Les foréts méditerranéennes problemes posés par leur signification historique, écologique et leur conservation
ABSTRACT The mediterranean forest are a naturel milieu, instable and deeply disturbed by man's action. From an historical point of view, their regression can be assessed from the beginning of the Neolithic and especially during the last century. The situation is quite different in the Northern mediterranean countries where, following an intensive land abandonment and in spite of dramatic fires, their surface is generally increasing whereas, in the Southern mediterranean countries, forests are quickly destroyed under combined action of man and cattle. From an ecological point of view, the mediterranean forests constitute very heterogenous units where, according to climatic and edaphic criteris, one can characterize forests, preforests and pre-steppic forests. Their dynamic significance varies essentially according to the types of bioclimate but also according to the species. Their phytosociological significance is nowadays known and a synthesis is attempted. The conservancy of the mediterranean forestsalready presents with serious problems as well for the species, some of them becoming nearly extinct, as for the structures of vegetation. Their protection press the urgency of immediate action. Les forets méditerranéennes représentent un milieu naturel fragile et profondément perturbé par l'action de l'homme. Du point de vue historique, il est utile d'estimer dans la mesure du possible, la regression qu'elles ont subie depuis le début du Néolithique, et tout spécialement au cours du dernier siècle. La situation est totalement différente dans les pays du revers septentrional oil á la suite dune intense déprise rurale et malgré de dramatiques incendies, leur superficie tend globalement á s'accroitre, alors que dans les pays du revers sud, on assiste a une destruction accélérée du capital forestier sous faction conjuguée de l'homme et de ses troupeaux. Du point de vue écologique, les foréts méditerranéennes constituent des ensembles tres hétérogenes, oil, en fonction des criteres climatiques et aussi édaphiques, Ion est amené á distinguer des structures franchement forestieres, des préforéts et des forks pré-steppiques, dont la signification dynamique vane essentiellement suivant les types de bioclimat, mais aussi des essences constitutives. Leur signification phycosociologique est actuellement assez bien connue et un essai de synthese est tente ici. Du point de vue de leur conservation, de dramatiques problémes se posent dés á present aussi bien au niveau des essences, dont certaines se trouvent en situation naturelle proche de l'extinction, que des structures de vegetation. Des solutions d'urgence devront étre trouvées dans les plus brefs délais, pour assurer leur sauvegarde
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- "The Juniperus woodsteppe at 2250 m asl (wood) is an open sclerophyllous forest (Quézel and Barbero, 1990). The area is characterized by steep slopes and shallow soils. "
ABSTRACT: Dryland rangelands are fragile ecosystems which are vulnerable to overgrazing and other forms of unsustainable land use. Their subsequent degradation is a phenomenon which results in a persistent decrease in productivity. To come to a functional understanding of degradation and restoration pathways, interactions between abiotic and biotic processes need to be disentangled. We studied soil and vegetation response to grazing removal along a steep climatic aridity gradient on the southern slopes of the High Atlas Mountains, Morocco. Data were collected on four altitudinal levels (semidesert, sagebrush steppe, woodsteppe and Oromediterranean shrubland), and for three grazing treatments (grazed, 1-year and 7-year exclosures). Grazing removal led to site-specific, functionally different pathways of rangeland recovery. At least at one of the four sites, we found either an accumulation of sand, the Aeolian component, or total nitrogen in the topsoil. Total standing crop, shrub ANPP and shrub performance (ANPPrel, i.e. ANPP indexed on initial biomass) also increased with grazing removal. An increased shrub density led to an increased water storage capacity and/or nutrient content of the soil. However, this improvement in plant resources was not connected to the observed increase in shrub performance. Thus we only found evidence for biotic recovery having a positive feedback on abiotic recovery. We conclude that correlations between biotic and abiotic recovery processes have to be interpreted carefully, as they may not necessarily be functionally connected. Moreover, the performance of perennial plants (ANPPrel) is, if interpreted together with abiotic parameters, a useful indicator for distinguishing functionally different pathways of pasture degradation and restoration in drylands.Catena 04/2013; 103:3-15. DOI:10.1016/j.catena.2012.02.002 · 2.82 Impact Factor
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- "Ecosystem disturbance is associated with vegetation changes, such as floristic variation and vegetation regression (Connell and Slatyer, 1977; Pickett et al., 1987). Nevertheless, it is difficult to describe and analyse the dynamics of vegetation regression because communities often represent an intermediate position between two different stages (Quezel and Barbero, 1990) and the vegetation units are arbitrary products of classification, rather than natural units that are clearly defined in the field (Whittaker, 1956). Such units are merely composed of plant species that coexist at a given point in space and time. "
