Clonal Growth in Grassland Perennials: I. Density and Pattern-Dependent Competition Between Plants with Different Growth Forms

Abstract

(1) Bellis perennis and Prunella vulgaris are grassland perennials with contrasting growth forms. Clones of Bellis perennis have tightly aggregated rosettes (phalanx type) and vary little in size. Rosette populations grow logistically, probably regulated by change in birth rate. Branches of Prunella vulgaris are only loosely aggregated within clones (guerrilla type). The frequency distribution of clone sizes in P. vulgaris is hierarchical. Branch populations grow exponentially and exceed the equilibrium density before regulation, through increased death rate, occurs. (2) This pair of species was used to investigate competition between and within clones and between species as functions of growth form, planting pattern, and planting density. (3) No differences in intensity of competition within and between clones were found in either species. (4) Plants of P. vulgaris showed a more fugitive behaviour in mixed than in pure populations. (5) Competition was density-dependent; in mixtures of Bellis perennis and Prunella vulgaris the phalanx species was aggressive at high but suppressed at low densities and the guerrilla species was aggressive at low but suppressed at high densities. This outcome is caused by the differences in growth form of the two species. (6) Different planting patterns had little influence on the competitive relationship of the two species.