相思樹(Acacia confusa Merr.)具有不擇土質、生長迅速、適應力強之特性，是良好的薪炭材。早期是重要的造林樹種，所以台灣低海拔普遍種植。在近三十年因薪炭材需求降低，相思樹人工林不再撫育，於是相思樹人工林逐漸被原生植物入侵，如今已成次生林。本研究在了解目前陽明山區相思樹人工林下自然更新及原生植物入侵生長後之狀態。樣區設於陽明山地區，放任後未再受人爲干擾的均質次生林三個，（GPS分別：東經121°32'08"北緯25°08'42"；東經121°32'41"北緯25°08'33"；東經121°32'23"北緯25°07'46''），在三個次生林內分別取足夠量相思樹樣株，並分別以相思樹爲中心，其樹蔭下3公尺爲半徑之(3×3)π平方公尺之圓形面積爲一小樣區。以個別次生林爲單位，由調查數據來計算個別調查據點之Simpson's歧異度指數及重要值指數(IVI)，以了解目前相思樹人工林自然演替之情況。由調查數據知大徑級相思樹下無相思樹小苗及稚樹，但林下的原生植物如紅楠、江某、樹杞、九節木、燈稱花等植物更新良好，稚樹數量多且分布均勻，此類耐陰性樹種日後將會逐漸演替而取代相思樹。
The Acacia confusa Merr. is an evergreen hardwood tree that grow very quickly and can tolerate all kinds of environment. It is the best raw material of artificial coal, so it was an important reforested species for the past 30 year. When the demand for artificial coal of A. confusa was decreasing, the A. confusa artificial forest without disturbance about 30 years. This study is to set up 3 site of secondary forest in Yang-Ming Mount (GPS: E 121°32'08"N 25°08'42" E 121°32'41" N 25°08'33" E 121°32'23" N 25°07'46"), and each site sampling enough number of A. confusa and around every A. confusa to make a circle of 3×3πm^2 as a sampling unit. To collect all data of sampling units and calculate Simpson's index､ Importance value index (IVI). Finally to estimate the vegetative structure under the canopy of A. confusa in the future. The result of this study are (1) there is no seedling or sapling under the canopy of A. confusa. (2) under the shadow of A. confusa, the native species as Machilus thunbergii Schefflera octophylla, Ardisia sieboldii Psychotria rubra, Ilex asprella not Only have lots of sapling but also have grown very well, so these species will replace the intolerant tree-A. confusa in the future.
