Abstract: A numerical model was developed to model the radiation distribution under an individual tree crown with different tree geometric parameters, different geographical locations and different topographical parameterrs and different transmissivity of the tree crown. The model was encoded into C and FORTRAN functions and could be utilized in agroforestry ecosystem modeling. The analysis showed that when the tree crown was more or less a conical shape with fixed tree height and crown radius, an increase in crown volume could even increase the average radiation under the tree.

Key words: Agroforestry ecosystem, Radiation under tree, Numerical models