Diversity of vegetation and soil seed bank in a chalk grassland of northwestern France

In a chalk grassland of the Seine valley in northwestern France, vegetation and seed bank were compared according to their composition, diversity, and spatial structure through use of a spatial sampling design. The results show (i) that it is possible to establish a successional gradient from short grasslands to early stages of forests with vegetation data; (ii) that there is a weak correspondence between vegetation and seed bank (mean similarity 41%), which was mainly dominated by opportunistic annual or biennial species (Hypericum perforatum, Blackstonia perfoliata); (iii) that there are differences between spatial patterns of vegetation and seed bank. These spatial patterns often exhibit a time lag and represent different levels of heterogeneity. The spatial heterogeneity of the seed bank and its independence from the vegetation structure were interpreted according to the functioning of the two compartments and their type of exchanges (through seed rain and seedling recruitment).