The significance of the asymmetric effect of crowding for coexistence in a mixed temperate forest

Abstract. The coexistence of coniferous (mostly Abies homolepis) and broad‐leaved tree species (mostly Fagus crenata) in a mixed temperate old‐growth forest in Japan was simulated by a size‐structure dynamics model incorporating the asymmetrical (one‐sided) effect of shading between these two life‐form guilds. The model assumes that the crowding effect due to one‐sided competition for light on a tree of a given size regulates the rate of size growth and recruitment. The cumulative basal area of trees larger than a given tree in the forest is employed to express the intensity of one‐sided competition on that tree. Cumulative basal areas of both guilds negatively affected the growth rate of any tree. The shading effect by conifers on the growth rate of either guild was stronger than that by broad‐leaved species. Two types of model were tested for recruitment; an additive and a reciprocal model. A reciprocal model, where basal area density of conifers and broad‐leaved species has a negative effect on the recruitment of its own guild but has a positive effect on that of the other guild, fit the observed data better than an additive model where total basal area of the two guilds suppresses recruitment rates. Simulations using these models showed that, within a particular range of the set of recruitment rates, the two guilds could coexist. The tendency for reciprocal replacement, incorporated in the reciprocal model, substantially widened the range of coexistence and shortened the time required for convergence. 1995 IAVS ‐ the International Association of Vegetation Science