Control of Tundra Plant Allocation Patterns and Growth 181 



and production the next year. Since this longer-term effect is most harm- 

 ful to evergreen shrubs and then deciduous shrubs, and least harmful to 

 graminoids, it is clear that vegetation units will change under different 

 kinds of grazing regimes. 



VARIABILITY IN GROWTH AND 

 ALLOCATION PATTERNS 



Substantial interspecific differences in the growth and allocation 

 patterns of three dominant graminoids (Dupontia fisheri, Eriophorum 

 angustifolium and Carex aquatilis) have resulted in niche differentiation. 

 Carex is generally dominant in phosphorus-poor sites such as pond mar- 

 gins and basins and rims of low-centered polygons, which receive low 

 grazing pressure. In contrast, Dupontia predominates on phosphorus- 

 rich sites such as polygon troughs. Eriophorum also tends to occur in 

 more phosphorus-rich sites, particularly where vegetative cover has been 

 broken by frost or human disturbance. 



Differences in allocation pattern between the three principal gram- 

 inoids partially explain distribution patterns (Table 5-8). Leaf produc- 

 tion and elongation occur earlier in the growing season and are more syn- 



TABLE 5-8 Characteristics of the Growth and Allocation Patterns of 

 Dupontia fisheri, Carex aquatilis and Eriophorum 

 angustifolium 



