48 J. E. Hobbie 



are saturated and ponds easily form. They are particularly abundant in old 

 lake beds where ice wedges form in the soil and eventually push up the 

 overlying soil into a ridge a few centimeters high. The ice wedges and 

 ridges form connected polygons with "diameters" of 20 to 50 m. Each 

 polygon is a separated basin; many contain ponds that form when the soil 

 subsides due to destruction of the insulating vegetation. 



The average temperature at Barrow is — 12.4°C while the summer 

 temperature averages are —7.3°, 0.9°, 4,1°, 3.3°, and —0.9° for May, June, 

 July, August, and September. Approximately 50% of the 10.8 cm of 

 annual precipitation falls in June, July, and August. Solar radiation in the 

 summer is reduced by the cloudy and foggy weather so that most of the 

 annual radiation occurs before the ponds melt. Winds are almost continual 

 during the summer at 6 m sec ~ ' from the east. Microinversions frequently 

 occur over a pond, however, so the wind speed at the water surface may be 

 only one-third the recorded speed. 



Snow normally reflects more than 85% of the solar radiation; in early 

 June when the snow begins to melt and becomes saturated with water, the 

 albedo drops to around 50% and the snow rapidly melts. Within a few days 

 the snow is gone and the pond ice begins to melt. This melting is complete 

 in 4 days. Lake ice is 2 m thick so does not disappear until mid- or late 

 July. 



The soils of the IBP site are highly organic, acid, and not very fertile. 

 Nitrogen and phosphorus are abundant but are tied up in organic matter. 

 Soil temperatures may reach 25°C at the surface while the horizons 20 to 

 30 cm below are at 2°C. There is some surface drying but soils are 

 saturated below 4 cm. 



The tundra vegetation at the site is a yellow-brown grassland. All 

 plants are short (10-15 cm) and the large amount of standing dead 

 vegetation hides the green plants. Although there are over 100 species of 

 vascular plants, a few grasses and sedges dominate: Carex aquatilis, 

 triophorum angustifolium, Poa arctica. and Dupontiafisheh. New leaves 

 sprout from green tissue at the base of the plant stems as soon as the snow 

 melts. Rapid growth occurs until about 1 August when the peak 

 aboveground standing crop (new growth) of 60 to 100 g m "Ms reached. 

 Production is reduced during lemming highs by summer grazing on stems 

 and leaves and by winter feeding on the green stem bases. Roots live 2 to 

 10 years; their biomass is 10 times the aboveground weight and production 

 is about 65 g m " ^ All reproduction is vegetative. 



Mosses and lichens are also abundant. Moss and liverwort production 

 may be as high as 160 g m '^ yr~' in wet meadows; lichen productivity is 

 low but biomass may exceed 50 g m '^ 



Plant adaptations to the arctic environment include the ability to 

 translocate carbohydrates and nutrients at 0°C, a low compensation level 

 so that net photosynthesis proceeds for 24 hours a day, and an average leaf 

 inclination (65° from the horizontal) that allows almost complete 

 interception of the low-angle solar radiation. 



