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To restore nonwooded stands dominated by dwarf bamboo species (Sasa kurilensis or S. senanensis) into forests, mechanical soil scarification has been applied in northern Japan since the 1960s. The treatment is followed both by natural regeneration and artificial planting. In this study, we quantified the total carbon stock (plants plus 0.3 m depth of soil) of these stands over 35-year age-sequences.The natural regeneration stands were gradually dominated by Betula ermanii. The carbon stock increased linearly to 215.1 ± 35.2 Mg C ha -1 for 37-year-old stand formerly dominated by S.kurilensis, and 181.1 ± 29.8 Mg C ha -1 for 34-year-old stand formerly dominated by S. senanensis.The latter was similar to that of a Picea glehnii plantation, formerly dominated by S. senanensis, with comparable stand age (160.3 ± 6.7 Mg C ha -1 for 35-year-old stands). Although the carbon stock in plants quickly offset the untreated level, that in the soil remained depressed even in the older stands. This resulted in small differences in carbon stock of these stands with untreated dwarf bamboo stands. We conclude that natural regeneration following scarification could be a prime option for carbon sink management in the region. However, we should take a long rotation period (i.e. > 50-year) to ensure a carbon sink state. A potential of further improvements of the practice, including that reduce intensity of soil disturbance, was presented.

Scarification is widely conducted in northern Hokkaido to remove understory dwarf bamboos in degraded forests, and to replace it with tree species. We investigated height growth and survival during 6 8 years after the treatment for nine major tree species naturally established in a site, and examined their contributing factors competition or facilitation. The height growth and survival rate were higher in Phellodendron amurense and Sorbus commixta, besides lower in Picea glehnii. The results of generalized linear model or generalized linear mixed model suggested that facilitation effects of surrounding broadleaved trees or understory vegetation were dominant for growth of many tree species. Regarding Betula platyphylla, however, the facilitation effect, which had been found in the former period 3 5 years after scarification , was changed into competition effect. For seedling survival, although negative effects of surrounding conifers were found, effects of broadleaved trees and understory vegetation were unclear. We concluded that weeding and cleaning treatments were ineffective for enhancing species richness in the site in this stage of stand development.

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