EGU2020-664, updated on 19 Jan 2021
EGU General Assembly 2020
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Soil Erosion in Mesic Forests: How do Biological Soil Crusts affect sediment transport and surface runoff?

Corinna Gall1, Martin Nebel2, Dietmar Quandt2, Michael Sauer3, Thomas Scholten1, and Steffen Seitz1
Corinna Gall et al.
  • 1Soil Science and Geomorphology, Department of Geosciences, Eberhard Karls University Tübingen, Rümelinstr. 19-23, 72070 Tübingen, Germany (
  • 2Nees-Institute for Biodiversity of Plants, University Bonn, Meckenheimer Allee 170, 53115 Bonn
  • 3Esslinger Str. 18, 72124 Pliezhausen

Soil erosion under forests occurs if forest layers get disturbed. Disturbances may arise from treefall, forest road works, skid trails or deforestation. In these disturbed areas, both an intact canopy and forest floor cover are missing, so that forest soils lack protection against water erosion. To counteract these negative effects a quick restoration of soil surface covers by vegetation is important. In particular, biological soil crusts (biocrusts) are able to quickly colonize gaps in higher vegetation and they are known to reduce soil erodibility. So far, the focus of biocrust research has been in drylands, whereas biocrusts have proven to be an important factor in mesic environments, especially as a pioneer vegetation in disturbed areas.

In this study, the natural succession of biocrusts in skid trails was observed on four different underlying substrates in a temperate European forest ecosystem (Schönbuch Nature Park in the state of Baden-Württemberg, Germany) and their influence on surface runoff, sediment discharge and nutrient relocation was investigated. Therefore, 144 micro-scale runoff plots (ROPs, 40 x 40 cm) were established with four replicates in the wheel tracks as well as in the center tracks and two replicates on undisturbed forest soil. In order to initiate splash and interrill erosion, four rainfall simulations were carried out from spring to winter with a constant intensity of 45 mm h-1. With the purpose to compare these small-scale erosion rates with a larger scale, additional turbidity sensors were installed in the catchment area. The biocrust succession was determined by regular vegetation surveys with a classification of mainly mosses and liverworts up to the species level. Additionally, DNA samples of the upper soil layer were collected to conduct DNA extractions specify other potential biocrust organisms such as lichens, cyanobacteria, fungi and algae.

First results show that surface runoff and sediment discharge are higher in the wheel track than in the center track and that both parameters are reduced with a higher developmental stage of soil surface cover. The vegetation survey demonstrates a quick development of moss-dominated biocrusts from April to October with up to ten different species in one ROP. Depending on the location of the skid trail, a quick development of the higher vegetation was observed as well. Lab work on nutrient relocation and DNA analysis is still in progress and further results will be presented at the EGU 2020.

How to cite: Gall, C., Nebel, M., Quandt, D., Sauer, M., Scholten, T., and Seitz, S.: Soil Erosion in Mesic Forests: How do Biological Soil Crusts affect sediment transport and surface runoff?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-664,, 2019

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Display material version 1 – uploaded on 04 May 2020
  • CC1: Comment on EGU2020-664, Alessio Cislaghi, 04 May 2020

    Congratulations for your work!
    Field campaign allows us not only to measure something but also to observe a process, in particular in the field of forest-hydrology.
    Just few questions:
    - Rainfall simulation. How did you establish the rate of rainfall for comparing the land-cover? Could the results change forcing different impact velocity of drops from a rainfall simulator?
    - Soil erosion. Could sediment transport be produced also by surface runoff? Which is the dominant process - according to your field experience?

    • AC2: Reply to CC1, Corinna Gall, 05 May 2020

      Thank you for your questions!

      Rainfall simulation:
      To measure the amount and intensity of rainfall as well as drop size distribution and raindrop velocity we used a Thies Laser Precipitation Monitor. Additionally we used small rainfall collectors to measure the spatial rainfall distribution.
      And yes, I think the sediment discharge would change if we have another velocity, but with the data of this study, I cannot say how much. In our runoff plots (40x40cm) we determine both splash erosion and interrill erosion and we cannot distinguish which erosion process is predominant.
      Therefore we plan in a further experiment to only measure splash erosion with splash cups using the same substrates than in the field experiments.

      Soil erosion.
      I think, sediment transport can be produced by surface runoff, but it depends on many factors like texture, aggregate size, aggregate stability, incrustation of soil, soil compaction etc. In our study side I would say the splash erosion plays an important role because we have a high clay content and very compacted soils so that it is important that the soil aggregates are first destroyed by the splash effect of the raindrops and are transported by the surface runoff afterwards.
      In another experiment - which is not part of the abstract I present today - we used the same substrates than in the field for rainfall simulations, but we first sieved the substrate. There I could observe that the mobilization of the soil aggregates by surface runoff was easier than in the field.

  • CC2: Comment on EGU2020-664, Elmar Schmaltz, 05 May 2020

    Thank you for sharing this interesting work!

    How did the underlying substrates of your study sites differ? Did you also take topsoil samples and performed respective analysis in the lab (bulk density, texture, organic matter)?

    • AC1: Reply to CC2, Corinna Gall, 05 May 2020

      Thank you very much for your questions!

      The research area of this study is located in the Schönbuch Nature Park between Tübingen and Stuttgart and there we investigate four skid trails with different underlying substrates. Two of the skid trails belong to the Upper Trias (Stubensandstein, Knollenmergel) and the other two to the Lower Jurassic (Angulatensandstein, Psilonotenton). In the field we determined further characteristis of the different sites like bulk soil density, soil compaction with a penetrometer, slope, water repellency and vegetation cover.

      We also collected topsoil samples for every installed runoff plot (in total 144 ROP`s) and conducted several lab analysis: soil pH, aggregate size, elemental analysis for C, N and S. The texture analysis is not yet performed. We plan to do it with a x-ray particle size analyser in the next two months.