本論文係針對南投縣信義鄉台大實驗林神木溪保護林之天然林進行研究調查,研究樣區海拔高度約1,490~1,530m間,為一面積0.7ha長方形樣區,其中共有70個10m×10m的小區。研究目的在於了解其森林植物組成、優勢樹種徑級族群結構與植株空間分佈型態。研究結果記錄到的維管束植物共有61科112屬163種。冠層優勢樹種為假長葉楠、台灣光臘樹、赤楊、長葉木薑子和瓊楠等。從群團分析與TWINSPAN分析分群結果得知,各小區間植物組成差異不大,顯示林內並無明顯孔隙小區存在。冠層優勢樹種的族群徑級結構呈多樣化類型:赤楊、台灣光臘樹等代表先驅樹種呈鐘型結構;長葉木薑子、瓊楠等林下更新良好的種類則呈反J形或L形結構;族群更新呈階段性的假長葉楠與台灣雅楠為扭曲S。由此可推論本樣區森林屬於演替中期。各小區中冠層樹種的小苗數量與草本覆蓋度呈中度負相關,相關係數為-0.42(P值=0.0002)。不同優勢樹種的植株空間分佈與其族群結構型態有密切相關。樣區中所有小苗的分佈呈現明顯的群聚分佈,但隨著徑級的增加則會逐漸偏向隨機分佈。
The aim of this study is to investigate the vegetation which is located at Shenmuhsi Forest Reserve of Experimental Forests of National Taiwan University, Nan-tou County, Taiwan One rectangular plot, occupying about 0.7 ha in size, was divided into 70 small plots, each one of 10m×10m. The altitude of the rectangular plot ranges from 1490 meters to 1530 meters above sea level. The composition of forest vegetation, population structure of dominant trees, and spatial patterns of the trees were investigated in this study. A total of 163 species of vascular plants were recorded in this study. These 163 species belong to 61 families and 112 genera. Among them, Alnus formosana, Beilschmiedia erythrophloia, Litsea acuminate, Machilus japonica, and Fraxinus griffithii were the dominant canopy species. The results from cluster analysis and TWINSPAN analysis showed no significant difference between small plots in plant composition. Therefore, it suggests that no obvious gap exists in the large plot. The analysis of diameter class distribution of the dominant species in the canopy resulted in three main distribution patterns are shown as follows. (1) Bell-shape represented by some pioneer trees, such as Alnus formosana and Fraxinus griffithii. (2) Inverse J-shape or L-shape represented by some well-generated trees, such as Litsea acuminate and Beilschmiedia erythrophloia. (3) Rotated-sigmoid-shape represented by some periodically-regenerated species, such as Machilus pseudolongifolia and Phoebe formosana. According to research the forest is still at a middle stage of the development. The numbers of seedlings of dominant species are negatively correlated with the coverage of herbaceous plant with a correlation coefficient -0.42 (P value=0.0002). Spatial patterns of canopy dominant tree species are closely related to their population-structure. Seedlings occurred with clumped pattern, but changed into a random spatial pattern when the tree diameter increased.