Abstract
Physical characteristics and moisture conditions of the soil in an experimental Hinoki (Chamaecyparis obtusa) stand located at Mt. Tsubakuroyama, Ibaraki Prefecture were observed and analyzed. This study examined slash that remained after thinning, and its effects of the surface soil moisture conditions. Observations and soil samples were collected in two plots in the stand : one was named the "Slash Plot", in which the slash remained on the forest floor and covered the surface of the ground after thinning; the other was called the "Control Plot", where no slash and litter covered the surface of the ground. Surface conditions there were similar to those observed before thinning. The results of observations and analyses are as follows: 1) Solid phase contents of respective soils at 5-, 10- and 30-cm depths were less than 20%. Pore contents of soils at each depth were more than 80% in the experimental plot. These observations emphasize the character of this black soil, which is volcanic in origin. 2) Total pore contents of soils at 5-, 10-, and 30-cm depths did not differ. Significant differences of pore contents were not observed among Control and Slash plot soils. 3) Matric potential of the Control plot was slightly less than that of the Slash plot at 5-cm depth during the period without rainfall. In contrast, the matric potential of the Slash plot was markedly less than that of the Control plot at 30-cm depth. The matric potential of each plot was not different at 10-cm depth. 4) The Slash plot soil temperature was 1-2℃ higher than that of the Control plot in winter, and 1-2℃ lower than that of the Control plot in summer. Those differences were engendered by temperature change moderation that is attributable to slash. 5) Effects of slash on surface soil moisture are derived from rainfall interception above the ground and reduction of evaporation from the ground surface. 6) Effects of rainfall interception by slash engender a decline in the water content of sub-surface soil. On the other hand, effects of evaporation reduction by slash moderate the increases in surface temperature and retain surface-soil moisture.
