The sensitivity of erosion and erodibility of forest soils to structure and strength

Long- and short-term variation in erosion and erodibility of soils occurs due to changes in the physical properties of soil with time. Any change in erodibility and related soil properties may be dependent on the structural sensitivity of the soil. We exposed three forest soils to four erosion treatments under simulated rain, to test the hypothesis that changes in erodibility are related to structural changes in soil arising from wetting and drying. We measured sediment concentration and soil physical conditions (including soil strength) before and after erosion. Erodibility of soil was estimated with a steady-state erosion model GUEST. For the well-aggregated soil with stable structure, there was little erosion irrespective of the treatments and soil strength changed little after a drying cycle. For the other two soils with less stable structure, variation in erosion agreed reasonably with variation in soil strength. However, erodibility did not vary consistently with strength, in particular, when the soils were rewetted after drying. Our analysis shows that interpretation of temporal variation of erodibility is uncertain, as strength of soil can change due to the development of cohesive bonds between structural units of soil with or without a change in packing density.