Soil-water characteristic curves and related properties of disturbed forest soils

Forest logging activities negatively affect various soil properties. In this study, we focus on the logging effects on soil water retention and associated pore size distribution. We measured the soil-water characteristic curves (SWCCs) on 21 undisturbed samples from three research plots: a reference area, a clear-cut area and a forest track. A total of 12 SWCC points between saturation and wilting point were determined for each sample with a sand box and pressure plate apparatus. The trimodal behaviour is highlighted by the dependence between soil moisture and suction. Therefore, we proposed a revised model by combining two exponential expressions with the van Genuchten model. The exponential terms describe the influence of macro-and-structural porosities, and the latter is used to calculate textural porosity. This new model with eight independent parameters was suitable to fit trimodal SWCCs in all samples. Results revealed that logging had the most destructive effect on large pores, and the soil on the forest track was the most affected. Both soil-air and available water capacity were reduced and the permanent wilting point increased as a result of damage to the soil structure and pore system. Observed increased organic carbon content in compacted soils can be attributed to slowed decomposition due to reduced air capacity and increased waterlogging susceptibility of damaged soils.