ヒノキ植栽地におけるノウサギによる被害判定と被害量推定

Abstract

奈良市此瀬町のヒノキ新植地においてノウサギによる被害を調べた。植栽後2年での被害は82. 1％にも達した。被害の形状は主軸・側枝の切断と剥皮の複合であったが, 主軸・側枝の切断が52. 8％, 主軸・側枝が切断され, さらに剥皮されたものが12. 2％あった。被害1年後の形状は, 前年度無被害であったものでは樹形の正常なもの83. 1％, 枯死していたものは4. 7％であった。ところが, 主軸・側枝が切断され, さらに剥皮されたものでは, 正常なものはわずか10. 9％であるのに対し, 枯死したものが28. 7％, 著しく樹形の悪いものが35. 6％にも達した。主軸・側枝の切断を受けたものでは正常なもの14. 4％に対し, 枯死していたものは23. 6％, 著しく樹形の悪いもの33. 4％であった。全本数では, 正常なもの36. 0％, 枯死していたもの17. 8％, 著しく樹形の悪いもの23. 1％であった。食害を受けても, ほぼ半分は正常に生育しているといえる。前年度食害を受けたものすべてを「被害」と判定することは問題であるが, ノウサギによっての多くの枯死が発生したことには注目すべきであろう。

Damage to newly planted Japanese cypress (Chamaecyparis obtusa) caused by wild hares was investigated in Nara. Rate of damage at two years after planting was estimated at 82.1%. Damage type could be divided mainly into two types, 1) cutting of stem and branches at the lower part and 2) peeling bark. However, in many cases it was a mixture of them. The percentage of cutting type damage was estimated at 52.8% and that of peeling type damage 12.2%. After one year, effects of damage and process of recovery were checked. Of the non-damaged trees 83.1% had normal growth and 4.7% had withered. However, of the trees with cutting type damage 14.4 had normal growth, 23.6% had withered and 33.4% had extremely abnormal growth. In addition, of the trees with cutting and peeling damage 14.4% had normal growth, 23.6% had withered and 33.4% had extremely abnormal growth. In total, 36.0% of the trees damaged by hares had normal growth, 17.8% had withered and 23.2% had extremely abnormal. About a half of the trees with cutting or peeling damage continued to grow. In conclusion, the rate of withering caused by the hares was extremely high.