We investigated how hoarding behavior by squirrels and wood mice affected the distribution of walnut trees in a riparian forest along the Kushiro River in eastern Hokkaido, Japan. We established a 200 × 100 m plot on the left bank of the river, mapped the locations of walnut trees, and estimated their ages(DBH > 10 cm)using annual ring cores. The topography was a predominantly flat site within 60 m of the river and sloped 60-100 m from the river. Walnut trees were distributed throughout the plot. The oldest walnut tree in the plot was 68 years old and located 10 m from the river. Walnut trees older than 50 years were located within 40 m of the river, while the trees at the upper part of the slope tended to be younger. These age differences suggested that the areas were not colonized at the same time. Five of the seven small trees in the plot grew near old trees, probably their mothers; the other two grew near trees of other species. Given the distribution and age structure, the walnut trees spread from the flat area to the slope. In flat areas, seeds disperse via the river, gravity, and squirrels or wood mice. On slopes, gravity and squirrels or wood mice disperse the seeds. We inferred that squirrels and wood mice helped the walnut trees expand into places where they could not spread via the river and gravity alone, especially to locations far from the river and on upper slopes.

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Bamboo often invades areas of anthropogenic disturbance in Japan and is Silicon (Si) accumulator. Silicon plays important roles in the global C cycle through silicate weathering and Si fluxes delivered into the ocean as part of the global Si cycle. Terrestrial vegetation influences the global Si cycle. However, there appear to be no reports showing regional terrestrial biogeochemical Si budgets of bamboo forests in a temperate climate. Therefore, in a temperate climate, we established two study sites with two plots each, one plot at each site was selected in forestland that had been invaded and dominated by bamboo and a second at each site in an adjacent evergreen broad-leaved forest or coniferous forest. To better understand the characteristics of biogeochemical Si cycling in bamboo forests, we compared biogeochemical Si cycling in the bamboo forests and other types of forests. Annual Si fluxes by litterfall of the bamboo forests were higher than those of the adjacent other forests. In both sites, the annual Si uptakes were greater in the bamboo forests than in the other forests, and in one site the available Si pool in the soil was also greater in the bamboo forest. We concluded that in the bamboo forests, those amounts of surplus Si to other forests might have been supplied by mineral weathering after bamboo invasion. Therefore, bamboo forests may have characteristics which enhance mineral weathering and dissolved Si release into soil solution from minerals, resulting in greater uptake of Si and return of Si to the soil.

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We investigated the changes in soil physical and chemical properties at five plots, approximately 3 km apart from Mt. Shinmoe, with the volcanic ejecta and buried soil from a half year to one and a half year elapsed time from 2011 eruption of Mt. Shinmoe. The volcanic ejecta were composed by thin volcanic ash and thick pumice layer. The water-extractable ions and sulfur content in the volcanic ejecta were relatively smaller than those in the previous reports with other volcanos. The sulfate and ammonium were dominant for the water-soluble fraction. The clay content increased along with the time in any layer, indicating that clay migration had occurred. The thickness of the layer, total carbon and nitrogen content, cation exchangeable capacity and exchangeable cation content little fluctuate during this period. The sulfate and ammonium ion in the water-soluble fraction, sulfur content, and available phosphate seemed to decrease gradually, but the trend is obscure. Although the ejecta did not absorb phosphate up to 1 year after eruption, the ejecta one and half year after eruption was slightly able to absorb phosphate accompanying the increase in oxalate-extractable aluminum and Alp/Alo ratio. With regard to the nutrient load to the soil, because the contribution from thick pumice layer was greater than that from thin fine ash layer, we suggest that the contribution from pumice layer could be more important in the long-term change.

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To assess the community structural change and to document temporal trends in biomass accumulation of an old-growth forest over a period of 17 years, we surveyed the forest structure and tree diameter in a 1-ha plot established in a cool-temperate deciduous forest on the eastern slope of Mt. Hakusan in 1995 and 2012. In a stand dominated by Fagus crenata (beech) and Quercus mongolica var. crispula (oak), the largest diameter at breast height (DBH) in 2012 was 100.3 and 194.7 cm, respectively. Although the tree density (DBH &ge; 5 cm) increased from 908 to 940 stems ha^<-1> from 1995 to 2012, nine large dead trees were found in this period. Because of dead canopy trees, the gap enlarged and a change in the forest structure occurred in the tree and subtree layers according to mean tree weight-weight of individual trees (M-w) diagrams. The forest biomass was estimated to be 537.8 and 536.7 t ha^<-1> for 1995 and 2012, respectively. The biomass in this forest was extremely high compared with those in old-growth beech forests studied elsewhere in Japan because of the existence of some huge oak trees. The loss of biomass (73.7 t ha^<-1>), partly because of large dead oak trees, was compensated by the growth of beech. Thus, the change in biomass in the 17-year period was very small. The results of the present study indicated that this old-growth beech-oak forest showed nonequilibrium in forest community dynamics; however, the forest biomass was at a steady state.

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