Interactions between earthworms, litter and trees in an old-growth beech forest

Forty plots were selected in an old-growth beech forest (Biological Reserve of La Tillaie, Fontainebleau State Forest, France), to embrace the whole r ange of site conditions and phases of vegetation dynamics. Soils are sandy, thus the nutrient status of the topsoil is very poor except when trees hav e access to an underlying limestone layer. The study was focused on the rol e of calcium in the sustainability of the beech ecosystem. Calcium is mostl y redistributed through leaf litter accretion and the activity of litter-co nsuming organisms, but other sources are fallen wood and uprooted mounds. I n each of the 40 plots, earthworm species were sampled, and measurements we re taken in order to describe humus profiles, growth of adult trees, litter quantity and quality, and access to lime. Densities of soil-dwelling earth worms, calcium content of beech leaf litter, height of tallest tries and de pth of the limestone layer were correlated, indicating a gradient of soil f ertility which mainly results from long-term interactions between soil orga nisms and trees in varying geological conditions. Possible causal relations hips and implications of calcium turnover for nature conservation were disc ussed in the light of existing knowledge.