Gj. Lawson et al., THE TREE-CROP INTERFACE - REPRESENTATION BY COUPLING OF FOREST AND CROP PROCESS-MODELS, Agroforestry systems, 30(1-2), 1995, pp. 199-221
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 (M
AESTRO) with a crop model (PARCH); and (c) incorporating a combined mo
del of evaporation and radiation interception by neighbouring species
(ERIN). The coupled Hybrid/PARCH was parameterised for maize and eucal
yptus, and run in five contrasting weather-types, As expected, shade i
s the most important factor limiting yield in wet sites; water in dry
sites. Year-to-year variability in crop yield is increased by light an
d water competition, MAESTRO/PARCH was run with similar assumptions, a
nd gave comparable yield predictions, except at the driest site where
it allows small areas distant from the tree sufficient water to produc
e a modest yield. Hybrid/PARCH predicted total crop failure in the sam
e climate. Yields on drier sites were higher in the shade, but water c
ompetition was severe close to the tree. ERIN is simpler than the abov
e models, but is unique in including the transfer of heat and water va
pour between the two canopies. Transpiration from a moist understorey
can humidify air in the overstorey, and reduce its transpiration; whil
st 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 t
he understorey may approach 15-20%.