Frank Graf

Does mycorrhizal inoculation improve plant survival, aggregate stability, and fine root development on a coarse-grained soil in an alpine eco-engineering field experiment?

Steep vegetation-free talus slopes in high mountain environments are prone to superficial slope failures and surface erosion. Eco-engineering measures can reduce slope instabilities and thus contribute to risk mitigation. In a field experiment, we established mycorrhizal and nonmycorrhizal research plots and determined their biophysical contribution to small-scale soil fixation. Mycorrhizal inoculation impact on plant survival, aggregate stability, and fine root development was analyzed. Here we present plant survival (ntotalu2009=u20091248) and soil core (ntotalu2009=u2009108) analyses of three consecutive years in the Swiss Alps. Soil cores were assayed for their aggregate stability coefficient (ASC), root length density (RLD), and mean root diameter (MRD). Inoculation improved plant survival significantly, but it delayed aggregate stabilization relative to the noninoculated site. Higher aggregate stability occurred only after three growing seasons. Then also RLD tended to be higher and MRD increased significantly at the mycorrhizal treated site. There was a positive correlation between RLD, ASC, and roots <0.5u2009mm, which had the strongest impact on soil aggregation. Our results revealed a temporal offset between inoculation effects tested in laboratory and field experiments. Consequently, we recommend to establish an intermediate to long-term field experimental monitoring before transferring laboratory results to the field.

Sclerotinia glacialis sp. nov., from the alpine zone of Switzerland

Sclerotinia glacialis sp. nov. is described from leaf bases of Ranunculus glacialis. The species is compared and contrasted with similar fungi already known from this host genus and other Ranunculaceae. Ecological characters related to the new fungus and its habitat are described.

Effects of Mycorrhizal Fungi on Slope Stabilisation Functions of Plants

Plants essentially contribute to the strength of soil and, in particular, steep slopes susceptible to erosion and shallow landslides. The corresponding functions of vegetation significantly control processes above and below ground such as interception, evapo-transpiration, soil aggregation and root reinforcement. Either way, they are all correlated with plant growth. Consequently, in order to unfold their soil stabilising potential, the plants must grow and sustainably survive. However, what sounds so obvious is anything but given under the often hostile conditions dominating on bare and steep slopes. This is exactly the point where mycorrhizal fungi come into play, known to improve the plants’ ability to overcome periods governed by strongly (growth) limiting factors. Within this scope, numerous investigations have been conducted in order to understand and quantify mycorrhizal effects on different plant and soil functions related to eco-engineering and, particularly, to soil and slope stability. Results on plant growth and survival as well as on soil aggregation and slope stabilisation are presented and discussed from a mycorrhizal perspective.

Shallow Landslides: Retrospective Analysis of the Protective Effects of Forest and Conclusions for Prediction

Landslides repeatedly cause damage in steep terrain and, therefore, the prediction of landslide susceptibility is important. In this context, comprehensive inventories with detailed information on shallow rainfall triggered landslides have been established in Switzerland. The present database includes information on more than 600 individual landslides. The data illustrate that slope inclination belongs to the most decisive parameters. Landslides occurred on slopes with inclinations from 20° to 50° with a majority on slopes of 35°–40°. The angles of internal friction of the landslide soil mostly range between 31° and 35°. Vegetation effects, particularly the existence of forest, are important reasons that slopes with inclinations of more than 35° were stable before the respective hazard events. This is supported by the fact that, in the majority of the event-inventories, landslide density is lower in forested areas than on open land. However, not only the presence of forest has an effect on slope stability but also its condition. Additionally, terrain morphology near the landslide seems to be relevant. A filtering procedure based on (i) soil mechanics and slope inclination, (ii) forest structure and (iii) terrain morphology explained more than 95% of 218 landslides in forested terrain. Additional case studies confirmed that forest structural characteristics do have an important influence on root reinforcement and shallow landslide susceptibility. For example a gap length of >20 m seems to be a critical threshold for landslide triggering. The study confirms that forest structure has—together with geomorphological and hydrological conditions—an important influence on shallow landslide susceptibility.