Effect of canopy structure on degree of asymmetry of competition in two forest stands in northern Japan

The canopy structure in terms of the vertical distribution of leaf mass and the degree of asymmetry of competition between individual trees was studied in two types of forest stand in Hokkaido, northern Japan: a naturally regenerated stand of Betula spp. and an artificial plantation of Picea abies. The canopy structure in the Betula stand was more hierarchical; larger individuals were nor heavily shaded even in the lowest part of their crowns and smaller individuals were heavily shaded by their larger neighbours. The canopy structure in the Picea stand was less hierarchical; even larger individuals were shaded in the lowest part of their crowns and smaller individuals were not heavily shaded by their neighbours. AI,plication of the general formula of size dependent mean growth rate revealed that competition in the Betula stand was more one-sided than that in the Picea stand. This result was consistent with the trends in the change over time in size equality in both stands. Even if competition is mediated by light, which often makes competition one-sided, the degree of one-sidedness in competition can be variable depending on canopy structure. (C) 1996 Annals of Botany Company.