Carbon sequestration and water-use by forested areas across the Sudanese gum belt

Drylands cover 47% of the worlds land area and offer considerable potential for carbon (C) sequestration. This potential, however, is largely constrained by water scarcity. Increasing C sequestration can contribute to the mitigation and restoration of degraded drylands through including nutrient and soil water retention, and through promoting infiltration rather than surface runoff generation. In order to assess the value of including tree species in agroforestry systems we have studied C sequestration and water use of forests across the "gum belt" of Sudan. We derived C pools in forest biomass and soil (0-1 m) using aggregated forest inventory data collected by Forest National Corporation of Sudan and soil data from the Harmonized World Soil Database, HWSD (FAO). Average stem volume/ha values, calculated from inventory plots on a 10 x 10 km grid were calculated for 1:250000 Satellite Map Sheet Series of Sudan, were converted to C pools using a wood density value of 0.65 t dm m-3 and a C content value of 50%. Soil C pools were calculated for sandy soils (mainly Arenosols) and clay soils (mainly Vertisols and Regosols) using C %, bulk density and depth values for mapped soil units. Monthly mean water-use (actual evapotranspiration) was estimated using a water balance model, WATBAL, and estimates of moisture contents at field capacity and permanent wilting point using soil texture data (HWSD) and published pedotransfer functions. Necessary climate data (rainfall, temperature and sunshine hours) were derived for each map sheet using the local climate estimator, LocClim (FAO). Once the model has been calibrated, we intend to look at the impacts of a number of climate change scenarios on water use and availability using simulated climate change data. The spatial pattern of current biomass and soil C pools will be evaluated in relation to location and soil type, and the impacts of climate change will be assessed.