The effects of sika deer
Cervus nippon on the structure and composition of the evergreen broad-leaved forests of the Tsushima Islands, western Japan, were studied in 1997. Four study areas with differing deer densities were established; these were a high-density area (area H) (74.9 deer/km
2), a medium density area (M) (22.8 deer/km
2), a low-density area (L) (3.6 deer/km
2), and an area without deer (N). Ground cover and numbers of plant species and individuals tended to be inversely proportional to deer density, and in particular the number of
Trachelospermum asiaticum became noticeably fewer in areas with higher deer densities. Dominance of
Cinnamomum japonicum and
Neolitsea sericea was highest in area M, while
Arachniodes exilis and
A. sporadosora were found only in area H.
Camellia japonica and
Eurya japonica trees were debarked only in area H. Plant species numbers became fewer in relation to higher deer density. The H' values of areas M and L were higher than those of areas H and N. No close relationships were found between the species composition of the four areas, and Sφrensen's quotient of similarity (QS) of area H differed greatly from those of areas N, L, and M. Changes in plant numbers in relation to deer density were classified into three response types according to the way in which deer density changed, (1) continuous decline, (2) first increase, then decrease, and (3) increase from an intermediate density. The shoots, seedlings, and saplings of
Castanopsis sieboldii, the dominant tree in the canopy, seemed to be vulnerable to deer browsing which may affect forest regeneration.
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