立地環境および林相の違いが林床被覆を通して表土侵食に与える影響

集水域内の林床被覆と表土侵食に違いをもたらす要因を明らかにする目的で，林相（ヒノキ林，スギ林，広葉樹二次林）および微地形（頂部斜面，上部谷壁斜面，下部谷壁斜面，沖積錐・段丘面）の異なる複数の林分で林床被覆と雨滴侵食および表面流侵食の発生状況を調査した。林床被覆率は林相別ではヒノキ林で低く，微地形別では下部谷壁斜面で低い傾向がみられた。また，雨滴侵食および表面流侵食が認められた林分では，表土侵食の痕跡が見られない林分に比較して林床被覆率が低い傾向がみられた。一般化線形モデルを用い侵食の発生にかかわる要因を検討した結果，説明変数が林床被覆のみのモデルよりも地形因子を含むモデルで有意にあてはまりがよかった。この結果は，林床被覆の安定性や林床被覆による侵食の抑止効果が地形によって異なることを示していた。

Ryoko Hirata, Koji Kizaki, Satoshi Ito, Yasushi Mitsuda, Osamu Shimizu：Influence of forest floor cover on soil erosion risks under different site conditions and forest types. Japanese Journal of Forest Environment 57:109―116, 2015.

We investigated forest floor cover (FFC) and evidences of splash and wash erosion in different stand types (hinoki plantations, sugi plantations and broadleaved secondary forests) established on various micro-topographies in order to clarify the factors affecting the surface soil erosion. Low FFCs were observed in hinoki plantations and on lower-side slopes compared to the other stand types and micro topographies, respectively. Lower FFCs were also recorded in the stands where the evidence of splash or wash erosion was observed than in the non-evident stands, indicating a relationship between FFC and surface soil erosion. Generalized linear models explaining the occurrence of splash or wash erosion demonstrated a better fitting of the model with topographic factors in addition to FFC as explanatory variables, than the null model without topographic factors. These results suggested that the stability of FFC or the effectiveness of FFC in preventing surface soil erosion could be modified by topographic factors.