Alpine plant trait combinations shape soil erosion dynamics and patterns

Soil erosion strongly affects high mountain slopes, such as deglaciating moraines, alpine grasslands and hiking trails. Plants can decrease soil erosion through adapted plant functional traits, such as high stem and leaf densities or dense root systems. However, due to trait trade-offs, a plant species cannot excel in all soil erosion reducing traits at once. Thus, to successfully protect and restore eroding mountain slopes, identification of common alpine trait combinations and quantification of their effects on soil erosion is needed. We used a semi-natural experiment in the Utrecht Botanic Gardens to test the effects of five different alpine plant species with contrasting trait combinations on soil erosion patterns and dynamics over two growing seasons. Our results show that trait combinations of relevant architectural, mechanical and life-history traits ranged from fast growth with high flexibility to slow, stiff and dense growth. We identified five different soil erosion plant strategies with contrasting effects developing over time. Two quickly growing species (“opportunist”, “conqueror”) swiftly reduced sediment yields (SYs) in the first year (up to 70%). Two more slowly growing species with stiff, dense stems (“blocker”, “builder”) significantly decreased SYs (up to 97%) in the second year, increased infiltration and built terraces. Adventitious roots and phenotypic plasticity additionally explain high soil stabilization effectiveness. A fifth species (“intensifier”) increased SYs by up to 250%. Using increasingly available trait data, more natural species with similar trait combinations and soil erosion strategies can now be identified. This will improve nature-based solutions on eroding hillslopes across mountain regions.