Soil-vegetation interaction on slopes with bush encroachment in the central Alps - adapting slope stability measurements to shifting process domains

In the European Alps many high mountain grasslands which were traditionally used for summer pasturing and haying have been abandoned during recent decades. Abandonment of mown or grazed grasslands causes a shift in vegetation composition and thus a change in landscape ecology and geomorphology. Alpine areas are very fragile ecosystems and are highly sensitive to changing environmental conditions, which can affect the geomorphic regime of these high energy environments. The effect of land use intensification on erosion rates is well documented, whereas the effect of land abandonment on erosion rates is still discussed controversially, particularly in relation to its short-term and long-term consequences. Generally, an established perennial vegetation cover improves the mechanical anchoring of the soil and the regulation of the soil water budget, including run-off generation and erosion. However, changing vegetation composition affects many other above- and below-ground properties like root density, diversity and geometry, soil structure, pore volume and acidity. Each combination of these properties can lead to a distinct scenario of dominating surface processes. The study of soil properties along a chronosequence of green alder (alnus viridis) encroachment on the Unteralptal in central Switzerland revealed that shrub encroachment changes soil and vegetation properties towards an increase of resistance to run-off related erosion processes, but a decrease of slope stability against shallow landslides. Copyright (c) 2014 John Wiley & Sons, Ltd.