We investigated the relation between the formation of abscission layer and the leaf shedding of Quercus serrata Thunb. ex. Muuray (the height of test plants were more than 4m, which standing at the height of 80m, 260m, 390m, 630m, 820m above sea level) and Quercus acutissima Carrutherus (the height of test plants were more than 6m, which standing at the height of 120m, 250m, 620m above sea level) on the different altitudes at the south side slope of Mt. Izumi-Katsuragi at Wakayama Prefecture, Japan. The measurement items were the chlorophyll content by SPAD value, the percentage of leaves left at the sampled shoot and photomicrographs of the sliced base of petioles. We measured them every two weeks from October 14, 2005 to January 24, 2006. As a result, the periods of autumn leaves, the formation of abscission layer and the leaf shedding on both species were advanced as the standing levels rising. But some leaves were not shed whether the abscission layer enough developed or not. And, those leaves were forcibly shed at the petiole by the strong wind. The factor of this phenomenon was decrease in strength of the petiole because of drying.
