The decay or hollow-area ratios in the stems of 240 living Japanese black pines in Jozan park of Matsue City were estimated by the lateral impact vibration method (LIV). The diagnosis index is a product (D・F_r) of the diameter D of a tree stem and the resonance frequency F_r after lateral impact. First the following two tasks were performed: (1) 30 healthy Japanese black pines were cut down to obtain the average and range of D・F_r of healthy trees, and (2) hollow disks made artificially were used to study the relationship between hollow-area ratios and the decreasing ratios of D・F_r. All the trees in the park at 1 m height were tested by LIV, and the decay or hollow-area ratios (R_iv) were calculated on the basis of the abovementioned two tasks. R_iv in 17% and 3% of the total trees were estimated to be in the range of 1∼30 and 30∼59% respectively. To evaluate the accuracy of LIV, the decay or hollow-area ratios (R_rg and R_am) were estimated by a drilling resistance method and measured by cutting investigation. R_iv had highly positive correlations to both R_rg (r=0.88, p<0.001) and R_am (r=0.80, p<0.001). This result reveals LIV is effective in estimating the decayed or hollow-area ratio inside a stem of Japanese black pine.

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Soil erosion has been progressing over a large area on the beech (Fagus crenata) forest floor with an understory impoverished by the feeding of deer (Cervus nippon) in Doudaira (located in East Tanzawa of Kanagawa Prefecture), and has a significant impact on the environment of the forest and streams. In previous studies at Doudaira, it is reported that the amount of washed soil is larger than the splashed soil, and washed soil is strongly affected by the overland flow. In this study, four erosion plots (2 m wide × 5 m long) with different understory cover percentage were installed on the beech forest slope in Doudaira. Throughfall, overland flow, forest floor cover percentage (the total values of understory cover percentage and litter cover percentage), soil erosion rate and other factors. were monitored during 2004∼2009, and the effect of forest floor cover percentage on the overland flow rate was examined. As a result, a significant negative correlation expressed by R_em = −18.9 ln (C_m) + 86.4 between the forest floor cover percentage (C_m) and the overland flow rate (R_em) was found. From the equation, when the forest floor cover percentage decreases, the overland flow rate increases. The overland flow rate changes seasonally; for example, such as in summer (Jul.∼Sep.) with less litter, the overland flow rate decreases compared to spring (Apr.∼Jun.) and autumn (Oct.∼Nov.) with a great deal of litter.

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The dense growth of dwarf bamboo creates shade stress against tree regeneration. How can dwarf bamboo grow under deep shade in the understory? To analyze the relations between light conditions and biomass or the growth characteristics of S. palmata, we investigated the canopy-openness and biomass at the belt transects set up in the gap-understory continuum. We also analyzed whether the biomass was dependent on light intensity or the distance from the gap. Canopy-openness showed a pattern dependent on the distance from the gap. The biomass peaked at the gap and gradually decreased up to the edges of the gap, while it remained constant in the understory. The biomass did not depend on light intensity. This phenomenon can mainly be interpreted two ways. One is that dwarf bamboo is a shade-tolerant species, and adapts to a low light environment due to its growth characteristics. The second is that S. palmata is subject to physiological integration. The result may indicate that physiological integration among ramets enables a compensatory growth through photoassimilate with connected neighboring ramets.

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We investigated how best to use the stand-density control diagram for Japanese cedar stands in regions with heavy snowfall. These matured stands were composed of tall canopy trees with many other trees whose height was suppressed due to snow-pressure damage occurring during stand initiation stage. The distribution of stem diameters was positively skewed by these suppressed trees that were left after thinning since they were suppressed one-sidedly by canopy trees. The error rates of estimated stand volumes for the stand-density control diagram were high in stands with a high ratio of suppressed trees. To reduce error rates, only dominant trees should be used in the model. Estimated stand volumes can be calibrated using the measured basal area. With this modification, the stand-density control diagram can be applied to Japanese cedar stands in heavy snowfall regions.

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We examined the relationships between actual stem profiles and relative stem profile equations (RSPE) based on Behre’s equation derived using the methods of Inoue and Kurokawa in planted forests of Cryptomeria japonica (61∼67 years old) and Chamaecyparis obtusa (50∼61 years old) located in the Hida district, Gifu Prefecture, central Japan. RSPE derived on the basis of Forestry Agency stem volume equations underestimated the actual stem profiles by 2 cm for C. japonica and by 1 cm for C. obtusa. This was due mainly to the fact that the Forestry Agency equations had underestimated actual stem volumes by 10%. A theoretical stem volume equation had a smaller error compared to the Forestry Agency equations. RSPE derived using the equation was in accord well with the actual stem profiles and the cubic RSPE made by Gifu Prefecture, indicating a wide applicability of the method proposed by Inoue and Kurokawa.

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We investigated the changes in stand structure and species composition from 5 to 11 years after clear-cutting of a Sugi (Cryptomeria japonica) plantation in the warm-temperate zone of eastern Kochi, Japan. Stem density of broad-leaved tree species in the study stand was 11,300 stems ha⁻¹ in 2003, 5 years after clear-cutting, and increased during the study period. The basal area of the study stand reached 29.8 m² ha⁻¹ in 2009. Approximately 65% of tree individuals in the study stands were multi-stemmed, suggesting the importance of sprouting in the regeneration process. The observed changes in stand structure and species composition during the study period showed that pioneer shrub species had been excluded from the stand, and that evergreen broad-leaved trees, especially Castanopsis species, had increased their dominance. These results suggest that the study stand is under a succession process comparable to that previously reported in evergreen broad-leaved secondary forests in the warm temperate zone in Japan.

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This paper discusses the pros and cons, effects on productivity and their mechanisms, and other issues related to mixed tree plantations as an alternative to pure tree plantations. Mixed tree plantations provide a broad range of goods and ecosystem services via the diversity of species planted. This diversity provides various habitats and ecological niches and can improve productivity through reduced competition and facilitation. Issues involved in experimental mixed plantations include the spacing and distribution of species and trees. Most previous studies have focused on young plantations. Because management practices need to vary according to the objectives of a mixed tree plantation, many issues need to be resolved for the practical introduction of mixed tree plantations.

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