Including competitive asymmetry in measures of local interference in plant populations

Summary. Although considerable evidence xists that plant competition is generally asymmetric or "one-sided", with larger plants having a disproportionate competitive ffect on smaller plants, currently employed measures of local in-terference generally assume that competition is "two-sided". We describe a simple measure of competitive asymmetry in which the effects of neighbors maller than a focal individ-ual are discounted by a constant factor, and include this variable in a composite measure of local interference. In this model competition varies between complete asymmetry (the effects of smaller plants are entirely discounted) and complete symmetry (the competitive ffect of a neighbor is proportional to its size). The proposed method is applied to two natural populations and one experimental monocul-ture. In all cases an asymmetric model provides the bes