Woody plant establishment during the early stages of volcanic succession on Mount Usu, northern Japan

Abstract

The establishment patterns of woody plants were investigated on the volcano Usu, 9 years after the 1977–1978 eruptions. The former vegetation was covered by a 1–3 m thick volcanic deposit. Trees producing wind‐dispersed seeds capable of long distance dispersal, such as Populus maximowiczii, Betula platyphylla var. japonica, Salix hultenii var. angustifolia, and Salix sachalinensis, were dominant. Most trees were only 2–4 years old in 1986, suggesting that chances for seedling establishment were restricted. The tree heights did not differ significantly among the species, while lengths of annual shoots differed due to herbivore preferences. Trees were established at higher densities on gravel‐dominated pumice surfaces than on fine‐textured surfaces. Tree density was not greatly affected by the nutrient content of deposits. From 1987 to 1990, tree height increments did not differ between the gravel and non‐gravel areas. Ground surface texture is an important factor in determining seedling establishment in the early stages of volcanic succession, and nutrient status is unimportant.