MULTISCALE CHARACTERIZATION OF INLAND VALLEY AGROECOSYSTEMS IN WEST-AFRICA

Inland valleys are the upper reaches of river systems, comprising vall ey bottoms and minor floodplains which may be submerged for part of th e year, their hydromorphic fringes, and contiguous upland slopes and c rests. Valley bottoms and hydromorphic fringes are estimated to occupy between 22-52 million ha of land in West Africa. In spite of their po tential for agricultural use, they are only marginally used and with l imited success. The high physical and biotic complexity and heterogene ity of inland valleys explain why little progress has been made in the systematic characterization of inland valley systems. We propose a mu lti-scale agro-ecological characterization with increasing detail at f our levels: macro level (scales between 1:1,000,000 and 1:5,000,000), reconnaissance level (1:100,000-1:250,000), semi-detailed level (scale s 1:25,000-1:50,000), and detailed level (1:5,000-10,000). Methods of characterization at each of these levels are discussed, and examples o f actual applications are given, as well as the mechanisms applied in desaggregation (scaling down) and aggregation (scaling up) between cha racterization levels. This approach allows (i) a systematic descriptio n of (different) inland valley agro-ecosystems; (ii) identification of constraints to sustainable agricultural use; (iii) targeting and impl ementation of research; and (iv) extrapolation of research results and transfer of newly developed technologies to other areas with similar agro-ecological conditions. Agro-ecological characterization of inland valleys carried out so far, shows that variation in (bio)physical and land use factors is considerable, both between levels and within vall eys. The set of descriptors now developed, allows for extrapolation in particular of the relation between biophysical driving factors and ac tual land use. Besides, it allows the identification of geographic are as where improved management is promising, as well as indications on t he types of improvement required to overcome constraints.