Apart from the use of the permanent waters of the river channel and floodplain pools for fisheries, the plain itself performs a number of functions which may influence the productivity of the aquatic phase. In its wild state the plain is colonized with grasses, which support populations of game animals including hippopotamus and on some plains the wild population is now maintained in parks or reserves. The dung dropped by such animals remains on the plain as a depository of organic material. In many areas the grasses are burnt off by natural or humanly induced fires toward the end of the dry season. This practice renders the organic components of the dessicated grassland into inorganic ash, thereby probably making it more easily available during the floods and also reducing the de-oxygenation which would result from the immersion of decaying grasses. Grazing is widely practised on the plain and traditional nomadic cycles have grown up around such areas, particularly the Central Delta of the Niger and Sudd of the Nile. The dung of the cattle performs a similar function to that of the game animals. Various forms of agriculture are common but by no means as widespread as they might be due to the difficulties of life in such areas. Only on certain rivers, such as the Ouémé, do stilt villages exist which are adapted to life during the flooded period. Maize, cassava, millet and a variety of vegetables are grown, and in some areas small irrigated agriculture projects have been initiated. Rice is moderately common but harvesting and most of the growth occurs during the high-water phase. Agriculture may affect the ecology of the plain adversely through the use of insecticides and the modification of the flood regime by irrigation schemes. The role of fertilizers remains obscure although these could increase productivity of both dry and wet season phases.
The dry season uses listed by respondants to the CIFA questionnaire are given in Table III.
TABLE III
Dry season uses of floodplains
Floodplain | Rice culture | Agriculture Vegetable gardening | General | Grazing | Game or forestry reserves |
Kafue | x | x (58%) (250 000 head) | x (2%) 93 000 head of Lechwe) | ||
Massili | x | x | |||
Shire | x | x | x (148 000 head) | x | |
Gambia | x (50%) | x | x | x (300 000 head) | |
Central Delta [Niger] | x ( 1%) | x | |||
Okavango | x | x | x | ||
Ouémé | x | x | x | ||
Ogun | x | x | x | ||
Oshun | x | x | |||
Pongolo | x | x | |||
Senegal | x | x | x | x | x |
Yaérés (Logone) | x | x |
( ) approximate percentage of floodplain used for activity