森林立地学会誌　森林立地47(1), 2005, 9〜20

Jpn.J.For.Environment 47(1), 9-20 2005

 

多雪地の皆伐跡地における更新作業の違いが森林の種組成と更新木の

密度に及ぼす影響

 

長谷川幹夫

富山県林業技術センター・林業試験場

 

　スギ植栽による人工更新および天然下種更新での除草剤散布の有無という３種類の異なる処理区間及び処理前の林床植生を比較することで更新作業の違いが森林の種組成と樹木の更新密度に及ぼす影響を明らかにした。調査区は約65年生のスギと広葉樹が混交した林分を皆伐し，地拵えを行った場所で1984年に設け，8年生と13年生時に調査を行った。植物種多様度（d,H’ ）が高いのは，人工更新地であり，大高木の更新密度が高いのは除草剤散布地と人工更新地であった。種多様度と更新密度を高める要因としては，皆伐後の光環境の改善，材の搬出作業や地拵え・植栽作業による地表攪乱とササなどの抑制が考えられた。一方，チシマザサの強度の優占や除草剤散布による草木類の枯死は，種多様度を低くする要因であった。8年生から13年生までの変化をみると，上層木が成長し，いくつかの先駆種が消滅して森林の階層化が進んだ。除草剤散布部分では草木の回復は，まだ認められなかった。人工更新地での作業（植栽と下刈り）は，ササを極端に優占させたり，草木植物を枯死させたりすることなしに，高い更新密度を得るという特徴があった。

 

Mikio Hasegawa: Effects of different regeneration methods on species composition and sapling density of regenerated forests within clear-cut areas in a heavy snow region

 To clarify the effects of different regeneration methods on plant species composition and regeneration density, investigations were conducted at three sites where different regeneration methods (artificial regeneration by Cryptomeria planting and weeding: PL, natural regeneration: NR, and natural regeneration with herbicide spraying: HS) were applied, comparing with the floor vegetation as control. The sites were set up in 1984, following clear cutting of a 65-year-old mixed forest consisting of artificial Cryptomeria and hardwoods and ground clearance. Investigations were conducted at the stands of age 8 and 13. The plant species diversity (d, H’ ) was the highest in the site of PL and the regeneration density was higher at sites of PL and HS. The factors of high species diversity and regeneration density were improved in a light environment by clear cutting and soil disturbance and repression of Sasa kurilensis growth by tasks such as yarding, ground clearance, planting and weeding. On the other hand, thick growth of S. kurilensis and herbicide treatment were factors of low species diversity. Vertical stratification in the forest had developed during the 8-13 year period with growth of trees and extinction of some pioneer species. However, no recovery of the herb species was observed in the site of HS. Afforestation such as planting and wooding were proven to be the most effective measures to gain high without regeneration density growing Sasa thickly or killing the herb species.

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