Soil Carbon Stock in Thinned and Un-Thinned Pine and Oak Stands.

The current study assessed the effect of thinning on soil carbon stock in pine and oak forests, which dominate the South Korean forest ecosystems. Three thinning intensity levels, consisting of un-thinned control (UTC), intermediate thinning (IT; 15–17% basal area removal), and heavy thinning (HT; 28–35% basal area removal), were implemented to two 51 to 60–year–old pine forests and two 31 to 50–year–old oak forests in central part of Korea. Soil carbon stock at 0–10, 10–20, and 20–30 cm depths was measured 6–7 years following thinning. Microbial biomass and carbon-degrading enzyme activities (β-glucosidase, cellobiohydrolase, β-xylosidase, and phenol oxidase) were also determined at 0–10 cm soil depth. Soil carbon stock at 0–30 cm depth in pine forests was 45.1–60.6 Mg C ha^-1 for UTC, 53.4–69.0 Mg C ha^-1 for IT, and 64.2–71.1 Mg C ha^-1 for HT, whereas that in oak forests was 29.8–53.2 Mg C ha^-1 for UTC, 42.2–64.6 Mg C ha^-1 for IT, and 44.1–59.2 Mg C ha^-1 for HT. No thinning × depth interaction effect was significant, although differences in soil carbon stock between depths were significant. In general, thinning had significant effects on soil carbon stock and microbial biomass, but no effects on enzyme activities. Therefore, increases in soil carbon stock might result from changes in the carbon balance between microbial biomass retention and carbon-degrading enzyme activities. Given that similar patterns were observed 3 years prior to the current study, our results also indicate that changes in soil carbon stock might occur in the relatively short term and then have persisted over the several years.

The current study was supported by the National Institute of Forest Science (project no: FM0101-2009-01) and the National Research Foundation (project no: 2015R1D1A1A01057124) of Korea.