東日本のブナ林に出現する広葉草本種の生育場所は少雪地と多雪地でなぜ異なるのか Forest floor conditions causing regional differences in the habitat of forb species in Japanese beech forest, eastern Japan

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1.蛭間・福嶋(2004)では,東日本の冷温帯において,サラシナショウマなど特定の広葉草本種群は,少雪地ではブナ林が成立する斜面に生育するが,多雪地ではブナ林に生育せず,これに隣接する谷に生育が限られることが示された.今回の研究はこうした生育場所の差異がどのような要因でみられるのかを明らかにした.この要因として,少雪地と多雪地の林床における,リターの堆積状態や展葉季の光環境の違いに着目した.2.林床におけるリターの堆積量は,多雪地,少雪地に関わらずブナ林(斜面)で多く,谷では少なかった.多雪地のブナ林では,少雪地のブナ林に比べ,堆積しているリターの層数・厚さあたりの層数が多かった.3.少雪地と多雪地のブナ林(斜面)における夏季の林床の光環境には違いが見られなかった.しかし,少雪地では,春季に草本層から展葉が始まり上層木の展葉は遅れるため,林床草本の展葉中の光環境は良好であった.一方多雪地では林床に遅くまで積雪が残るため,展葉が上層木から始まり,林床草本の展葉中の光環境は悪かった.谷をみると,多雪地であっても低木よりも草本の展葉が先行していた.これは谷沿いの低木が谷底の残雪に埋没し,展葉が遅れるためであった.4.多雪地のブナ林における広葉草本の生育を制限している要因として,林床ではリターの層数・厚さあたりの層数が多く,広葉草本の定着,発芽の妨げになることと,春から初夏にかけて雪が残存し,林冠のブナの展葉が広葉草本の展葉に先行するため,生産性の高いこの時季の林床の光環境が暗いことが考えられた.しかし,多雪地の谷では広葉草本が生育可能である要因として,リターの量が少ないことと,低木層よりも,草本層のほうが先に展葉を開始,完了できることが考えられた.

<p>In cool temperate forest zones in eastern Japan, certain forb species like <i>Cimicifuga simplex</i> in light<sup>-</sup>snow regions grow on slopes of beech forests, while in heavy<sup>-</sup>snow regions its habitat is rather limited to valleys adjacent to beech forests. This research study reveals reasons for this difference in forb species habitats. As key factors, the study focuses on differences in the lighting environment during the leafing season as well as the state of tree leaf litter sedimentation on the forest floors in both light<sup>-</sup>snow and heavy<sup>-</sup>snow environments. Regardless of the amount of snow, the volume of tree leaf litter sedimentation on the forest floor was large on slopes of beech forest and small in valleys. In heavy<sup>-</sup>snow beech forests, the number of layers of litter sedimentation as well as the density of litter compaction within a certain thickness of sedimentation were larger compared to light<sup>-</sup>snow regions. In terms of the lighting environment during the summer season, no difference was observed on slopes of beech forest between light<sup>-</sup>snow and heavy<sup>-</sup>snow environments. However, over the spring season in light<sup>-</sup>snow regions, the lighting environment of the forest floors was good during the leafing seasons, because foliation begins with the herbaceous layer and leaf expansion of canopy trees comes later. On the other hand, in heavy<sup>-</sup>snow regions, the lighting environment of the herbaceous layer was poor during the leafing season, since foliation starts from canopy trees as snow covering the floor remains longer. In valleys, foliation of herbaceous layer preceded that of shrubs even in heavy<sup>-</sup>snow regions. This phenomenon was attributed to the fact that lingering snow in the valley floor covers the shrubs alongside the valley, which in turn delays foliation of the shrubs. Two factors are considered reasons restraining the growth of forb species in beech forests in heavy<sup>-</sup>snow regions: 1) the large number of layers and the high density of litter sedimentation at the forest floor constrict the establishment and germination of forb species, and 2) the poor lighting environment from spring to early summer (which are supposed to be productive seasons) is due to lingering snow that makes the crown canopy of beech forests foliate before forb species. However, the study found that forb species are able to grow in valleys in heavy<sup>-</sup>snow regions, because the volume of litter sedimentation is small and herbaceous layer begins and completes foliation before shrubs do.</p>

収録刊行物

  • 植生学会誌

    植生学会誌 31(2), 179-192, 2014

    植生学会

各種コード

  • NII論文ID(NAID)
    110009911083
  • NII書誌ID(NCID)
    AA11347548
  • 本文言語コード
    JPN
  • ISSN
    1342-2448
  • NDL 記事登録ID
    026001337
  • NDL 請求記号
    Z18-3499
  • データ提供元
    NDL  NII-ELS  J-STAGE 
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