Complementarity of light and water use in tropical agroforests II. Modelled theoretical tree production and potential crop yield in arid to humid climates.

摘要

A generic, process-based model described in the previous paper (Mobbs et al. Forest Ecology and Management 102 pp. 259-274) was used to calculate 50-yr mean potential sorghum grain yields and overstorey tree (tropical forests/woodlands) annual net primary productivities (NPP) in nine West African climates (with 348-2643 mm rainfall, ranging from Mali, through Burkina Faso, Ghana to southern Nigeria) with uniform overstorey 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 <800 mm rainfall without jeopardizing food security - unless tree roots tap the watertable, and trees improve soil fertility and/or they produce biomass of high value (fuel, gum, fodder, fruits).