京都大学北海道演習林における "ヤチダモ" の育林学的研究 : 第II報 ヤチダモ壮令林における林分構造 成長経過並びに植生型について

Abstract

(1) 京都大学北海道演習林標茶経営区におけるヤチダモ壮令林分の林分構造, 成長量, 並びに林床植生についての調査をおこなつた｡ (2) 調査壮令林分は軍馬補充部発足時に更新されたものと推定され, 樹令は30年前後である｡ (3) 林分構造上からは壮令林と老令林との間に差は認められず, ヤチダモの侵入経路も老令林におけると同様にミズナラ, ハルニレについで成林したものと考えられる｡ (4) 極端に被圧された壮令林分は老令林分におけると同様な成長経過を辿つており, 両林分の相関性が考えられる｡ (5) 正常な壮令林分の胸高直径及び材積の成長量は道内優良ヤチダモ林よりも良好である｡ (6) 壮令過密林分におけるヤチダモ枯損木の年数, 樹高, 胸高直径から, その成長回復の最低限度を割り出すと, 樹令は25年, 樹高8m, 胸高直径5cm前後となる｡ (7) 本調査林分は混牧林としての影響を受けており, そのため胸高直径, 材積成長量は他林分を凌駕して良好である｡ (8) 林床植生型は① ミヤコザサ―灌木型, ② ミヤコザサ―庇陰性草本, 大型草本型, ③ ミヤコザサ―庇陰性草本型, ④ 庇陰性草本型の4型に分けられ, これらはいずれも放牧の影響によりミヤコザサ型の植生型から移行したものと考えられる｡ (9) 樹高, 胸高直径, 両成長量は林床植生を庇陰性草本型としてもつ所に良好であつて針葉樹における優良林分下のDryopteris型植生と類似している｡ (10) ヤチダモ壮令林の成長量の良否は立地条件によつて左右せられ, 台地上の緩斜面, 沢の上部等において良好である｡ これは第I報における老令林の場合と同様である｡ (11) 林床植生及び立地条件からヤチダモは養分要求度, 土地要求度 (特に水分要求度) の強い樹種であることが推測された｡

In a partial area of Kyoto University Forest in Hokkaido (along the boundaries of Nemuro), there are small area of middle aged Yachidamo forests (area=20 ha, tree age=30~50 years). These stands have much more volume than the old aged stand. Attending to this feature of volume we tried to make clear a distinctive feature of standing structure and growing process between the middle and old aged stand. We also investigated the land plants with these standing investigation. The result of this studying is as follows: (1) This stand was presumed to reproduce when the section of war horse established. The tree age is about 30 years before and after. (2) In the structure of stand, there are no differences between the middle and old aged stand. (3) So extremely suppressed middle aged stand shows the same growing process as the old aged stand. We think that, there is mutual relation in these stand. (4) The growth of diameter breast high and volume of unsuppressed stand is better than superior forest of Yachidamo in Hokkaido. (5) When we presume the limit of recovery of the growing from ages, height, and diameter breast high of the dead standing trees of Yachidamo in so extremely suppressed stand, that is about 25 years old, 8 meter height, and 5 centi meter diameter breast high. (6) It is because of pasturage stand that the growth of diameter breast high and volume of this stand is much better than the other stand. (7) Land plant types in this stand are distinguished 4 types. That is, (1) Miyakozasashrub type, (2) Miyakozasa-shady herbs type, (3) Miyakozasa-shady large herbs type, (4) shady herbs type. (8) The growth of height and diameter breast high are superior in the shady herbs type. This is similar to Dryopteris type in the coniferous trees stand which has much growth. (9) It is presumed that Yachidamo has a strong requirement for nutrient and soil (especially soil water) from condition of the land plants and situation of the Yachidamo stand.