The Vegetation: Pattern and Succession 215 



lake basins occurs by seedling establishment within 10 to 20 years in the 

 Barrow area (Dennis 1968), seeding with grasses of temperate origin has 

 often been attempted to speed the revegetation process in areas disturbed 

 by man. These grasses have higher nutrient and soil temperature require- 

 ments than most native tundra graminoids (Chapter 5; McCown 1978) 

 and become established only with heavy and repeated fertilization 

 (Mitchell 1973, Younkin 1976, Van Cleve 1977). Such grasses are often 

 effective in stopping erosion but generally slow down reinvasion by 

 native species (Hernandez 1973, Younkin 1976, Johnson and Van Cleve 

 1976). The fertilization required to maintain cover of temperate-origin 

 grasses may have secondary effects such as attraction of herbivores and 

 eutrophication of adjacent aquatic systems. 



Oil Spills 



Oil is an environmental factor foreign to most tundra communities, 

 so that recovery from oil spills cannot be readily predicted from our 

 knowledge of the responsiveness of the natural vegetation. Alaskan 

 crude oil and fuel oil are toxic to plant leaves, but if the oil does not pene- 

 trate the soil, the tundra system responds much as it would following 

 lOO^Vo defoliation by lemmings (Figure 6-12). There is a temporary de- 

 crease in albedo and increased heating of the soil (Haag and Bliss 1974, 

 Everett 1978), but regrowth of the vegetation allows the community to 

 approach its original condition within a few years. Flooding of the com- 

 munity with water largely prevents oil penetration into the soil until toxic 

 volatile fractions have evaporated and thereby minimizes the local im- 

 pact of an oil spill. 



Most of the live biomass of all trophic groups in the coastal tundra 

 at Barrow is in the top 10 cm of the soil and is rapidly killed if oil pene- 

 trates into the soil before toxic volatile fractions evaporate (Jenkins et al. 

 1978). In wet soils, oil penetrates more slowly, much of the toxic fraction 

 evaporates, and less vegetation dies than in dry sites (Walker et al. 1978). 

 Species differ in their sensitivity to oil, and often the response is seen as 

 decreased winter hardiness rather than as immediate mortality (Deneke 

 et al. 1975, Linkins and Ant'bus 1978). 



Other effects of oil upon system function are more subtle but equal- 

 ly important. Hydrocarbons may remain in the active layer for at least 30 

 years after an oil spill (Lawson et al. 1978). Addition of a large carbon- 

 rich, nutrient-poor substrate to the soil increases the demands of mi- 

 crobes for nutrients from the available soil pools so that nutrients 

 become less available to vascular plants. Moreover, oil kills at least cer- 

 tain mycorrhizal fungi, further decreasing the ability of plants to extract 

 nutrients from the soil (Antibus and Linkins 1978). Thus, oil may effec- 



