森林立地学会誌　森林立地47(2),2005,77〜84

Jpn.J.For.Environment 47(2),  77-84  2005

 

ヒノキ人工林の下層植生管理のための温度域区分

―土壌保全を目的として―

 

深田英久^＊・渡辺直史^＊・梶原規弘^＊＊・塚本次郎^＊＊＊

^＊高知県立森林技術センター・^＊＊高知県森林局

^＊＊＊高知大学農学部附属暖地フィールドサイエンス教育研究センター

 

 

　ヒノキ人工林の土壌保全を目的とする下層植生管理に資するために，温量指数傾度上で下層植生の温度域区分を行い，植生管理への応用を検討した。高知県全域にわたる多数のヒノキ人工林で下層植生の種ごとの植被率（％）を６段階評価し，これを指数化（被度指数）。針葉樹，常緑木本，落葉木本，草本・地表植物，ウラジロ・コシダ，ササの６生活型を設け，各々に属する種の被度指数の和（被度指数小計）を算出した。温量指数の傾度上で，常緑木本とウラジロ・コシダの被度指数小計の散布状態に変化の見られた点（それぞれ，寒さの指数−10と暖かさの指数105〜110）を境界とし，常緑木本類の繁茂できない落葉樹域，常緑木本類は繁茂できるが，ウラジロ・コシダの繁茂できないカシ域，常緑木本類とウラジロ・コシダが共に繁茂できるウラジロ・コシダ域の３域を区分した。ウラジロ・コシダ域では，土壌侵食抑制効果の高い植生タイプである草本・地表植物型の出現頻度が他の２域に比べて低かった。土壌侵食抑制効果の低い貧植生型の相対頻度は，ウラジロ・コシダ域＜カシ域＜落葉樹域の順に上昇した。これらの事実に基づいて，ヒノキ人工林における土壌保全を目的とした下層植生管理には温度域ごとに異なる方法が必要であることを指摘した。収量比数と植生タイプとの関係が温度域間で異なることを明らかにし，林分密度管理による下層植生管理を行う場合は，温度域ごとに別個の管理モデルが必要であることを指摘した。

 

Hidehisa Fukata, Naoshi Watanabe, Norihiro Kajihara, Jiro Tsukamoto : Altitudinal zoning of understory vegetation in planted Hinoki cypress (Chamaecyparis obtuse Endl.) forest from the view of surface soil erosion control

Zoning of understory vegetation by temperature was made, and application of it to vegetation control was discussed from the view of protection of surface soil loss by using the data collected from 68 Hinoki cypress plantations distributed over the Whole area of Kochi Prefecture, Southwestern Japan. Based on percent coverage, “species coverage index” was determined for every undergrewth species with visual observation. All species were classified into the following six life forms : conifer seedling, evergreen tree, deciduous tree, herb-Chamaephyte, Gleichenia japonica-Dicranopteris linearis (the commonest two species of fern under Hinoki plantations in southweatern Japan, being referred to as “ commonest fern” in the following) and dwarf bamboo. “Life form coverage index” was calculated as the total of “species coverage index” of every species belonging to each life form. Three zones were distinguished along the gradient of Kira’s Warmth Index. They were separated by breaks of distribution pattern of life form coverage indices of evergreen tree (Coldness Index, -10) and commonest fern (Warmth Index, 105-110) ; Gleichenia japonica-Dicranopteris linearis zone, the warmest zone, being with both evergreen tree and commonest fern, Evergreen oak zone without commonest fern, and Deciduous tree zone without both evergreen tree and commonest fern. Relative frequency of five vegetation types that are known to have different efficiency of erosion control, poor vegetation type, Gleichenia japonica-Dicranopteris linearis type, herb-Chamaephyte type, deciduous tree type and evergreen tree type differed between the zones. The relationship between relative frequency of different vegetation types and stand density (Yield Index) also differed from zone to zone. Based on these results, we concluded the applicability and usability of the zoning to understory vegetation control from the view of protection of surface soil loss.

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