Contenu du sommaire

The river margins of floodplains in the temperate zone are normally forested. The functional relationship between channels and their wooded corridors are particularly important in piedmonts and intra-mountain plains. These forests are characterized by a vegetal mosaic which is extremely diversified, but which equally has a social and economic importance. The riparian forest structures valley landscapes, influences hydraulics, fluvial forms, sediment and organic matter transfers. On the margins of the Ouvèze river, a sixth order tributary of the Rhône river (south section), we demonstrate that after a 1 in 400 year flood, the median sediment size of deposits was ten tintes lower in the forest than in the vineyeard units. Forest corridor filters coarse woody debris. Their mass are quickly reduced from the channel-forest contact to the internal part of the forest. These wooded areas are very young. Although forests began development in the XVIIIe and XIXe centuries on the margins of the intra-mountain rivers, they only colonized piedmont river margins between 1945 and 1970. In the first case, colonization is due to volontary change in management policy. By protecting cultivated floodplains from erosion and major flooding and by afforesting watersheds, Sarde or French state services favored, directly or indirectly, tree growth in the riparian corridors of the Giffre and Ubaye rivers. In the second case, after the end of the Second World War, forest colonization results from the abandon of the riparian corridor by farmers who, became increasingly specialized while cultivating only the best soils. Although these forests are recent, they are in danger. As they become increasingly disconnected or subdivided, these original hydrosystem components may be to a ephemeral stage of evolution at the scale of our century. Similar to other wetlands, floodplain forests must be taken into account by managers. In some cases, conservation measures are necessary. In other cases, restoration or at least rehabilitation must be favored on very damaged reaches. Moreover, maintenance policies must be encouraged, organized and sectorized : interventions must be made gradually and weighted in light of responses and upstream - downstream variations of margin vulnerability and ecological quality of wooded corridors.

The Sfax agglomeration (Tunisia) which covers 15,200 hectares within the municipal framework, has about 396,000 inhabitants 58.4 % of whom reside in the central municipality. The mean density does not exceed 26 inhabitants per hectare in the whole agglomeration. It rises up to 41.3 inhabitants/hectare in the peripheral municipalities. The weak density rates are accounted for by the immoderate extent of the Greater Sfax, due to specific mecanisms of the Sfax land ownership market, to the specific strategies of public and private operators, and to the characteristics of the topography. The present paper is a review of the main macromorphological and space-functionnal components of the Sfax agglomeration located in a plain site. It underlines the evolution processes at work and the planning arrangements they have undergone or which be implemented. The lack of transversal road-network, the significance of self-financed an self-initiated building in the garden area (« J'nen ») and the excessive stretch of the Sfax agglomeration in relation to its demographic weight do not favour any command on the urban space open to land speculation and informed by the strategies of individual, private profit. The success of the new long range development scheme will depend on the land ownership choices and on the solutions adopted by the long range transport scheme.

In the context of Southeast Asia, a region of the world where agricultural expansion is particularly dynamic, Vietnam stands out almost as a model. Strongly linked to the country's history, the nearly permanent advance of the agricultural frontier has even been accelerated after the 1975 reunification. Since then, land pioneering has been concentrated in the Central Highlands provinces, among which Lam Dong. In this region, until recently still predominantly inhabited by representatives of ethnic minorities, the rapid penetration of Viet people is having a major impact on land use and on demographic structure. While it remains difficult to obtain clear and reliable data on the nature of the frontier, toponymy does illustrate its magnitude as well as reveals the origin of the new settlers.