214 P.J. Webber et al. 



nutrient availability, and changes community composition to that char- 

 acteristic of wetter sites. Such communities are generally highly produc- 

 tive (Hernandez 1973, Wein and Bliss 1974). Drainage patterns also 

 change naturally in tundra, with consequences similar to those described 

 above, and are part of the thaw lake cycle (Britton 1957). Both natural 

 and man-induced changes lead to irreversible permanent changes in the 

 natural community, and recovery may require thousands of years until 

 the landscape is modified by the thaw lake cycle. Vehicle impact upon 

 various tundra communities can be predicted and mapped in order to 

 manage vehicle use in areas of development (Everett et al. 1978, Webber 

 and Ives 1978). 



Vegetation and Organic Mat Removal 



In general, tundra graminoids, if defoliated, regrow readily from 

 belowground stems and rhizomes, especially in wet sites. Simulations 

 suggest that wet meadow tundra can tolerate 50% foliage removal and 

 still recover in 3 to 5 years. This situation is comparable to that which oc- 

 curs naturally during lemming cycles (Bliss 1970, Babb and Bliss 1974). 

 Vegetation in xeric sites generally recovers more slowly because of lower 

 productivity, slower nutrient cycling, and greater exposure of dry-site 

 species (e.g. evergreen shrubs) to disturbance (Hernandez 1973, Babb 

 and Bliss 1974, Van Cleve 1977). The most serious consequences of re- 

 moving aboveground vegetation are decreased albedo and increased heat 

 penetration into the soil, which leads to thawing of permafrost, as de- 

 scribed above, especially in wet sites. 



The highly organic surface soil horizons of wet coastal tundra at 

 Barrow serve an important function in nutrient retention. Removal of 

 this organic mat from the tundra surface not only eliminates potentially 

 resprouting vegetation but also removes a large proportion of the ac- 

 cumulated nutrient capital and most of the cation exchange capacity of 

 the soil system. The 40 to 60% of the accumulated system nitrogen that is 

 contained in the organic horizon of several tundra sites would require 

 5,000 to 10,000 years to replenish at current fixation rates (Chapin and 

 Van Cleve 1978). In ice-rich permafrost, thermokarst continues over dec- 

 ades and relatively flat areas are recolonized by the native vegetation 

 (Lawson et al. 1978). Perhaps the most serious consequence of organic 

 mat removal has been serious erosion following thawing of permafrost 

 on sloping terrain. An aquatic or emergent vegetation may eventually 

 stabilize such erosion patterns (Hok 1969, Hernandez 1973, Haag and 

 Bliss 1974), but the system probably will not return to its former state for 

 thousands of years. 



Although revegetation of naturally disturbed sites such as drained 



