北海道中央高地, 大雪山における高地湿原の起源とその植生変遷 (II)
1986 年 25 巻 2 号 p. 113-128
詳細
1986 年 25 巻 2 号 p. 113-128
Two upland bogs in the Daisetsuzan Mountains, the Yutomuraushi bog and the bog lying on the eastern slope of Ponchubetsudake, have been investigated for the physical requisites for bog formation and vegetational succession.
The Yutomuraushi bog lies on a gentle slope facing a landslide area, although the bog seems little affected by this landslide. 14C dating of a peat obtained from 175cm in depth of the bog suggests that the accumulation of peat began ca. 5000y.B.P. The bog lying on the eastern slope of Ponchubetsudake is developed on a plateau, which consists of Quaternary andesitic lava. 14C dating of a peat collected from the bottom of the bog indicates deposition ca. 7500y.B.P. Both of these bogs have blanketed the original slopes, filling up hollows and masking the original topography, and are considered to be affected by solifluction during periods of cool climatic conditions.
The vegetational succession revealed by pollen analysis during the last ca. 7500 years is as follows:
1) ca. 7500-5000y.B.P. (Zone Po-III)
In the upper part of the Daisetsuzan Mountains, Pinus, most probably P. pumila, was the dominant tree, whereas in the lower part such trees as Picea jezoensis or Picea glehnii were well represented, although an increase in Quercus occurred with climatic amelioration. In the bog lying on the eastern slope of Ponchubetsudake, there were ponds with Menyanthes during the early stage of this period.
2) ca. 5000-2000y.B.P. (Zone Po-II, Zone Yu-II)
In the upper part, Pinus pumila decreased its area. In the lower part, Quercus dominated at the beginning of this period, while Picea, Abies and Betula were fairly well represented later, between ca. 3500 and 3000y.B.P. The vegetation of the bogs usually comprised Cyperaceae, Umbelliferae, Liliaceae and Artemisia. In the Yutomuraushi bog, ponds with Menyanthes were scattered during the early stage of this period.
3) ca. 2000y.B.P.- present (Zone Po-I, Zone Yu-I)
An increase in Picea and a decrease in Quercus were noted. This would imply that the climate was cooler and wetter during this period.
