Relationship between Mire Vegetation and Volcanic Activity: A Case Study in Tadewara Mire, a Volcanic Mire in the South-Western Japan

Relationship between volcanic activity and vegetation change with special reference to chemical environmental change in soil by volcanic activity has been investigated in Tadewara mire in the Aso-Kujyu volcano area, south western Japan. A core of 420.0 cm depth was collected for peat forming plants analysis and chemical analysis. A distinct peak of sulfur content in peat core was found at the depth of 105.0-115.0 cm. Chronological changes of dominant species within the peat forming plants community showed both progressive and retrogressive successions. Vegetation change of Tadewara mire within recent 1000 years showed retrogressive succession from Sphagnum community to Moliniopsis and Phragmites communities after the sulfur compound deposition, whereas vegetation showed progressive succession after the deposition of sulfur became smaller. Enrichment of sulfur in sediment core appeared over the water impermeable layer with clay texture on volcanic ash horizon, and then vegetation change could be induced by the paludification caused by the clay layer. Deposition of volcanic ash layer and the following formation of water impermeable layer were dated at 970 ± 40 yBP by 14C dating data, and it corresponded to the eruption of Mount Kurotake recorded at 980 ± 30 yBP. Retrogressive succession can be the result of hydrological change rather than direct chemical changes in soil.