Ninth International Conference on Permafrost ... - IARC Research

Long-Term Winter Seismic Vehicle Impacts in Permafrost TerrainJanet C. JorgensonArctic National Wildlife Refuge, U.S. Fish and Wildlife ServiceSeismic exploration was conducted on the coastal plainof the Arctic National Wildlife Refuge, Alaska, during thewinters of 1984 and 1985. Approximately 2000 km of seismicline were completed in a 5 x 20 km grid. At least 2000 kmof additional trails were created adjacent to the seismic linesby D-7 Caterpillar tractors, pulling ski-mounted trailersbetween camps. U.S. Fish and Wildlife Service initiated amonitoring program in 1984 to document vegetation and soildisturbance and natural recovery (Felix & Raynolds 1989,Emers & Jorgenson 1997).Color-infrared aerial photographs were taken of 20% ofthe trails in 1985 and 1988, and disturbance levels werephoto-interpreted at 4914 systematic plots (Raynolds & Felix1989). A two-stage cluster sample was used to randomlychoose 200 of the plots to monitor in the field. Twenty 3-kmtransects, each consisting of ten 18-m diameter circularplots spaced 300 m apart, were randomly selected. A semiquantitativesystem for ranking vehicle disturbance based onvegetation and soil changes was used. Ranks were assignedinitially in 1985 by photo-interpretation and subsequently byfield evaluations in 1989, 1993, 1998, 2002, and 2005. Allplots were visited in 1989. From 1993 to 2005, plots ratedas undisturbed in a previous year were assumed to remainundisturbed thereafter and were not revisited.Disturbance and recovery were summarized by trail type(seismic line or camp-move trail) and vegetation types,which included Wet Sedge Tundra, Moist Sedge-WillowTundra, Moist Sedge-Dryas Tundra, Moist Sedge-Tussocktundra, Low Shrub Tundra on high-centered polygons,Riparian Shrublands, and Partially Vegetated. The vegetationtype Dryas River Terrace was not represented in the 200-plot sample, but data were available from the larger photointerpretedsample. Ten Dryas River Terrace plots werevisited in 2007 to assess recovery.Snow was usually less than 30 cm deep and did not providecomplete protection from vehicle damage. The followingsummer, most trails had at least some scuffing of vegetationand deeper summer-thawed soil. The greatest damage wasdestruction of shrubs and sedge tussocks, scraping of groundcover to bare soil, and standing water on trails. TussockTundra, Low Shrub Tundra, and Dryas River Terrace werethe vegetation types with the highest initial disturbance.About one-half of these plots had medium- and high-leveldisturbance in 1985. Sedge-Dryas Tundra and Sedge-Willow Tundra were intermediate in disturbance levels, withmedium- and high-level disturbance found at about onethirdof the plots. Medium- and high-level disturbance wasabsent in Riparian Shrublands, which collect deep snow, andoccurred in