Density-dependence in the establishment of juvenile Allium ursinum individualsin a monodominant stand of conspecific adults

摘要

We studied the establishment of new genets in a wild garlic population (Allium ursinum L) in the herblayer of an oak-hornbeam forest. We tested whether establishment could be successful in relatively smallgaps (25 cm) surrounded by adult individuals. Furthermore, we asked whether more empty space in theneighborhood would increase the success. Newly germinated individuals were selected, and observedthroughout the growth season. The success of establishment was characterized by the biomass of thebulb at the end of the season. The surrounding vegetation cover was recorded in a 25 cm resolution. Wefound that the success of establishment had a peak at intermediate neighborhood density. At higherdensities, a significant, linear decline was found, indicating competition with the neighbors. At lowervalues, this trend did not continue, but a plateau was observed, indicating the effect of inverse density-dependence (an Allee effect). The results suggest that a rather broad radius (>25 cm) should beconsidered when predicting the establishment of new genets in A. ursinum, and beside competition,facilitative interactions should also be taken into consideration. This may explain the tendency of thespecies for maintaining high, often monodominant cover in the herb layer. Due to the observed efficiencyof gap-filling and lateral spreading by sexual reproduction, we predict considerable genetic diversityeven in high-cover A. ursinum patches.