The study site lies on a flat terrace inside the Teshio Experimental Forest of Hokkaido University. Its soil, mainly a Gleyic Cambisol, has a surface organic horizon that is about 10 cm thick. Prior to clear-cutting, the dominant tree species were Quercus crispula, Betula ermanii, Abies sachalinensis, and Betula platyphylla var. japonica. Maximum and mean tree heights were 24 and 20 m, respectively. The forest floor was covered with dense evergreen dwarf bamboos (Sasa senanensis and Sasa kurilensis). The plant area index (PAI) values for the canopy trees and the Sasa bamboos, measured using an LAI-2000 leaf-area meter (Li-Cor, Lincoln, NE, USA), were 3.2 and 4.1, respectively, at this parameter''s seasonal maximum in 2002. From January to March 2003, trees covering an area of 13.7 ha were clear-cut. The total biomass volume of trees at the site was 2193 m3 (Koike et al. 2001), of which 1203 m3 (~19 t C ha–1) were removed as logs by clear-cutting. Sasa was left intact under the snowpack, but 7 months later, just before the planting of hybrid larch seedlings (in late October 2003), they were strip-cut into alternating 4-m-wide cut and uncut rows in the clear-cut area to give space for the planting of ca 30 000 2-yr-old hybrid larch (Larix gmelinii × L. kaempferi) at a density of 2500 ha–1 (0.04 t C ha–1). In the rows where Sasa remained, Sasa PAI increased steeply from 1 yr after clear-cutting until 2007, reaching a peak at 8.0 in 2010, which is about double the value in 2002 before clear-cutting. In the rows where Sasa was strip-cut, Sasa weeding in the strip cut rows was conducted from once (2005 and 2006) to three times (2004) per year between late May and late July until 2006. Weeding eliminated all Sasa growing between the larch trees. The Sasa was no longer weeded starting in 2007 because the larch were higher than the surrounding Sasa, and were able to receive enough solar radiation to grow without interference. Sasa soon recovered in the strip-cut rows, and in 2008, 2 yr after the last weeding, the PAI was almost the same as that in the surrounding uncut rows, blanketing all gaps between the trees. On the other hand, the PAI of the larch remained low (1.7 in 2010) at its seasonal maximum and was minor compared with that of Sasa. A closed-path eddy covariance system was established in August 2001 on a 32-m-tall tower in the mixed forest to evaluate the CO2 fluxes. A sonic anemometer (DA600-3TV, Kaijo, Tokyo, Japan) and an infrared gas analyzer (IRGA, LI-7000, Li-Cor) were used to evaluate the fluxes. In addition to the existing equipment installed at a height of 32 m, another closed-path system comprising the same instruments was installed at a height of 4.6 m in October 2003 after clear-cutting, and the measurements were on going, although the height and instruments were changed several times.
