桶後溪為南勢溪上游之一支流,位於台北縣烏來鄉境內,海拔由烏來標高150m上昇至發源地烘爐地山標高1,166m。 本區濱溪植群研究以36個樣區及八項環境因子加以分析,應用雙向列表歸類法配合降趨對應分析,可將之分為三植群型及五亞型。分別是:A大葉楠林型,其下再分三亞型,即A1大葉楠-豬母乳亞型、A2大葉楠-山桂花亞型、A3大葉楠-九節木亞型;B烏來柯林型;C紅楠林型,其下再區分為:C1紅楠-森氏紅淡比亞型、C2紅楠-短柱山茶亞型。而植群之分化與海拔高度、海拔方位指數、溪流寬度、全天光空域等因子相關性較高;顯示影響植群變異的可能原因為海拔高度、土壤水分及太陽輻射量。
Tonghou Stream is a tributary of the upper Nansi River located in Wulai, Taipei County. It covers on elevations ranging from 150m at Wulai to 1166m at Honglue Mountain. A total of 36 plots, with S environmental factors in the riparian area were studied. Two-way indicator species analysis (TWINSPAN) in conjunction with detrended correspondence analysis (DCA) were applied to classify the riparian vegetation of Tonghou Stream into 3 types and 5 subtypes: A. Machilus kusanoi Type: Al Machilus kusanoi-Ficus fistulosa Subtype, A2 Machilus kusanoi-Maesa japonica Subtype, A3 Machilus kusanoi-Psychotria rubra Subtype. B. Castanopsis uraiana Type, C. Machilus thunbergii Type: C1 Machilus thunbergii-Cleyera japonica var. morii Subtype, C2 Machilus thunbergii-Camellia brevistyla Subtype. The differences of various types of plant associations were related to differences in elevation, land exposure index, stream width, and full light spaces. In other words, variances of plant associations were possibly influenced by altitude, soil moisture, and solar radiation.