Deer populations have caused serious degradation of biodiversity though overgrazing in some regions in Japan. Deer impacts brought some variety of plant responses even under the same density. These differences might be caused by different intensity of deer herbivory, and the relationship between intensity of herbivory (habitat use intensity ; HUI) and vegetation diversity is not clear. This study aims to know effects of different HUI on herbaceous communities.

The study site was marshy ground and was fully covered by Unpalatable species, Juncus effusesin 2007. Deer habitat use has been controlled by 10 small fences, 6m by 6m, from 2007 to 2011. Fences were open periodically every month with different open days, 0, 2, 4, 8, 16 days in each month from May to November and fully open plot (control). HUI was estimated by number of pellet groups added to the plots.

In the less opened plot, J. effuses became more decreasing and palatable species such as Microstegium vimineumbecame dominating. Polygonum nipponensewas most dominated in 2 days open plot. This result showed some species can dominate under moderate deer herbivory. As Deer HUI go down, then biodiversity goes up. But some species will decrease according to HUI declining, even though they are palatable. To conserve plant community with higher biodiversity, it is better that various HUI sites exist in a mosaic.