註釋 A generic, process-based model [Mobbs, D.C., Cannell, M.G.R., Grout, N.M.J., Lawson, G.L., Arah, J., Friend, A.D., 1997. Complementarity of light and water use in tropical agroforests: I. Model outline, performance and sensitivity. For. Ecol. Manage. 102, 275-282] was used to calculate 50-yr mean potential sorghum grain yields and overstory tree annual net primary productivities (NPP) in nine climates (with 348-2643 mm rainfall, ranging from Mall to southern Nigeria) with uniform overstory leaf area indices (LAIs) of zero to 1.5. It was concluded that in regions with less than about 800 mm rainfall, simultaneous agroforestry may enable more light and water resources (current rainfall) to be 'captured' than sole cropping, giving complementarity of resource use. However, owing to the low water use efficiency of (C3) trees at dry sites and the sensitivity of (C4) crop yield to shading, it may be difficult to increase total site productivity by growing trees with crops in regions with less than 800 mm rainfall without jeopardising food security-unless tree roots tap the water table, trees improve soil fertility and/or they produce biomass of high value (fuel, gum, iodder, fruits). 