1988 Volume 52 Issue 4 Pages 245-254
Around the crater of Mt. Kusatsu-Shirane, located on the prefectural boundary between Nagano and Gunma, a volcanic desert landscape has been formed on fall-out from sporadic volcanic eruptions. This landscape includes the habitat of Vaccinium uliginosum, a wild fruit tree, which is important resource of food for liqueur and jam.
On the straight slope near the crater, colluvial loam is exposed and the surface is covered with volcanic sand and gravel which have moved on the slope. These materials show that soil erosion has been caused actively up to the present in this area. On the other hand, from the plain area to the upper concave slope, a humic horizon is accumulated and an old humic horizon is also recognized under a pumice layer, the surface is covered with a litter layer. The vegetation of this area is distributed in response to these soil materials and landscape features and divided into 5 types as follows:
(I) Clumped vegetation composed of small-size (under 2m2) colonies of herbs and dwarf shrubs.
(II) Clumped vegetation composed of large-size (5-10m2) colonies of dwarf shrubs.
(III) Grassland of Sasa kurilensis including broad-leaved shrubs.
(IV) Scrub of needle-leaved trees; herb layer is dominated by Sasa kurilensis.
(V) Coniferous Forest of Abies. spp; herb layer is dominated by Sasa kurilensis.
In the volcanic desert (I), the extension of Abies forest and Sasa grassland is disturbed because of inadequate soil. But in the other area, where soil process has advanced to some degree, the accumulation of some humic horizons and the distribution of dead clumps show that this area is former Abies forest area and up to the present destructions and restorations of forest has been repeated several times. Therefore Abies forest and Sasa grassland can extend easily if a volcanic eruption does not occur.
V. uliginosum is included in plant communities growing in the transitional zone between the volcanic desert (I) and Sasa grassland (III). In the volcanic desert near the crater a major controlling factor in distribution of V. uliginosum is the soil condition caused by soil erosion. In the other area (III) V. uliginosum habitat is controlled by light intensity and does not extend into the Abies forest and Sasa grassland where shading is sufficient to preclude growth. It is suggested that the erosion factor affects the colony size, the shading affects not only the size but total area. So the change to low light intensity caused by the development of Abies forest and Sasa grassland is disadvantageous to the growth of V. uliginosum which is a pioneer species.
Therefore it is concluded that maintenance of the V. uliginosum habitat depends on destruction of the coniferous forest by the volcanic eruption and so this habitat moves as the forest expands and retreats.
