228 V. Alexander et al. 



the season but these did not complete their life cycle before senescence 

 began in mid-August. Carex in the ponds actually produced a seventh leaf 

 and the average number of leaves produced was 6.8 by 17 August 1972. 

 These last leaves (5, 6 and 7) were still growing after the environmentally 

 induced senescence had begun. In the late fall there is some dieback but the 

 lower parts of the leaves remain green and will be productive next season. 

 In the pond, Carex leaves had a maximum length of 190 mm which is 

 about double the length of Carex in drier locations. Over the course of its 

 4- to 7-year life, a tiller may produce 20 to 25 leaves before dying above- 

 ground (Shaver and Billings 1975). 



As far as is known, the seasonal cycle of growth of A rctophila fulva is 

 similar to that of Carex. The leaves are much wider than those of Carex, 8 

 to 11 cm versus 0.3 cm (Miller and Tieszen 1972), and the pure stands of 

 A. fulva are the densest vegetation on the tundra. For example, the highest 

 leaf area index (total area of leaves per unit area of ground) was 8.5 for a 

 stand oi A. fulva (Dennis et al. 1978). The usual maximum leaf area index 

 in the wet meadow habitat at Barrow is 1.0 to 1.4 (Johnson and Tieszen 

 1973). 



Biomass 



The aboveground biomass of the plants in Pond J was measured by 

 clipping and weighing (dried at 95°C for 24 hours). Peak biomass in 1971 

 was reached around 9 August in both the pond (Table 5-7) and in the dry 

 tundra (Figure 5-30). These terrestrial data show very well the peak in 

 chlorophyll that precedes the biomass peak by about 10 days. In fact, 

 judging from these data the plants appear to reach their peak of 

 photosynthetic capability in mid-July (chl(g dry wt) '). The data from 

 1972 (Figure 5-31) suggest that the Carex in Pond C continued to 

 accumulate biomass until 29 August but we can not really say that these 

 plants were basically different from the terrestrial plants. These biomass 

 data agree well with the Pond C data for 1972 and 1973 (sampled in mid- 

 August) when 219 and 89 g dry wt m^^ were found (Tieszen, Mandsager 

 and Vetter unpublished data). This biomass represented 1100 and 370 

 tillers m ^ 



Arctophilafulva was collected from Pond J in 1971 and from Pond L 

 in 1972. Arctophila was only a minor part of the total biomass in Pond J 

 but was the dominant aquatic plant in Pond L. It did not occur at all in the 

 main ponds we studied (B and C). 



Most of the living biomass of these plants is in the belowground 

 rhizomes and roots. If we take the single measurement of roots and 

 rhizomes in Table 5-7 and assume that it does not change over the season, 

 then 91 to 95% of the total plant material is underground for Carex and 57 

 to 78% rt)r Arctophila. This agrees with the statements of Dennis and 



