Ojitetun Kalevansuon historialliset kasvillisuusmuutokset ja turpeen kertyminen

Peatlands influence the atmospheric circulation of carbon dioxide and methane. Because of changing climate, there is a growing interest to study northern peatlands, because they contain up to one-third of the total pool of soil carbon. Climate change is expected to be strongest in the high-latitudes. The prediction is that in the north a rise in the temperature is highest and the changes in precipitation are most pronounced. The purpose of this study was to examine mire development and carbon dynamics of one forestry-drained ombrotrophic mire. The aim was to determine vegetation history, changes in peat and carbon accumulation patterns and the effects of drainage on mire development. The research material consisted of peat samples collected from Kalevansuo. The vegetation development was examined by using macrofossil analysis and correspondence analysis (CA). Peat properties, such as LOI and bulk density, were also studied. The studied peat cores were radiocarbon dated. Flux measurement data on greenhouse gases were also used to interpret data. Kalevansuo started to develop more than 10,000 years ago through terrestrialisation. The development includes an initial fen phase followed by a cotton grass phase which changed further to a Sphagnum phase. The top peat layers represent drainage-affected phase. The fen-bog transition occurred around 4,100 years ago. Kalevansuo expanded to its southern margins about 5,200 years ago whereas lateral expansion in the east has been an ongoing process even after 1950. Peat and carbon accumulation has been slow when compared to some other bogs in the southern Finland. As a result of drainage Kalevansuo now functions as a significant CO2 sink, a small sink of CH4 and a small source of N2O. According to the flux measurement data it can be concluded that the forest-drainage did not have a positive climate warming feedback impact. A combination of autogenic and allogenic factors such as climate, fires and human disturbance have affected Kalevansuo development. The development was slow lasting for thousands of years, but also rapid, fire-induced changes occurred. This study agrees with the theory that climate change may strengthen the carbon sink feedback effect of boreal bogs, if forest-drainage simulates the effect of a warming climate on northern bogs.