An agroecosystem is in essence an ecosystem designed to capture the energy in sunlight and use it to x atmospheric carbon for the production of edible biomass. An important aspect of agroecosystem function, therefore, is the efciency with which the capture of light energy takes place. How much of the solar energy reaching the system strikes leaf surfaces? How much of this energy is absorbed and how much is transmitted and reŽected? The efciency of light capture, in turn, is in large part a function of the structure of the vegetative canopy. Does the canopy allow a signicant portion of the incident light to reach the ground, where it can only promote the growth of weeds? Does an upper layer of foliage from one species receive more light than it can capture, reducing the amount of light received by the foliage of other crop species given in the following?