Are clonal traits and their response to defoliation good predictors of grazing resistance?

Abstract

Grazing resistance in plants, which can be defined as the ability to grow and reproduce under grazed conditions, is either associated to defoliation avoidance or tolerance. Clonal traits are often neglected when studying functional responses to grazing, despite frequent occurrence in grassland vegetation. We investigated whether clonal traits and response to defoliation were associated to increased grazing resistance. First, grazing resistance was estimated for eight clonal species using abundance patterns in a long-term field study. We then analysed its correlation with traits in undisturbed conditions and responses to defoliation in a garden experiment. A few traits were correlated to grazing resistance, though only one was a clonal trait (belowground clonal biomass). Grazing resistance was negatively correlated to shoot height and belowground clonal biomass and positively correlated to inflorescence biomass, suggesting that tall rhizomatous species investing little in sexual reproduction were at a disadvantage under grazed conditions. Both shoot height and belowground clonal biomass were negatively affected by defoliation but their decrease was significantly less for species that expressed the greatest grazing resistance in the field. Our findings show that incorporating clonal traits slightly improved predictions about field grazing resistance in the eight investigated species.