Pa-Chang River is in Southwestern Taiwan. It originates from Fenchihu, Alishan and flows between Chiayi County and Tainan County. Its total length is 81 kilometer and total basin area is 475 square kilometer. The natural forest communities are mostly in the upper section and fragmentarily spread in the small areas that locate between farms or in complicated topography, e.g. steep slope, area difficult to reach. It is necessary to make inventory and research about these natural forest communities now to gather sufficient vegetation data which will be served as basic reference in the future local environmental management. This study is to investigate and analyze the species composition of broad-leaved forest vegetation in the upper section of Pa-Chang River. The analysis results of the vegetation data by detrended correspondence analysis¡]DCA¡^ and two-way indicator species analysis¡]TWINSPAN¡^classified the sampling plots into four forest types: I. Litsea hypophaea forest type The range of elevation is 743~1003 m. The topographic position is mainly in ridge and upper slope. II. Ficus irisana -Dendrocnide meyeniana forest type The range of elevation is 381~825 m¡CThe topographic position is mainly in lower slope and valley. III. Machilus japonica var. kusanoi -Ficus fistulosa forest type The range of elevation is 764~1229 m¡C IV. Prunus phaeosticta forest type The range of elevation is 1559~1804 m. The topographic position is mainly in upper slope. The study of correlations among environmental gradients and ordination axes indicated that the elevation is the most important environmental factor affecting the vegetation composition and distribution. Topographic position also has obvious influence on vegetation. In addition, the study of population structure shows that regeneration is continuous in present broad-leaved forest, but the forest is also continuously disturbed by artificial activities. The area of natural forest in this area might continuously be decreased, so it is important to gather sufficient vegetation data in time.

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