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 histories of subarctic fens—explicitly, orohemiarctic peatlands—are scarce, and overall, permafrost‐free peatlands located in the immediate vicinity of permafrost zones have received little attention in Fennoscandia. Here, we use a multiproxy approach to study the millennial‐scale dynamics of two neighbouring peatlands located in Finnish Lapland (Katsapuli and Maader). In addition to studying autogenic succession and external forcing, we aimed to resolve the impact of surrounding landscape changes, potentially related to reindeer herding. The pollen data did not indicate major changes in regional vegetation, except for an increase in the proportion of sedges towards modern times and a decrease in the proportion of tree pollen. This, together with an increase in regional fire (microcharcoal) and erosion rates (measured as the mineral component in the sediments) in the area, coincided with both colder temperatures (Little Ice Age) and the emergence of reindeer‐based pastoralism. The macrofossil peat plant data of the two profiles suggested a clear and relatively simultaneous local regime shift from sedge‐dominated local habitat conditions to a Sphagnum community, where S. lindbergii became increasingly dominant towards the present day, suggesting a prevalence of relatively moist conditions. In both sites, the regime shift was coeval with the onset of Medieval Climate Anomaly climate conditions and is sustained thereafter. Vegetation changes in Sphagnum mosses induced high peat growth rates, and most of the peat stock is relatively young. 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.