森林立地学会誌 森林立地40（2），1998，83〜90
Jpn.J.For.Environment40 (2), 83−90 1998
御岳岩屑流堆積域における発生後10年目の植生発達と立地環境
藤本 潔1・酒井 寿夫1・森貞 和仁2・古澤 仁美1
中嶋 敏祐3・布施 修4・小林 繁男1
1 森林総合研究所森林環境部 3 青森県林業試験場
2 森林総合研究所四国支所 4 宮城県林業試験場
1984年の長野県西部地震に伴い発生した御岳岩屑流は，森林域にも多大な被害をもたらした。この岩屑流発生から10年目の植生発達状況と立地環境との関係を明らかにするため，岩屑流堆積物が薄く堆積する標高約2000mの小三笠山北側の緩傾斜地（田の原）と，厚さ数10mの岩屑流堆積物で埋積された標高約950mの王滝川谷底部（氷ケ瀬）にトランセクトを設け，地形断面測量，堆積物の粒径分析および植生調査を行った。波長数10〜100m程度，振幅10m程度の波状起伏がみられる田の原では，流水の影響を受けやすい谷部で粒径2mm以下の細土含有率や細土中のシルト・粘土含有率に顕著なばらつきがみられ，細土がほとんど存在しない箇所で出現種数・被度とも低い値を示すものの，細土含有率が5％程度以上ある地点では，微地形条件に関わらず，これらは同様の値を示した。氷ケ瀬では岩屑流堆積面が現河床を含め3段に段丘化しており，岩屑流堆積後，河川による侵食作用を被ることなく安定した地形環境下にあった上位面が出現種数・樹高・被度のいずれも最も高い値を示した。これらの結果は，流水による侵食プロセスが初期植生発達過程に大きな影響を及ぼしていることを示す。岩屑流発生後，同じ期間を経ていると考えられる田の原と氷ケ瀬上位面を比較すると，樹高およびそれぞれの種の被度百分率の合計値のいずれも標高の低い氷ケ瀬上位面の方が高い値を示した。
Kiyoshi FUJIMOTO, Hisao SAKAI, Kazuhito MORISADA,
Hitomi FURUSAWA, Toshihiro NAKAJIMA, Osamu FUSE and Shigeo KOBAYASHI:Vegetation
development and site environments on the Ontake debris avalanche deposits
l0years after the occurrence, Central Japan. Jpn. J. For. Environment40, 83-90,
l998
In order to clarify the relationship
between revegetation and site environments during the first 10years on the 1984
Ontake debris avalanche deposits, two transect lines were set up at Tanohara
(2000m.a.s.l.) and Korigase (950m.a.s.l.). Topographical survey, grain-size
analysis and vegetation investigation were carried out along the lines. At
Tanohara, where the wavelike relief was formed by the debris avalanche
deposits, there was no significant difference in the number of species and
coverage between the plots which have more than 5 % of fine earth content in
spite of topographical variations. However, in the troughs which have been
susceptible to the influence of running water, dispersion of fine earth content
varied widely and the number of species and coverage in a plot which has only
1% of fine earth content was extremely low. At Korigase, the debris avalanche
deposits which had buried the river bed of the Otaki River were dissected and a
three-tiered terrace was formed. The number of species, maximum height of
vegetation and coverage were highest on the top terrace, which is an original
depositional surface of the debris avalanche and has been free from river
erosion. This result suggests that the erosional process by running water is
one of the important factors affecting vegetation development on debris
avalanche deposits. Compared with Tanohara situated at a higher elevation,
maximum height of vegetation and sum of cover percentage of each species on the
top terrace were significantly higher.