Vegetation changes from 1984 to 2008 on Mount Usu, northern Japan, after the 1977–1978 eruptions

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AbstractThe revegetation patterns after volcanic eruptions were monitored annually on Mount Usu, northern Japan, using over 25 years to detect successional changes. The vegetation was monitored by 2 × 5 m plots from 1984 and 2008 and by 5 × 5 m plots that were enlarged from the original plots from 1994 to 2008 due to increasing vegetation height. The thick tephra from these eruptions destroyed the former vegetation in 1977 and 1978. Diversity indexes were calculated, and nonmetric multidimensional scaling (NMDS) was conducted using the vegetation data with environmental factors. The cover of dominant species was higher in the large plots probably due to the vegetative expansion. Species richness and diversity continued to increase annually for 30 years after the eruptions. Well‐established plants were perennial forbs and trees and the species replacement occurred consistently. NMDS of small plot data suggested that elevation was related to the first axis, and year, litter volume and distance to the caldera rim were related to the second axis. Plot scores on the first axis suggested that deterministic factors, that is, elevation and its related factors, produced vegetation convergence but those on the second axis suggested that the vegetation change was in response to stochastic factors, such as litter accumulation and its related unmeasured factors, with year. The results indicated that the convergence or divergence was determined by the conflict between the net effects of deterministic and stochastic factors on vegetation development.