REVEGETATION PROCESS ON A SUB-ALPINE MUDFLOW

The process of revegetation on a subalpine mudflow was analyzed on the basis of the vegetation-soil relationship of the revegetated stands, and of the age structure and height growth process of the trees. Based on evidence derived from five independent sources, it was concluded that this mudflow was caused by a typhoon in 1959. The revegetated stands were classified into three vegetation types. An Alnus maximowiczii stand was established where the surface soil was unstable; a Betula ermanii stand was established where the degree of disturbance by the mudflow was small; an Alnus-Betula stand was the intermediate type and occupied most of the area on the mudflow. Alnus had colonized concentrically 4-6 yr after the mudflow, and Betula and conifers had followed 1-2 yr later. As revegetation proceeded, the trees became differentiated into two populations, a canopy population and a suppressed one. The former was dominated mainly by Alnus and the latter by Betula and conifers. This differentiation was caused by the faster growth of Alnus during the initial years of colonization. Some Betula trees have recently grown faster than Alnus, suggesting future replacement in dominance. Conifers have grown slowly even during recent years; the highly oligotrophic condition of the soil appears to have been responsible for this delayed growth.