Fraxinus mandshurica is a representative broad-leaved tree species for planted forest in Hokkaido. This study focused on a stand that was planted in 1924 and then largely abandoned until 56 years of age. We described the changes over 40 years (from 56 to 96 years of age) and clarified the factors that influenced the dbh growth of individuals. At the age of 96 years, the volume of F. mandshurica was 190 m³/ha with the average dbh 36.9 cm, indicating that the stand had reached a mature state for harvesting. Significant positive effects of basal area (individual size) and crown length ratio were consistently shown on the dbh growth during the 40 years. No competitive effect from neighboring tree individuals was observed in this period. To reach the mature state earlier, it was thought that early thinning was necessary to ensure crown length ratio of about two-thirds of the tree height. On the other hand, when aiming for a long rotation management, there was a concern that frost injuries would occur frequently in the stem, especially in large-diameter trees.

We measured the surface soil (fine soil, gravel, and litter) movement under four types of undergrowth in a planted Japanese cypress (Chamaecyparis obtusa) forest. We also clarified the differences in surface soil erosion among the different types. The patches of undergrowth were all growing next to each other under the same conditions in the same stand on the same slope. The transport rate of fine soil per 1 mm precipitation increased in the order of the following types: fern (Diplopterygium glaucum) dominant, shrub with herbaceous layer, shrub without herbaceous layer, and poor vegetation. Greater cover of floor litter and undergrowth reduced the transport rate of fine soil. The fern-dominant and shrub-with-herbaceous-layer types therefore had a greater deterrent effect on surface soil erosion because of their multilayered cover of floor litter and herbaceous (≤30 cm) and shrub (>30 cm) layers. The shrub-without-herbaceous-layer type had a smaller deterrent effect than the former two types, because it had only a single shrub layer and lacked herbaceous and floor-litter layers. However, it had a greater deterrent effect than the poor vegetation type, which had no floor cover. These results suggest that we can improve surface-soil-erosion deterrence by controlling the type of undergrowth.