8 J. Brown et al. 



Prudhoe Bay — have only a limited subset of its total flora. This is a re- 

 flection of the particularly severe summer climatic conditions that exist 

 near the coast, but moderate inland across the plain to the south. This 

 zone of littoral tundra (Figure 1-1) is characterized by low species diver- 

 sity, dominance of grasses and sedges (Cantlon 1961), rarity of tussock 

 tundra, and the absence of erect shrubs. The limit of littoral tundra fol- 

 lows roughly the 7°C July mean temperature isotherm. 



The floras of the coastal tundras at Barrow and at Prudhoe Bay are 

 strikingly dissimilar, with Sc^renson Coefficients of Similarity (Sdrenson 

 1948) that are much lower than those describing the comparisons be- 

 tween provinces (Table 1-2). The Barrow peninsula is dominated by wet, 

 acid soils. The Prudhoe Bay region, in contrast, is influenced by two 

 large rivers, the Sagavanirktok and Kuparuk, that originate in the moun- 

 tains and contribute carbonates to the soils. However, even in this 

 region, acid soils occur beyond the influence of the rivers. 



Differences in parent materials and topography have a marked ef- 

 fect on the vegetation of the two regions. The lichen genera Cladina and 

 Cladonia, which are associated with acid soils, are represented by 19 taxa 

 in the Barrow region, but only 4 at Prudhoe Bay. The species Collema 

 tunaeforme, Evernia perfragilis and Fulgensia bracteata, which are char- 

 acteristic of calcareous substrates, are present at Prudhoe Bay but not at 

 Barrow. The absence of sphagnum mosses and the scarcity of polytrica- 

 ceous mosses around Prudhoe Bay are examples of probable pH control 

 of distribution in the bryoflora (Steere 1978a). The effect of pH on 

 vascular plants is noticeable in the distribution of Carex species; the cal- 

 ciphiles C. atrofusca, C. membranacea and C. misandra are common in 

 the vicinity of Prudhoe Bay but are absent from the Barrow area (Mur- 

 ray 1978, Walker and Webber 1979). A rich arctic-alpine floristic ele- 

 ment is found on the numerous exposed and well-drained habitats that 

 form on the coarse-textured soils of river banks, gravel bars, dunes and 

 pingos close to Prudhoe Bay. The vegetation in this area shows a greater 

 affinity with that of more southerly tundra than does the vegetation of 

 the Barrow peninsula. 



The terrestrial vertebrate fauna of northern Alaska is composed en- 

 tirely of homeothermic birds and mammals and lacks the heterothermic 

 reptiles and amphibians which extend well into the Asian Arctic. Pitelka 

 (1974) listed 189 species of birds for the Arctic Slope, 76 of which are 

 considered to be regular breeders (Table 1-2). Because of the mobility of 

 birds, there are many records of accidental or casual visitors to the Arctic 

 Slope. The number of species is very similar in the three physiographic 

 provinces: 45 species are found in both the Coastal Plain and Foothills, 

 and 50 in the Brooks Range. However, the composition of the bird fauna 

 changes considerably from the coast to the mountains. Thirty species of 

 waterfowl and shorebirds and three species of passerine birds occur on 



