Abstract
Retention forestry, a part of silvicultural system that retains important forest structures and organisms at harvest time, is a promising way to conserve biodiversity in managed forests. This harvesting method is being widely adopted
in many countries and tested in field experiments. A large number of conifer plantations in Japan are reaching the planned harvest age, and their harvest is expected to help meet the domestic demand for wood. On the other hand, the restoration of conifer plantations to natural broad-leaved forests and the maintenance and enhancement of ecosystem services other than wood production are required in plantation landscapes. In this context, we launched a large-scale retention forestry experiment (the REFRESH project) in Sakhalin fir (Abies sachalinensis) plantations in central Hokkaido, northern Japan. The REFRESH project has six treatments (clear-cutting, three levels of dispersed retention, aggregated retention with a 0.36 ha intact patch, and gap cutting) and two controls (unharvested natural forest and unharvested plantation) with three replicates each. In dispersed retention, naturally regenerated broad-leaved trees are retained at three levels to maintain and restore elements of natural forests. After harvesting, fir seedlings are planted in the harvested area. We conducted pre- and post-harvest surveys on water and soil conservation; forestry efficiency; and the diversity of plants, arthropods, and birds. The initial surveys indicate how tree retention provides continuity in the forest structure in the harvested area, and long-term surveys until the next harvest will reveal the degree of structural and compositional enrichment of the plantations.
