Alpine plant trait combinations shape soil erosion dynamics and patterns

Soil erosion strongly affects high mountain slopes, such as deglaciating moraines and hiking trails. Plants can decrease soil erosion through adapted plant functional traits, such as high leaf densities or dense root systems. However, due to trait trade-offs, a plant species cannot excel in all beneficial traits at once. Thus, to successfully protect and restore eroding mountain slopes, quantification of effects of common alpine trait combinations on soil erosion dynamics and patterns is needed. We used a semi-natural experiment in the Utrecht Botanic Gardens to test how five alpine plant species with contrasting trait combinations affect soil erosion dynamics and patterns over two growing seasons, combining sediment collection with structure-from-motion techniques. Our results show that trait combinations of key architectural, mechanical and life-history traits ranged from fast growth with high flexibility to slow, stiff and dense growth. Based on trait combinations, we identified five soil erosion plant strategies with distinct effects on sediment yields (SYs) and deposition patterns developing over time. Two quickly growing species (“opportunist”, “conqueror”) swiftly reduced SYs in the first year (up to 70%), storing sediment in-plant or a low terrace. Two more slowly growing species with stiff, dense stems (“blocker”, “builder”) significantly decreased SYs (up to 97%) in the second year, building cm-high, up to 40 cm long terraces. A fifth single stem species (“intensifier”) increased SYs by up to 250%. Our plant strategies create a key link between plant functional ecology and soil erosion research to improve nature-based solutions on eroding hillslopes across mountain regions.