Abstract
Flowers of Rhododendron japonicum in the semi-natural grassland of Mt. Amari in Yamanashi prefecture have been recently decreased and many branches have been damaged. To consider the conservation and maintenance of R. japonicum population, we investigated flowering and sprouts survivorship of R. japonicum in three different study area, the mountain top with treatment (i.e., mowing of dwarf bamboo [Sasa nipponica] and removal of damaged branches) and without treatment, and southern slope without treatment. We also surveyed temperature and snow depth at each study area in a winter. On the slope it was higher temperature and shorter period with snow cover than the mountain top. R. japonicum on the slope was the largest individual size and had more flower-buds and flowers. Totally 61% of flower. bud bloomed although all buds were out of snow cover in a winter, irrespective of differences in the sites. Although there were no significantly differences of individual size and flowering ratio among the sites, flowering ratio was the highest in the slope and the lowest in the mountain top without treatment. Individual on the mountain top with treatment had the highest number of current-year sprouts and 83% of those survived one year later. Therefore, although the number of flowers of R. japonicum is affected by the individual size regulated by the habitat with different meteorologic, a factor of decrease of flowers seemed to be suppressed by dwarf bamboo.
