Desertification in southern Europe
The threat of desertification appears in southern Europe when periods of prolonged drought are followed by torrential rains falling on steep, unstable terrain. The plant cover of many regions has been degraded since very ancient times. Some are now recovering as a result of emigration and reduce pressure on the land. Tourist and commercial agricultural developments threaten habitat values and water supplies, especially in certain coastal areas. Relatively abundant archeological and literary resources offer excellent opportunities for tracing land use histories and throwing more light on the nature and direction of environmental change. Such longitudinal studies should be integrated with remote sensing and nested sampling on the ground of current landscape conditions and monitoring of current processes.
Diagnosing plant water status as a tool for quantifying water stress on a regional basis in Mediterranean drylands
Cette etude rapporte les mesures de conductance stomatique, de la teneur relative en eau et du potentiel hydrique (Ψ L ) d'arbres a feuilles persistantes (Ceratonia siliqua L., Quercus coccifera L, et Olea oleaster Hoffmgg. et Link) croissant sur 4 sites cotiers de Turquie. En particulier, un site totalement recouvert de vegetation (H) a ete selectionne et compare, pour les parametres ci-dessus, a 3 sites degrades (Dl, D2 et D3) ayant une couverture vegetale de plus en plus faible. A partir de l'integrale de Ψ L pour le cycle diurne, l'impact du stress hydrique de chaque espece (WSIS) a ete calcule. C. siliqua et Q. coccifera montrent des WSIS similaires, augmentant significativement de H a D3. O. oleoaster a ete sensible a la fois a la secheresse estivale et a l'accroissement de la degradation du site. Un changement d'echelle, du niveau de l'espece a celui de la vegetation, a ete realise pour l'impact du stress hydrique (WSIV) par la transformation WSIV = Σ WSISs (1-f s ) ou f s est la frequence relative de l'espece etudiee. WSIV est particulierement sensible a l'appauvrissement de la vegetation et est correle a la densite de la vegetation estimee a la fois par des observations aux champs et par l'indice normalise de differentiation de la vegetation par observation satellitaire.
Bromine Content of Mediterranean Halite
Bromine content of a 15-cm halite core from Deep Sea Drilling Project Leg XIII Hole 134 was analyzed at 1.5-cm intervals. The Br varies from 140 to 254 ppm, and three maxima were found to coincide with three postulated horizons of desiccation. The Br profile confirms the interpretation from sedimentologic evidence that Mediterranean salts were deposited in a desiccating basin.