Article ID: 2119
The recovery of threatened forb species from cumulative deer grazing may require long-term protection using deer exclosures. In this study, we surveyed the species richness and density of threatened forb species within several groups of deer exclosures including three established in 1997 (E1997), four in 2003 (E2003) and three in 2010 (E2010), as well as outside deer exclosures in a beech forest of the Tanzawa Mountains. Sika deer have grazed the understory vegetation intensively at this site since the late 1980s, and have been culled since 2003. In E1997, six threatened forb species were found in the fifth year, and declined thereafter. In E2010, the number of threatened forb species increased following exclosure establishment, reaching a peak after 10 years. The density of threatened forb species observed in E1997 decreased except for two species (Maianthemum robustum and Anemonopsis macrophylla), whereas it increased over time in E2010. A comparison of fifth-year data between E1997, E2003, and E2010 showed that the density of both species was higher in E1997. These results suggest that long-term cumulative impacts of deer grazing may impede the recovery of threatened forb species; however, some species may recover after a period of deer exclusion. One species, Spuriopimpinella koreana, emerged continuously for 10 years outside of the exclosures, and four species, including Lilium medeoloides and M. robustum, emerged for the first time in the eighth year. The density of threatened forb species was lower outside than inside the exclosures. Together, our results show that some species emerged over 5 years after exclosure establishment in the Tanzawa Mountains, whereas species recovery outside of the exclosures was restricted. Future studies should compare our data with those for deer exclosures in other regions with and without culling, to determine whether these are regional effects.
