Background: As the decomposition of lignocellulosic compounds is a rate-limiting stage in the nutrient mineralization from organic matters, elucidation of the changes in soil enzyme activity can provide insight into the nutrient dynamics and ecosystem functioning. The current study aimed to assess the effect of thinning intensities on soil conditions. Un-thinned control, 20 % thinning, and 30 % thinning treatments were applied to a Larix kaempferi forest, and total carbon and nitrogen, total carbon to total nitrogen ratio, extractable nutrients (inorganic nitrogen, phosphorus, calcium, magnesium, potassium), and enzyme activities (acid phosphatase, β-glucosidase, β-xylosidase, β-glucosaminidase) were investigated. Results: Total carbon and nitrogen concentrations were significantly increased in the 30 % thinning treatment, whereas both the 20 and 30 % thinning treatments did not change total carbon to total nitrogen ratio. Inorganic nitrogen and extractable calcium and magnesium concentrations were significantly increased in the 20 % thinning treatment; however, no significant changes were found for extractable phosphorus and potassium concentrations either in the 20 or the 30 % thinning treatment. However, the applied thinning intensities had no significant influences on acid phosphatase, β-glucosidase, β-xylosidase, and β-glucosaminidase activities. Conclusions: These results indicated that thinning can elevate soil organic matter quantity and nutrient availability, and different thinning intensities may affect extractable soil nutrients inconsistently. The results also demonstrated that such inconsistent patterns in extractable nutrient concentrations after thinning might not be fully explained by the shifts in the enzyme-mediated nutrient mineralization.

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This study examined the effects of thinning intensities on carbon (C) storage of soil, forest floor and coarse woody debris (CWD) in Larix kaempferi stands, Korea. Two study stands were located in Gwangneung Experiment Forest (Stand 1: 31-40 years old) and Muju (Stand 2: 51-60 years old). These stands were thinned in 2011. Each stand was divided into three plots by different thinning intensities based on removed volume: no thinning (control, 0%), moderate thinning (M, 20%), and heavy thinning (H, 30%). The C storage of soil at 0-50 cm depth, forest floor, and CWD was measured in 2011. Total C storage of H plot was significantly higher than that of control plot and M plot in Stand 1 (control: 64.6 t C ha 71 , M: 62.2 t C ha 71 , H: 83.7 t C ha 71 ). A similar tendency was also found in Stand 2; total C storage of H plot was significantly higher than that of control plot and M plot (control: 137.8 t C ha 71 ; M: 138.0 t C ha 71 ; H: 169.6 t C ha 71 ). Initial effects of thinning intensities on C storage were analyzed as a part of the 10-year study, and we expect to determine the correct thinning intensity that optimizes C storage of soil, forest floor, and CWD by long-term monitoring of changes in C storage at this experimental site.

Soil organic carbon (SOC) is a primary regulator of the forest–climate feedback. However, its indicative capability for the soil CH4 sink is poorly understood due to the incomplete knowledge of the underlying mechanisms. Therefore, SOC is not explicitly included in the current model estimation of the global forest CH4 sink. Here, using in-situ observations, global meta-analysis, and process-based modeling, we provide evidence that SOC constitutes an important variable that governs the forest CH4 sink. We find that a CH4 sink is enhanced with increasing SOC content on regional and global scales. The revised model with SOC function better reproduces the field observation and estimates a 39% larger global forest CH4 sink (24.27 Tg CH4 yr−1) than the model without considering SOC effects (17.46 Tg CH4 yr−1). This study highlights the role of SOC in the forest CH4 sink, which shall be factored into future global CH4 budget quantification.