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...

We report the results of descriptive and functional analyses of a representative forest and watershed in the southwestern Alps, where the Forest Service has attempted reforestation of badlands for erosion control since 1860, relying on the non-native Pinus nigra ssp. nigra (Austrian black pine). One hundred twenty years after the first tree plantings, the plant communities are still early seral assemblages for the most part, with Austrian black pine occurring alone in the canopy. In contrast, most of the marly soils have physically recovered part of their total depth, with layers of fragmented and altered material equal to 50 cm, but their structure and chemical fertility is still poor. Autogenic soil restoration is proceeding however, largely engineered by earthworms (up to 49 individuals and 27 g/m 2 ). Two dominant species are presumed keystone: Lumbricus terrestris and Octolasion cyaneum (Lumbricidae). The reestablishment of indigenous tree species is apparently not inhibited by site fertility or lack of nearby seed pools. We hypothesize that ex-cessive stand density is responsible for the poor regeneration because it discourages the birds and rodents that control seed dissemination. Mortality of pines due to infestation by Viscum album subsp. austriacum (mistletoe) is creating large openings and should be specially managed. One hundred twenty years after the first plantings, the nineteenth-century vision that restoration of badlands was ecologically feasible is validated, as is the strategy to establish pioneer tree species. Here Austrian black pine acts as a nurse stand and enables the return of indigenous broad-leaved trees and a wide array of herbaceous species as well. However, our results clearly indicate that appropriate silvicultural tactics should now consist of tree thinning to promote the true restoration of native biodiversity and ecosystem functions.

Quercus ilex sensu lato plays an important role in Western Mediterranean ecosystems, but is poorly developed in the Eastern Mediterranean where it is often replaced by Quercus calliprinos.The occurrence of Quercus ilex in the different bioclimates and their thermic subdivisions is presented on a small scale. Under certain geographical and ecological conditions, Quercus ilex participates in the organization of vegetation ecosystems from the meso-Mediterranean to the oro-Mediterranean altitudinal zones.Quercus ilex imposes microclimatic constraints on its associated species; it thus organizes an original understory vegetation structure (ethoh)gical groups) which will be defined in this study.One of the reasons for the success of Quercus ilex stems from its remarkable resistance to ecological constraints. A broad synthetic presentation of foliar area index variations in relation to different types of stress serve as a basis for an explanation of the sclerophyllous model in the Mediterranean region.Finally, historical factors are outlined as being critical characteristics in the determination of the present organization and spatial structure of Quercus ilex ecosystems. These considerations will be analyzed from a paleobioclimatical point of view, including data related to human pressure. Distribution and biogeography of sclerophyllous oaks (Fig.

Gli autori studiono la posizione fitosociologica delle foreste della Grecia nella parte centrale e meridionale del Paese. La significazione biogeografica, climatológica delle foreste viene studiata. L'evoluzione dei raggruppamenti dal punto di visto dinamico viene proposta e paragonata con altre formazione forestale del bacino mediterraneo.

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En conformité avec les règles du code de nomenclature phytosociologique, les auteurs valident par la désignation de lectotypes, les unités supérieures et les associations non valablement décrites, qu’ils avaient publiées dans divers travaux relatifs à la végétation de la Méditerranée Orientale. Un certain nombre de modifications mineures sont apportées dans la désignation des syntaxa.

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Classées dans deux sections voisines mais distinctes du sous-genre Sabina (integrae Gaussen sensu), les deux espèces Juniperus thurifera L. et Juniperus excelsa Bieb. présentent un ensemble de caractères morphologiques, biométriques, écologiques et biochimiques les rapprochant bien plus qu’ils ne les opposent. -Le Genévrier thurifère et le Genévrier élevé jouent des rôles homologues dans la constitution du paysage, surtout à l’étage oro-méditerranéen ; la cohabitation avec d’autres Genévriers est fréquente, de même qu’avec le Cèdre au Maghreb (Atlas) et en Turquie (Taurus). -Les galbules – de taille, de forme et de couleur comparables – contiennent en moyenne 4,8 graines (3 origines de Turquie) chez J. excelsa, contre 3,0 en Europe occidentale et 1,3 au Maghreb chez J. thurifera, réalisant ainsi un continuum d’un bout à l’autre de la Méditerranée. Les graines du Genévrier élevé sont toutefois plus légères, non seulement comme unités, mais aussi comme contenu absolu et relatif des galbules. -Du point de vue proanthocyanique, un large polymorphisme de la prodelphinidine est observé chez les deux taxons, entre et à l’intérieur des origines considérées comme populations. Un même modèle chimiogénétique permet de reconnaître 3 phénotypes (conformément à la loi de Hardy-Weinberg), délimités par les valeurs 20 et 30 % de la teneur relative en prodelphinidine ; à cet égard, J. thurifera englobe J. excelsa. Il semble donc légitime : -de transférer de la section IX Sabina (= Chinensioides Gaussen), le taxon J. thurifera dans la section VIII Excelsioides Gaussen, où ses affinités avec J. excelsa seront ainsi mieux reconnues ; -de considérer ces deux espèces affines comme des vicariants écogéographiques et syntaxonomiques méditerranéens respectivement occidental et oriental, dérivant d’une hypothétique souche commune présentant les caractères primitifs suivants : nombre de graines (légères) par galbule élevé (> 5) ; teneur relative en prodelphinidine élevée (> 30 %) ; corrélativement, fréquence allélique élevée du gène «prodelphinidine forte» (> 0,5).