A Quaternary geoecological study on disturbance regime and vegetation structure in volcanic areas

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Landform evolution can cause changes in habitat environments even on a geological time scale, keeping vegetation landscape in disequilibrium state for a long period of time. It is important to clarify landform effects on vegetation over a timescale of centuries and millennia, as well as at a timescale of years and decades. The structure and causal factors of vegetation boundaries were studied on Mounts Daisen, Yakedake, and Abo to clarify the long-term influences of mountain evolution on vegetation. On Mount Daisen, a distinct forest line formed at between 1100- and 1300-m elevation, which coincided with the geological boundary of the lava dome and talus deposits. No forest stands were able to develop on the summit lava dome because of poor soil development, and the position of the forest line was controlled not by macroclimatic or topoclimatic conditions but rather by the immature soils on the lava dome that formed during the late Pleistocene to early Holocene. In the Yakedake-Abo area, a subalpine-montanous forest boundary formed at between 1100- and 1700-m elevation, which coincided with the landform boundary of the smooth and dissected slopes. On steep slopes created by post-glacial dissection, frequency of canopy-gap formation is higher. This may cause broad-leaved trees to establish at the elevation of altitudinal limit of the distribution. In some cases, boulder cover prevents broad-leaved trees from establishing on smooth slopes. Post-glacial dissection has removed the boulder cover, improving edaphic conditions. These suggest that the vegetation boundary has been developed along with post-glacial slope dissection in the Yakedake-Abo area.