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Exposure of tree roots and its control factors in a mixed temperate forest with no understory vegetation

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Abstract 九州大学宮崎演習林の三方岳団地では,ニホンジカの植生採食に伴い1980年台から土壌侵食が生じていると考えられる。しかし,本地域でこれまでに生じた土壌侵食の程度は明らかになっていない。土壌層の剥離に伴い土中から空中へ露出した樹木の根系(露出根)は,土壌侵食の程度を示す有用な痕跡である。本研究は三方岳団地で出現した露出根の分布や露出高さとその制御要因を明らかにすることを目的に行った。調査ではツガ,ウラ...ジロガシ,ブナ,ミズナラ,ホオノキを対象に,土壌面から露出根までの垂直高さ(露出高)を計測した。また,樹高や林床のリター量などの要因と露出高の関係から樹木周りの土壌侵食の制御要因を検討した。調査地では調査木より斜面下方に露出根が出現する傾向があった。全樹種の露出高の最大値(最大露出高)は17.1 ± 6.5 cmで,樹種に関わらず樹高と正の相関関係があり(ピアソン相関係数:r=0.35,p=0.07),リター量と負の相関関係があった(r=-0.35,p=0.07)。以上から,本調査地では樹木周りの土壌侵食が空間的に不均一に発生し,また樹高が高く林床のリター量が少ない立木の周囲では強い土壌侵食が発生していると言えよう。
Since around 1980, soil erosion has been progressing due to the reduction of the understory vegetation caused by the overpopulation of Sika deer (Cervus nippon) in the Shiiba Research Forest, Kyushu University. The exposed tree roots can be used as an index of soil erosion. This study aims to evaluate the characteristics of the exposed roots and clarify the factors relating to the exposed root in the Siiba Research Forest. We investigated the vertical height from the soil surface to exposed roots (exposed root height) of Tsuga sieboldii, Quercus salicina, Quercus crispula, Fagus crenata, and Magnolia obovata. We evaluated the relationship between exposed root height and tree size, slope angle, and litter amount on the forest floor. Exposed roots tended to appear downslope of the study trees. The maximum exposed root height of all tree species was 17.1±6.5cm. Regardless of tree species, the maximum exposed root height was positively correlated with tree height (Pearson correlation coefficient: r=0.35, p= 0.07) and negatively correlated with litter amount (r=-0.35, p= 0.07). These results suggested that extent of soil erosion around trees and among trees were spatially heterogeneous, especially strong in around trees with high tree height and low litter amount on the forest floor.
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Created Date 2022.04.13
Modified Date 2023.11.20

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