Changes in Stand Structure and Species Composition From 5 to 11 Years After Clear-cutting of a Sugi Plantation in the Warm-temperate Zone in Shikoku, Japan

27 Mar Changes in Stand Structure and Species Composition From 5 to 11 Years After Clear-cutting of a Sugi Plantation in the Warm-temperate Zone in Shikoku, Japan

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Abstract

高知県東部の暖温帯域に位置するスギ人工林皆伐跡地において, 皆伐5年後から11年後までの林分構造と種組成の変化を明らかにした。調査地では, 皆伐5年後の2003年の時点で胸高直径2 cm以上の広葉樹の幹密度が11,300本 ha−1に達し, 調査期間中一貫して増加した。2009年には胸高断面積合計が29.8 m2 ha−1に達した。個体の約65%が多幹個体であったことから, 前生樹からの萌芽再生が更新に重要であったことが示唆された。期間中の林分構造と種組成の変化から, クサギなどの先駆性の低木種の大部分が枯死し, 常緑広葉樹林の林冠構成種, 特にシイ類が優占する傾向が強まったことが示された。これらの結果から, 本研究の調査地では針葉樹人工林の皆伐後に常緑広葉樹林が成林し, その植生回復過程は, これまでに報告されている萌芽更新由来の常緑広葉樹二次林の遷移とおおむね同様の経過をたどっていると考えられた。

English Abstract

We investigated the changes in stand structure and species composition from 5 to 11 years after clear-cutting of a Sugi (Cryptomeria japonica) plantation in the warm-temperate zone of eastern Kochi, Japan. Stem density of broad-leaved tree species in the study stand was 11,300 stems ha−1 in 2003, 5 years after clear-cutting, and increased during the study period. The basal area of the study stand reached 29.8 m2 ha−1 in 2009. Approximately 65% of tree individuals in the study stands were multi-stemmed, suggesting the importance of sprouting in the regeneration process. The observed changes in stand structure and species composition during the study period showed that pioneer shrub species had been excluded from the stand, and that evergreen broad-leaved trees, especially Castanopsis species, had increased their domi nce. These results suggest that the study stand is under a succession process comparable to that previously reported in evergreen broad-leaved secondary forests in the warm temperate zone in Japan.