COMPLEMENTARITY OF LIGHT AND WATER-USE IN TROPICAL AGROFORESTS - II -MODELED THEORETICAL TREE PRODUCTION AND POTENTIAL CROP YIELD IN ARID TO HUMID CLIMATES

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, perform ance and sensitivity. For. Ecol. Manage. 102, 275-282] was used to cal culate 50-yr mean potential sorghum grain yields and overstory tree an nual net primary productivities (NPP) in nine climates (with 348-2643 mm rainfall, ranging from Mall to southern Nigeria) with uniform overs tory leaf area indices (LAIs) of zero to 1.5. It was concluded that in regions with less than about 800 mm rainfall, simultaneous agroforest ry 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 s ites and the sensitivity of (C4) crop yield to shading, it may be diff icult to increase total site productivity by growing trees with crops in regions with less than 800 mm rainfall without jeopardising food se curity-unless tree roots tap the water table, trees improve soil ferti lity and/or they produce biomass of high value (fuel, gum, iodder, fru its). (C) 1998 Elsevier Science B.V.