Can traits predict the competitive response of herbaceous Mediterranean species?

This study tested whether (i) functional traits, measured on individually grown plants, can be used to predict species response to competition; (ii) species competitive response depends on the standing biomass of neighbouring vegetation. Nine herbaceous Mediterranean species (targets) were grown as isolated plants or in mixture with one of three grasses (neighbours) differing in RGR, in pots during 4 months. Ten traits of targets, related to plant size, resource acquisition and conservation ability, and the above-ground biomass of neighbours were measured. Species with large basal area when individually grown were least suppressed by competition. No relationship was found between species competitive response and other traits measured on plants grown in isolation, including height and RGR. This result suggests that plant basal area could be used to predict the competitive ability of species in herbaceous communities. The competitive response of targets varied with the standing biomass of neighbours: it decreased with increasing neighbour biomass for low-productive mixtures, then reached a minimal value as neighbour biomass became larger, whatever the identity of neighbours. The implications of this relationship are discussed.