| Summary: | 亜寒帯林における森林衰退現象のモニタリング調査・研究の一環として，ヤツバキクイムシによる虫害木が発生している東京大学北海道演習林の標高400m～850mの天然林においてエゾマツを対象に調査を行った。前報のトドマツと同様に観察木を設定し，着葉，葉の色調，着果による健全度調査を開始した。さらに，健全木，衰弱木，虫害木を各2本ずつ伐倒し，着葉・着果の状況，伸長および肥大成長量の解析を行った。その結果，トドマツ衰退木にみられた樹冠梢端部の集中的な疎化現象は認められなかった。最近20年間における伸長・肥大成長量は健全木は優れ，衰弱木は減退していたが，虫害木の成長は衰弱木よりも旺盛であった。エゾマツの枯損はヤツバキクイムシの加害によって急速に進行し，着葉量，葉の色調などに基づく健全度や成長量からこれを予測することは困難であることがわかった。衰弱木に対する菌類調査およびナラタケ病調査からは，病原性の菌類とナラタケ病菌は検出されなかった。したがって，この衰退の原因は菌類（病原菌）によるものではなく，他の要因によるものと思われた。 Continuous observations of forest decline in sub-arctic coniferous forest were started in the Tokyo University Forest in Hokkaido in 1991, and the health condition of Yezo spruce (Picea jezoensis) growing in the forest damaged by spruce beetles (Ips typograhpus japonicus) was investigated between 400m and 850m above sea level in the same area. The health condition of Yezo spruce trees was investigated by an assessment of volume and color of needles, in a similar way to that in an investigation of Todo-fir in a previous report (Yamamoto et al., 1991). According to this information, the trees were classified into two categories: normal and abnormal. To analyze the volume of needles, cone bearing and stem growth of sample trees, two trees from both the normal and abnormal categories and insect damaged trees were cut. In addition, the presence of pathogenic fungi on these trees was investigated. Concentric defoliation of the crown top was not found in the sample trees. Height and diameter increment of the normal trees were larger than those of abnormal ones during the latest twenty years. However, insect damaged trees grew larger than abnormal trees. Based on this information, we estimated that healthy grown trees were killed by the spruce beetles within a few months. Consequently, it is difficult to predict insect damage on the basis of health indicators and stem growth. No pathogenic fungus or the mycelial mat of Armillariella-root rot were found. Therefore, it was considered that the decline of Yezo spruce observed on the sample trees was caused by factors ...
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