Les grandes structures de végétation en région méditerranéenne: facteurs déterminants dans leur mise en place post-glaciaire

The present-day large vegetation units, taking into account their historical value, can, at least partly, be compared with those which have taken place since the end of the Wiirm. The present-day pre-steppic forests, pre- forest units and actual forests enable us to understand: the progressive evolution of the woody vegetation, at least up to the Atlantic, according to the global climatic changes; its regressive evolution in connexion with the increasing anthropic pressure during the following periods. This anthropic pressure, nearly stabilised at the end of the last cen- tury, has been getting weaker in most of the north mediterranean countries, inducing a clear biological revival, whe- reas, in the southern ones, man's action goes on intensifying, due to an uncontrolled increase in population. The pro- blem set by the steppes, matorrals and grasslands has also been taken into consideration but historical data are often too fewer to allow an accurate reconstruction. The present-day dynamism of these formations enables us to understand that their spreading has been and nowadays still remains under the direct influence of man's action, particularly by the way of voluntary fires, grazing and land-clearings.