Soil erosion negatively affects terrestrial ecosystems since humanity started to cultivate land. Most prominent soil losses appear in agricultural environments. This might be one reason why soil erosion under forest is much less in focus of research. Nevertheless, important soil losses can be observed in forests, if the protecting soil surface cover is disturbed e.g. on skid trails after timber harvesting. Those gaps in higher vegetation layers can be quickly colonized by biological soil crusts (biocrusts); assemblages of cyanobacteria, green algae, bryophytes, fungi or lichens. As such, biocrusts are an integral part of erosion prevention under forest. Nevertheless, their influence on soil erosion in temperate climates and especially in forest environments has been largely disregarded and mechanisms and processes to protect the soil are still not well understood.
In this respect, we will address the influence of biocrusts on soil erosion after vegetation disturbance by skid trails in a temperate European forest ecosystem (Schönbuch Nature Park, Germany). We hypothesize that (H1) biocrust covers are a major factor in mitigating soil and nutrient losses after vegetation disturbances and (H2) they vary in species composition with different underlying substrates and surrounding forest vegetation and thus affect soil erosion processes differently. Furthermore, we hypothesize that (H3) the protecting effect of biocrusts relies not only on their ability to physically protect the soil surface, but also on reduced soil erodibility by altered soil organic matter content and soil aggregation.
To test these hypotheses, we will set up an integrated soil and biocrust diversity study with three experiments. They will comprise measurements with a terrestrial laser scanner and rainfall simulations with micro-scale runoff plots in skid trails (Ex I) to investigate soil and nutrient losses after vegetation disturbances (H1) and the role of species composition and different underlying substrates (H2). An accompanying biodiversity analysis of biocrust communities in the field and by state-of-the-art DNA-barcoding in the laboratory will reveal patterns of biotic soil surface covers. In a second rainfall simulation (Ex II), fast-growing moss species in water suspension will be applied with spraying-up technique on a forest skid trail to test for soil loss from biocrusted soils under controlled conditions (H1 and H2). In a third experiment (Ex III) the effect of biocrusts on soil losses by altering soil physical characteristics such as aggregate stability will be tested (H3). The results of this study will help to attain a better understanding of the role of biocrusts for soil erosion control in temperate European forests including the development and succession of biocrusts after vegetation disturbances. Moreover, they will allow assessing the application of biocrusts (e.g. selected moss species) for soil conservation under forest.