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DOI: 10.1191/0959683606hl952rp Effects of volcanic activity on mire development: case studies from Hokkaido, northern JapanInstitute of Botany, University of Regensburg, 93040 Regensburg, Germany; Laboratory of Conservation Ecology, Graduate School of Agricultural and Life Sciences, University of Tokyo, Yayoi I-1-1, Bunkyo-ku, Tokyo 113-8657, Japan; ash{at}mail.ecc.u-tokyo.ac.jp
Institute of Botany, University of Regensburg, 93040 Regensburg, Germany
Hokkaido Institute of Hydro Climate, Frontier 14, N 14 W 3, Kita-ku, Sapporo 001-0014, Japan Field stratigraphy and macrofossil composition of four mires in Hokkaido, northern Japan, were investigated to test whether tephra deposition induces long-term vegetation shifts. Macroscopic tephras of known origin ranging from 0.5 to > 25 cm in thickness were found in two or more of the study sites, allowing correlation of the stratigraphic development of the mires. Major peat types and position of macroscopic mineral layers were determined in the field, and selected cores were analysed by quantitative macrofossil analysis. Some macrofossil groups and the content of unidentifiable organic matter showed changes in the vicinity of tephra layers, but they did not indicate a clear response pattern of the vegetation or the decomposition dynamics of plant material. Mosses were expected to be most strongly affected by tephra deposition, but even in cases where tephra fell on Sphagnum-dominated vegetation, no fundamental shifts to new plant communities were found. This suggests that disturbance by widespread tephras less than 10 cm thick did not alter site conditions sufficiently to induce shifts in the peat-forming plant communities, or short-term changes did not become manifest in the macrofossil record. A correlation between tephra deposition and vegetation change from nutrient-and mineral-poor bog communities to richer fen communities that had been postulated by some authors was not found at our study sites.
Key Words: Tephra macrofossils peat stratigraphy mire development vegetation shifts resilience Hokkaido Japan late Holocene
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