ABSTRACT: In Mediterranean plant communities, grazing induces severe floristic changes affecting the life histories of grazed and non-grazed species. Alteration of the grazing regimen causes important changes in the structure and dynamics of the plant community and ecosystem stability. To determine the susceptibility of different plant functional types to landscape management, we measured changes in Plant Functional Types (PFTs) in response to grazing by goat and sheep in an inland dwarf-palm matorral and a marine-exposed thorny-shrub matorral in Cabo de Gata Natural Park (SE Spain). We classified the major life forms into PFTs, and identified six PFT shrubs (dwarf-palms, sclerophyllous small trees, xeric thorny-shrubs, spiny legumes, glaucous dwarf-shrubs, and xeric half-shrubs), four PFT forbs (leafy stem herbs, xeric prostrate herbs, rosette herbs, and clonal spiny herbs), and two PFT grasses (steppe and short grasses). Morphological traits measured include sclerophilly, leaf presence, leaf size, shape of leaf margins, hairiness, position of dormant buds (growth form), clonality, plant coverage, canopy structure, phenological deciduousness (drought resistance), and regeneration (reproduction type, pollination type, inflorescence position, and seed size). There was a higher correlation within and between morphological growth forms, leaf and phenological traits, than within regenerative traits (only seed size was correlated with main dispersal type). We analysed the importance of these PFTs at several sites of the two communities, which were subjected to different livestock rates. In inland and marine-exposed communities, the same PFTs decreased in response to medium-high grazing: sclerophyllous small trees (Quercus coccifera, Olea europaea var. sylvestris), glaucous dwarf-shrubs (Phlomis and Cistus spp.) and short grasses (Brachypodium retussum). In both communities, the decrease of these grazing-susceptible PFTs was widely associated with an increase in steppe grasses (Stipa tenacissima, “alfa-grass”) and xeric prostrate herbs (Fagonia cretica, Paronichia sufruticosa), the latter of which is a reliable indicator of degradation in semi-arid systems. Instead, different PFTs behave as either grazing-averse and/or grazing-tolerant in each community: Dwarf-palms (Chamaerops humilis) and xeric thorny shrubs (Periploca laevigata) in the marine-exposed community, and xeric half-shrubs (Thymus hiemalys, Sideritis osteoxylla, Teucrium spp., Artemisia herba-alba) in the inland community. The latter functional group resists disturbances, such as medium-moderate grazing and drought, in semi-arid zones and is an indicator of long-term degradation.Journal of Arid Environments 01/2006; 64(2-64):298-322. DOI:10.1016/j.jaridenv.2005.05.005 · 1.64 Impact Factor
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- "Succession and land abandonment are equally knotted, although successional trajectories differ in disturbance and land abandonment origins. Successional mechanisms have been studied throughout the Mediterranean region ͑Godron et al. 1981; Quezel 1983; Escarre et al. 1983; Barbero et al. 1990; Quezel and Barbero 1990; Tatoni et al. 1994; Tatoni and Roche 1994; Debussche et al. 1996; Ne'eman and Izhaki 1996͒. Among the different types of succession dynamics described by van der Maarel ͑1988͒, secondary succession and regeneration in Mediterranean vegetation have been identified and studied by Tatoni and Roche ͑1994͒. "
ABSTRACT: Plant community dynamics in Mediterranean basin ecosystems are mainly driven by an alternation of episodes of human intervention and land abandonment. As a result, a mosaic of plant communities has evolved following different stages of degradation and regeneration. Some authors has relate secondary succession to abandoned culture lands and regeneration to natural systems with abandonment of livestock or forestry exploitation. In this paper, the dynamics of shrublands in mid-mountain areas in the South of Spain after disturbance and land abandonment has been studied. The plant cover and 13 environmental variables of 137 selected sites on the Grazalema mountains was analysed to determine the vegetation pattern in relation to environmental factors and the succession types, either regenerative or secondary succession. The results show that today the Grazalema mountains have a heterogeneous vegetation pattern. Besides physical factors such as altitude or soil , human disturbance has modulated current vegetation patterns and dynamics. Two main types of vegetation dynamics can be distinguished in the study area. In areas affected by cutting, regeneration results in rich and dense shrub land, with resprouters as dominant species. In areas affected by recurrent wildfires or agriculture, secondary succession became dominant, resulting in less diverse shrubland, due to the dominance of seeders and decrease in resprouter species richness and cover.Plant Ecology 04/2004; 172(1):83-94. DOI:10.1023/B:VEGE.0000026039.00969.7a · 1.46 Impact Factor