Evaluation of the mid- and long-term effects of thinning on nutrient cycling in sugi and hinoki forests

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Nitrogen (N) input by litterfall and N release during decomposition in the organic horizon (O horizon) were evaluated in the sugi and hinoki forests 10 years after thinning. We hypothesized that understory vegetation which has higher N concentration in leaf litter enhances N cycling after thinning. N inputs by litterfall in thinned plots were similar to those in unthinned plots. The effect of thinning on N release in the O horizon was dependent on the amount of O horizon before thinning. In the sites with low accumulation of O horizon, the N release in the O horizon was not affected by thinning. On the other hand, in the sites with high accumulation of O horizon, N release in the O horizon was increased and this increase was partly due to higher input of leaf-litter of understory vegetation. These results suggest that enhancement of N cycling by understory vegetation after thinning is substantial in low-fertility sites and N cycling was not affected by thinning in high-fertility sites.