Fruit removal, pyrene dispersal, post-dispersal predation and seedling establishment of a bird-dispersed tree

The recruitment of a dioecious bird-dispersed tree, the holly Ilex aquifolium (Aquifoliaceae), was studied considering the stages of fruit removal by birds, seed rain, post-dispersal seed predation, seed germination and seedling survival. The main objective was to test the effect of different microhabitats within a beech forest on recruitment stages. Migrant thrushes were the main dispersers of this tree whose fruit crops were entirely removed during two study years. Seed rain was greatest beneath holly trees regardless of their sex and lowest in the open sites. Post-dispersal seed predation was examined by two experiments and did not differ between microhabitats despite its quantitative importance (about 70%). Seedling emergence, which probably corresponded to seeds from several cohorts, was greater beneath trees than in open sites and the density of second-yr to 5 cm seedlings depended on the presence-absence of ungulate herbivores and litter. While the former had a detrimental effect, the latter had a beneficial effect on seedling abundance. Seedling survival showed no significant variations between microhabitats but depended on seedling density in some microhabitats (holly, beech). Finally, the initial seed arrival seemed to determine microhabitat suitability for holly seedling establishment. However, under heavy browsing the density of seedlings may be strongly reduced leading to microhabitat homogeneity for holly seedling establishment.