A simplified description of the three-dimensional structure of agroforestry trees for use with a radiative transfer model

To simulate transmitted radiation in agroforestry systems, radiative transf er models usually require a detailed three-dimensional description of the t ree canopy. We propose here a simplification of the description of the thre e-dimensional structure of wild cherry trees (Prunus avium). The simplified tree description was tested against the detailed one for five-year-old wil d cherry. It allowed accurate simulation of transmitted radiation and avoid ed tedious measurements of tree structure. The simplified description was t hen applied to older trees. Allometric relationships were used to compute t he parameters not available on free-grown trees. The transmitted radiation in an agroforestry system was simulated at four different ages: 5, 10, 15 a nd 20 years. The trees were planted on a 5 m square grid. Two row orientati ons, chosen to provide different transmitted radiation patterns, were teste d: north/south and north-east/south-west. The simulations showed that the d aily mean transmitted radiation was reduced from 92% of incident radiation under five-year-old trees to 37% under 20-year-old trees. The variability o f transmitted radiation increased with tree growth. The row orientation had only small effects on the shaded area at the beginning and end of the day when solar elevation was low.