Mechanisms by which
invasive species affect native communities have been intensively
studied. Invasive plants may influence other species through
competition, altered ecosystem processes, or other pathways. It has been
suggested that allelochemical interference is the key mechanism
explaining a lower species richness of herbaceous plants below
non-native than native shrubs. We studied plant recruitment from seeds
sown inside and outside patches formed by Sorbaria sorbifolia, a shrub non-native to Finland, and a native shrub Rubus idaeus.
Recruitment of seedlings was lower below non-native than native shrubs,
in contrast to recruitment outside the shrub patches. Biotic filtering
of subdominant plants was a stepwise process affected by the difference
between non-native and native shrubs. Our results suggest that
allelochemicals released by non-native species may be responsible for
this difference. They thus give support to the hypothesis emphasizing
the importance of allelopathy in the invasion of non-native plants. The
slow and stepwise action of biotic filtering cautions against defining
plant community membership merely based on the presence of seedlings.