京都市市街地北部森林のマツ枯れに伴う林相変化

Abstract

京都市周辺の都市林では, 1980年代以降に激化したマツ枯れにより, 多くのアカマツが枯死した.京都市市街地北部における近接3地域(宝ヶ池, 神山, 上賀茂)の都市林について, マツ枯れ前後の植生図を比較し, 林相変化を明らかにした.植生図は1982年, 1990年, 1998年撮影の航空写真から作成し, 各林分を優占種によってアカマツ林などの林分タイプに分類した.1982年には, アカマツ林が最も多くみられ, 宝ヶ池及び神山地域で60%以上, 上賀茂地域でも約30%の面積を占めた.しかし, 3地域のアカマツ林の面積は, 1998年にはそれぞれ0.6%, 4.6%, 2.1%にまで減少していた.宝ヶ池及び神山では, マツ枯れ後, 谷地形で落葉広葉樹が順調に林冠層に現れたのに対し, 尾根地形では林冠層を欠く林分が多く出現した.上賀茂では, マツ枯れ後, ヒノキが林冠層に現れた林分と, ヒノキ以外の樹種が優占した林分が存在し, その後それぞれが地形に応じて様々な林相に変化した.以上より, これらの地域におけるマツ枯れ後の林相変化にはいくつかのパターンが存在し, その違いには地形やマツ枯れ以前の林分構造が影響していると考えられる.

Around Kyoto City, many Japanese red pine (Pinus densiflora) trees in the urban forests have died because of heavy damage by pine wilt disease after the 1980s. For three adjoining urban forests in the northern part of Kyoto City (TAKARAGAIKE, KOUYAMA and KAMIGAMO), we compared the vegetation maps of different years to clarify the changing patterns of forest cover. Vegetation maps were made from aerial photographs taken in 1982. 1990 and 1998, and the forest cover types were decided based on the dominant canopy species, e.g. Red pine forest dominated by P. densiflora. In 1982, Red pine forest type was the largest, and it occupied 60% or more in area in TAKARAGAIKE and KOUYAMA, and 30% in KAMIGAMO. In 1998, however, Red pine forest type occupied only 4.6% or less of the area. In TAKARAGAIKE and KOUYAMA, deciduous broad-leaved tree species appeared in the forest canopy soon after the damage to red pine in the valley, while many stands on the ridge remained lacking in tree species to provide cover. In KAMIGAMO, two types of stands were identified : those in which Chamaecyparis obtusa appeared in the forest canopy quickly and those in which species other than C. obtusa occupied the site, and then each stand tended to change according to topographic factors. Our results revealed that there were several types in the changing patterns of forest cover through damage by pine wilt disease in these forests, and suggested that those changing patterns were affected by topographic factors and stand structure before the damage.