FONT SIZE:
カラマツ人工林における除間伐が広葉樹の侵入・成長に及ぼす影響と混交林化の施業指針
岩﨑, ちひろ;渋谷, 正人
Permalink : http://hdl.handle.net/2115/52013
KEYWORDS : カラマツ;混交林;広葉樹;間伐;天然更新;Larix kaempferi;mixed-forests;broadleaved trees;thinning;natural regeneration
Abstract
天然更新した広葉樹によるカラマツ人工林の混交林化を検討するため、北海道内のカラマツ高齢級人工林13林分で、広葉樹の種組成、樹齢構成、サイズ構造を調査し、広葉樹の侵入や成長と除間伐歴の関係を明らかにした。さらに、広葉樹の成長に重要な林内照度を維持し混交林化を図るための密度管理シミュレーションを行った。調査林分は収量比数0.6 未満の疎な林分が多かった。多くの広葉樹が間伐後に更新していたが、肥大成長の変動と除間伐歴には関係はみられなかった。このことから、疎に管理されたカラマツ林では、間伐は広葉樹の更新の契機であるが、成長への影響は大きくないといえる。密度管理シミュレーションでは、80年生頃に林冠層に達する広葉樹が出現し始め、100年生頃には林冠層の広葉樹混交率は約30%となると予測された。以上のことから、混交林化の施業指針として、保育段階では、広葉樹の更新を促すために繰り返し間伐を行うことが必要で、疎仕立てが適しており、収穫段階では広葉樹の成長を促すため、収量比数0.6以下での密度管理が必要といえる。これらの管理により、80年生頃に広葉樹が林冠に達し始め、100年生頃から相観的にも混交林化すると考えられる。
We investigated species composition, age and tree size of natural broadleaved trees and examined influences of thinning on invasion and growth of the broadleaved trees in 13 Larix kaempferi plantations older than 50 years old in Hokkaido. In addition, we simulated density management necessary for conversion of the larch plantations into mixed stands of larch and broadleaved trees. In this simulation, relative light intensity in larch plantations was assumed to be kept favorable for growth of broadleaved trees, and we examined a management guideline to convert larch plantations into mixed stands. Yield indices of most investigated plantations were lower than 0.6. Most broadleaved trees regenerated in two years after thinning. No apparent influence of thinning on diameter growth of broadleaved trees was observed. Therefore, thinning was the chance of regeneration of broadleaved trees in larch plantations. In the simulation for the management guideline, it was expected that broadleaved trees became to be canopy trees about 80 years old in plantation age, and the ratio of broadleaved trees in the canopy layer was estimated to be about 30% at approximately 100 years old. In the management guideline for stand conversion, repeated thinning is necessary for natural regeneration of broadleaved trees in larch plantations, and sparse management is recommended in tending stage of the plantations. Sparse management (yield index < 0.6) is also recommended in harvest stage of the plantations for stand conversion into mixed stands of larch and broadleaved trees. According to this management guideline, broadleaved trees will reach the canopy when larch stands are approximately 80 years old, and the plantations will be mixed-forests physiognomically when plantations are about 100 years old.
We investigated species composition, age and tree size of natural broadleaved trees and examined influences of thinning on invasion and growth of the broadleaved trees in 13 Larix kaempferi plantations older than 50 years old in Hokkaido. In addition, we simulated density management necessary for conversion of the larch plantations into mixed stands of larch and broadleaved trees. In this simulation, relative light intensity in larch plantations was assumed to be kept favorable for growth of broadleaved trees, and we examined a management guideline to convert larch plantations into mixed stands. Yield indices of most investigated plantations were lower than 0.6. Most broadleaved trees regenerated in two years after thinning. No apparent influence of thinning on diameter growth of broadleaved trees was observed. Therefore, thinning was the chance of regeneration of broadleaved trees in larch plantations. In the simulation for the management guideline, it was expected that broadleaved trees became to be canopy trees about 80 years old in plantation age, and the ratio of broadleaved trees in the canopy layer was estimated to be about 30% at approximately 100 years old. In the management guideline for stand conversion, repeated thinning is necessary for natural regeneration of broadleaved trees in larch plantations, and sparse management is recommended in tending stage of the plantations. Sparse management (yield index < 0.6) is also recommended in harvest stage of the plantations for stand conversion into mixed stands of larch and broadleaved trees. According to this management guideline, broadleaved trees will reach the canopy when larch stands are approximately 80 years old, and the plantations will be mixed-forests physiognomically when plantations are about 100 years old.
FULL TEXT:PDF