Introduction and Site Description 39 



day. The leaves of the dominant graminoids are inclined at 65° from the 

 horizontal; at the low solar altitude at Barrow (averaging 25° on 21 June), 

 the erect leaves intercept almost all the solar radiation. 



Herbivores 



The brown lemming {Lemmus sibericus) is by far the dominant 

 consumer at Barrow (Pitelka 1973). One leafhopper (Homoptera) and one 

 leaf beetle do occur and root-piercing nematodes are present, but their 

 impact on the vegetation is slight. In years when lemmings are abundant 

 (Figure 2-6), every 2 to 5 years, their impact is great. Because they do not 

 hibernate, they are active during winter and even reproduce as soon as 

 there is a protective layer of snow (MacLean et al. 1974). By the end of the 

 winter and before a summer high, the lemmings are at peak abundance 

 and will have completely cut all standing plants. This accounts for 40% of 

 the previous season's production; even more important, the lemmings eat 

 the stem bases and parts of the rhizomes, which slows down the initial 

 growth of plants in the spring. Usually, the population declines throughout 

 the summer follo\ying a spring high and about 25% of the primary 

 production is consumed. At low population levels, lemmings consume 

 about 0.1% of the total aboveground production. 



Lemming grazing may sustain the monocotyledon dominance at 

 Barrow. Some adaptations of these plants, such as vegetative reproduction 



Year 



FIGURE 2-6. Abundance of lemmings at Barrow (based on trapline data 

 from Pitelka 1973). Bars indicate summer. (After Bunnell et al. 1975.) 



