We studied the floristic composition and environmental factors of the beech forests in the Kyusyu District to clarify details of their compositional differentiation, compared with that of adjacent communities such as fir forests, hemlock forests, oak forests, elm forests, wingnut forests, ash forests, pine forests, and shrub communities. Phytosociological classification using the Braun-Blanquet method indicated that the beech forests had a relationship with the adjacent communities in terms of floristic composition ; in particular the closest relationship was with the ravine forests. Using the DCA ordination technique, the score of AXIS 1 correlated most closely with temperature and altitude, while the score of AXIS 2 correlated most closely with topographical gradient which determined the soil water condition. The pattern of coordinate distribution of sample stands on AXIS 1 and AXIS 2 varied in relation to geology of mountains (Paleozoic system, Tertiary system, and Quaternary system). Generally speaking, in the Quaternary system there was the least community differentiation, while in the Paleozoic system there was the greatest community differentiation. In the Tertiary system the community differentiation was intermediate between that of the Quaternary and that of the Paleozoic. Our study also showed that changes in compositional differentiation corresponded to the variation in site conditions. In the Paleozoic system, which is geologically the oldest system, the compositional differentiation along topographical gradient was most remarkable. This was mainly due to the presence of the "Sohayaki" element plants in the ravine forests.
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