Influence of earthworms and termites on runoff and erosion in a tropical steep slope fallow in Vietnam: A rainfall simulation experiment

Earthworms and termites, as soil engineers, play a major role in the regulation of biogeochemical processes and the provision of ecosystem services. They create biogenic aggregates on the soil surface, e.g., earthworm casts and termite sheetings, which can influence soil erosion and the downward transfer of fertility. We assessed the effect of the micro-relief generated by earthworms and termites on soil hydrodynamic properties, and soil and nutrient losses. Eighteen 1 m × 1 m plots were established for rainfall simulation experiments (2 runs of 40 min rain, intensity 90 mm h −1 ) in a steep slope fallow in Northern Vietnam. The soil surface of the micro-plots differed in the proportions of earthworm casts and termite sheetings. The results confirmed the importance of soil biostructures in the regulation of pedohydrological properties of soils. Although globular water-stable earthworm casts promote water infiltration in soil and decrease soil and nutrient losses, the unstable termite sheetings break-down rapidly and generate structural crusts which foster water runoff and soil detachment. No relation was observed between the abundance or biomass of earthworms or termites and the pedohydrological properties measured during the rainfall simulations. This therefore suggests that soil engineers can have greater impact on ecosystem functioning through their biogenic structures rather than as a result of their own abundance or biomass.