Competition depends more on the functional structure of plant community than on standing biomass

Hypothesising that competition is a major ecological factor that filters plants on the basis of traits, we tested whether competition intensity and importance were better explained by the functional structure of communities than by standing biomass. We re-analysed data of three experiments in which one to four species of phytometers have been transplanted with or without vegetation in communities displaying a range of standing biomass. Changes in performance of phytometers among communities were used to assess competition intensity and importance. The functional structure of each community was characterized by the mean and functional divergence of plant height, a trait significantly related to resource depletion by competition. Relationships between competition components and standing biomass or functional structure of communities were calculated for each experiment. Competition importance was explained more significantly by the mean of plant height than by the standing biomass of communities. When the range of functional diversity was large enough, the importance of competition was high in communities with low functional diversity because of similarity in functioning among highly competitive plants, and low in more diverse communities. Competition intensity generally showed lower or no relationship with standing biomass or functional structure of communities. These results confirm the dependence of competition on functional structure of communities.