SEED DISPERSAL AND VEGETATION DEVELOPMENT ON A DEBRIS AVALANCHE ON THE ONTAKE VOLCANO, CENTRAL JAPAN

Seed dispersal and early revegetation processes were studied in an are a devastated by a debris avalanche that occurred on volcano Ontake, Ce ntral Japan in 1984. The avalanche was initiated by a volcanic earthqu ake, and a 3.4 x 10(7) m3 land mass destroyed the vegetation over 700 ha. The revegetation of the first five years was slow in the area of h igher elevation (subalpine area). Both the speed of revegetation and t he species richness of trapped seeds varied with the elevation. The po st-disturbance vegetation on the deposit with surface soil or plant fr agments was richer in species than that without any surface soil. Almo st all of the seeds caught by sticky traps and most of the species wit h frequent occurrence in the vegetation after disturbance were wind di spersed. Wind dispersal was especially important on the deposit withou t surface soil or plant fragments.