B51G-0510
Thermokarst Rates Intensify Due to Climate Change and Forest Fragmentation in an Alaskan Boreal Forest Lowland
Friday, 18 December 2015
Poster Hall (Moscone South)
Mark J Lara1, Helene Genet1, Anthony David McGuire2, Eugenie Susanne Euskirchen1, Yujin Zhang3, Dana Nossov Brown1, Torre Jorgenson4, Vladimir E Romanovsky1, Amy Lynn Breen5 and William R Bolton1, (1)University of Alaska Fairbanks, Fairbanks, AK, United States, (2)University of Alaska Fairbanks, Institute of Arctic Biology, Fairbanks, AK, United States, (3)Organization Not Listed, Washington, DC, United States, (4)Alaska Ecoscience, Fairbanks, AK, United States, (5)University of Alaska Fairbanks, Scenarios Network for Alaska & Arctic Planning, Fairbanks, AK, United States
Abstract:
Lowland boreal forest ecosystems in Alaska are dominated by wetlands comprised of a complex mosaic of fens, collapse scar-bogs, low shrub/scrub, and forests growing on elevated ice rich permafrost soils. Thermokarst has affected the lowlands of the Tanana Flats in central Alaska for centuries, as thawing permafrost collapses forests that transition to wetlands. Located within the discontinuous permafrost zone, this region has significantly warmed over the past half-century, and much of these carbon-rich permafrost soils are now within ~0.5o C of thawing. Increases in the collapse of lowland boreal forests in response to warming may have consequences for the climate system. This study evaluates the trajectories and potential drivers of 60 years of forest change in a landscape subjected to permafrost thaw in unburned dominant forest types (paper birch and black spruce) associated with location on elevated permafrost plateau and across multiple time periods (1949, 1978, 1986, 1998 and 2009) using historical and contemporary aerial and satellite images for change detection. We developed (i) a deterministic statistical model to evaluate the potential climatic controls on forest change using gradient boosting and regression tree analysis, and (ii) a 30x30 m land cover map of the Tanana Flats to estimate the potential landscape-level losses of forest area due to thermokarst from 1949 to 2009. Over the 60-year period, we observed a nonlinear loss of birch forests and a relatively continuous gain of spruce forest associated with thermokarst and forest succession, respectively. Gradient boosting and regression tree models identify precipitation and forest fragmentation as the primary factors controlling birch and spruce forest change, respectively. Between 1950-2009 landscape-level analysis estimates a transition of ~15 km² of birch forest area to wetlands on the Tanana Flats, where the greatest change followed warm periods. This work highlights the vulnerability of lowland ice-rich permafrost ecosystems to recent and ongoing climate change.
