FOREST DISTURBANCE BY THE 1926 MUDFLOW AND REVEGETATION PROCESSES AT MT.TOKACHI VOLCANO

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The 1926 mudflow at Mt.Tokachi Volcano created a vast, bare land mass with heterogeneous and edaphic conditions. Forests were regenerated mainly by seedings supplied from remaining vagetation islands and surrounding areas. Vagetative regrowth was possible in downstream and boundary areas of the mudflow where forests suffered light damage. Revegetated forests display a mosaic structure, consisting of small or large elongated patches. Atands can be classified by dominant soecies, such as Picea glehnii, P.jezoensis, Abies sachalinensis, and betula spp. Pure Betula stands are found at the boundary areas of the mudflow where fine sediment was deposited. Picea glehnii stands were established in the central areas of bounder-rich soil deposits. Dwarf bamboo(Sasa spp.) dominated the floor of Betula stands, and it is likely that its rapid recovery playd an important role in forming Betula stands. Soil analysis clearly indicated the strong linkage between edaphic conditions and stand types. We concluded that differences in atand structures of revegetated forests could be attributed the heterogeneous site conditions created by the mudflow.