九州大学北海道演習林のカラマツ人工林および落葉広葉樹天然林における斜面方位と斜面上の位置の違いによる植生の特徴

We investigated the difference in forest structures among slope directions and slope positions in the larch (Larix kaempferi) plantations and in the deciduous broad-leaved natural forests of Ashoro Research Forest (ARF). The ratio of broad-leaved understory trees to larch in basal area was ranged from 3.8 to 46.8% in two plantations. Basal area of larch was higher in north-slopes than in south-slopes, whereas basal area of understory vegetation was lower in north-slopes than in south-slopes in the plantations. In the natural forests, total basal areas were not different among slope directions and positions. Both in natural and plantation stand, Quercus crispula was dominant in the south-slopes; Ulmus davidiana var. japonica, Fraxinus lanuginosa, and Syringa reticulate were dominant in the valley. There were various dominant species in the north-slopes as Quercus crispula, Fraxinus mandshurica, Tilia maximowicziana, Ostrya japonica, Carpinus cordata, Fraxinus lanuginosa, Cercidiphyllum japonicum, Styrax obassia and Acer pictum subsp. mono by forest types and slope positions. Both in natural forests and in understory vegetation in plantation, diversity index (Shannon-Weighner's H') was higher in north-slopes than in south-slopes. Deversity index was the highest in the upper of north-slopes of the plantation forests and the valley of the natural forest. The distribution and diversity of understory broad-leaved species in the larch plantation was corresponded to the differences in the slope direction and positions on the slope as natural forest in ARF, suggesting that the vegetation and diversity of broad-leaved trees in ARF may relate with soil fertility.