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Northern peatlands store globally-important amounts of carbon in the form of partly decomposed plant detritus. Drying associated with climate and land-use change may lead to increased fire frequency and severity in peatlands and the rapid loss of carbon to the atmosphere. However, our understanding of the patterns and drivers of peatland burning on an appropriate decadal to millennial timescale relies heavily on individual site-based reconstructions. For the first time, we synthesise peatland macrocharcoal re-cords from across North America, Europe, and Patagonia to reveal regional variation in peatland burning during the Holocene. We used an existing database of proximal sedimentary charcoal to represent regional burning trends in the wider landscape for each region. Long-term trends in peatland burning appear to be largely climate driven, with human activities likely having an increasing influence in the late Holocene. Warmer conditions during the Holocene Thermal Maximum (similar to 9e6 cal. ka BP) were associated with greater peatland burning in North America's Atlantic coast, southern Scandinavia and the Baltics, and Patagonia. Since the Little Ice Age, peatland burning has declined across North America and in some areas of Europe. This decline is mirrored by a decrease in wider landscape burning in some, but not all sub-regions, linked to fire-suppression policies, and landscape fragmentation caused by agricultural expansion. Peatlands demonstrate lower susceptibility to burning than the wider landscape in several instances, probably because of autogenic processes that maintain high levels of near-surface wetness even during drought. Nonetheless, widespread drying and degradation of peatlands, particularly in Europe, has likely increased their vulnerability to burning in recent centuries. Consequently, peatland restoration efforts are important to mitigate the risk of peatland fire under a changing climate. Finally, we make recommendations for future research to improve our understanding of the controls on peatland fires.(c) 2023 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Sediments from an oxbow lake located in the Prosna River valley (Poland) were analysed to investigate the developmental history of the wetland ecosystem and any response to abrupt climatic changes. High resolution plant macrofossil analysis and radiocarbon dating were undertaken on two cores, with lower resolution geochemical analysis conducted on one of these cores. We provide evidence of a palaeolake with a late Glacial origin (older than 12,500 years). Abundant fossil presence of macrophytes (e.g. multiple Potamogeton species) in the studied palaeomeander may indicate that the north–south orientation of the Prosna valley made it an important route for the spreading of aquatic plants during the late Glacial. Chara sp., Batrachium sp. and Potamogeton spp. were the pioneer plants that colonised cold water with a high Ca2+ content. Early Holocene warming trigged a decrease in water level at the oxbow lake and facilitated the expansion of thermophilous water plants, for example, Ceratophyllum demersum, Typha sp. and Lemna trisulca, which usually occur in shallow water. A decreasing water level resulted in the gradual isolation of the study site from the influence of groundwater, leading to acidification of the habitat and the development of a Sphagnum population, with S. contortum and S. teres as dominant species. The presence of S. contortum (the oldest occurrence in the European lowlands) and S. teres during the early Holocene may indicate that river valleys and the peatlands that developed in this region acted as an important habitats (and possibly refugia) for some minerotrophic Sphagnum species.

The response of Arctic wetland ecosystems and their associated organic carbon stores to future warming is uncertain. For the first time in the Canadian High Arctic I use a multi-proxy palaeoecological approach to test how organic-rich wetlands have responded to pronounced warming since the mid-twentieth century. This approach enables ecological analysis on a timescale beyond that of contemporary studies. An ice-wedge polygon mire was a dual-state system with the raised centre mound showing no response to recent warming, but ~AD 2000 the surrounding trough exhibited a shift to wetter conditions and a transition from sedge and herb-dominated to brown moss-dominated vegetation. The accumulation of this vegetation layer may have the effect of insulating ice-wedges and provide a negative ecological feedback to permafrost degradation, mitigating potential carbon losses. In a valley fen, an increase in growing degree days above 0°C (GDD0) since ~AD 1950 is linked to greater inundation from increased snow and ice melt early in the growing season, coupled with increased drying towards the end of the growing season from elevated evapotranspiration. This may have initiated a pathway to wetland desiccation – although wetland persistence is likely to be determined by future Arctic precipitation patterns. In a coastal fen, greater GDD0 combined with isostatic uplift induced shrubification ~AD 1950 and led to rapid carbon accumulation. After this, increasing bird grazing pressures from ~AD 2000 may have affected vegetation and carbon accumulation. My results illustrate a variety of pathways for change in High Arctic wetlands in response to rapid warming. The results of this study suggest that predictions of the future extent and carbon accumulation rates of northern peatlands should consider the marked, yet complex response of High Arctic wetlands to warming alongside external non-climatic factors such as increased bird grazing pressures.