SPECIES ATTRIBUTES IN EARLY PRIMARY SUCCESSION ON VOLCANOS

We predicted that plants that can establish on volcanic soils with sim ilar disturbance histories will have similar growth characteristics. W e tested this prediction by a multivariate analysis of 27 traits of 84 species found six years after an eruption on Mount St. Helens, Washin gton State, USA, and Mount Usu, Hokkaido, Japan. These traits include vegetative, life-history, phenological and seed-biology characteristic s. Cluster analysis revealed five species groups: annual herbs, perenn ial forbs, graminoids, shrubs and trees. Each group has distinct veget ative, life-history, and seed-biology traits. Except for shrubs, which were lacking on Mount Usu, both floras were well represented in each group. On intensely disturbed sites on both volcanoes, perennial forbs , whose development is dependent primarily on well-developed below-gro und organs and wind-dispersal, expanded their cover more rapidly than did graminoids. These graminoids generally produce gravity-dispersed s eeds and have close-set rhizomes and/or shoots. These results suggest that species that can establish during the early stages of succession on each volcano have similar vegetative, life-history, and seed-biolog y traits.