Biophysical Processes and Primary Production 69 



types recognized at Barrow, weighted by the surface area of each type 

 (Table 3-1). 



Net aboveground primary production of vascular plants at Barrow 

 in 1972, estimated by the harvest method and averaged according to the 

 relative surface area of the different vegetation types, was 42 gdw m"^ 

 (Webber 1978, Table 3-1). Aboveground production of vascular plants 

 ranged between 18 gdw m"^ for Luzula heath and 115 gdw m"^ for Arcto- 

 phila pond margins. Eighty-four percent of the area had aboveground 

 vascular plant production of 39 to 51 gdw m"^ Although the average 

 productivity within a tundra region is frequently near the low end of the 

 range of productivities of the vegetation types in that region (Beschel 

 1970, Webber 1971), the average in the coastal tundra at Barrow is near 

 the middle of the range for the vegetation types near Barrow because this 

 area is dominated by reasonably productive vegetation types. The least 

 productive vegetation type, the Luzula heath, occupies 3% of the entire 

 area. 



Aboveground vascular plant productivity increased along a mois- 

 ture gradient from the tops of high-centered polygons to pond and stream 

 margins. The wetter areas have reduced soils and moderately high phos- 

 phate levels and are dominated by graminoids. The productivity of forbs 

 was highest in dry areas with moderate levels of phosphate and more ox- 

 idized soils, but productivity rarely exceeded 6 gdw m"^ yr"'. The produc- 

 tivity of woody dicotyledons was also highest in dry oxidized areas with 

 moderate levels of phosphate, and was about 20 gdw m"^ yr'. Bryophyte 

 productivity, calculated as 56% of the green biomass or about 66 gdw 

 m'^ yr"' (Oechel and Sveinbjbrnsson 1978), differed widely in the differ- 

 ent vegetation types, with the highest rates in the mesic meadow where 

 many acrocarpous mosses such as Dicranum elongatum and Pogonatum 

 alpinum are abundant. The principal factor controlling the distribution 

 of bryophytes appears to be slight differences in microrelief, moderated 

 by the vascular plant canopy, which influence the moss and soil moisture 

 regimes (Webber 1978, Oechel and Sveinbjornsson 1978, Stoner et al. 

 1978b). 



Belowground productivity estimated from the belowground biomass 

 (Webber 1978, Table 3-2) and from longevities of belowground plant 

 parts (Shaver and BiUings 1975, Billings et al. 1978, Chapter 5) was 120 

 gdw m'^ yr"'. The belowground productivities ranged between 47 and 217 

 gdw m'^ yr"' from the Luzula and Salix heaths to the Dupontia meadow. 

 The ratio of above- to belowground productivities varied from about 1:1 

 to 1:4 and averaged 1:2.9. Dennis (1977), using a regression approach, 

 estimated that belowground productivity was 143 gdw m'^ yr"' in 1971. 



Total standing crop of live and intact dead plant material was 5292 

 gdw m"^ weighted by the relative area of the different vegetation types 

 (Table 3-2). The standing crop was dominated by graminoids, bryophytes 



