212 P.J. Webber et al. 



Vehicle Tracks 



Human impact in the Arctic is a subject of current concern because 

 of both increasing human activity associated with arctic resource devel- 

 opment and the unexpectedly severe ecological impact of human activity 

 over the past 25 years. The severity of vehicle impacts upon tundra de- 

 pends upon the nature of both the disturbance and the community and 

 can be predicted from an understanding of natural and controlled pertur- 

 bations of tundra (Figure 6-11). 



Vegetation changes triggered by tracked vehicle damage and by 

 water impoundments resulting from road construction fit into the thaw 

 lake successional scheme presented here (Figure 6-9). Total destruction 

 of any vegetation type because of catastrophic thermokarst activity leads 

 to either the alluvium or the thaw lake starting points. Most commonly, 

 water impoundment results in deepening of troughs through partial ice- 

 wedge melting. In some instances this has caused both drier inter-trough 

 areas and wetter trough areas. For example, at one site following disturb- 

 ance by tracked vehicles the vegetation type has changed from the Du- 

 pontia meadow to both the Carex-Oncophorus meadow and the Arcto- 

 phila pond margin, and from the Carex-Oncophorus meadow to both 

 the Carex meadow and the Dupontia meadow. Vegetation changes may 

 occur within a very few years. 



Multiple passes by ACV's or a single pass by a Rolligon (balloon-tire 

 vehicle) produce similar effects in winter or early spring. However, if the 

 traffic occurs during the summer months, live vascular plants and mosses 

 are crushed; passage of a wheeled vehicle may also produce some depres- 

 sion of the tundra surface (Abele et al. 1978, Everett et al. 1978). Soil 

 temperature and, in following years, depth of thaw, nutrient availability 

 and primary production increase. Recovery time is estimated at 2 to 4 

 years and is comparable to that associated with intense winter grazing by 

 lemmings (Bliss and Wein 1972, Hernandez 1973, Wein and BHss 1974, 

 ChaUinor and Gersper 1975, Gersper and Challinor 1975, Brown and 

 Grave 1979). The effect is greater in shrub tundra due to greater break- 

 age of rigid stems, and recovery time is longer. Vehicle passage with 

 greater frequency and later in the season increases damage to live leaves, 

 prolongs recovery, and makes the impact more nearly comparable to that 

 of summer lemming grazing by removing productive tissue and decreas- 

 ing primary production. 



Use of tracked vehicles, or repeated passage by low pressure wheeled 

 vehicles, frequently compacts the low-bulk-density organic mat and de- 

 presses the soil surface below the water table, particularly in poorly 

 drained meadow soils (Gersper and Challinor 1975). Standing water de- 

 creases albedo and increases soil temperature and thawing of permafrost, 



