Species Composition and Vegetation Pattern of a Lowland Rain Forest at the Nanjenshan LTER Site, Southern Taiwan

This study focused on a remnant of lowland rain forest in the Nanjenshan Reserve of southern Taiwan. During 1989-1994, two long-term plots of 2.1 and 3 ha were set up at Lanjenchi (hill) and Nanjenshan (valley) sites, and forest composition, structure and species diversity were compared between the two plots. In the Lanjenchi plot, the most important families (sum of basal areas of all species within that family) were Fagaceae, Theaceae, Aquifoliaceae, Illiciaceae, Lauraceae and Myrtaceae, while in the Nanjenshan plot, the most important families were Euphorbiaceae, following by Moraceae, Meliaceae, Lauraceae, Aquifoilaceae, Urticaceae and Lythraceae, which bore some similarities to the tropical rain forests both in physiognomy and structure. Both TWINSPAN classification and DCA ordination separated the windward forest from the leeward forest stands in the Lanjenchi plot, but no such pattern could be recognized for the Nanjenshan plot. In the Lanjenchi plot, both species composition and forest structure changed dramatically with exposure due to chronic monsoon wind-stress. As wind stress increased, canopy height decreased from 15-20 m in the creek bottom to 3-5 m in the most exposed windward habitat. Stem density increased steadily with increasing exposure, and mean similarity among quadrats become higher as well. Total basal areas were comparable between the plots and forest stands. Dominance-diversity curve for each of the forests conformed to a lognormal distribution. There was a strong tendency for species diversity to be higher in the less exposed forests.