144 F. S. Chapin III et al. 



0.12 



0.10 



0.08 



o 

 "o. 0.06 



o 

 cr. 



o 



0.04 



o 



«, 0.02 





-0.02 - 



-0.04 



n — I — I — I — r~ 



(o)Carex aquatilis 

 (•)Dupontia fisheri 



1 



J L 



A M J 



J L 



T \ I I I I I r 



(o) Agropyron smithii 

 (•) Bouteloua gracilis 



N D J 



FIGURE 5-3. Mean relative growth rates of graminoids observed in situ 

 in a) tundra (calculated from Tieszen 1972b), and b) temperate grass- 

 land at Cottonwood, S.D. (Lewis et al. 1971). 



The most striking feature of plant growth at Barrow is the high pro- 

 duction rate at low temperatures. Graminoids in the Biome research area 

 have relative production rates (g g"' day"') comparable to those of some 

 dominant grasses of a mid-latitude grassland, in spite of a 15 to 20 °C dif- 

 ference in average air temperature during the growing season (Figure 

 5-3). The principal difference in their patterns of production is not the 

 rate of growth but the short period during which growth occurs in the 

 tundra. The capability of tundra plants to grow effectively at low tem- 

 perature is further seen in controlled environment experiments where 

 graminoids from Barrow exhibit maximum rates of leaf initiation, 

 elongation, and hence growth at 15°C (Tieszen, unpubl.). This is com- 

 parable to the optimum temperature for growth of some alpine grasses 

 (Scott 1970), but some 10 to 15° cooler than the optimum growth tem- 

 perature of temperate zone grasses (e.g. Evans et al. 1964, Warren Wil- 

 son 1966a). However, the 15 °C temperature optimum for growth of tun- 



