Wetland succession in a permafrost collapse: interactions between fire and thermokarst
1Institute of Arctic Biology, 311 Irving I Bldg., University of Alaska Fairbanks, Fairbanks, Alaska, 99775, USA
2US Geological Survey, 345 Middlefield Rd. MS 962, Menlo Park, California, 94025, USA
3Institute for Botany and Landscape Ecology, Grimmer Strasse 88, Greifswald University, 17487, Greifswald, Germany
4US Geological Survey, Alaska Cooperative Fish and Wildlife Research Unit, 214 Irving I Bldg., University of Alaska Fairbanks, Fairbanks, Alaska, 99775, USA
*now at: Department of Biological Sciences, CW 405, Biological Sciences Centre, University of Alberta, Edmonton, Alberta, T6G 2E9, Canada
Abstract. To determine the influence of fire and thermokarst in a boreal landscape, we investigated peat cores within and adjacent to a permafrost collapse feature on the Tanana River Floodplain of Interior Alaska. Radioisotope dating, diatom assemblages, plant macrofossils, charcoal fragments, and carbon and nitrogen content of the peat profile indicate ~600 years of vegetation succession with a transition from a terrestrial forest to a sedge-dominated wetland over 100 years ago, and to a Sphagnum-dominated peatland in approximately 1970. The shift from sedge to Sphagnum, and a decrease in the detrended tree-ring width index of black spruce trees adjacent to the collapse coincided with an increase in the growing season temperature record from Fairbanks. This concurrent wetland succession and reduced growth of black spruce trees indicates a step-wise ecosystem-level response to a change in regional climate. In 2001, fire was observed coincident with permafrost collapse and resulted in lateral expansion of the peatland. These observations and the peat profile suggest that future warming and/or increased fire disturbance could promote permafrost degradation, peatland expansion, and increase carbon storage across this landscape; however, the development of drought conditions could reduce the success of both black spruce and Sphagnum, and potentially decrease the long-term ecosystem carbon storage.