On the Influence of Biological Soil Crusts and Bryophytes on Soil Erosion and the Soil Water Balance in Temperate Forests

Abstract

Soil erosion is a serious threat to the soil because it impairs the provision of important ecosystem services such as filtering water, providing nutrients and habitat for biology activity, storing carbon, and producing biomass. This also plays a crucial role in forest ecosystems where natural and anthropogenic disturbances expose bare soil to erosion. An important countermeasure is the rapid recolonization by vegetation. Especially in arid regions, biological soil crusts (biocrusts) are known to be pioneer colonizers of disturbed soils and to reduce soil erosion. Bryophytes also protect the soil and can have a positive effect on the soil water balance. However, the influence of bryophytes and biocrusts on soil erosion and the soil water balance in temperate forests is largely unexplored. This thesis investigated how biocrusts and bryophytes influence soil erosion and the soil water balance in skid trails of a temperate forest ecosystem in the Schönbuch Nature Park in South Germany. This included in-situ studies of soil erosion in the skid trails during vegetation succession and ex-situ studies of the influence of combinations of soil substrates and moss species (soil-moss combinations) on soil erosion. In addition, the water absorption and evaporation patterns in the soil-moss combinations were examined, also taking into account the structural traits of the moss species. Within this thesis, it was shown that bryophyte-dominated biocrusts significantly affected soil erosion and that bryophytes not only contributed more to erosion reduction than vascular vegetation, but also positively influenced the soil water balance. Surface runoff and soil erosion were decreased with moss covers, while the amount of percolated water was increased; however, these processes were superimposed by desiccation cracks and water repellency. Moss treatments exhibited lower water contents over time compared to bare treatments, highlighting the strong influence of moss covers and desiccation cracks on the soil water balance. Mosses were no barrier for infiltration in case of high precipitation rates and they did not store much of the applied water themselves, but passed it on to the soil. During desiccation, mosses with high leaf area index (LAI) had lower evaporation rates than mosses with low LAI, and they prevented desiccation of the soil substrates, although even dense moss covers did not completely seal the surface.