Effects of Stone Mulch on the Growth of Seedlings in a High Altitude Zone of Hokkaido

27 Mar Effects of Stone Mulch on the Growth of Seedlings in a High Altitude Zone of Hokkaido

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Abstract

北海道十勝岳の砂防工事跡の荒廃裸地において, 礫の体積合計や地表投影面積率の異なるストーンマルチ試験区を設定し, 表土層の地温とpFを連続観測し, 播種試験と自然侵入稚樹を対象に木部圧ポテンシャルの測定を行った。地表面を長径20~40cmの礫で覆うと, 裸地や小サイズの礫を用いた被覆区より表土層の地温日較差が小さく, 特に最高地温が低く抑えられた。また地表投影面積率で7割以上となるように高率で被覆するとpFがより低く保たれる傾向があった。2年間の播種試験から, 礫による地表被覆の効果は発芽よりも, その後の実生の定着段階において現れ, 霜害や表面流などの攪乱に対しても保護効果を持つ可能性が示唆された。2~4日間降雨が無い場合, 裸地に自然侵入した稚樹の木部圧ポテンシャルは礫周辺の個体に比べて有意に低く, 相対的に慢性的な水欠差状態にあると考えられた。礫による地表の被覆は表土層の水分環境を緩和し, 北海道の高標高域においても植生回復により適した環境条件を生み出す可能性が示唆された。

English Abstract

Field experiments using stone mulch were carried out in order to examine the effects of stone mulch on the germi tion and growth of seedlings in a devastated, high altitude area of Mount Tokachi, in central Hokkaido. The sites mulched with boulders (2040 cm in maximum diameter) had lower daily maximum soil temperatures and smaller diur l ranges than the sites with cobbles and the bare site. However, the sites mulched with a high percentage of stones (6876%), had lower maximum pF values of the surface soil in rainless periods than the sites mulched with a lower percentage and the bare site. The two-year long field germi tion experiment suggests that using stone mulch provides favorable conditions for seedling germi tion and growth, by protecting against disturbances, such as frost or surface runoff. When there was no rain for two to four days, the xylem pressure potential of turally regenerating seedlings at the bare site showed significantly lower values than at the stony site. The seedlings at the bare site also might suffer from a relatively severe water deficit. This result suggests that stone mulch affects the water regime of surface soil and produces better conditions for tural re-vegetation in high altitude zones of Hokkaido.