Soil physical properties and soil moisture conditions were investigated on three experimental plots to study influence of forest treatment. Those plots comprised a clear-cut plot, thinned plot that was thinned 50%, and a control plot with standing trees. Those plots were settled in a Hinoki (Chamaecyparis obtusa) stand which was located at Mt. Tsubakuroyama, Ibaraki prefecture. Results of the investigation are as follows: 1) Volumetric contents of total soil pores at 10cm depth on each plot were 70-77%; those at 30cm depth were 65-73%. However, volumetric contents of total soil pores at each depth (10cm depth and 30cm depth) were almost equal among plots. 2) Size distributions of volumetric soil pore contents were nearly equal on each plot. 3) Soil pores were filled with water at each depth just after rainfall events that were over 20mm. Also, soils were drying during the no rainfall period. 4) Soil matric potential of the clear-cut plot was from -50 to -30kPa, seldom reaching -60kPa. Individual soil matric potentials of thinned plots and control plots were from -20 to -10kPa. Soil matric potential of the clear-cut plot was lower than the other plots. However, low soil matric potential periods were insufficiently long to prevent plants from smooth growth on each plot. 5) Soil moisture content of the clear-cut plot was less than the thinned plot and the control plot at each relief point. On the convex relief point, the clear-cut plot showed significantly less content than either the thinned plot or the control plot. On the other hand, there is not significant difference between the thinned plot and control plot. 6) Soil temperatures of the clear-cut plot and the thinned plot were higher than the control plot. In addition, soil temperature of the clear-cut plot was slightly higher than the thinned plot on the convex relief point. 7) Increase of soil moisture content of the clear-cut plot was greater than either the thinned plot or the control plot on the convex relief point after a rainfall event. On the other hand, soil moisture increase of the thinned plot was slightly greater than other plots on the concave relief point.

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Soil pH, total carbon, total nitrogen and net nitrogen mineralization were measured in Japanese cedar (Cryptomeia japonica D. don) and Hinoki cypress (Chamaecyparis obtusa Endlicher) plantations on a precipitation gradient (1,690〜3,300mm) in Shikoku District. Net nitrogen mineralization rates by a laboratory incubation (25℃, 14-31days) showed substantial differences among forests ranging from 0.2 to 2.5mg N kg^<-1>d^<-1>. In high precipitation areas, soils had larger C/N ratio, lower nitrate pool and nitrogen mineralization rates than in low precipitation areas. This indicates that forest ecosystems in high precipitation areas have efficient nitrogen cycling with small nitrogen losses.

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In order to apply an easily and speedily method measuring microbial activities using FDA hydrolysis to forest soils, we improved the measuring condition using different from microbial activities soil on same geology. Fluorescence of FDA was measured by absorbance at 490nm(A_<490>). 0.25g(dry weight) of soil was added to 20ml of 60mM sodium phosphate buffer (862.5mL of 0.06M Na_2HPO_4+137.5mL of 0.06M NaH_2PO_4), pH7.6, then about 1ml of FDA solution (2mg/mL) was added. Immediately, the mixture solution was shaken at 25℃ for 30 minutes, and added with acetone to terminate the hydrolysis of FDA. Mixture solution filtered through no.3 filter paper was used to determine absorbance at 490nm. The resultant A_<490> reflected microbial biomass C, soil respiration rates, fungal counts and organic matter decomposition rates in soils. These results showed that A_<490> represented microbial activities as decomposer in forest ecosystem.

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In order to clarify the effects of the conversion of the forest management type from natural deciduous broad-leaved forests to artificial Japanese cypress and Japanese cedar forests on the soil fertility, we investigated the amounts and nutrient contents of the forest floor and soil chemical characteristics (0-30cm depth) in the natural deciduous broad-leaved forests and adjacent artificial Japanese cypress and Japanese cedar (evergreen coniferous) forests. In the artificial evergreen coniferous forests were planted Japanese cypress (Chamaecyparis obtusa) on the upper slope and Japanese cedar (Cryptomeria japonica) on the lower slope. In this study, comparisons of the results were between the natural deciduous broad-leaved forests and artificial evergreen coniferous forests. The soil exchangeable base contents in the cypress forest were almost the same to those of the natural deciduous broad-leaved forest on the upper slope. The soil exchangeable calcium contents in the cedar forest were about 1.9 times greater than those in the natural deciduous broad-leaved forest on the lower slope. The soil carbon and nitrogen contents and CEC in the cypress forest were about 0.6, 0.6, and 0.8 times smaller than those in the natural deciduous broad-leaved forest on the upper slope, respectively. The soil carbon and nitrogen contents and CEC in the cedar forest were almost the same to those of the natural deciduous broad-leaved forest on the lower slope. The amounts on the forest floor were about 7.1Mg/ha in the natural deciduous broad-leaved forests, and about 9.5Mg/ha in the artificial evergreen coniferous forests regardless of the slope position. The C/N ratios of the forest floor in the artificial evergreen coniferous forests were higher than those in the natural deciduous broad-leaved forests. The amounts of calcium in the forest floor significantly correlated with the contents of exchangeable calcium in the soil. The accumulation of calcium in the forest floor was inferred to bring the increase of the exchangeable calcium in the soil.

