Biophysical Processes and Primary Production 71 



and dead material. At peak season the average dry weight of above- 

 ground plant material was: graminoid biomass 35 gdw m'\ forb biomass 

 4 g m'\ woody dicotyledon biomass 16 g m"^ bryophyte biomass 117 g 

 m'\ lichen biomass 28 g m'\ vascular standing dead 36 g m"^ vascular 

 litter and prostrate dead 91 g m"^ and belowground intact dead 4116 g 

 m'^ The aboveground vascular standing crop averaged 54 gdw m"^ and 

 ranged between 19 and 119 gdw m"^ depending on the vegetation type. 



Primary productivity in the Carex-Oncophorus meadow vegetation 

 type (Biome research site 2) was estimated from cuvette photosynthesis 

 measurements on vascular plants and mosses, by canopy photosynthesis 

 models for vascular plants and mosses, and by the aerodynamic method. 

 In this vegetation type, gross primary productivity, estimated by the har- 

 vest method and by respiration costs, was 450 gdw m"^ yr"', including 414 

 gdw m"^ yr"' for vascular plants and 36 gdw m~^ yr"' for mosses. Net pri- 

 mary productivity was 209 gdw m"^ yr"', including 187 gdw m"^ yr"' for 

 vascular plants and 22 gdw m"^ yr"' for mosses. The respiratory cost for 

 growth of above- and belowground tissues was 57 gdw m"^ yr"', and the 

 respiratory cost for maintaining these tissues was 170 gdw m"^ yr"'. The 

 growth and maintenance costs for mosses were 6.6 gdw m"^ yr"' and 7.2 

 gdw m"^ yr"', respectively. 



The gross primary productivity for vascular plants of 414 gdw m"^ 

 yr"' was equivalent to a carbon dioxide uptake of 609 g CO: m'^ yr"'. 

 The conversion was made using glucose as a base to be consistent with 

 the calculation of growth respiration (Penning de Vries 1974). Based on 

 his cuvette measurements, Tieszen (1975) estimated carbon dioxide up- 

 take at 602 g CO2 m"^ yr"'. Using the canopy photosynthesis model Miller 

 et al. (1976) estimated 610 g CO2 m'^ yr"'. The simulated gross primary 

 productivity for mosses was equivalent to a carbon dioxide uptake of 53 

 g CO2 m"^ yr"' (Miller et al. 1978a), which is only slightly lower than the 

 cuvette measurement of Oechel and Sveinbjbrnsson (1978) of 57 g CO2 

 m"^ yr"'. The gross primary productivity for the community of vascular 

 plants and mosses was 667 g CO2 m"^ yr"', which was similar to the 

 estimate by the aerodynamic method (Coyne and Kelley 1975) of 632 g 

 CO2 m"^ yr"'. The general agreement of these estimates for Biome re- 

 search site 2 gives support to the calculations for the other vegetation 

 types and for the coastal tundra at Barrow as a whole. 



Seasonal Progression of Primary Productivity 



The seasonal progression of primary productivity was estimated in 

 the Carex-Oncophorus meadow (site 2) by periodic harvests of above- 

 ground material, periodic photosynthesis measurements in cuvettes, 

 simulations based on photosynthesis, light and temperature relations, 



