Fundamental Study on Regeneration Process of Forests - Regeneration Patterns of Subalpine Forests by Larix kaempferi and Betula ermanii
To clarify the regeneration process of subalpine forests, the regeneration patterns by Larix kaempferi and Betula ermanii on four tracks of snow avalanches that destroyed forests in 1992, 1980, 1938 and 1936 respectively, were investigated on the northern slope of Mt. Fuji.(1) Site conditions on the tracks of snow avalanches Site conditions were classified into four types according to the gradient of disturbance by the avalanches. Type 1 was parts of the track that only canopy layer had been disturbed by the avalanches. Type 2 was similar to type 1, but it was thinly covered with sediment transported by snow from the upper part of the track. Type 3 and 4 were intensively disturbed by the avalanches and they were thickly covered with sediment. The surface soil of the type 3 and 4 showed higher temperature and lower water content than those of the type 1 and 2.(2) Seedling establishment of L. kaempferi and B. ermanii The process of seedling establishment was investigated at each of the sites on the track of avalanche. At type 1 and 2, seedling establishment of B. ermanii began within a year after the avalanche. At type 3 and 4, seedling establishment of L. kaempferi began about three or four years after the avalanche, though mortality of the seedlings was very high in their first winter and in the following summer.(3) Time series changes in regenerated L. kaempferi and B. ermanii communities At the slightly disturbed sites like type 2, B. ermanii shrubs accompanied by other pioneer trees such as L. kaempferi and Alnus maximowiczii regenerated about 20 years after the avalanche. However, pioneer trees had been gradually suppressed by B. ermanii. About 60 years after the avalanche, B. ermanii stands had been dominated and many Abies veitchii saplings, which is a climax species, were found in the stand's understory. At the intensively disturbed sites such as type 3 and 4, only L. kaempferi had regenerated about 20 years after the avalanche and their single-layered stands had developed after 60 years. However, only a few A. veitchii seedlings had emerged in their forest floor. From the above results and our previous reports, it is clear that three patterns of regeneration are found on the track, depending on the gradient of disturbance by the avalanche, as follows: (1) At the intensively disturbed sites, only L. kaempferi regenerates; (2) At the slightly disturbed sites, B. ermanii regeneration dominates; (3) At sites where the forest floor is not disturbed, advanced seedlings of A. veitchii start to regrowth rapidly after the avalanche.