APPENDIX B: THE BARROW WORD MODEL 



The International Tundra Steering Conunittee of IBP has recommended 

 that a narrative description or word model be prepared for each national 

 site. This word model revised in September 1970, summarizes the current 

 understanding of how the wet arctic tundra ecosystem is structured and 

 how it functions. Such word models permit initial circumpolar compari- 

 sons among sites and provide the basis from which predictable models will 

 be constructed. The following represents the contributions of numerous 

 U.S. scientists who have carried out independent research at Barrow over 

 the years . 



The arctic tundra near Barrow, Alaska, encompasses a complex of habi- 

 tats arrayed along a moisture-dominated gradient. Vegetation and soils 

 are distributed along micro-, meso-, and macro-environments according to 

 type and size of polygons, regional relief, and land form type. These 

 range from upland meadow communities (arctic brown and upland tundra 

 soils) to wet meadow and marsh types (meadow and bog soils) to emergent 

 aquatics (hydrosols) and open water in small ponds and lakes. Ponds, an 

 integral aspect of all principal habitats, show various stages of succes- 

 sion resulting from both filling and erosion. Large shallow lakes occupy 

 30% of the area north of 71 latitude. These vegetation, soils, micro- 

 relief and aquatic environments form a complex mosaic which influences 

 plant productivity and animal population and diversity throughout the 

 year. Ridges, polygon tops, and slopes commonly contain in decreasing 

 order of occurrence Carex aquatilis , Petasites f rigidu s , Salix pulchra , 

 Arctagrostis latifolia , Poa arctica , Luzula confusa , Salix rotundifolia , 

 and Eriophorum scheuchzeri . Dupontia f isheri , Carex aquatilis , Eriophorum 

 angustifolium and E^. scheuchzeri , Petasites f rigidus , and Poa arctica 

 occur in meadows and wet polygonal troughs . Arctophila fulva is found in 

 shallow ponds. 



Primary production during the 45- to 90-day growing season is con- 

 trolled by a combination of temperature, soil moisture, day length and 

 nutrient supply. Production varies from a low of approximately 20 g dry 

 weight/m on dry exposed ridges and eroding high center polygons to maxi- 

 mum values of 200 g/m'^ in wet terrestrial habitats. Thus, the more pro- 

 ductive habitats on micro- and meso-scales are near the wetter end of the 

 soil moisture gradient (meadows and polygon troughs). The mean above- 

 ground production for all community type ranges between 70 and 110 g/m . 

 This is associated with a live leaf area index of about 1.2. The majority 

 of this leaf area is positioned within 5 cm of the soil surface. Maxi- 

 mum production is usually attained 50 days after snowmelt, although some 

 leaf senescence at the bottom of the canopy occurs 30 days after snow- 

 melt. All habitats are controlled by the presence of permafrost (0°C 

 ground temperature or colder) near the surface throughout the growing 

 season. 



Especially significant to the amount of seasonal primary production 

 are the climatic conditions of the first two or three weeks of the growing 

 season, the previous summer's stored reserves, and environmental factors 



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