Effects of Deer Browsing on Broad-leaved Tree Invasion After Heavy Thinning in Conifer Plantations

27 Mar Effects of Deer Browsing on Broad-leaved Tree Invasion After Heavy Thinning in Conifer Plantations

View Original

Abstract

シカの生息密度が高い地域内で強度間伐 (本数間伐率47.5∼71.2％) を行った針葉樹人工林に獣害防護柵を設置し, 間伐後の広葉樹侵入に及ぼすシカ採食の影響を調査した。獣害防護柵内では先駆種を中心とする多数の広葉樹が間伐後に侵入し, その生残率は高く, 樹高成長も良好であった。しかし, 柵外では柵内よりも広葉樹の侵入が少なく, 生残率も低かったため, 2年後まで生残した個体はわずかであった。このことから, 柵外ではシカの採食により間伐後の広葉樹侵入が強く阻害されていると考えられた。シカ生息密度が高い地域において, 人工林の針広混交林への誘導を目指すには, 強度間伐を行った場合にシカ採食が顕在化する生息密度の解明と施業地へのシカの集中を防ぐ簡便な手法の開発が必要である。

English Abstract

We investigated the effects of deer browsing on broad-leaved tree invasion after heavy thinning (47.5∼71.2% reduction in stem density) in fenced and unfenced plots in conifer plantations with a high population of sika deer (Cervus nippon). In fenced plots, a number of broad-leaved trees, which comprised mainly pioneer species, invaded and grew well after thinning; further, they exhibited a high survival ratio. However, in unfenced plots, the number of broad-leaved trees that invaded was lesser than that in fenced plots, and they exhibited a low survival ratio. Only a few broad-leaved trees survived for 2 years after thinning in unfenced plots. Thus, these results suggest that deer browsing strongly inhibited the invasion of broad-leaved trees after thinning. The deer density levels affecting broad-leaved tree invasion after heavy thinning should be evaluated, and easy methods to prevent the concentration of deer populations in thinned stands should be developed. Such studies will help achieve the conversion of conifer plantations to mixed conifer—broad-leaved forests in locations with high deer populations.