DYNAMICS OF BIODIVERSITY IN A CHANGING SPACE - THE CASE OF CHALK GRASSLANDS IN THE LOWER SECTION OF THE SEINE VALLEY

Research has been carried out on the biodiversity of chalk grassland e cosystems in the Seine valley. We have recorded vegetation (plant comm unities, seed bank) and soil characteristics (macrofaunal communities and abiotic conditions) following several sampling procedures balled a n temporal or spatial gradients. The aim is to test two research hypot hesis concerning i) the different rythms of compartimental changes in a dynamic ecosystem, and ii) the spatial dimension of biodiversity. Fo r the taxinomical groups studied, results show significant changes in biodiversity along successional gradients. However, these dynamics do not occur at the same rate, which suggests inertia between ecosystem c omponents and differences in recorded dynamics. We underline that meas ures of biodiversity must take into account this temporal dimension in order to have a predictive value (notion of ecological organization). It is also suggested that the scale at which biodiversity is measured is not necessarily that of the studied ecosystem (notion of functiona l unit of a compartiment). (C) Elsevier, Paris.