Seed bank and vegetation composition of forest stands of varying age in central Belgium: consequences for regeneration of ancient forest vegetation

Vegetation composition differs significantly between ancient and recent forest, due to slow colonization capacity of typical forest species and the higher abundance of early successional species in recent forest. However, little is known about differences in persistent seed bank composition between ancient and recent forest and about the interaction between seed bank and vegetation in relation with forest age. We surveyed the seed bank and the understorey vegetation composition in transects from ancient to recent forest. Seed bank and field layer vegetation characteristics and similarity between seed bank and vegetation were analysed in relation to recent forest age and distance to the ancient forest. A total of 39 species and 14,911 seedlings germinated, which corresponds with a seed density of 12,426 seeds/m(2). Total seed density is significantly higher in the youngest recent forest parcel (55 years). Also the seed bank composition in the youngest forest parcel differs significantly from the other parcels. After a longer period of reforestation, the seed bank approaches that of the ancient forest, suggesting seed bank depletion, although the seed bank is permanently replenished to some extent by seed bank forming species from local disturbances. Seed bank composition does not change significantly with distance to the ancient forest. Similarity between seed bank and vegetation composition, no matter the forest age, is very low, but decreases with increasing forest age. The most frequent species in the vegetation are absent in the seed bank and vice versa. The contribution of forest species is high in the vegetation and they almost not occur in the seed bank, while species of forest edges and clearings, and species of disturbed environments are more frequent in the seed bank. The seed bank is mainly composed of early successional species of former forest stages or species which temporary occur in small-scale disturbances. The seed bank may enhance the negative effects of early successional, mainly competitive species to the forest species richness in the recent forest. In this respect, forest management should minimise forest disturbances, to prevent germination of competitive species form buried seeds.