Natural regeneration patterns of the introduced larch, Larix kaempferi (Pinaceae), on the volcano Mount Koma, northern Japan

The 1929 eruption of Mount Koma (1140 m in altitude) completely deforested the vegetation on the summit area of the volcano. An alien species of larch, Larix kaempferi (=L. leptolepis) was planted on the lower slopes of the volcano between 1953 and 1963, but since then has become abundant on the summit. To determine the regeneration patterns of the larch, we measured stem densities on aerial photographs taken in 1963, 1973 and 1994, and in the field during 1996. Larix kaempferi stems with crown diameters > 2 m were mapped on aerial photographs divided into 1083 100 m×100 m grids. Stem densities on the summit increased from 0.8/ha in 1963, to 14.1/ha in 1994. Willows and birches also established there but did not grow as large as the larch. All these species are wind dispersed, and larch densities were higher in areas closer to the plantations, suggesting that wind intensity and direction determined seed migration. Four environmental factors—slope gradient, direction, elevation, and distance from the plantations in each grid—were correlated with larch stem densities. Multiple regression showed that establishment patterns of L. kaempferi in the early stages were mainly related to distance from seed source (the plantations). Later, geographical disturbances and/or physiological stresses became more important. Density effects on tree invasion have been weak until now. We concluded that revegetation primarily depends on the chance of seed immigration, and that the larches may be an earlier successional species than any other native tree species.