Impacts of Truck Traffic across Unfrozen Tundra near Toolik Lake, Alaska

In September 2006, caribou hunters illegally drove 2 vehicles across unfrozen tundra on land managed by the U.S. Bureau of Land Management in the Toolik Lake Area of Critical Environmental Concern on Alaska's North Slope. The vehicles became stuck in the tundra and were eventually excavated from frozen ground in April 2007. The extent of the impacts were evaluated in July 2007 and reevaluated in July 2008. The level of disturbance, as measured by categorical classes, thaw depth, and surface elevation, all increased significantly between years. The truck trails impacted 1457 m2 of tundra. Habitat disturbance was quantified at 5 different levels with Level 1 being the least disturbed and Level 5 the most disturbed. In 2008 most of the trails (61 %) were Level 2 disturbance, while 25% were Level 1, 8% were Level 3, 3% were Level 4, and 2% were Level 5. Since the previous year, the trails had become deeper, more water-filled, and also more visually evident. The excavation sites measured approximately 75 m2 each, with 25 m2 and 36 m2 of Level 5 disturbance at the close and far excavations, respectively. In contrast to 2007, areas with Level 5 disturbance were covered with water in 2008. Soil thaw depths were significantly deeper on the disturbed areas than at the control areas for most transects, and deeper in 2008 than 2007. Similarly, surface profile elevations were lower in the disturbed areas than the control areas, and lower in 2008 than 2007. Future monitoring is recommended for 2012 and 2017, 5 and 10 years from the initial disturbance.