Sphagnum-dominated peatlands in North America since the last glacial maximum: Their occurrence and extent

Sphagnum-dominated peatlands occupy extensive tracts of land throughout the Boreal and Subarctic regions of North America, extending north onto the Lo w Arctic of the Canadian Shield and south along the west coast of Oregon, R ocky Mountains of Wyoming, and Appalachians of West Virginia. Iii addition, short pocosins found along the southeastern coast also can be considered a s Sphagnum-dominated peatlands, even though they differ significantly from traditional concepts of boreal peatlands. Along the southern limit of Sphag num-dominated peatlands, where climate is limiting, edaphic factors allow f or the development of outliers. As the current distribution of Sphagnum-dom inated peatlands is related to Sphagnum spore rain, past distributions of S phagnum-dominated peatlands can be constructed from spore records preserved in lakes and peatlands. Here we present six time slices extending back to the Last Glacial Maximum to determine how Sphagnum-dominated peatlands have varied in both time and space. The spore record indicates that Sphagnum-do minated peatlands were present in North America during the Last Glacial Max imum although they were spatially limited to central Alaska, the Olympic Pe ninsula and Puget Trough of Washington, and to a narrow band ill the easter n states of Kentucky, North Carolina, Tennessee, and Maryland. During the L ate Wisconsinan Sphagnum-dominated peatlands shifted northwards in eastern North America and expanded farther into Alaska and the Midwest. The Late Wi sconsin/Holocene transition marks a time of overall increase in the area su pporting Sphagnum-dominated peatlands, While extending farther ill eastern Canada and western continental and coastal regions, they almost completely disappear in the Midwest where they were extensive Earlier. Sphagnum-domina ted peatlands generally reach their current extent about 2,000-3,000 years ago. Sphagnum-dominated peatlands have dramatically changed their distribut ion and abundance since the Last Glacial Maximum, and hence the carbon that is stored in these present-day important sinks has also changed dramatical ly. When compared to the estimated 220 Pg of carbon stored in North America n peatlands today: less than 10% of this carbon was present in these peatla nd during the LGM.