Effects of Sika Deer on the Retrogressive Succession of the Vegetation on Kinkazan Island

Research Project

Project/Area Number	01540539
Research Category	Grant-in-Aid for General Scientific Research (C)
Allocation Type	Single-year Grants
Research Field	生態学
Research Institution	Tohoku University
Principal Investigator	TAKATSUKI Seiki Tohoku University, Biol. Inst., Assistant, 理学部, 助手 (00124595)
Project Period (FY)	1989 – 1990
Project Status	Completed (Fiscal Year 1990)
Budget Amount *help	¥1,200,000 (Direct Cost: ¥1,200,000) Fiscal Year 1990: ¥400,000 (Direct Cost: ¥400,000) Fiscal Year 1989: ¥800,000 (Direct Cost: ¥800,000)
Keywords	Island Ecosystem / Sika deer / Grazing / Browsing / Herbivory / Zoysia japonica / Gap Formation / Retrogressive succession / ギャップ / 更新
Research Abstract	Effects of Sika deer grazing and browsing upon the retrogressive succession of the vegetation on Kinkanzan Island, northern Japan were studied. 1. Regeneration of a Fagus crenata forest was studied comparing inside and outside a 15 yr old deer proof fence. Densities of Fagus seedlings and saplings were 0.1/m^2 and 1.1-1.2/m^2 inside and outside, respectively. Distribution of diameter at breast height (DBH) of the island forest was unique in that the density of small trees (< 20 cm in DBH) was quite low. It was, however, improved by fencing because the forest floor was not covered by dwarf bamboos and therefore brighter than usual Japanese beech forests. 2. Abies firma stands were compared between Kinkazan Island and Oshika Peninsula facing tobether. Forest floor was much poorer on the island. The Abies stands of the peninsula included different successional stages while those on the island were in the late climax stage. The latter were composed of big trees (> 20 cm in DBH). The annual rings of Abies trees of the critical size (20 cm DBH) were counted as 64 at 30 cm high, which suggests that the deer effects became intensive 80-100 yr ago. 3. A Pleioblastus chino grassland was replaced by a Zoysia japonicagrassland through the last 20 years under the deer density at 100 deer/km^2. 4. Productive characteristics of Zoysia japonica was studied. A clipping experiment showed that the annual yield was not different between the clippings of 10, 20 and 30 day intervals. Grazing intensity of Sika deer on Kinkazan Island was heavier than 10 day interval clipping. If fenced, Zoysia grew more erect, leaves became longer, and stem density decreased. One year after fencing, Zoysia decreased by shading of other taller plants though the total biomass increased. It was considered that Zoysia was dependent to grazing rather than tolerant to grazing becarse it is benefited by grazing in that other plants were removed by grazing.