The use of Beer's law to describe the radiation regime in plant canopies is valid for a sufficiently large volume filled densely with phytoelements. This set a limit to the scale at which models, based on Beer's law, can account for structural features of vegetation canopies and provide an adequate prediction of the radiation regime. The aim of our paper is to analyze radiation interaction in vegetation canopies and consequent photosynthetic rates at a scale at which Beer's law loses its validity. We use fractals to simulate the structure of vegetation canopies at this scale. It is shown that both the radiation regime and the photosynthesis depend on the fractal dimension of the plant stand. The development of radiative transfer models in fractal-like media as well as measurements and modeling of fractal characteristics of trees and tree communities are essential for better understanding and scaling of radiative transfer and photosynthetic processes from an individual leaf to the canopy. ¿ 1998 American Geophysical Union