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Title: ニホンジカが多雪地域の樹木個体群の更新過程・種多様性に及ぼす影響
Other Titles: The effects of deer browsing on forest regeneration processes and diversity of tree communities in a mountainous region with heavy snowfall of Central Japan
Authors: 阪口, 翔太  kyouindb  KAKEN_id  orcid (unconfirmed)
藤木, 大介  KAKEN_name
井上, みずき  KAKEN_name
山崎, 理正  kyouindb  KAKEN_id  orcid (unconfirmed)
福島, 慶太郎  KAKEN_name
高柳, 敦  KAKEN_name
Author's alias: SAKAGUCHI, Shota
FUJIKI, Daisuke
INOUE, Mizuki
YAMASAKI, Michimasa
Keywords: 防鹿柵
Deer fence
Life-history trait
Mixed conifer-broadleaf forest
Old-growth forest
Species preference
Issue Date: 28-Sep-2012
Publisher: 京都大学フィールド科学教育研究センター森林生物圏部門
Journal title: 森林研究
Volume: 78
Start page: 57
End page: 69
Abstract: ニホンジカ (シカ)の過採食圧下にある日本海側針広混交林において, 防鹿柵内外での樹木個体群構造の5年間の変化を調査した. 調査地では地形に対応して樹木群集の組成が変化するため, 尾根地形に発達するアシウスギ変群集と谷地形に成立するサワグルミ群集で調査を実施した. 地上高130cm以上の個体の直径階分布は, アシウスギとブナにおいて柵内外ともに負の指数分布型を示し, 調査期間を通じて大きな変化はなかった. それに対し, 低木層 (50-130cm)では, 両方の群集において柵外で構成種数が減少した. この結果は, 低木層に分布する高木性種の稚樹や低木性種が, シカの影響によって消失していることを示唆している. シカの採食が今後も継続した場合, アシウスギ変群集では, 不嗜好性種であるアシウスギが単優占する種多様性の低い林分へと移行すると考えられる. 一方で谷地形上のサワグルミ群集では, オオバアサガラやテツカエデといった不嗜好性種から成る疎林へ移行する可能性がある. 柵外での樹木群集の種多様性を維持するためには, 森林内のシカの生息密度をさらに減少させる努力が必要であると考えられる. また, 柵内は森林下層の稚樹の個体密度と種数が増加したが, 再生してきた群集には撹乱依存的な樹種が多く含まれ, 気候的極相下での群集組成とは異なっていた. シカという撹乱要因に対する樹木群集の回復可能性を評価するためには, 柵内の過渡的な群集がどれほどの時間スケールで極相状態に近づいていくのか, もしくは復帰できないのかを, 長期観測していくことが重要と考えられる.
Population structure of tree and shrub species within cool-temperate forests under high impacts of sika deer, Cervus nippon, was investigated in- and outside a deer exclosure fence over a five year period, Ashiu, Kyoto, Central Japan. The fixed plots were established in the Cryptomeria-dominated stands at ridgetop sites and Pterocarya-dominated stands at streamside sites. Size class distribution of the dominant tree species, Cryptomeria japonica var. radiacans and Fagus crenata, in the upper layer (> 130cm in height) displayed negative exponential class distributions both in the fenced and control plots. On the other hand, in the tree sapling and shrub species layer (50-130cm in height) , it was observed that the number of tree species decreased in the controls, except for the non-preferred species C. japonica var. radicans. The result would be most likely caused by severe deer browsing on tree saplings and shrubs. If deer browsing continues to be a selective force against many preferred species in this area, the ridgetop stands are projected to be mono-dominated by the C. japonica var. radicans. In streamside areas, deer overabundance could lead to the formation of steppe type vegetation consisting of unpalatable ferns and graminoids with scattered non-preferred trees, Pterostyrax hispida and Acer nipponicum. Deer exclosures such as a deer fence is shown to be effective in increasing plant species richness and stem density of tree species in the lower layer. However, the regenerated community within the deer fences differed from climatic climax vegetation of this area by the high abundance of disturbance-dependent species. In order to examine whether climax understory community can fully recover after deer exclusion, it is necessary to continue monitoring the future vegetation changes in the exclosures. Overall, this study shows the paramount importance of controlling the density of deer population in Central Japan to maintain the mixed diverse conifer-broadleaf forest stands that are still characteristic of this area.
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