Changes in Labile Soil Carbon and Enzyme Activity after Thinning of Japanese Red Pine Forests.

Assessing consequences of common forest management practices is essential, because forest management may affect ecosystem functioning as well as wood production. Particularly, growing attentions are paid to labile soil carbon and enzyme activity as sensitive indicators reflecting the impacts on soil carbon dynamics and fertility. Since thinning, selective logging to improve the value of forests, is one of the most widely conducted management practices, the current study determined the effects of thinning on labile soil carbon and enzyme activities degrading cellulose (β-glucosidase; BG) and lignin (phenol oxidase; POX). Different thinning intensities (based on removed basal area; un-thinned control, 15% and 30% thinning) were applied to two 51 to 60-year old Japanese red pine (Pinus densiflora) forests in central Korea. The forests shared similar stand age, but differed in topography and soil conditions. Total carbon (TC), labile carbon [microbial biomass carbon (MBC), permanganate oxidizable carbon (POXC)], and BG and POX activities were investigated at 0–10 cm soil depth, seven years after thinning. Despite the differences in topography and soil conditions, thinning consistently influenced labile soil carbon and enzyme activity within the forests. In both forests, the 15% and 30% thinning treatments resulted in 19–24% and 35% increased TC than the control, respectively. Similarly, MBC and POXC were highest in the 30% thinning treatment, followed by the 15% thinning treatment and the control. The elevated MBC and POXC corresponded to increasing TC due to thinning. However, thinning had no significant influences on MBC and POXC fractions within TC, and on BG and POX activities. BG and POX activities showed no consistent correlations with TC across the forests. Our results illustrated that thinning could affect both total and labile soil carbon quantities; nevertheless, the altered soil carbon quantities did not necessarily accompany the stimulated microbial potential to decompose soil organic matters.

This study is supported by the National Institute of Forest Science (FM0101-2009-01) and the Ministry of Environment (2014001810002).