Lichenometry has been applied to blocks, canyon walls and terrace deposits. A growth curve, specific to Corsica, was made based on information obtained from tombstones, old monuments from the Genoese occupation of Corsica and Roman megaliths. This allowed us to create a curve going as far back as 2000 years. The curve is similar to those developed in Mediterranean environments (C! evennes and Eastern Pyrenees), but is very different from those developed in Alpine and Arctic regions.Lichens present on boulders of the bedload allow the time at which the boulders were laid down to be determined. The lichenometric study of the Figarella shows firstly that there is high stream competence. Blocks approximately 100 cm wide are moved during the 5-year flood. Recent important flood events were identified in 1973 and 1869. These correspond well with historical sources. Other older and much more important floods were also identified. This analysis has allowed us to extend the specific streampower curves proposed by Costa (Geol. Soc. Am. Bull. 94 (1983) 986) and Williams (Geogr. Ann. 65A (1983) 227) to blocks of more than 2 m wide.Lichens present on the canyon walls and on terrace sides in the plain allowed the last main incision phase to be dated to the Little Ice Age. Aerial photograph analysis has shown that the present braided system in the lower course of the river is no longer active.

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South-western Mauritania is located in a semi-arid environment exposed to large rainfall variations and affected by a severe drought since the mid-1960s. The studied area includes the right bank of the Senegal River and the southern extension of the Saharan sandy dunes and is based on the analysis of climatic data, field studies, and four aerial surveys realized since 1954.The climatic analysis shows that, after a strong decline of yearly rainfall started in the mid-1960s, a significant increase is observed from the early 1990s. In the meantime, dust storms frequency has dramatically increased while the threshold wind speed declined as a result of vegetation contraction. The comparison of the four mosaics of aerial photos reveals the major impact of both drought and human on recent environment changes with the strong decline of the forest, the reactivation of sandy soils and the apparition of large rice fields.If the increase of active dunes activity is likely to be a consequence of the persisting drought, forest decline is more likely to be attributed to fuel wood collection in a first time, then to the creation of rice fields since the late 1980s. Although the 2003 aerial photos show a timid return of vegetation in very limited and specific areas, field surveys show that wind erosion is still very important and water erosion is developing very rapidly because of the absence of vegetation cover. r

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L'influence des actions anthropiques dans l'évolution historique d'un littoral sableux à forte dérive sédimentaire : la baie de Port-Bouët (Abidjan, Côte d'Ivoire)The influence of anthropic actions in the historical coastal evolution of a sandy coast with high sediment drift: the Bay of Port-Bouet (Abidjan, Ivory Coast