464 F. S. Chapin III et al. 



11). The standing crop of lemmings, the only major herbivore, ranges 

 from 0.00002 to 0.12 g C m "^ depending upon the stage in the lemming 

 cycle. Carnivorous birds attain a maximum standing crop of only 

 1.4x10* g C m"^ The small size of the herbivore-based relative to the 

 saprovore-based trophic system emphasizes the importance of below- 

 ground interactions in the Barrow region. 



The amounts of nitrogen and phosphorus in the coastal tundra at 

 Barrow are comparable to those in other ecosystems (Table 12-1). In 

 fact, tundra communities generally have more accumulated nitrogen (960 

 g N m'^ at Barrow) than do temperate systems, including grasslands (270 

 g N m-^), alder shrub (700 g N m"^), Douglas fir forest (250 g N m"'), and 

 oak forest (250 g N m"^). The parent materials of tundra soils at Barrow 

 are not unusually phosphorus-deficient, because they are derived largely 

 from marine sediments (Chapter 1). Limitation of primary production 

 by nitrogen and phosphorus (Chapter 5) is thus not a result of small 

 quantities in the system but rather of their slow rate of cycling. It should 

 be noted that in tundra permafrost limits the quantity of nutrients avail- 

 able for exploitation whereas deeper soil horizons often play an impor- 

 tant role in long-term replenishment in temperate and tropical ecosys- 

 tems. As with carbon, the proportion of nutrients in the living compo- 

 nents of the tundra system is quite small, approximately 1% in the case 

 of nitrogen and phosphorus. This is typical of wet tundra (e.g. Babb and 

 Whitfield 1977, Dowding et al. 1981) and differs from forests, where the 

 biota constitute a significant reservoir of nutrients (Table 12-1). 



Tundra thus appears to represent an end-point on the latitudinal 

 spectrum by having the smallest proportion of the system's nutrient capi- 

 tal tied up in live biomass. Ovington (1968), Marks and Bormann (1972), 

 and Whittaker et al. (1979) have pointed out the importance of vegeta- 

 tion as a nutrient reservoir that retains nutrients within the system by ab- 

 sorption from soil and internal recycling. In the tundra it is primarily the 

 dead soil organic matter that serves this function by structurally binding 

 a large proportion of the nutrients, by providing exchange sites for ca- 

 tions that otherwise would move through the soil during runoff, and by 

 physically preventing thermokarst (thawing and subsidence) and erosion 

 of the underlying mineral soils. 



The distribution of nitrogen and phosphorus among biomass com- 

 partments follows a pattern similar to that of carbon. However, living 

 soil organisms, microbes plus invertebrates, contain 8% of the nitrogen 

 and 18% of the phosphorus, but only 2.5% of the carbon in living mate- 

 rial. The live belowground vegetation contains almost 80% of the carbon 

 but only 68% of the nitrogen and less than 60% of the phosphorus in liv- 

 ing material. Thus, soil organisms are more concentrated sources of nu- 

 trients than are plants or plant-derived detritus, and form the major 

 avenue of nutrient and energy flow through the saprovore-based trophic 



