The Vegetation: Pattern and Succession 213 



Original terrestrial community in equilibrium 



Wheeled or 

 tracked 



Depressed 



vegetative 



mat 



Increased soil 

 temperature 



Increased 

 thaw 



Increased 



nutrient 



availability 



ACCESS 



Increased plant 

 production 



5-15 years 



Off-road vehicles 



Soil compaction; 

 depressed soil surface 



Modified 

 drainage 



Increased soil 

 temperature 



Erosion 



Increased 

 thaw 



Thermokarst 

 and ponding 



Aquatic or emergent 

 community 



100's to 1000'sof years 



ACV 



Removal of 

 standing dead 

 from canopy 



Slightly increased 

 soil temperature 



Increased 

 thaw 



Increased 



nutrient 



availability 



Increased plant 

 production 



2-4 years 



New terrestrial communities in equilibrium 



FIGURE 6-11. Impact of air cushion vehicles (ACV) and wheeled and 

 tracked vehicles upon the coastal tundra at Barrow. Recovery times are 

 estimated from observations by Hok (1969), Hernandez (1973), Rickard 

 and Brown (1974), Abele et al. (1978), and Lawson et al. (1978). 



causing increases in nutrient availability and primary production as well 

 as further subsidence of the soil surface. Where the vehicle track crosses 

 ice wedges or ice lenses, deep permanent ponds may form (Kryuchkov 

 1976, Peterson 1978). Sites with low ice content are less susceptible to 

 this positive feedback and ponding (Webber and Ives 1978). On slopes, 

 compaction by vehicles promotes drainage of water from surrounding 

 areas, and thus speeds decomposition and permafrost thawing, increases 



