Deer have been regarded as a keystone species that has significant effects, both directly and indirectly, on vegetation, invertebrates, vertebrates and soil. Impacts of increasing deer populations on forest ecosystems have become an issue in many places, such as Europe, North America, New Zealand and Japan. In many Japanese forests, dwarf bamboo is the dominant under-story plant. However, in some forests the biomass of dwarf bamboo has been kept down due to grazing by high population densities of Sika deer. Odaigahara- a flat area at higher altitude within the Nara Prefecture on the Kii Peninsula of the Japanese archipelago- is also known for its high population density of Sika deer, with an estimated population density of 17.5-30.9 individuals /km2. The basin is from 1300 m to 1695 m a.s.l. (above sea level) and covered by forests principally composed of temperate mixed forests of evergreen coniferous and broadleaved deciduous trees. Dwarf bamboo, such as Sasa nipponica and Sasamorpha borealis, has historically been prevalent within Odaigahara. However, there has recently been a large decrease in height and biomass of dwarf bamboo. The development of riparian vegetation plays an important role in the succession of benthic invertebrates in the stream. Current benthic invertebrate assemblages in Odaigahara stream were different from that in old days.