Effects of Fencing for 7 Years on the Regeneration of Tree Species After Dwarf Bamboo on the Forest Floor Has Been Diminished by Sika Deer Browsing

27 Mar Effects of Fencing for 7 Years on the Regeneration of Tree Species After Dwarf Bamboo on the Forest Floor Has Been Diminished by Sika Deer Browsing

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Abstract

シカの採食圧でスズダケが退行した丹沢山地の冷温帯自然林に植生保護柵を設置して，7年後に柵内外で林床植生の種組成と高木性樹木の稚幼樹を調査し，樹木の更新に及ぼす植生保護柵の効果を検証した。林床植生全体の植被率やスズダケの植被率・桿高，稚幼樹の密度・樹高のいずれも柵内で高かった。種組成は柵内ではスズダケや高木類，低木類を中心に構成されていたのに対し，柵外では一年生草本や小型の多年生草本が多かった。稚幼樹の密度は柵内で高く，その差は6倍以上であった。ほとんどの樹種の樹高は柵内で40∼60 cmの範囲にあり，シナノキやリョウブなど9樹種の一部の個体はスズダケの桿高を上回っていたが，柵外ではほとんどの樹種が10 cm程度であった。これらのことから，植生保護柵は退行したスズダケを回復させるとともに高木性樹木の稚幼樹を定着・成長させる効果をもち，シカの更新阻害地における冷温帯自然林の再生手法として有効であると結論づけた。どの樹種が後継樹になるかを見きわめ，将来的な管理方針を決定するためには，さらに長期の継続調査が必要である。

English Abstract

Forest-floor vegetation and regeneration of tree species were investigated inside and outside a deer-proof fence that had been constructed 7 years earlier in a cool temperate deciduous forest in the Tanzawa Mountains, where dwarf bamboo (Sasamorpha borealis) had been browsed and diminished by sika deer. This study examined the effect of the deer-proof fence on tree species regeneration. The vegetation cover on the forest floor, cover and culm height of dwarf bamboo, and density and height of seedlings and saplings were higher inside the fence than outside the fence. Species composition consisted of dwarf bamboo, trees, and shrubs inside the fence, whereas annual herbs and short perennial herbs were found outside the fence. The density of regenerated trees was higher inside the fence than outside the fence, and the difference was more than 6-fold. The heights of almost all tree species inside the fence ranged between 40 and 60 cm, and though some tree heights for 9 tree species were higher than that of dwarf bamboo inside the fence, many trees outside the fence had heights of only about 10 cm. Based on these findings, it was concluded that the deer-proof fence facilitated the establishment and growth of tree species as well as the recovery of dwarf bamboo, and that the fence was an effective means of restoring cool temperate deciduous forest. Further monitoring is required to predict the future development of regenerating trees and to determine an optimal vegetation ma gement plan.