Species Composition and Structure of the Lowland Subtropical Rainforest at Lanjenchi, Southern Taiwan

The forest in Lanjenchi is a remnant patch of subtropical rainforests in southern Taiwan. In 1998, the previous Lanjenchi plot was enlarged from 3 ha to 5.88 ha in order to include more topographical variation and understand how the gradient of wind stress controls forest structure and species composition. All free-standing woody plants in these plots with diameter ≥ 1 cm were identified, measured, tagged and mapped. A total of 60,146 individuals belonging to 136 vascular tree species in 83 genera and 42 families was recorded. Families with the largest cumulative basal areas were Fagaceae, Theaceae, Araliaceae, Aquifollaceae, Lauraceae and Illiciaceae. The size-class distribution of all species showed that most species were in good recruitment patterns with the most stems in small size classes. The results of two-way indicator species analysis (TWINSPAN) classified the sampling plots into four forest and habitat types: 1. Rhaphiolepis indica var. hiiranensis - Illicium arborescens (Windward I) type; 2. Cinnamomum brevipedunculatum - Illicium arborescens (Windward II) type; 3. Sloanea formosana - Ilex cochinchinensis (Leeward) type; and 4. Glycosmis citrifolia - Helicia formosana (Creek) type. The forest composition changes formed a sequence on the topographic gradient from the most exposed windward ridges and north-east-facing slopes to more sheltered leeward footslopes and creeks. Further studies using detrended correspondence analysis (DCA) and canonical correspondence analysis (CCA) confirmed the results of TWINSPAN, and showed the important roles of the topographic variables in the distribution of most tree species.