We examined how site conditions in selection cutting stands of natural forests relate to the regenerate distribution of Abies sachalinensis, which is a main species of mixed conifer-broadleaved forests in Hokkaido, northern Japan. We established 200 quadrats in 50 stands and investigated the number of Abies sachalinensis current-year seedlings, seedlings (H <30 cm, seedlings ≥2 years old), saplings (30≤H <130 cm), and juveniles (H ≥130 cm, DBH <5 cm). We also measured five site conditions in each quadrat: dwarf bamboo coverage, basal area of the overstory Abies sachalinensis, canopy openness, degrees of slope, and slope direction. The average density (trees per hectare) of current-year seedlings, seedlings, saplings, and juveniles was 4,800, 11,980, 805, and 285, respectively. The results indicate that the density of Abies sachalinensis decreased drastically in successive demographic stages from seedling to sapling. Regenerated trees of Abies sachalinensis in all stages were detected more in the sites characterized by low dwarf bamboo coverage and high basal area of overstory Abies sachalinensis. Current-year seedlings and seedlings occurred more on northeast slopes, while saplings and juveniles did more on southwest slopes. In conclusion, to maintain regeneration of Abies sachalinensis continuously, we should establish a system which seedlings can survive to be saplings and juveniles.

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Factors affecting forest formation were studied in abandoned terraced paddy fields in a mountainous region of Sado Island, Niigata Prefecture, Japan. Shortly before or after the study area was abandoned about 40 years ago, the migration of Quercus serrata, Castanea crenata, and other tree species started in the terraced paddy fields and progressed gradually until about 20 years ago. Forest formation in the abandoned fields was affected strongly by groundwater levels due to the slope position and the soil water environment caused by differences in microtopography, namely, paddy plane, levee, and levee slope. At higher positions on the slope, where the groundwater level was low and hence the soil water content was not excessively high, trees had grown in every part of the paddy field. However, at lower positions on the slope, where the groundwater level was high and hence the soil water content at the paddy plane was high, the forest canopy was closed by trees growing mainly on the levees or levee slopes where there was lower excess soil water. Soil water content and tree growth were affected by the inclination of the levee slopes. The different distribution patterns of tree species by microtopography of the terraced paddy fields might be related to the seed dispersal types and physiological tolerance of individual species to the soil water environment.

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To examine the potential of Alnus faurei for use in revegetation of disturbed steep hillsides, its growth and tree form were compared to those of traditionally used species: A. maximowiczii and A. hirsuta. The height and crown diameter of these three species, planted on disturbed slopes in a heavy snowfall region, were investigated for 9∼18 years. Also, the stem length and basal diameter of sprouts were compared between A. faurei and A. maximowiczii for 18 years. Results show that, more than the other two species, A. faurei favored crown enlargement over height growth; in spite of the tree height of 130 cm, the mean crown diameter reached 110 cm at the third growing season after the planting. At the ninth growing season, A. hirsuta showed a decline mainly by snow pressure injury; in contrast A. faurei became dominant with little damage, which apparently resulted from its tree form, with many sprouts per plant. A. maximowiczii showed intermediate traits. In conclusion, we recommend that A. faurei be used for revegetation of disturbed steep slopes in heavy snowfall regions.

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Soil erosion has been progressing over a large area in Doudaira (located in East Tanzawa of Kanagawa Prefecture) due to the sika deer (Cervus nippon) feeding which has in turn resulted in a reduction in the understory of beech (Fagus crenata) forests. Three test plots which have different understory coverage were set in Doudaira and the soil erosion rate from July 2004 to December 2006 was monitored. The results revealed that if the coverage of understory is smaller, the litter depositional volume will be smaller and erosion amount increase. At the 1% coverage of understory plot erosion depth was 2∼10 mm per year. At the study site, litter mostly from overstory beach tree deposited on the forest floor. However, the amount of litter is decreased partly through the processes of decomposition and partly washed away through the process of overland flow. Therefore the amount of litter changes season to season. At the 1% coverage of understory plot, in summer (Jul.∼Sep.) with less litter, infiltration rate decreased and surface flow rate increased rather than in Spring (Apr.∼Jun.) and Autumn (Oct.∼Nov.). Even in the case of equal rainfall amounts, soil erosion progresses more in summer. It is clear that most of the soil erosion occurred in summer, because of abundant rain in this season and decrease of amount of litter.

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To measure spatial variation in soil CO₂ efflux in a secondary beech forest in northern Japan, we took measurements five times over two years at 49 sampling points in a 35 m×35 m grid using a closed chamber method. There were relatively large variations in soil CO₂ efflux in space over the study area (CV=15.8∼26.7). A tree index using tree position and size explained about 10% of spatial variation in soil CO₂ efflux. The spatial variation in soil CO₂ efflux was negatively correlated with an index of volumetric soil water content. Volumetric soil water content was negatively correlated to the distance and size of trees around the chambers. This suggests that stand structure altered volumetric soil water content and indirectly affected soil CO₂ efflux.

