Effect of Accretion Cutting and Deer-exclosure Fences on Regeneration of Broad-leaved Trees in Riparian Conifer Plantations Diminished by Sika Deer Grazing

27 Mar Effect of Accretion Cutting and Deer-exclosure Fences on Regeneration of Broad-leaved Trees in Riparian Conifer Plantations Diminished by Sika Deer Grazing

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Abstract

シカの影響の強い神奈川県丹沢山地の3流域（白石沢，用木沢，本谷川）の落葉広葉樹で構成される渓畔林に隣接した針葉樹人工林において，受光伐直後にシカの採食圧を排除する植生保護柵（以下，柵）を設置して，5，6年後に柵の内外で天然更新による高木性樹木稚樹（以下，更新木）の種名と個体数，樹高を調べた。3流域で更新木は18～36種出現して，フサザクラとケヤキ，オニイタヤなど13種は3流域に共通して出現した。更新木の種数と個体数ともに風散布型が多く，更新木の種の50％以上および個体数の80％以上には，調査地の外側30m圏内に種子供給源となりえる同種個体があった。柵内における樹高150cm 以上の更新木の個体数は，ha 換算して白石沢では27,500本，用木沢では2,083本，本谷川では7,500本であった。3流域ともにフサザクラなどの先駆性樹種が樹高の上位を占めていた。一方，柵外では更新木の種数と個体数は柵内よりも少なく，樹高が30cmを超えたのはオオバアサガラのみであった。以上のことから，シカの影響の強い渓畔林に隣接した針葉樹人工林では受光伐直後に柵を設置することにより周辺の渓畔林を種子供給源とした更新木が多数侵入，定着して，針葉樹との混交林化の可能性が示された。

English Abstract

We investigated species number, number of individuals and height of regenerated trees inside and outside of deer-exclosure fences 5 or 6 years after construction following accretion cutting in three riparian conifer plantations, to examine the possibility of restoring riparian forests of the Tanzawa Mountains in Ka gawa Prefecture. Eighteen to 36 species of regenerated trees emerged in three study sites, Shiraishisawa (SH), Youkisawa (YO), and Hontanigawa (HT). Regenerated trees such as Euptelea polyandra, Zelkova serrata, Acer pictum subsp. pictum f. ambiguum, Carpinus tschonoskii, Carpinus japonica and 8 other species emerged in all three study sites. Anemochory comprised the largest number of species and individuals of regenerated trees, and more than half of regenerated tree species and 80% individuals of regenerated trees were accordant with riparian tree species within 30 m from the study sites. The individual number of regenerated trees over 150 cm in height inside the fences was 27,500/ha in SH, 2,083/ha in YO and 7,500/ha in HT. Regenerated pioneer trees such as Euptelea polyandra ranked relatively high in height. There were fewer species and individuals of regenerated trees outside the fences than inside them, and Pterostyrax hispida alone was over 30 cm in height. These results indicate that three riparian plantations hold the possibility of shifting to mixed forests with coniferous and riparian broadleaved species after construction of deer-exclosure fences following accretion cutting.