Influence of tephra deposition on mire vegetation in Hokkaido, Japan

Volcanic eruptions can have a drastic impact on vegetation, and the reaction of plant communities to proximal volcanic disturbance - explosive blasts, pyroclastic flows and lava flows - is well documented. Distal effects of volcanic activity, on the other hand, have rarely been studied in detail. Following large-scale explosive eruptions, vast areas are blanketed by fine-grained volcanic particles known as tephra. The aim of the research that is presented here was to elucidate the impact of tephra on the vegetation of mires in Hokkaido, northern Japan. Stratigraphical and experimental studies were conducted to investigate the influence of tephra deposition on mire vegetation at different spatial and temporal scales. Peat and sediment cores were taken from six mires in different parts of Hokkaido. Macrofossil analysis was employed to detect vegetation changes in relation to tephra layers during the Holocene. Field experiments were carried out at Sarobetsu Mire in northern Hokkaido to test the impact of artificial tephra layers of different thickness and grain size on a Sphagnum lawn community. The nutrient limitation of Sphagna and vascular plants was studied in a separate experiment. The results indicate that tephra thickness is the dominant parameter determining the vegetation response, but grain size and the season also play an important role. The long-term effects of tephra deposition are less pronounced than previously suggested. No evidence for fundamental vegetation changes at tephra layers was found.