Carbon storage in agroforestry: an estimate for sub-Saharan Africa

Abstract

Massive reforestation has been proposed as one means for stabilizing the concentration of carbon dioxide in the atmosphere, but the proposal seems academic in the face of current rates of deforestation in the tropics and the growing need for additional agricultural land. Agroforestry offers a compromise solution because it increases the storage of carbon on land and, at the same time, may enhance agricultural production rather than compete with it. Although the storage of carbon per unit area is generally less for agroforestry than for forests or tree plantations, the area suitable for agroforestry, worldwide, is large. In this study, we estimated the amount of carbon stored in different agroforestry systems in sub-Saharan Africa and the potential storage possible, region-wide, if agroforestry were to be implemented throughout. The potential distribution of ddferent agroforestry systems was determined from a comparison of current practices of agroforestry with current land use. Land use was determned from a combination of satellite data and ground studies. A total of about 1550 X 106 ha were class~f~ed as su~table for some type of agroforestry. Although certain types of agroforestry accumulate much more carbon than others, practical implementation of agroforestry must consider existing landuse practices. Those types of agroforestry that included fuel~vood production were most consistent with current land use and thus had the greatest potential to accumulate carbon. Tulal potential a.ccumulation of carbon in aboveground woody biomass in agroforestry ecosystems throughout sub-Saharan Afnca was estimated to be 6 , 13, or 23 Pg C, depending on the densily of trees used in the various systems. Including belowground biomass and the potential for soils to accun~ulate carbon under agroforestry raised these estimates to between 8 and 54 Pg C. Accumulation of that much carbon would offset global emissions of carbon from fossil fuels for only 1.7 to 9 yr, but would offset African emissions for 20 to 125 yr The secondary effects of agroforestry in reducing rates of deforestation and, hence, emissions of carbon, may be more important than the primary effect of sequestering carbon.