Soil hydraulic conductivity differences between upslope and downslope of two coniferous trees on a hillslope

Abstract

ABSTRACTStanding trees influence the redistribution of soil water around the trunk and alter water movement under the canopy on hillslopes. We investigated soil properties around trees to clarify the effect of trees on soil hydraulic properties of soil surface layers on a slope. The intact tree and cut tree plots of two coniferous tree species, Cryptomeria japonica and Chamaecyparis obtusa, were considered in the northern part of Kyushu, Japan. The soil properties on the upslope and downslope of individual trees or stumps were compared. The soil near-saturated hydraulic conductivity (kns) on the upslope of individual trees and stumps was higher than that on the downslope for both species. Although the distribution patterns of kns were similar in all plots, the determinant factors of kns seemed to be different. In the Cr. japonica intact tree plot, more litter tended to accumulate on the upslope of individual trees, and it seemed to indirectly enhance kns. However, the results of the cut tree plot suggested that kns was affected by factors other than the litter layer biomass. In the Ch. obtusa intact plot, high water repellency of soil on the downslope of individual trees reduced kns. Organic matter tended to accumulate on the upslope of Ch. obtusa individual stumps and in combination with water repellency appeared to affect kns. Our findings showed that soil hydraulic conductivity was affected by the distance and direction from a tree on a slope and that the effect was maintained for a few years after cutting.