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I sprayed the trunk surface lower than 6 m above ground level with 1.6% fenitrothion once before the occurrence of Platypus quercivorus adults in Quercus serrata and Q. crispula forests. The number of captured males and this attack density were five times higher in the Q. serrata forest than in the Q. crispula forest. In the Q. serrata forest, the control rate of initial attacks was 100% for 1∼3 weeks and it decreased to 50% five weeks after spraying. The incidence of capturing more than six males, which indicated the control effect on the initial attacks emerged 22 times and concentrated on 1∼5 weeks after spraying. The mass-attack controlling effect was also observed during this period. In the Q. crispula forest, the rate of control of the initial attack was 100% for 5∼7 weeks and it decreased to about 80% there after. The boring density on the trunk surface lower than 6 m height, where fenitrothion had been sprayed, was less than in non-sprayed trees, and the difference was the largest in the 0.5∼1.5 m height range in the Q. serrata forest. These results suggest that spraying fenitrothion should be effective to control boring by P. quercivorus adults and that spraying of 1.6% fenitrothion once can have a high control effect on boring over a period of more than three weeks.

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Scarification is widely conducted in northern Hokkaido to remove understory dwarf bamboos in degraded forests, and to replace it with tree species. We investigated height growth and survival during 6∼8 years after the treatment for nine major tree species naturally established in a site, and examined their contributing factors (competition or facilitation). The height growth and survival rate were higher in Phellodendron amurense and Sorbus commixta, besides lower in Picea glehnii. The results of generalized linear model or generalized linear mixed model suggested that facilitation effects of surrounding broadleaved trees or understory vegetation were dominant for growth of many tree species. Regarding Betula platyphylla, however, the facilitation effect, which had been found in the former period (3∼5 years after scarification), was changed into competition effect. For seedling survival, although negative effects of surrounding conifers were found, effects of broadleaved trees and understory vegetation were unclear. We concluded that weeding and cleaning treatments were ineffective for enhancing species richness in the site in this stage of stand development.

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To clarify the manner of bark stripping to coniferous trees by sika deer (Cervus nippon) on Mt. Ohdaigahara, central Japan, we investigated: (1) the relationship between bark stripping and tree size, (2) the difference in bark stripping between trunk and butt swelling, and (3) the difference in bark stripping between the parts adjacent to wounds that debarked formerly and untouched parts. We surveyed the number, position, and the area of bark stripping wounds on trunks and butt swellings of Abies homolepis and Picea jezoensis var. hondoensis, which are declining species, in the 45 plots in Mt. Ohdaigahara. Bark stripping on trunks of both A. homolepis and P. jezoensis in every DBH (diameter at breast height) class showed no clear trend, suggesting no DBH preference. There were significantly more bark stripping wounds on butt swellings than on trunks in both A. homolepis and P. jezoensis, while the wound area is significantly larger on trunks than butt swellings in both A. homolepis and P. jezoensis. There were significantly more stripping wounds on the part adjacent to wounds that debarked formerly than on untouched parts, indicating that deer selectively debark the parts adjacent to wounds, probably because the wound edge is more easily accessible. Thus, deer seem to debark butt swellings and wound edges, enlarging them little-by-little.

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The effect of forest works on volunteer’s mental state are measured by Profile of Mood States (POMS). The investigation places are thinning of forest by a volunteer group and a student group. POMS is tested before and after the work and fluctuation during the period is analyzed. The results are following. A man who exercises daily or is in the habit of forest work can feel refreshed and relaxation. For a volunteer who is beginner in forest work or do not exercises daily, there is possibility of feeing these if he works in his own way and do not overwork himself. In aging society, it is expected that because of forest volunteer’s work not only over middle age will be able to maintain his mentally and physically health but also the forest will grow and recover his health.

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High concentrations of CO₂ in soil air affect subsurface water quality and weathering reactions; however, few simple methods have been proposed for the collection of soil air from deep soils. Therefore, we have developed a gas sampler that enabled soil air collection and soil temperature measurement at several depths using commercially and reasonably available materials. The sampler was then used at a headwater hillslope that had a thick soil layer (a maximum depth of approximately 5 m). The soil temperature showed typical seasonal changes, whereas the CO₂ concentration in soil air reached the maximum and formed a peak near the ground surface in summer. The depth of the peak then moved downward from autumn to winter. The sampler developed in this study can be used to clarify the characteristics of CO₂ dynamics in deep soils and its effect on groundwater quality and basal weathering.

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Height growth and maximum tree height vary among species as well as with site conditions. Maximum tree height is an important factor determining the outcome of competition for light, vertical stratification of the canopy, and productivity of forest ecosystems. Recent advances in canopy access techniques have allowed direct measurement of physiological processes at the tops of tall trees. These studies indicated that height grow may be limited by constraints on water transport from soil to leaf, which reduces photosynthesis of leaves and by the gravitational gradient in water potential, which constrains cell elongation in leaves and shoots. Theoretical and experimental research suggests that mechanical requirements to prevent buckling and wind damage and genetic changes due to maturation are unlikely to contribute to height-growth limitation. Further research investigating the relationships between maximum tree height and succession, crown interactions, species variation in natural stands are needed for comprehensive understanding of height growth in trees. Such knowledge could potentially be used to predict variation in productivity among various forest types.

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