ハンノキ属の葉はなぜ夏に落ちるか WHY DO ALDER LEAVES FALL IN SUMMER?
Leaf-fall pattern of six alder species (subgenus Gymnothyrsus : Alnus hirsuta, A. inokumae, A. glutinosa, A. japonica ; subgen. Alnaster : A. maximowiczii, A. pendula) was investigated from 1976 to 1979. A large quantity of leaves of the species belonging to the subgen. Gymnothyrsus fell in summer, which reached 30-50% of the yearly leaf fall. The first, second and/or the third leaves counted from the shoot base of these species almost fell in summer. These two or three leaves near the shoot base are small-sized, which indicates that these leaves are in course of reduction, and they fall early in summer after they have played a role as early leaves. In the subgen. Alnaster, the lamina of the first node is reduced and disappeared, and the remaining two stipules are connate in a bud scale which fall in late spring or early summer after it has played a role of the bud protection, while the leaves did not fall until autumn. Thus the extraordinary leaf fall in summer was not observed on the species of this group, and it was less than 10% of the total fall.
日本生態学会誌 30(4), 359-368, 1980