エゾマツ天然林の択伐にともなう虫害枯損木の発生経過

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天然林択伐後のヤツバキクイムシによるエゾマツ虫害枯損木の発生経過を伐採後5年間にわたり，土場及びその周辺とそれ以外の地域に分けて調査し，とりまとめた。今回の調査で次の3点のことが分かった。(1)土場及びその周辺ではエゾマツ虫害枯損木が高い率で発生する。(2)伐採後の早い時期には，エゾマツ虫害枯損木は土場跡を含め土場跡に近い所を中心に発生し，年数が経過するにつれて枯損木の発生は周辺部に広がっていく。(3)エゾマツ混交率の高い土場及びその周辺で，虫害枯損木の発生率が高くなる傾向がある。エゾマツ天然林を施業する際に虫害枯損木の発生量を減らすためには，土場の設定には周辺にエゾマツの少ないところを選定し，特に土場内とその周辺5m以内にはエゾマツが残存しないようにすることが肝要であり，伐採後にはフェロモントラップを設置することが望ましい。The process of the spread of the attack of Yezo-spruce (Picea jezoensis) by spruce beetles (Ips typographus japonica NIIJIMA) around timber yards was observed for five years after selection cutting in natural forests of the Tokyo University forest in Hokkaido. Observed trees were divided into two groups, the marginal standing trees within 25 m distance from the timber yard edge and others. The conclusions derived from the analysis are as follows: 1) The mortality of marginal standing trees near the timber yard is higher than that of the others. 2) In the early stages after cutting, spruce beetles attack Yezo-spruce trees which stand close to the timber yard. As time proceeds, the attack spreads to the trees in the vicinity of the yard. 3) The mortality of Yezo-spruce in the timber yard increases in proportion to the proportion of Yezo-spruce. Consequently, the timber yard should be placed in an area where the number of Yezo-spruce is small, and it should be stressed that Yezo-spruce standing within 5 m of the timber yard should be cut, and it is desirable that pheromone traps are set in the yard after cutting in order to reduce the number of trees attacked by spruce beetles in the natural forest.
東京大学大学院農学生命科学研究科附属演習林,The Tokyo University Forests,東京大学農学部附属演習林北海道演習林,東京大学農学部林学科,University Forest in Hokkaido, Faculty of Agriculture, The University of Tokyo,Department of Forestry, Faculty of Agriculture, The University of Tokyoの論文

エゾマツ天然林の択伐にともなう虫害枯損木の発生経過

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