Effects of thinning on soil nitrogen mineralization in a Japanese larch plantation

We measured soil nitrogen (N) mineralization and litter decomposition for four different thinning intensities [control (C), 10% (T10), 20% (T20), 40% (T40) thinning] during the first year after treatment in a 15-year-old Japanese larch plantation in central Korea. Initial soil moisture content increased in the thinned plots. Air temperature also increased with thinning intensity, however, soil temperature did not. Annual net N mineralization rates (mg N kg^-1) for C, T10, T20, and T40 were 6.7, 7.2, 6.6, and 11.5, respectively. The heavily thinned plot showed higher annual N mineralization than control, lightly and moderately thinned plots, but differences were not statistically significant. Except for the T40 treatment, the ratios of annual net nitrification to annual net N mineralization were greater than 100%. Dry weight and N concentration in decomposing needle litter did not show any significant patterns with thinning intensity. The current results indicated that various levels of thinning for a young Japanese larch plantation had only a minor influence on soil N mineralization and litterfall decomposition during the first year following thinning.