Relationship Between Dwarf-bamboo Growth and Small Rodents on Mt. Ohdaigahara, Central Japan, With Special Reference to Construction of Deer-proof Fences

27 Mar Relationship Between Dwarf-bamboo Growth and Small Rodents on Mt. Ohdaigahara, Central Japan, With Special Reference to Construction of Deer-proof Fences

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Abstract

植生がニホンジカの採食下にある大台ヶ原では, その採食から樹木を保護するために防鹿柵が設置されている。この点に着目し, ササの形態特性とネズミ類の生息状況との関係を明らかにすることを本研究の目的とした。ササの繁殖状態の相違に基づき6プロットを設定し, 各プロットでミヤコザサの形態特性などを調べた。同時にネズミ類の捕獲調査を行い, 100トラップ・ナイト当たりのネズミ類各種の捕獲個体数を算出した。捕獲されたネズミ類は, アカネズミ, ヒメネズミ, およびスミスネズミであった。ニホンジカ個体群密度のより高い地域では, 防鹿柵内外でアカネズミおよびヒメネズミの捕獲個体数が異なり, 柵内で多く捕獲された。一方, スミスネズミは柵内でのみ捕獲された。防鹿柵内のミヤコザサは柵外よりも稈高が高く, 稈密度が低く, 乾燥重量が大きかったことから, これらがカバー (避難所) として作用し, ネズミ類の活動に有利に働いていると推察された。

English Abstract

We examined the relationship between dwarf-bamboo growth and small rodents on Mt. Ohdaigahara where the population density of sika deer (Cervus nippon) has been increasing and trunk debarking by the deer has become a serious problem, causing dieback of barked trees. As a result, deer-proof fences have been erected to protect the vegetation on Mt. Ohdaigahara from further damage. We established six plots with different types of dwarf-bamboo growth. Three rodent species were caught in Sherman traps: Apodemus speciosus, A. argenteus, and Eothenomys smithii. A significant negative correlation was found between the number of captured Apodemus argenteus per 100 trap-nights and dwarf-bamboo density. In areas where the deer population density has been high, the densities of Apodemus speciosus and A. argenteus inside the fence tended to be higher than those outside the fence. Eothenomys smithii was trapped inside the fence. The dwarf-bamboo (Sasa nipponica), which is the main forage of sika deer, inside the fence was higher in culm height, lower in density, and heavier in biomass than that outside the fence. The results suggest that thick dwarf-bamboo inside the fence acted as cover for rodents.