Changes and disturbances of forest ecosystems caused by human activities in the western part of the mediterranean basin

Autor: Marcel Barbero, Pierre Quézel, Roger Loisel, G. Bonin
Rok vydání: 1990
Předmět:
Zdroj: Vegetatio. 87:151-173
ISSN: 1573-5052
0042-3106
DOI: 10.1007/bf00042952
Popis: 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: 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. In all bioclimatic groups, the increase in grazing pressure throughout the southern Mediterranean ecosystems can even lead to the total disappearance of perennial species from the ecosystem with the exception of the dominant tree. Regardless of the altitude or ecosystem, invasive therophytes are then the only plants to occupy the understory and indicate hyperdegradation (forest therophytization).
Databáze: OpenAIRE
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