A General Theory for Species Coexistence in Various Forests : the Diffusion Model for Plant Communities

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I investigated growth dynamics, competition and recruitment processes in the following climax forests : sub-boreal forest on Mt.Taisetsu, Hokkaido (Abies sachalinensis, Picea yezoensis), warm-temperate forest in Miyakejima island, Tokyo (Castanopsis cuspidata), sub-alpine forest on Mt.Kitayatsugatake in Shinshu (Abies veitchii, A.mariesii) ; and in an early-successional Betula ermanii forest in Ashibetsu, Hokkaido. I analyzed the growth data based on the diffusion model (Hara 1984), and found that (i) in the climax forests, both intra-and interspecific competition between canopy trees was much weaker than that between saplings and the mode of competition was usually symmetric ; (ii) sapling recruitment process was determined by the species-specific combination of stand structural attributes such as fallen-log abundance, Sasa density in the forest floor ; (iii) in the early-successional Betula ermanii forest, competition between canopy trees was intense and asymmetric ; (iv) these results obtained in the field were confirmed by the canopy photosynthesis model, i.e.broad-leaved trees tend to show intense and asymmetric competition while coniferous trees weak and symmetric competition ; (v) it was shown by a theoretical model that the effect of disturbances on spatial pattern dynamics of plant communities is larger under symmetric competition than under asymmetric competition ; (vi) it was concluded that growth and spatial pattern dynamics are governed by deterministic factors (competition) in early-successional forests while these are governed by stochastic factors (disturbances) in climax forests.