Response of plant communities to climate change during the late Holocene: palaeoecological insights from peatlands in the Alaskan Arctic

High-resolution plant macrofossil records were examined alongside pollen, micro- and macro-charcoal, and testate amoeba data to elucidate the dynamics of two permafrost peatlands in the northern foothills of the Brooks Range, Alaskan Arctic. The vegetation dynamics of these two peatlands were driven by autogenic processes reflecting the development trajectory of the peatlands towards ombrotrophic status, and allogenic climate change. We observe an increase in shrub pollen and macrofossils (e.g. Ericaceae, Betula nana) during two Late Holocene warm episodes and in recent decades. Pollen data suggest that regional forest cover also responded to temperature increase since ca. 1950 CE. An increase of Picea pollen (up to 13%) in the upper part of peat profile is probably associated with long distance pollen transport from populations of Picea mariana and Picea glauca located at the southern foothills of the Brooks Range. Relatively small amount of micro- and macrocharcoal in the two profiles indicates little fire activity around the sampling sites over the last ca. 2000 years, which is in agreement with regional findings. The lack of surface and groundwater influence under prolonged warmer/drier condition can allow Sphagnum to expand in Arctic peatlands. Cold climatic conditions might have been detrimental to Sphagnum populations, that were replaced by Carex spp. and other vascular plants owing to wetter conditions in the peatland.