広島県宮島の常緑広葉樹林における植物の分布と地形 <論文>

We studied the vegetation of an evergreen broadleaf forest on Miyajima Island (also known as Itsukushima Island) Hiroshima Prefecture, Japan, with respect to topography. We established two 0.6-ha plots (P-1 and P-2) at an elevation of about 100 m in the northeastern part of the island. In the P-1 and P-2 plots, we found 1,212 and 1,478 trees, respectively, over 15 cm in girth at breast height, which consisted of 29 and 28 species. The basal areas of the plots (27.9 m² ha⁻¹ and 31.0 m² ha⁻¹ in P-1 and P-2, respectively) were much smaller than basal areas of old-growth forests in warm-temperate Japan. This may suggest that the forests at the study site are not yet fully developed. Only three large Abies firma trees accounted for over 10% of total basal area in P-2, which demonstrates that large trees provide important carbon-storage microsites in this forest. Hierarchical and non-hierarchical cluster analyses both revealed that a close relationship exists between tree distribution and topography. A. firma, Symplocos glauca, and Neolitsea sericea occurred more frequently in valley sites; Pinus densiflora, Lyonia ovalifolia var. elliptica, Ilex pedunculosa, and Eurya japonica occurred more frequently on ridge sites. A comparison of our vegetation data to data collected some 40 years ago indicates that the population of Rhododendron kaempferi has declined in size. This reduction may be attributed to browsing stress caused by the dense population of sika deer (Cervus nippon) that inhabit the island.