STORMS DRIVE SUCCESSIONAL DYNAMICS IN NATURAL FORESTS - A CASE-STUDY IN FONTAINEBLEAU FOREST (FRANCE)

The biological reserves at Fontainebleau forest are almost unique with in the lowlands of western Europe, having been preserved for at least four centuries. This study, performed by the same team for 30 yr, look s closely at the behaviour of two plots of about 35 ha, largely domina ted by European beech (Fagus sylvatica L.). Since the turn of the cent ury, several fierce storms have followed one another at fairly regular intervals (25 yi). The consequences of the two latter storms (1967 an d 1990), together with the evolution between them, were examined. The immediate consequence was a violent disturbance, eliminating or mutila ting healthy trees as well as senescent ones, and opening gaps of vari able sizes in the canopy. During the quiet period between the two hurr icanes, a healing phase was observed, characterised by the extension o f crowns, the development of shade-repressed saplings and/or a regener ation of seedlings. Considering the former evolution, several indices are commented upon, thus making a reconstitution possible. As a conclu sion, storms play a major role in the cyclic dynamics of unmanaged for ests, taking them away from a steady state they nearly never reach. A 25-yr recurrence period was observed, being short compared with a tree lifetime (200-300 yr). However, at the scale of a plot, even strong s torms were unable to upset the population structure, mostly causing on ly small gaps. in these conditions, spreading out or survival of woody species other than shade-tolerant beech is questionable (a modest pre sence of hornbeam [Carpinus betulus] and holly excepted). One may not reject totally this hypothesis: storms of an outstanding intensity or climate change may affect beech supremacy. Since previous papers on th is subject were published in French only, the authors took the liberty of mentioning by places some results that are not fully original. (C) 1997 Elsevier Science B.V.