Tural Regeneration of a Mixed Conifer-broadleaf Forest, Including Various Timber Species, After Strip Clear-cutting and Scarification of a Larix Kaempferi Plantation

27 Mar Tural Regeneration of a Mixed Conifer-broadleaf Forest, Including Various Timber Species, After Strip Clear-cutting and Scarification of a Larix Kaempferi Plantation

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Abstract

岩手県雫石町のカラマツ人工林において地掻き処理を伴う帯状皆伐を行った事例について, 更新林分の構造を解析した。伐採されなかった残存林分の下層ではミズナラ, ホオノキ, クリなどの高木種が胸高直径3cm 以上で693幹 (500個体) /ha, ウワミズザクラ, ヤマグワ, アズキナシなどの中高木種が236幹 (207個体) /ha みられ, 二段林を呈した。更新林分では, 伐採14年後に前生樹からの萌芽由来と考えられる複幹個体が高木種で777幹 (173個体) /ha, 中高木種で138幹 (58個体) /ha みられた。さらに伐採後に実生更新したと考えられる単幹個体が高木種で1,854幹 /ha, 中高木種で323幹 /ha 出現した。単幹主体の樹種にはウダイカンバ, カラマツ, シラカンバ, アカマツのように残存林分下層に出現しなかったものもあり, 樹種数は更新林分の方が多かった。本事例は, 皆伐と地掻き処理の併用が前生樹の萌芽再生とともに陽性樹種の実生定着も促進したことを示唆しており, この施業が, 下層に広葉樹が混交したカラマツ人工林を伐採した後に, 有用樹種を含む多様な樹種の混交林を更新させるのに有効な手段となり得ることを示している。

English Abstract

We examined the tural regeneration of trees after strip clear-cutting and scarification of a Larix kaempferi plantation in Iwate Prefecture, northern Japan. In the understory of the intact plantation, the density of broadleaf trees with DBH more than 3 cm was 693 stems/ha (500 individuals/ha) for canopy species such as Quercus crispula, Acer mono, and Magnolia hypoleuca, and the density was 236 stems/ha (207 individuals/ha) for subcanopy species such as Padus graya , Morus australis, and Aria alnifolia. Fourteen years after clear-cutting and scarification, the density of multi-stem regenerating trees was 777 stems/ha (173 individuals/ha) for canopy species and 138 stems/ha (58 individuals/ha) for subcanopy species. The density of singlestem regenerating trees was 1,854 stems/ha for canopy species and 323 stems/ha for subcanopy species. Some single-stem-domi nt species such as Betula maximowiczia , Betula platyphylla, L. kaempferi, and Pinus densiflora were not found in the understory of the intact plantation. It was concluded that clear-cutting facilitated sprouting from advanced trees and that scarification facilitated seedling emergence and establishment of light-demanding species. Therefore, combining clear-cutting with scarification has the potential to promote successful tural regeneration of various timber species and to convert a L. kaempferi plantation to mixed conifer-broadleaf forest.