Three process-based approaches to agroforestry modelling are described. These are (a) coupling a continuous-canopy forest model (Hybrid) and tropical crop model (PARCH); (b) coupling an individual-tree model (MAESTRO) with a crop model (PARCH); and (c) incorporating a combined model of evaporation and radiation interception by neighbouring species (ERIN).The coupled Hybrid/PARCH was parameterised for maize and eucalyptus, and
run in five contrasting weather-types. As expected, shade is the most
important factor limiting yield in wet sites; water in dry sites.
Year-to-year variability in crop yield is increased by light and water
competition. MAESTRO/PARCH was run with similar assumptions, and gave
comparable yield predictions, except at the driest site where it allows
small areas distant from the tree sufficient water to produce a modest
yield. Hybrid/PARCH predicted total crop failure in the same climate.
Yields on drier sites were higher in the shade, but water competition
was severe close to the tree.
ERIN is simpler than the above models, but is unique in including the
transfer of heat and water vapour between the two canopies.
Transpiration from a moist understorey can humidify air in the
overstorey, and reduce its transpiration; whilst a dry understorey will
give off sensible heat, which increases the vapour pressure deficit in
the overstorey and causes its transpiration to increase. Changes in
overstorey transpiration due to fluxes from the understorey may approach
Agroforestry Systems (1995) 30 (1-2) 199-221 [10.1007/BF00708921]