A simple formulation of interaction between individuals competing for light in a monospecific stand

1. A new method to evaluate the interaction between individuals competing f or light in a monospecific stand is presented. 2. Light intercepted by a leaf of a target individual is influenced by its own leaves and those of neighbours higher in the canopy. We assume that lig ht intercepted by the leaf is the sum of the light that penetrates the foli age of the target and the foliage of neighbours. We define the degree of th e interaction as the fraction of the intercepted light that penetrated the foliage of neighbours. 3. To determine the degree of interaction, we established experimental stan ds of an annual, Xanthium canadense Mill., and measured tight interception directly with light-sensitive films attached to leaves. We calculated the i nteraction using light absorption of individuals within the stand and of th ose isolated from the stand. Light interception of an individual was influe nced more by its neighbours' leaves than by its own. The degree of interact ion was greater in the stand of higher density. 4. The method presented here may be useful in studying the role of architec tural characteristics in light competition in relation to evolutionarily st able strategies of individuals in monospecific stands.