本文旨在探討臺灣北部羅培山山地雨林之森林結構及物種組成，於１９８９年起在海拔1,136-1,164 m處設立一公頃之永久樣區，樣區內所有胸高直徑（dbh）≧1 cm之木本植物均加以標定、鑑別、度量及紀錄。總共記錄12,934株植物，分屬於70分類群及31科。植株數量最多之科為殼斗科、八角茴香科以及茶科，總計為所有植株之51.5%。依據植株之總底面積之大小，優勢種分別為錐果櫟、紅楠、毽子櫟、紅花八角、山紅柿及綠樟。雙向指標種分析法（DCA）同時可將本樣區畫分成二種林型，其分佈與坡向及暴露程度有密切相關。所區分出之林型以優勢種及特徵種命名之，各為錐果櫟－大明橘型及紅花八角－小花鼠刺型。前者生長於稜脊及東北向坡地，面對強烈東已季風吹襲；後者則分部於隱蔽之西南向坡地及溪谷。兩種林不論在結構及物種組成上均有明顯區別。樣區中大部分的物種在徑級結構上多呈現反J-型或L-型分佈，表示在樣區中均能維持良好之更新狀態。

　　The forest structure and woody species composition were investigated in a montane rainforest of Mt. Lopei in northern Taiwan. All stems ≧ 1 cm dbh were measured and identified for a permanent plot of 1-ha (1,136 to 1,164 m asl.). Approximately 12,934 stems of 70 taxa in 31 families were found . the most abundant families were Fagacease, Illiciaceae, and Theaceae, representing 51.5% of the individual. The dominant species, based on basal areas were Cyclobalanopsis longinux, Machilus thunbergii, Cyclobalanopsis sessilifoia, Illicuium arborescens, Diospyros morrisiana, and Meliosma sequimulata. Comparison of TWINSPAN groupings with the DCA ordination showed a definitive separation of forest types along a topographic gradient. The categorized forest types were the Cyclobalanopsis longinux-Myrsine seguinii type on the ridgetop and northeastern slope facing strong northeastern monsoon, and the Illicium arborescens-Itea paviflora type on the relatively protected southwestern slope. Evident differences of the composition and structure were observed between these two forest types. Size-class structures of most species showed an inverse J-shaped or an inverse L-shaped distribution, both indicators of a continuous recruitment in this permanent plot.