Long-term ecological research in the Yuanyang Lake forest ecosystem I. Vegetation composition and analysis

The Yuanyang Lake Nature Preserve is located in the northeastern part of Hs inchu County, Taiwan. It is the uppermost head water of the Tahan River wat ershed at 1,650-2,432 m altitude. The total area of the natural preserve is about 374 ha, of which the lake occupies about 3.6 ha and the marshy area encircling the lake about 2.2 ha. The surrounding hillsides are dominated b y cypress forests. Floristic analyses by means of Two-Way Indicator Species Analysis (TWINSPAN) and Detrend Correspondence Analysis (DCA) were conduct ed at the site. The findings of the former analysis concluded that the fore st could be divided into two communities, namely a coniferous-hardwood comm unity, and a swamp or early succession community. The former comprises (a) Chamaecyparis formosensis, C. obtusa var. formosana, Tsuga chinesis and (b) Rhododendron mariseii-Rhamus cranata. The swamp or early succession commun ity comprises (a) Potamogeton octandrus, Sparganium fallax and Schaenoplect us mucronatus, (b) Miscanthus transmorrisonesis and Schoenoplectus morrison ensis. In total, there are 185 species of vascular plants, in 115 genera an d 71 families. The cypress community has reached its stable stage, and Cham aecyparis species are capable of self regeneration. A successional trend of vegetation in the nature preserve area was proposed; however, the mechanis m of the successional trend on the aquatic communities needs further invest igation.