Carbon and Nutrient Budgets 459 



pool sizes (Chapter 3, Table 12-2). The Carex-Oncophorus meadow 

 values are based upon more thorough study and may thus be more accu- 

 rate, whereas the data for the mosaic of wet meadow vegetation types are 

 more representative of the coastal tundra of northern Alaska. Unless 

 otherwise specified (e.g. Table 12-2) data refer to the Carex-Oncophorus 

 meadow. 



Although relatively little carbon is fixed by tundra vegetation in any 

 one year, up to 20 kg m"^ of carbon has accumulated in the top 20 cm of 

 tundra (Table 12-1). This is similar to the carbon content of other wet 

 tundras (17 to 32 kg m'^), tropical rain forests (17 to 34 kg m"^) and a red 

 alder shrub stand (20 kg m"-). It is greater than the carbon accumulation 

 in grassland (3 kg m"^), chaparral (6 kg m"^), and a Douglas fir forest (12 

 kg m"^) (Table 12-1). Many tundra communities, including those near 

 Barrow, have buried organic horizons preserved in the permafrost. Tem- 

 perate communities with their deeper soil profiles often contain consider- 

 able carbon which has been leached from upper horizons and thus also 

 have more total carbon than is shown in Table 12-1 . Because tundra con- 

 stitutes a significant fraction (5%) of the total terrestrial landscape 

 (Whittaker 1975) and because wet and moist tundra (including coastal 

 and tussock tundra) make up a substantial proportion of all tundra com- 

 munities, a major alteration of the carbon balance of tundra could sig- 

 nificantly modify the global carbon balance. 



Tundra differs from most other ecosystems in that the bulk of its 

 carbon is contained in soil, rather than in live biomass (Table 12-1; 

 Schlesinger 1977). At Barrow over 96% of the organic carbon is bound in 

 dead organic matter or peat, and only 1 .7% or less is in living organisms. 

 The remainder is dead plant parts. In contrast, 50 to 75% of the organic 

 carbon in forests and 10% of the carbon in grasslands is in living organ- 

 isms (Table 12-1). This implicates decomposer organisms as a major 

 bottleneck for carbon and energy flow at Barrow and other wet tundra 

 sites. Like the tundra, mid-latitude grasslands contain a substantial pro- 

 portion of carbon in dead organic matter. But in grasslands, roots pene- 

 trate 1 to 2 m so that carbon from dead roots and associated microorgan- 

 isms is distributed throughout the soil (Weaver 1958, Clark 1977). In 

 contrast, tundra soils typically exhibit a distinct surface horizon 10 to 20 

 cm thick, in which the percentage of organic matter is 90 to 96%. Such 

 high concentrations of organic matter are associated with low pH and 

 consequently with reduced nutrient availability, as discussed in Chapters 

 7 and 8. 



Most of the carbon in living organisms is in plants, and most of this 

 is below ground in roots and rhizomes (Figure 12-1, Table 12-2). The 

 average aboveground vascular standing crop for the coastal tundra at 

 Barrow is 24 g C m'^ (Table 12-2), half that of the intensive study site 

 (Figure 12-1). The greater vascular aboveground standing crop in the 



