A comparative approach to examine competitive response of 48 wetland plant species

Competitive ability can be separated into competitive effect (ability to suppress neighbours) and competitive response (ability to tolerate suppressive effect from neighbours), but little is known about the competitive response of plants. A screening trial was conducted in outdoor plant pots where competitive response was measured for 48 wetland species during four months grown with seven established sward species: Acorus calamus, Carer crinita, Eleocharis smallii, Lythrum salicaria, Penthorum sedoides, Scirpus acutus and Typha angustifolia. Competitive response was calculated as 100 (x(1)-x(2))/x(1), where x(1) is the weight of the target plant grown alone and x(2) the weight of the target plant grown in the swards. Despite significant differences in biomass and survivorship of the target plants between the sward species, the correspondence, W, of the rank order of the competitive response of target plants grown in the seven sward species was 0.70 (P < 0.001). The competitive response values were not significantly correlated with independent measures of competitive effect, relative growth rate or functional classification. Published competitive effect values, however, were significantly positively correlated with RGR. The results suggest a different approach towards the study of competitive response, with a conceptual model including three different response types: (1) escape; (2) foraging; and (3) persistence.