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The development of socio-economic activity over the past ten years in the Mediterranean region has induced severe changes in the main natural forest ecosystems.In the northern Mediterranean, rural depopulation has accelerated since the end of the second World War, particularly since the establishment of Common Market agricultural policies, and led to an under-utilization of species causing a strong biological resurgence of the forest, even at high altitudes. This means that, at the present time, the extension of expansion model coniferous forests is favored by their capacities for spatial, biological and ecological selection. Along with this, the under-utilization of sclerophyllous (resistance model) and deciduous (stabilization model) oak coppices has led to the establishment of new forest structures and architectures which are notably different from the main climatic groups defined up to now by phytosociological and synchronic methods. Two new forms of disturbances have appeared: -increasingly important wild fires have replaced disturbances caused by burn beating and are at the origin of the very strong spatial and temporal heterogeneity of current forest species. -In addition, the geographical continuity of the main groups of same-aged sclerophyllous and deciduous species, due to their non-use over the past ten years, has accelerated a phytosanitary imbalance by an increase in the action of pests.In the southern Mediterranean, particularly in North Africa, demographic pressure and grazing have widely disturbed the main forest ecosystems which show a continual regression of their surface. Many forest tree species with a low spatial and biological selection, such as Mediterranean firs and black pines (Pinus nigra subsp, mauritanica), are threatened with extinction, as are the deciduous oak forests which, considering the climatic stress and edaphic constraints, are permanently in a state of imbalance. Human disturbances induce a complete modification of structures and architectures tending towards the installation of simplified forest models (trees-grasses) where tree regeneration is nearly impossible. The sclerophyllous coppices well-adapted to stress are also threatened by shorter and shorter cutting cycles and by the high usage of tree canopies for grazing. -The forest understory structures have witnessed a decrease in their characteristic sylvatic species and the matorralization of most of the forests can be seen by the replacement of typical forest groups by preforest groups (Tetraclinis forests, Aleppo pine forests). 152-New geopedological constraints linked to the removal of the surface soil layer combined with regular climatic stress (duration of drought periods) strongly decrease the resilience of these ecosystems which are under continual pressure (unbalanced models).-In diverse regions, particulary in semi-arid bioclimates, hyperdegradation affects the shrub cover which disappears for a time in favor of perennial grasses (forest steppization): Andropogon div. sp., Ampelodesmos, Stipa div. sp.In all bio...

After defining the state of knowledge and reviewing national inventories, the author looks at the reasons whieh led him to study Mediterranean and Saharan Africa and to detail their biogeographical significance.For Mediterranean and Saharan Africa, the generic and specific richness, the richness of endemics, and the entire biogeographical range are first analyzed at the family level. In the second part, the various biogeographical elements which play a part in the formation of the floras at the generic and specific levels are defined; several examples are provided respectively for the Mesogean (Mediterranean, Saharo-Arabian and Irano-Turanian) and tropical elements, A third part is devoted to endemism: first generic and specific endemism, then the biogeographical significance of the endemic taxa. It appears that the flora of Mediterranean Africa is about three times richer than that of Saharan Africa and that endemism there is two times greater. Whereas the flora of Mediterranean Africa is for the most part made up of Mediterranean taxa, in Saharan Africa there is a nearly equal distribution of Mediterranean, Saharo-Arabian, and tropical elements. These characteristics are related to the hostile ecological conditions which govern the Saliara now, but also reflect the climatic disturbances which took place during the Pleistocene. A special chapter is devoted to a discussion of the historical interpretation of the flora of Mediterranean and Saharan Africa, taking into account the new data provided by paleoclimatology and paleobotany. It is concluded that the Mediterranean flora is relati\'ely old and goes back at least as far as tlie middle Miocene, whereas the present Saharan flora is a reflection of intense chmatic changes which have severely affected this region since the Pliocene. In each of these cases emphasis has been placed on the role elements of African origin played in the de\'elopment of the present flora.

V]~Gi~TATION DES HAUTES MONTAGNESDE LA GRACE MI~RIDIONALE par P. QUEZEL (avec IO photos, 2 fig. et 5 cartes) Si la flore des hautes montagnes de la Grhce continentale est actuellement bien connue, bien peu de travaux ont dtd consacrds .... rode de leur v4g4tation. En effet, la richesse et la varidtd de la nore des montagnes des Balkans et du proche Orient ont attir4, depuis le ddbut du dix-neuvihme sihcle, l'attention de nombreux botanistes systdmaticiens. Citons en particulier les noms et les travaux de SIBTHORP et SMITH, BOISSIER, HELDREICH, ORPI-IANIDIS, HALACSY, FORMANECK, et plus prhs de nous MAIRE et PETIMENGIN, K. H. RECHINGER, MARKGRAF, REOEL et RIKLI. Au contraire, Au-dessus de ces altitudes et mSme c~ et 1~ dans les zones oCa la for~t a disparu, d~s r6oo m, apparaissent les pelouses culminales. Le Kyllini (Ziria) (Carte No. 3), situ6 au SW de Xylocastron, en bordure du golfe de Corinthe, est beaucoup plus massif et s'dtend en demi-cercle sur une vingtaine de kilom~tres en largeur; il culmine ~ 2325 m. La for~t ne d6passe gu6re ici 16oo met, comme sur le Tayg~te, est constitu4e soit par Abies cephalonica soit par Pinus nigra ssp. pallasiana. Le Parnasse (Carte No. 4) constitue une chMne de 25 km de long environ, constitude par un plateau dolomitique sur lequel se dressent divers sommets qui sont, du Nord au Sud: le G6rontovrakhos, le Kotrona et le Liakoura; tous trois ddpassent 24oo m YIAUTES MONTAGNES DE GRI~CE MI~RID1ONALE 293 Carte 2 \" \~--__LJ