Nitrogen budget of a rehabilitated forest on a degraded granitic hill

Rehabilitated forests established about 100 years ago on denuded lands in a hilly granitic area are widespread in the Kyoto—Osaka area, the second largest megalopolis in Japan. From 2001 to 2003, we monitored the annual nitrogen (N) budget of a rehabilitated forest watershed dominated by Quercus serrata and Ilex pedunculosa. The ion concentrations of bulk rain in the watershed were similar to those of other watersheds in Japan. The annual bulk rain input of N ranged from 5.1 to 6.3 kg N ha−1 year−1, and the N deposition from throughfall and stem-flow ranged from 7.5 to 8.2 kg N ha−1 year−1. Estimated annual outputs of N from the stream ranged from 3.3 to 10.6 kg N ha−1 year−1. These results indicate that the amount of N deposition in this area is less than that in urban Tokyo (>10 kg N ha−1 year−1), but the N output of the watershed is comparable with that of the Tokyo area. We discuss the characteristics of N dynamics in rehabilitated forests, focusing on the biogeochemical processes of this watershed.