Regeneration of Cryptomeria japonica on a sloping topography in a cool-temperate mixed forest in the snowy region of Japan

Abstract

Cryptomeria japonica D. Don shows a limited distribution on and around ridges in its native habitat. To clarify the regeneration process of this species, we analysed spatial patterns among five size classes on a slope extending from a ridge to a valley bottom, and growth patterns of understorey trees related to their slope position, in a cool-temperate old-growth mixed forest in Japan. Although the largest size-class trees ([Formula: see text]20 cm diameter at breast height (DBH)) were confined to the upper part of the slope, understorey size-class trees ([Formula: see text]50 cm stem length and <10 cm DBH) extended their range below the upper regions by layering. The annual growth of understorey size class stems increased towards the lower slope in relation to the understorey light conditions. However, snow pressure injured understorey trees and killed many regenerating medium-sized trees on the steeply inclined expanding site. These results indicate that increased snow pressure, influenced by slope topography, may inhibit the clonal expansion of C. japonica. We concluded that snow pressure gradient on a sloping topography strongly influences the regeneration success of C. japonica, restricting its distribution to ridges in natural forests in snowy regions.