Tolerance to mechanical damage in ten herbaceous grassland plant species

The establishment of plants with high damage tolerance may provide a means for soil protection on sites exposed to strong disturbance. In a pot experiment, we investigated the tolerance to mechanical strain of ten grassland plant species representing three growth form groups (cespitose: Festuca arundinacea, Lolium perenne, Taraxacum officinale; rhizomatous: Achillea millefolium, Elymus repens, Poa pratensis; stoloniferous: Agrostis stolonifera, Festuca rubra rubra, Poa supina, Trifolium repens). We hypothesised that growth form and pre-disturbance biomass allocation to the root serve as predictors of damage tolerance. With a tool imitating the action of cleated football boots or scratching chicken, we applied three standardized levels (moderate, medium, strong) of a torsional force which exceeded the shear strength of the sward and impacted on shoots and roots. Post-treatment shoot biomass in relation to shoot biomass of the non-treated control plants served as a measure of damage tolerance. Species, but not growth form groups, differed significantly in damage tolerance, with F. arundinacea and P. pratensis showing the best performance. Shoot re-growth was strongly correlated with relative post-treatment root biomass across all species and treatment levels (R2 = 0.25, P < 0.001), but not with pre-treatment root biomass. We conclude that root resistance to mechanical damage is the prevalent determinant of tolerance to disturbance.