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We studied how the dominant factor affecting stem volume growth changes during stand development in a monoclonal stand of Cryptomeria japonica D. Don. Stem analysis was used to compare growth history of trees in an unthinned plot (closed canopy) and a thinned plot (open canopy). In the unthinned plot, the dominant factor affecting stem volume growth was basal area (BA) before canopy closure, whereas neighborhood competition index (CI) was the dominant factor after canopy closure. In contrast, the dominant factor affecting stem volume in the thinned plot was BA throughout stand development. Spearman’s rank correlation coefficient between BA and CI continued to increase after canopy closure and size rank among individuals became increasingly fixed. Our results indicated that stem volume growth shifts from size-dependent to competition-dependent growth at canopy closure. The apparent correlation between tree size and growth rate observed in many previous studies may be the result of competition-mediated positive feedback between size and growth. [ABSTRACT FROM AUTHOR]

Soil carbon cycling was studied in Japanese cedar plantations with different stand ages after clear-cutting and was analyzed by a compartment model. The amount of biomass and the litterfall rate increased rapidly with the growth of Japanese cedar, which were approximated by a simple logistic function of stand age. The accumulation of A0 layer decreased from 21 t ha−1 to 5 t ha−1 during the 10 years following clear-cutting, and then recovered to nearly the same level as before clear-cutting within 20 years after clear-cutting, although the amount of soil carbon in the mineral soil recovered more than 40 years after clear-cutting. The total and mineral soil respiration rates increased rapidly after clear-cutting and gradually decreased in young stands and stabilized in old stands. The relative decomposition rate of the A0 layer and organic matters in mineral soil was high in the young stands because of the relatively high soil temperature rather than the soil moisture content. After the closing up of the canopy, the relative decomposition rates of the A0 layer and humus in the mineral soil stabilized at 0.14 to 0.16 y–1 and 0.005 to 0.013 y−1, respectively. Consequently, soil carbon cycling was strongly affected by clear-cutting. The amount of soil carbon rapidly decreased because of the cessation of litterfall and the increase of the relative decomposition rate of the A0 layer and humus, and recovered gradually to the level before clear-cutting with the growth of the cedar plantation. The change in soil carbon cycling with stand development was partly caused by the change in soil temperature and moisture content but was mainly caused by the amount of cedar litterfall which changed significantly in the early stage of the stand following clear-cutting, and became slower and leveled off in the late stage with stabilization of the environmental conditions and litterfall rate. [ABSTRACT FROM AUTHOR]

Forest ecosystems are self-fertilizing systems, and development of forest stands depends on nutrient supply via biogeochemical cycling within the ecosystem. Therefore, it is important to clarify the nutrient cycle mediating growth and development. In addition, long-term hydrochemical monitoring is needed to understand the influence of environmental changes on biogeochemical cycling in forest ecosystems. The Oyasan Experimental Forest Watershed (OEFW) is located in the Field Museum Oyasan, the university forest of Tokyo University of Agriculture and Technology, in Gunma prefecture, Japan. OEFW comprises two small adjacent forested watersheds-A-watershed and B-watershed-with respective areas of 1.3 and 1.8 ha. A-watershed is a reestablished forest planted with sugi (Japanese cedar; Cryptomeria japonica) and hinoki (Japanese cypress; Chamaecyparis obtusa) in 1976, and has been managed intensively with fertilizer application. By contrast, B-watershed is an established forest planted with sugi and hinoki in 1907. No forest practices have been carried out except for thinning of suppressed trees in 1983. However, the sugi plantation on the lowest slope (18% of the watershed area) was cut in 2000, and sugi was replanted the following year. In this data paper, we present data on the daily precipitation, discharge, pH, and concentrations of major nutrients (Ca, Mg, K, Na, NH, Cl, NO, and SO) in rainwater and stream water since November 1978. The arithmetical mean pH of precipitation, stream water in A- and B-watershed from the beginning of the monitoring to the present were 4.77 ± 0.67, 6.85 ± 0.41 and 6.88 ± 0.36 (average ± SD), respectively. The arithmetical mean concentrations in precipitation in mmol L were 0.030 ± 0.030 for Ca, 0.010 ± 0.011 for Mg, 0.009 ± 0.013 for K, 0.020 ± 0.024 for Na, 0.035 ± 0.041 for NH, 0.026 ± 0.029 for Cl, 0.033 ± 0.038 for NO, and 0.046 ± 0.043 for SO. The mean concentrations in stream water in A-watershed were 0.180 ± 0.032 for Ca, 0.073 ± 0.013 for Mg, 0.018 ± 0.009 for K, 0.182 ± 0.024 for Na, 0.010 ± 0.010 for NH, 0.060 ± 0.008 for Cl, 0.111 ± 0.038 for NO, and 0.074 ± 0.012 for SO; whereas for B-watershed the mean concentrations were 0.169 ± 0.025 for Ca, 0.079 ± 0.016 for Mg, 0.018 ± 0.005 for K, 0.192 ± 0.026 for Na, 0.010 ± 0.010 for NH, 0.065 ± 0.010 for Cl, 0.093 ± 0.025 for NO, and 0.087 ± 0.011 for SO. [ABSTRACT FROM AUTHOR]