Notes on Beech (Fagus crenata Blume) Seed and Seedling Mortality Due to Rodent Herbivory in a Northernmost Beech Forest, Utasai, Hokkaido

Abstract

We investigated the mortality of post-dispersal seeds and current-year seedlings of a beech species (Fagus crenata Blume) at the northernmost extent of its geographical range at Utasai (Kuromatsunai), Hokkaido, Japan. Introduced seeds that were protected from rodent predation by wire cages had a higher survival rate from winter to the following spring (mean ± SD: 84 ± 16.7%,n = 10) than controls without cages (mean ± SD: 12 ± 17.9%,n = 10). Unprotected transplanted current-year seedlings with almost fully opened primary leaves never survived more than three days (0%,n = 30), while more than 80% (n = 30) of seedlings within cages survived to the end of the growing season. These results indicate that rodent herbivory is a major mortality factor that strongly prevents the establishment of beech seedlings. In a natural population, we observed that 90% of seedlings (n = 197) disappeared within 10 days after their emergence and rodent herbivory caused this heavy mortality. A herbivorous rodent, the gray-backed vole, Clethrionomys rufocanus bedfordiae, was remarkably abundant in late June (101.5 voles/ha), suggesting that this species strongly affects the formation of the seedling bank. The presence of C. rufocanus bedfordiae may be one of the reasons for the scarcity of beech seedlings and saplings and the rarity of recruitment in this northernmost beech forest.