Spatial distribution of soil water repellency in a Japanese cypress [Chamaecyparis obtusa] plantation and an adjacent deciduous broad-leaved forest
2006
Kobayashi, M.(Forestry and Forest Products Research Inst., Tsukuba, Ibaraki (Japan)) | ; Tsurita, T. | ; Itoh, Y. | ; Kato, M.
Water repellency is recognized as an important soil property that can affect the flow and storage of water in forest soils at the slope scale, since it causes overland flow or preferential infiltration. However, the spatial distribution of water repellency on forested slopes and the factors that control it have not been investigated sufficiently. We examined the spatial pattern of soil water repellency on slopes (180 x 60 m in each area) in a Japanese cypress (Chamaecyparis obtusa) plantation and a nearby deciduous broad-leaved forest. The water drop penetration time (WDPT) and ethanol percentage (EP) were used as indices of repellency. In the cypress plantation, the fresh-soil WDPT (WDPT (f)), which is thought to indicate the actual water repellency, exceeded 600 sec at more than 40% of the sampling points during a dry period in summer, including those points in the middle slope. During a wet period in winter, the WDPT (f) was less than 60 sec at most of the sampling points. The air-dry WDPT (WDPT (d)), which indicates the potential water repellency, exceeded 1 h at more than 80% of the sampling points in the plantation, except on the lower slope near a stream. In contrast, potential water repellency was observed over the entire slope in the deciduous forest, although fewer than 20% of the sampling points had a WDPT (d) exceeding 1 h. Positive correlations between the total carbon content of the sampled soils and the WDPT (d) and EP were observed. Comparing soils with similar carbon contents, the soil of the cypress plantation had a greater potential water repellency than that of the deciduous forest.
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