The authors examined the effects of fertilization on the growing process of the trees and on the soil chemical and physical properties in an Akamatsu, Japanese red pine (Pinus densiflora SIEB. et ZUCC.) stand which was regenerated naturally under poor nutrient conditions. For this purpose, three types of plots were established-a control plot, and plots fertilized once and four times. The stem volume at the time of the last investigation when the stand was 33 years old was 172, 187, and 255m³/ha for the control plot, the plot fertilized once, and the plot fertilized four times, respectively. In other words, the volume increase of the plot fertilized once was 9% more than that of the control plot, and that of the plot fertilized four times was 48% more. The authors also investigated the changes of soil conditions during the test period of 27 years. Among the various soil conditions, the development of the A₁ horizon was one of the noticeable point. The thickness of the A₁ horizon was measured at 50cm intervals along a 10m stretch which was established on each plot. The mean thickness of the A₁ horizon was 1.0cm on the control plot, 4.1cm on the plot fertilized once and 5.1cm on the plot fertilized four times. The concentration of inorganic nitrogen (NH₄-N and NO₃-N) in the A₁ horizon was different on each plot. NO₃-N/NH₄-N+NO₃-N of fresh A₁ soil was higher on the fertilized plots than on the control plot. The difference of the ratio increased more after the soil was incubated for 3 weeks. The results suggest that the fertilization accelerated nitrification even under the acidic conditions (pH 5.1) of the soil.

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The purpose of this paper is to obtain fundamental data for fore-casting the occurrence of debris flow and for a plan to counter them by investi-gating the situation and theoretically analysing the data, that is, the criteria for the occurrence of debris flow because of heavy rainfall, its infiltration, and runoff on a slope; the primary flow characteristics; the confluent process of debris flows; and the mechanical characteristics of the leading edge of the debris flow. Results are (1) formulas are proposed concerning the time of occurrence, its criteria, and the depth of the surface flow which are defined by the motion and continuity of the runoff on the slope, (2) the effect of cohesion is not negligible in describing the stability of the slope, and the dynamic function between the moving flow and the static sediment bed must be taken into consideration in predicting the occurrence of debris flow, (3) the formula adopted for describing the occurrence of the surface flow agrees fairy well with the experimental data, (4) the formula for sediment discharge was put forth by a model of debris flow with a constant wave-height and velocity which shows that the discharge due to debris flow is about 20 times that of the surface flow due to rainfall, (5) a debris flow occurring after a previous flow has a faster propagation velocity than the preceding flow and soon catches up with it; together, they then become a steady debris flow, and (6) the propagation velocity for a debris flow is expressed by that of the ideal hydraulic bore.

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The following are the basis for an analysis and a synthesis of the root network structure of trees for this simulation model. (1) The orders of tree-root networks are 1st order for the main tap root, 2nd order for branch roots, and so forth. (2) Dimensionless expressions of the orders of the root system are obtained by dividing the lengths of the roots and their diameters by their basal diameters. (3) The average decreasing rates of root diameters of the respective orders of roots. (4) An assumption of the distribution of 2nd order roots toward the horizontal or oblique directions. As a result of the dimensionless expression, L/D_O_??_d_O/D_O and l/d_O_??_αO/d_O matrix tables are made where L and l are the length of the 1st and 2nd order root, respectively, and D_O, d_O, and α_O are the basal diameter of the 1st, 2nd, and 3rd order roots, respectively. These tables are the core part of the model. The results of the above analyses were synthesized for making a simulation model of a pine stand. Compared with the total root volumes, the sample and simulated values coincided satisfactorily.

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It is a well-known theory regarding forest soils on the hilly topography of Japan that the influence of soil-moisture conditions on the decomposition of leaflitter is greater than that of the chemical composition of the leaflitter. This investigation is a re-examination of this theory. The effect of the species composition of the leaflitter on the decomposition rate of the A_o horizon was examined along the slope where no apparent effect of the soil-moisture conditions had been observed. The species composition of the leaflitter evidently was different on the ridge and on middle and lower parts of the slope. Mixed leaflitter collected on the ridge decomposed most slowly, and that on the lower part of the slope decomposed most rapidly. These results agreed not only with the estimated rate of decomposition calculated from the values of each species examined and their mixture ratio, but also with the annual decomposition rate calculated from the amount of the A_o horizon and the litterfall. This investigation suggests that the influence of the species composition of the leaflitter on decomposition should not be underestimated along the slope where the moisture conditions of the soil intensively affects the decomposition of the A_o horizon.

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