Abstract
The Nansi forest dynamic plot, 8.37 ha, was set up during January 2005 to February 2006 in the upstream region of the Nantzuhsien River in south-central Taiwan. This study was conducted on the mid-western ridge of the Nansi plot in a transitional zone between an Alnus formosana deciduous forest and an evergreen broad-leaved forest to understand differences in species composition and vegetation structure in the ecotone between these 2 forests. We studied a total of 2.56 ha (256 quadrats) on the mid-western ridge of the Nansi plot, which we divided into 5 sections, including 1 section of deciduous forest and 4 ecotone sections (0~10, 10~20, 20~30, and 30~40 m away from the edge into the evergreen broad-leaved forest). Tree density and basal area were calculated based on the quadrat (10×10 m2) of each section. Both the total density and mean basal area were highest in the section of 10~20 m. Fifty percent of the total recorded 52 species were found in the deciduous forest, and 96% were found in the evergreen broad-leaved forest. Alnus formosana was dominant in the deciduous forest, whereas Castanopsis carlesii, Litsea acuminata, and Eurya leptophylla were dominant in the broad-leaved forest. The density and mean basal area of A. formosana decreased along the gradient from the deciduous forest to the evergreen broad-leaved forest, and disappeared in the section of 20~30 m. These factors reflected the depth of edge influence (DEI) presenting 20 m into the interior of the evergreen broad-leaved forest. In the deciduous forest section, there were many small trees of evergreen broad-leaved species, e.g., L. acuminata, Machilus japonica, Cyclobalanopsis stenophylloides, Neolitsea sericea, Pasania kawakamii, M. zuihoensis, Gordonia axillaris, and L. akoensis. Thus, this A. formosana deciduous forest is likely to be gradually replaced by these evergreen broad-leaved tree species, and its vegetation structure and species composition are likely to change in the future.