北八ヶ岳坪庭溶岩台地に成立するハイマツ群落の組成と構造

抄録

Japanese stone pine（Pinus pumila）is a high-elevation species that usually occurs above forest line（≧ 2500 m a.s.l.） in central Japan.　In Tsuboniwa, Mt. Kita-Yatsugatake, a volcanic eruption 600 years ago led to the formation of a lava plateau at 2250 m a.s.l.　The plateau uniquely supports a community of P. pumila below the elevational limit of subalpine conifer forest.　We investigated the composition and structure of this species’ stand with a focus on its community development. We placed 26 plots（ 5 m × 5 m） across a 270 m length from the periphery of the lava plateau to the center, encompassing an associated gradient of vegetation height and cover.　There were 31 vascular plant species across all plots.　Dominant species, in terms of both occurrence frequency and cover, were P. pumila, Tsuga diversifolia, and Empetrum nigrum var. japonicum.　The height and cover of T. diversifolia were greater than those of P. pumila at the periphery of the plateau, but the former decreased and the latter increased toward the center, suggesting that P. pumila has acted as the primary pioneer tree species on the plateau.　Seedlings of P. pumila are known to establish in vegetation mats formed by moss and E. nigrum var. japonicum, which has presumably structured the current distribution of the species on the plateau.　There were many common species between the periphery and center plots, suggesting that the area has moved through an early stage of community development.