CARBON DYNAMICS IN SLASH-AND-BURN AGRICULTURE AND LAND-USE ALTERNATIVES OF THE HUMID FOREST ZONE IN CAMEROON

One of the environmental consequences of slash-and-burn farming is the loss of forest system carbon which in turn contributes to atmospheric change and impacts upon global climates. International attention has become focused upon the development of alternatives to slash-and-burn agriculture to alleviate poverty, protect biodiversity and reduce clim ate change. Before alternative land use systems can be evaluated in te rms of carbon sequestration, baseline measurements of carbon dynamics resulting from current practices are required. We have characterized t he carbon stocks in six slash-and-burn chronosequences in the humid fo rest zone of Cameroon, Each chronosequence consisted of original fores t, two year-old cropland, a cacao plantation, bush fallow, tree fallow and secondary forest. Four, nine and seventeen years, respectively, h ad passed since the original forest was cleared for the latter three l and uses. At each of 36 site x land use combinations, tree, understore y, litter, root and soil (0-50 cm) carbon were measured in five 100 m( 2) quadrates, The original forest contained 308 t C ha(-1) and lost 22 0 t C ha(-1) upon conversion to agriculture, The most vulnerable carbo n pool was the above ground tree biomass and the most stable was soil organic matter. Carbon reaccumulated in the recovering fallows at a ra te of 9.4 t C ha(-1) yr(-1) (r = 0.83). When these results were extrap olated using a geographic information system, deforestation rates in S outhern Cameroon were estimated to be 1,355 km(-2) yr(-1) between 1973 and 1988 resulting in annual forest system carbon losses of 13.5 mill ion t C. During the course of this study, three alternatives to slash- and-burn were identified: commercial cassava cultivation, improved for est conversion, and stratified agroforestry. These alternative land us es have the potential to reduce C losses over current practices by 10, 55 and 75 t C ha(-1), respectively, and also differ greatly in their potential to alleviate rural poverty, protect biodiversity and deflect additional deforestation. (C) 1997 Elsevier Science B.V.