Drastic Peatland Regime Shift and Landscape Disturbances Connected to Warm and Cold Climate Events Over the Past Centuries in Subarctic Finland

Palaeoecological studies reporting long-term development history of subarctic fens are scarce and overall permafrost-free peatlands located at the immediate vicinity of permafrost zone have deserved little attention in Fennoscandia. We use a multiproxy approach to study millennial-scale dynamics of two peatlands located in Finnish Lapland (Katsapuli and Maader). In addition to study autogenic succession and external forcing, we aimed in resolving the impact of surrounding landscape changes, potentially related to reindeer herding. The pollen data does not indicate major regional-scale vegetation changes but suggest an increase in the proportion of sedges towards modern times and decrease in tree pollen. These, together with an increase in regional fire events based on micro-charcoal and erosion rates measured as sediment mineral component coincide with both colder temperatures (Little Ice Age) and the emergence of reindeer-based pastoralism. The peat macrofossil data of the two profiles suggest a clear and relatively simultaneous local regime shift from sedge-dominated local habitat conditions to a Sphagnum community, where S. lindbergii becomes increasingly dominant towards the present day, suggesting prevalence of relatively moist conditions. In both sites, the regime shift is coeval with the onset of Medieval Climate Anomaly (MCA) climate conditions. Newly- established communities are sustained thereafter. Vegetation changes to Sphagnum mosses resulted in high peat growth rates, thus most of the peat stock is relatively new. Based on these data, we suggest that Sphagnum moss communities are resilient to climate fluctuations and might continue to act as effective carbon accumulation systems under warmer climates.