Les réserves biologiques de la tillaie et du gros-fouteau en forêt de fontainebleau, écocomplexes climaciques

Abstract

The beech stand of the biological reserves located on the calcareous tablelands of Fontainebleau forest represents an ecocomplex which is rather close to the climacic evolution. Despite a global domination by beech, this complex consists of three floristically different ecosystems. Their distinctive mesological factors are edaphic The global structure is close to a steady state:a moving mosaic of sm ali surfaces, from regeneration in gaps to senescent forest. Hurricanes can cause a loss of biomass compensated by beech only, with the exception of rare openings closed with shade intolerant species. The distribution of stems in diameter classes shows a gap occuring at an age thal differs in Tillaie and in Gros-Fouteau. This is attributed to the recent and non simu˜aneous replacement of oak by beach in the two reserves. To these cyclic or random fluctuations around a mean state, leant changes are superimposed. The anthropogenic oak stand, maintained until the end of Middle-Age, is still represented (mainly in Gros-Foute au and in the most acidic ecosystems) by old declining trees. The he avy shade of beach canopy does not allow a correct growth of oak seedlings. In Gros-Fouteau, holly, of recent appearance, is in expansion and inhibits beech regeneration. The climacic stability of the beech stand ecocomplex is not yet tully reached. © 1990 Taylor and Francis Group, LLC.