Effects of Site Preparation before Planting on the Growth of Alnus inokumae Saplings at a Site of Heavy Clay Soil in a Heavy Snow Region

Abstract

To demonstrate the optimal planting method at site of heavy clay soil in heavy snow regions, we planted saplings of Alnus inokumae in an abandoned pasture in Tobestu, Hokkaido, after the site preparation. Mounded- and plowed treatments were conducted for the site preparation in addition to no treatment (control). We investigated the growth of saplings for 6 successive years. Soil of the study site showed typical impermeable heavy clay soil with high solid-phase and low gaseous-phase ratio. We also found a hardpan horizon caused by the passage of vehicles at depth in the soil. Though water contents (pF value) at the mounded 10-20 cm site often proved favorable for plant growth, water contents at the plowed site occasionally showed saturation. Many saplings suffered snow damage during winter, and the number of damaged trees (N_damage,t) increased with an increased maximal depth of snow cover, and decreased with height growth. N_damage,t at the plowed and control sites tended to be greater at the mounded site. No significant difference in height growth was found among the three treatments, whereas a significant difference was found in radial growth. The difference in radial growth effected a difference in the slenderness of the trunk, and it was reflected in the sensitivity to snow damage. These results suggest that the mounded treatment is effective site preparation compared with the plowed treatment at the site of heavy clay soil in heavy snow region.