Interference in Dune Annuals: Spatial Pattern and Neighbourhood Effects

SUMMARY Interference among four autumn-germinating annuals (Cerastium atrovirens, Mibora minima, Phleum arenarium and Vulpia fasciculata) native to the stabilized dunes near Aberffraw, Anglesey, North Wales, was examined at the individual plant level in monocultures, in all combinations of two species in mixture, and in a mixture of all four species. Frequency histograms of individual plant weights for each species from the four-species mixtures became skewed through time. Species with low competitive ability had a larger proportion of the cohort in the smaller size classes. Density is a crude abstraction of the precise neighbourhood relationship of individuals: up to 69%Y of variance in individual plant weight and fecundity is accounted for by linear regression on a measure of neighbourhood effects that takes into account the weight, distance and angular dispersion of neighbours within 2 cm.