域而異。拉拉山區以大樹較多，塔開山及羅培山之植株偏小，幼樹所佔比例較拉拉山為大。羅培山山毛櫸年齡結構之分析顯示山毛櫸森林是由不同年齡之植株所組成，但幼齡植株偏低。

In Taiwan, Fagus hayatae Palib. ex Hayata (Taiwan beech) is of particular interest because of its limited and relic-like distribution within the Lalashan Nature Reserve in northern Taiwan. It forms nearly pure stands extending about 18 km along the ridges at elevations of 1,300 to 2,000 m. Three stands, representing northern, middle, and southern ranges of the beech forests, were sampled using thirty-two 10×10 m quadrats. They were surveyed for physiognomy, structure and floristic composition. About 172 species of vascular plants were encountered. Species richness per plot averaged 39. Diversity of trees with a DBH > 1.0 cm was calculated as Shannon-Wiener index (2.34) and Simpson index (0.12). The density was 5700 stems with an average basal area of 56 m2 per ha. The beech contributed more than 76% of the total basal area. Other important species were Rhododendron formosana and Enkianthus perulatus in the subcanopy layer. ln the understory, Yushanian niitakayamensis (dwarf bamboo) usually formed extremely dense layers. Sum of square agglomerative cluster analysis led to the recognition of 3 vegetation types. Reciprocal averaging ordination of the plots suggested a vegetational continuum in response to topographic gradient. Size-class distribution of the beech indicated a unimodal pattern with underrepresentation exhibited in the smallest size-class; however, variation among sampling locations might be present. It also suggested that Taiwan beech was likely to be shade-intolerant. In terms of physiognomy and generic composition, closest affinity appeared to be with the Fagus lucida forest of Mt. Fangchingshan in southeastern China.