THE SIZE AND DIVERSITY OF THE SOIL SEED BANKS AND THE LIGHT REQUIREMENTS OF THE SPECIES IN SUNNY AND SHADY NATURAL COMMUNITIES OF THE BIALOWIEZA PRIMEVAL FOREST

The research was conducted in two natural forest communities: Potentil lo albae-Quercetum ('oak forest') which allows much light to reach the forest floor and Tilio-Carpinetum typicum ('hornbeam forest') which s hades the herb layer heavily. The seed banks were estimated from numbe rs of seedlings emerging from soil samples over one growing season. (1 ) Our results confirm the hypothesis that persistent seed banks are ma inly formed by species with high light requirements. Of the species fo und predominantly in the seed bank and absent from the herb layer or o ccurring there very rarely in both communities 83% of species and 70% of seedlings were strongly light-demanding (Ellenberg's light index 6- 9). However, the results do not support the hypothesis that seed banks in natural deciduous forest communities are small, poor in species an d do not reflect the species composition of herb layer. (2) The seed b anks of both communities were rich in species and relatively large. Sp ecies richness in the oak forest turned out to be higher than in the h ornbeam forest (51 vs 45 species/2.4 m(2)), but size was smaller (2659 vs 5789 seedlings/2.4 m(2)). In the oak forest the most abundant spec :ies in the seed bank was Galium boreale, but it constituted only 19% of the total number of seedlings, whereas in the hornbeam forest the d ominant species, Urtica dioica, constituted 57% of the total. (3) In e ach community the species composition of the seed bank and the herb la yer was very similar (>70%). (4) The seed bank was more diverse in the oak forest than in the hornbeam forest (H' 2.34 vs 1.68). (5) The see d banks of both communities differed in the contribution of species wi th varied light requirements; in the sunny oak forest species with hig h light requirements dominated, whereas in the shady hornbeam forest b oth strongly and moderately light-demanding species had similar contri butions.