Negative effects of shrub, herbaceous and bryophyte cover on the establishment of grassland and forest dominants have been observed (Wardle 1959; Niering & Goodwin 1962; Webb et al. 1972; Pons 1989) and it is widely accepted (Fenner 1992) that many small-seeded herbs, trees and shrubs are incapable of establishment where there is a closed cover of vegetation