Development history of Sarufutsugawa mires, northern Hokkaido, Japan, reconstructed from plant macrofossil assemblages

Yano Azumi, Momohara Arata, Kondo Reisuke, Miyairi Yosuke, Shigeno Kiyoyuki, Kito Norio, Inoue Takashi, Yokota Akihiro, Sagayama Tsumoru, Yokochi Minoru

doi:10.34596/hisbot.27.1_17

Sarufutsugawa mires in northernmost Hokkaido provide habitats for boreal wetland plants, such as Carex livida. To clarify developmental processes of mire vegetation since ca. 9200 cal BP, we took drilling core samples from the Asajino-nishi Picea glehnii forest at 5.8 m a.s.l. in the lower reach of the Sarufutsu river and the Sarufutsugawa-naka mire at 11.8 m a.s.l. in the middle reach. We did additional AMS14C dating of plant macrofossils and reinvestigated Carex achene fossils from the Sarufutsugawa-maruyama mire at 15.6 m a.s.l. Caused by a drop of the sea level during ca. 6320–5290 cal BP, mires began to develop in this area after the burial of an estuary with brackish-water plant assemblages. Then vegetation of the three mires changed from wetland with submerged plant assemblages to wetland Alnus japonica scrubs. Finally, the Sarufutsugawa-naka and Sarufutsugawamaruyama mires became ombrotrophic, and Picea glehnii forests developed in the lower reach. This hydrosere was caused by a rise of the minerotrophic peatland surface above the flood level of nearby rivers with accumulation of peat, finally promoting ombrotrophy. In the Sarufutsugawa-maruyama mire, frequent silt layers in the sediments indicated that more frequent and prolonged floods than in lower reaches caused a delay in vegetation change to Alnus scrubs and ombrotrophic mire vegetation. Carex livida assemblages in this mire were established with the development of ombrotrophic mires since 1100 cal BP.

Development history of Sarufutsugawa mires, northern Hokkaido, Japan, reconstructed from plant macrofossil assemblages

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