The abundance of Picea jezoensis, a major conifer tree species in Hokkaido, northern Japan, is currently decreasing due to the lack of suitable conditions for recruitment and intensive harvests. To contribute to the development of sustainable forest management in Hokkaido, suitable substrates for natural regeneration of P. jezoensis were evaluated during a 4-year experimental study using seed additions in a natural coniferous forest. The environmental conditions (moss height, log hardness, extent of the humus layer, and light conditions) of fallen logs were measured. Moss height was categorized into three groups: 0 mm, Bark; 0 - 20 mm, Mthin; and ≥ 20 mm, Mthick. The germination rates of P. jezoensis were highest on Mthin, intermediate on Bark, and lowest on Mthick. Survival rates were low on Mthick, did not differ between Bark and Mthin, and increased with enhanced light. Growth increased with light, but the root allocation of seedlings was not affected by any environmental conditions. From these results, we determined that fallen logs with no or thin moss cover under bright conditions were most suitable for P. jezoensis regeneration. We discussed the generality of our results in relation to a co-occurring tree species in Hokkaido and the results of other regions.
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