Carbon dynamics in slash-and-burn agriculture and land use alternatives of the humid forest zone in Cameroon

Abstract

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 climate change. Before alternative land use systems can be evaluated in terms of carbon sequestration, baseline measurements of carbon dynamics resulting from current practices are required. We have characterized the carbon stocks in six slash-and-burn chronosequences in the humid forest zone of Cameroon. Each chronosequence consisted of original forest, two year-old cropland, a cacao plantation, bush fallow, tree fallow and secondary forest. Four, nine and seventeen years, respectively, had passed since the original forest was cleared for the latter three land uses. At each of 36 site × land use combinations, tree, understorey, 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 220 t C ha −1 upon conversion to agriculture. The most vulnerable carbon pool was the above ground tree biomass and the most stable was soil organic matter. Carbon reaccumulated in the recovering fallows at a rate of 9.4 t C ha −1 yr −1 ( r = 0.83). When these results were extrapolated using a geographic information system, deforestation rates in Southern 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 million t C. During the course of this study, three alternatives to slash-and-burn were identified: commercial cassava cultivation, improved forest conversion, and stratified agroforestry. These alternative land uses 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.