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

Abstract

To simulate transmitted radiation in agroforestry systems, radiative transfer models usually require a detailed three-dimensional description of the tree canopy. We propose here a simplification of the description of the three-dimensional structure of wild cherry trees (Prunus avium). The simplified tree description was tested against the detailed one for five-year-old wild cherry. It allowed accurate simulation of transmitted radiation and avoided tedious measurements of tree structure. The simplified description was then applied to older trees. Allometric relationships were used to compute the parameters not available on free-grown trees. The transmitted radiation in an agroforestry system was simulated at four different ages: 5, 10, 15 and 20 years. The trees were planted on a 5 m square grid. Two row orientations, chosen to provide different transmitted radiation patterns, were tested: north/south and north-east/south-west. The simulations showed that the daily mean transmitted radiation was reduced from 92% of incident radiation under five-year-old trees to 37% under 20-year-old trees. The variability of 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.