Effects of a Selective Cutting on the Recruitment and Survivorship of Seedlings in a Tural Thujopsis Dolabrata Var. Hondai Forest

27 Mar Effects of a Selective Cutting on the Recruitment and Survivorship of Seedlings in a Tural Thujopsis Dolabrata Var. Hondai Forest

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Abstract

岩手県川井村の早池峰山北麓のヒバ天然林において, 択伐がヒバ稚樹の消長に及ぼす影響を明らかにするために,択伐区と対照区における稚樹の発生密度, 生存率の推移, 成長を比較した。択伐の翌年に発生した実生の2年目の秋における生存率は, 対照区で11%, 択伐区で29%であり, 択伐区の方が有意に高かった。択伐後8年目での生存率は対照区で0.6%, 択伐区で14.5%であり, サイズも択伐区の方が有意に大きかった。択伐後3年目に発生した実生も択伐区の方がサイズが大きく, 密度も高かった。前生小稚樹 (樹高10cm未満) は択伐翌年の夏に択伐区で多くが枯死したが, 択伐後8年目には対照区との生存率に有意差はなくなっており, 高さは択伐区の方が有意に大きくなった。前生大稚樹 (樹高10cm以上) では択伐の有無に関わらずほとんど枯死はみられず, 樹高成長は択伐区の方が大きかった。択伐による生存率の改善は特に択伐後に発生した実生で大きく, 択伐は稚樹の成長を促すだけでなく, 実生の定着を促進させるためにも有効であることが示された。

English Abstract

The recruitment, survivorship and height growth of Thujopsis dolabrata var. hondai seedlings were compared between the treatment and control plots in a tural T dolabrata forest, located in the Kitakami Mountains, Iwate Prefecture, in order to clarify the effects of a selective cutting of upper trees on the seedling population dy mics. Survivorship of newly-recruited seedlings, emerged in the next year of the cutting, was significantly larger in the treatment plot at the second year after germi tion. Mean survivorship of those seedlings at the end of the seventh year after germi tion was 14.5% in the treatment plot, which was much larger than that in the control plot (0.6%). The differences in density between the treatment and control plots were also observed for another seedling cohort that emerged in the third year after cutting. Mortality of the advanced seedlings (height ?? 10cm) that emerged before cutting was significantly larger in the treatment plot than in the control plot in the first summer after cutting. In the 8th year, however, the survivorship in the both plots did not differ significantly. As for the saplings (height ?? 10cm, when cutting was carried out), most of them survived over eight years after the cutting in the both plots. Mean heights of the newly-recruited seedlings, advanced seedlings and saplings in the treatment plot were significantly larger than those in the control plot. These results suggested that a selective cutting increased the survivorship of seedlings, especially of newly-recruited seedlings after the cutting, and enhanced their height growth.