Differentiation of vegetation zones and species strategies in the subalpine region of Mt. Fuji

Abstract

The floristic and structural differentiation of vegetation along the altitudinal gradient in four subalpine forests of different developmental stages on Mt. Fuji has been studied. Near the forest limit a micropattern of vegetation corresponding to the altitudinal zonation has been observed which elucidated the mechanisms of development of the vegetation zonation. As to early stages of vegetation development only two types can be distinguished: the volcanic desert above 1500 m and the pioneer forests below. As to later stages a differentiation of subzones includes from higher to lower altitudes: the Alnus maximowiczii, Betula ermanii, Abies veitchii and Tsuga diversifolia forests. Larix leptolepis and Sorbus americana ssp. japonica, appear as co-dominants in ecotonal communities between the principal subzones and are also important pioneers in early stages. Similarity analyses reveal that the upper subalpine Alnus-Betula forests can be regarded as early successional phases of the climax Abies-Tsuga forests of the lower subalpine zone. The regular arrangement of A. maximowiczii-B. ermanii-A. veitchii is studied along the gradient from the margin to the interior of the forest growing near the forest limit where locally favourable conditions prevail. Growth form, height growth, photosynthetic activity, seed supply, and seedling distribution of the three principal species have been compared, as well as biomass and production relations in contiguous forests of these species. The marginal Alnus type community is productive and disturbance-tolerant, and has a wide ecological and sociological amplitude along the gradient, while the central Abies community is accumulative and disturbance-intolerant, and has a narrower tolerance range, but is superior in competition under stable habitat conditions. A vegetation organization, ‘temporal multi-storeyed structure’, is suggested which means that a zonal pattern of vegetation within a climax region develops by successive replacement of successional species along an environmental gradient.