Plants as seed traps: inter-specific interference with dispersal

Established plants may disrupt patterns of seed deposition by physically trapping dispersing seed. In this study we quantified seed trapping at very fine spatial scales, by measuring seed fall of two ericaceous dwarf shrub species at a range of distances from allospecific shrubs within a matrix of short grass vegetation. Next to allospecific bushes, seed deposition densities of Calluna vulgaris and Erica cinerea were between 7- and 20-fold higher than those in the short grass. This increase is comparable to deposition densities next to conspecific bushes, caused by local dispersal, which were 19–33-fold greater than the background seed rain. Seed densities decayed rapidly with distance from the allospecific bush, so that in general the bush’s influence on deposition extended <0.1 m. By causing localised, extreme peaks in seed density around established plants, seed trapping could have large effects on the fitness of plants dispersing seed and on the spatial pattern of recruitment across plant communities.