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The present report describes an estimation of the potential of the water holding capacity (WHC) on the basis of soil pore distribution, and an analysis of related factors. Each sample was collected from 905 spots of 246 forests and plains in Oita Prefecture using a soil sampling cylinder (400cc). WHC was calculated by the product of the soil depth (up to 1m) and soil porosity as to soil classes which were divided into 3 classes according to pore size. The water holding capacity of these three classes WHC was correlated to the pF value, and was expressed as follows. WHC of coarse size pores (pF0〜2.7; for short: Sc) indicates a reserve of rain water and potential of deliverability. WHC of small and medium size pores (pF0.6〜2.7; for short: Sms) indicates available a reserve of rain water as a water resource. WHC of large size pores (pF0〜0.6; for short: Sl) indicates conduction of rain water into soils and the potential of water delivery in the soils. The average (±standard deviation) WHC (Sc, Sms, and Sl) within the whole forest stands and plains was 339.6 (±75.9) mm, 243.6 (±56.9) mm, and 96.9 (±40.5) mm respectively. Every WHC was greater in broad-leaved forests and poor in plains. As for each item of the water holding capacity, factor analysis was executed as an objective variable using Hayasi's quantification method (I), for five environmental factors and three soil characteristic factors. The result was that soil characteristic factors have a dominant influence upon the WHC. Though environmental factors effect the WHC unsignificantly, the category score was greater in the soil of broad-leaved forests than in the soil of conifer forests and plains. Therefor, it was elucidated that the water holding capacity was promotive, and its capacity was increased by aging. This suggests that an increase in water holding capacity is possible through human efforts, namely careful treatment to increase soil porosity.

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The purpose of this study was to clarify the effect of soil factors on the decline of Clyptomeria japonica in Kanto plains. Soil features, such as parent material, types of deposition, soil texture, bulk density(soil depth: 0-8, 8-16 cm), porosity and hardness of surface soil were investigated in 34 study sites, where the decline index previously reported. The index performed damaged at lowland sites with sandy alluvial soil, although healthy at upland or hill sites with clayey or loamy soils derived from volcanic ash or weathering products of sedimentary rock. These results showed locations and parent materials affected to the tree decline. Furthermore, the remarkable correlation was observed between bulk density and the decline index. Thus, compact surface soil was correlated with the decline, however, thick soil layer eases the influence of compact surface soil. Most of sites were located in the grounds of temples and shrines. Extremely compact surface soil often occurred by treading, and trees were damaged. The forest decline was effected by soil factors relating to density and was accelerated by artificial impacts.

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The present conditions of the tree and forest declines were investigated all around the Kanto Plain, central Japan. The decline of Criptomeria japonica was the most remarkable. The declines of evergreen conifer species (Chamaecyparis obtuse, Pinus densiflora, P. thunbergii, Abies firma, Tsuga sieboldii, Podocarpus macrophyllus, Torreya nucifera, Chamaecyparis pisifera, Picea sp., and so on), Ginkgo biloba, and Zelkova serrata were observed. However, declines were hardly observed Matasequoia glyptostroboides and Cadrus deodara. The decline of Criptomeria japonica was observed in the whole area of the Kanto Plain. Especially, the heaviest decline areas of all are an area along Tone River in Gunma Prefecture and Saitama Prefecture, northwestern part of the Kanto Plain, areas along Naka River, and Kuji River and an area around Choshi city, faced to the Pacific Ocean. There were also heavier declined trees around Chiba city and Machida city.

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The relationship between root biomass and environmental factors were examined using the root biomass data provided by previous reports. It was shown that tree species, stand age, and parent materials strongly correlated with root biomass. On the other hand, root biomass were influenced little by soil type and stand site. Estimation of root biomass showed a significant amount and indicated its considerable role in the functions of carbon storage in forests. Thus, root biomass as well as aboveground biomass, the mass of deposited organic matter, and the amount of soil organic matter are very important factors in the carbon storage of forest resources.

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