Effects of competitive exclusion by the dominant Sasa tsuboiana on associate species

Abstract

To detect changes in the competitive exclusion ability of Sasa tsuboiana, a dwarf bamboo, I compared the number and total cover of associate species among habitats that had various heights and cover of S. tsuboiana on Mt. Horai (1174 m a.s.l.), 24 km northeast of Kyoto, Japan. S. tsuboiana was tall and dense on the lower slope, but decreased in height towards the upper slope. It grew short and sparse in a few places on the ridge and in the habitats disturbed through gnawing by hares and mowing by humans. The number of species per unit area was small and no herbaceous plant covered more than 1% in the tall and dense S. tsuboiana community on the lower slope. However, once S. tsuboiana decreased in abundance, more herbaceous species appeared with larger covers in comparison with the tall and dense S. tsuboiana community. These results clearly show that the competitive exclusion ability of S. tsuboiana is large in undisturbed suitable habitats, and the ability decreases when S. tsuboiana abundance decreases. In contrast with herbaceous species, woody ones did not always increase in number and total cover with a decrease in S. tsuboiana abundance. Large susceptibility of woody species to winter wind and disturbance was assumed to prevent the increases of the woody species despite decreases in S. tsuboiana abundance.