Mycorrhizal fungi are essential partners of nearly all plants used in soil bioengineering. After severe soil degradation due to erosion and sliding processes, the natural mycorrhizal infection potential is drastically reduced and the rate of regeneration often extremely low. Concomitant application of plants and their relevant symbiotic fungal partners considerably rises the success of soil bioengineering measures. The fungi increase the root growth of their hosts up to several times and are essential for their nutrition as well as
plant successional processes. Furthermore, the vast mycelia form soil micro- and macro-aggregates that finally contribute to a stable soil matrix and pore structure and, therefore, to a sufficient retention capacity of water and nutrients. Laboratory experiments with moraine soil of an area with frequent erosion and shallow landslides confirmed the increase in soil stability due to mycorrhizal fungi and better rooting; in terms of the angle of internal friction (φ') an increase of up to 5° was found compared to untreated soil.