| Abstrakt: |
Soil pipes or large horizontal macropores are hillslope–hydrologic features affecting critical processes such as subsurface drainage, streamflow, erosion, hillslope stability, and discharge response to rain fall and snow melt. However, information on soil pipe formation, morphology, and distribution on forested hillslopes is very limited, impeding the incorporation of these important preferential flow pathways into mechanistic hydrologic models. The objectives of this study were to (i) quantify the spatial distribution and physical characteristics of soil pipes, (ii) investigate soil pipe origin, and (iii) examine the role of fire in pipe formation. We excavated three 6.12‐ by 6.12‐m plots down to a water‐restricting horizon within a 2‐ha portion of a steep forest hillslope in northern Idaho. Excavation followed consecutive timber harvest and prescribed burning operations. Detailed documentation of soil pipe diameter, direction, gradient, and connectivity from these excavated soil profiles were used to derive morphologic attributes and distribution of soil pipes. The majority of soil pipes were attributed to decayed tree roots with a median depth of 0.32 m corresponding to the beginning of the restrictive soil horizon. Median path length for branched and nonbranched soil pipes was 2.21 m and 0.89 m, respectively with a median tortuosity of 1.23. Our findings indicate that soil pipe formation and distribution within this hillslope was influenced by tree root growth, decay, slope gradient, and root limiting soil horizons. Fire and the combustion of roots and tree stumps was the primary mechanism that connected soil pipes to the surface. The large frequency and extent of soil pipes documented in this study suggests that estimations of water transport without consideration for these macropores, while useful, are likely underestimated. |
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