Changes in carbon stock following soil scarification of non-wooded stands in Hokkaido, northern Japan

To restore non-wooded 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 +/- A 35.2 Mg C ha(-1) for a 37-year-old stand formerly dominated by S. kurilensis, and 181.1 +/- A 29.8 Mg C ha(-1) for a 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 +/- A 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 years) to ensure a carbon sink state. A potential of further improvements of the practice, including that reduce intensity of soil disturbance, was presented.