Investigating effects of different vegetation layers on soil erosion with a portable rainfall simulator

Small-scale field rainfall simulators provide scientists with a tool to investigate complex interconnections between landcover and soil erosion experimentally. In particular, specific effects of vegetation such as plant structure or traits on sediment translocation are of key interest in erosion studies. A main feature of portable rainfall simulators is the formation of repeatable precipitation patterns with a kinetic energy corresponding to natural rainfall events at different locations in the field. Despite not measuring the whole process chain of water erosion, they assist to shed light on individual influences on sediment transport with an enhanced number of replications and thus adding to field measurements under natural rainfall.

In this context, the Tübingen Rainfall Simulator (TRS, single-nozzle, <1-2 m²) has been used in the last two decades to investigate the effect of plant diversity, individual plant species as well as fauna on soil erosion in different forest and agricultural ecosystems. Results show among others, that higher forest vegetation does often not show an erosion-reducing effect and the kinetic energy of rainfall in young forest plantations can exceed freefall kinetic energy several fold. Impacts on sediment transport are strongly species-specific and depending on individual plant traits such as plant height, height of the first branch, branch angles or leaf sizes and shapes. Therefore, surface-near soil covering vegetation layers and contained mesofauna play a larger role than expected. Important reducing impacts can be initiated by biological soil crusts as a pioneer stage after vegetation disturbances, which also show severe impacts on water fluxes and infiltration in woodlands. Furthermore, these results from forestry are transferable to crop production and agriculture, where a positive impact of modern organic farming systems with short fallow periods and reduced soil-turning techniques on soil erosion control can be underlined.

In summary, portable simulator systems have proven reliable even under difficult operating conditions and could be successfully used to gather data sets with a high number of data points and to supplement large-scale erosion studies. They therefore help answering fundamental questions on the principal effects of vegetation on sediment translocation. For a better comparability of different studies and to further widen existing data sets, a harmonization of different field measurement approaches would be desirable.