SIMULATION OF LIGHT-DISTRIBUTION IN DENSE ORCHARD SYSTEMS

A model for the assesment of light transfer through orchard systems is described. Tree shape is approximated as conic, parabolic, cylindrical or as intermediate between a cone and a cylinder. Trees may vary in dimensions. The foliage is assumed to be black and uniformly distributed throughout the crown. Any number of similarly shaped trees can be positioned in any desired arrangement. The model incorporates three dimensions and distinguishes between direct and diffuse components of light. The agreement between calculated and measured interception and distribution of light was generally good for spindle-type apple and pear orchards. Discrepancies may arise from incorrect assumptions concerning tree parameters such as tree size and leaf area. The relative importance of tree density, spacing, and shape is discussed. It was found that multi-row systems, in which two or more rows of trees are separated by alleyways, may have a greater light interception than single rows. However, the model suggested that poorer light distribution is associated with multiple rows, particularly where tree crowns overlap. Under these constraints, the single-row pattern might deserve preference.