Fire history and vegetation recovery in two raised bogs at the Baltic Sea

Questions: What were the bog fire patterns and frequencies in two boreal peatlands during the last 5000 years? What is the nature and time-scale of post-fire vegetation successions? Were fire events related to climate? Location: Männikjärve bog, central east Estonia; Kontolanrahka bog, southwest Finland. Methods: Macroscopic charcoal, plant macrofossils and radiocarbon dating were examined. Redundancy analysis was used in the assessments. Results: During the last 5000 years, both of the above peatlands have experienced several fire events. A typical pre-fire vegetation community consisted of dry hummock Sphagnum spp., often accompanied by Calluna vulgaris. Only the most severe occasional fires resulted in a dramatic change in the vegetation composition. In these cases, a wet shift occurred, where the pre-fire hummock community was replaced by a wet hollow community. Calluna vulgaris was found to be a key species in both pre- and post-fire vegetation dynamics. The recovery time of dry microtopes following severe combustion and the subsequent hydrological change could take up to 350 years. Even after a long-lasting wet phase, the post-fire disturbance succession led towards a dry hummock community. Conclusions: Fire succession appeared to be cyclic, starting as and developing towards a dry hummock community. Fires have been a regular phenomenon in boreal bogs, even in regions with rather low human impact. The fire history records did not indicate any direct link to the regional long-term climate.