Plant composition and diversity of broad-leaved coppices and conifer plantations in southern Japan: implications for biodiversity conservation

Improving the ecological understanding of semi-natural and artificial forests is necessary to conserve forest species and biodiversity in temperate regions. We investigated plant composition and diversity of semi-natural broad-leaved ( Castanopsis sieboldii ) coppices and artificial conifer ( Cryptomeria japonica ) plantations in Tanegashima Island, southern Japan, to evaluate the potential of these substitutional vegetation to conserve original lucidophyllous forest species. Vegetation surveys were conducted using 100-m 2 plots. Species composition was analysed using non-metric multidimensional scaling and indicator species analysis. Species richness, diversity indices, and rarefaction curves were compared between the two forest types. The stands in the Castanopsis coppice and Cryptomeria plantation were separately distributed in the ordination diagrams, and those in the latter were more aggregated than those in the former. The Castanopsis coppice was characterized by evergreen broad-leaved trees of lucidophyllous elements (component species of lucidophyllous forests) whereas the Cryptomeria plantation was characterized by ground ferns containing non-lucidophyllous elements. Species richness was greater in the Castanopsis coppice than in the Cryptomeria plantation for lucidophyllous elements, and the same was true for diversity indices. The rarefaction curve of the Castanopsis coppice also lay above that of the Cryptomeria plantation for lucidophyllous elements. These results suggest that replacing Castanopsis coppices with Cryptomeria plantations could promote the homogenization of species composition by causing a decline in many evergreen broad-leaved tree species and reduce plant diversity for lucidophyllous elements at both plot-sized and broader spatial scales. Expanding Cryptomeria plantations into Castanopsis coppices should be avoided from the perspective of biodiversity conservation.