Control of Tundra Plant Allocation Patterns and Growth 177 



species (Bliss 1971). Rough calculations based on carbon cost of inflores- 

 cence production, percentage seed set, percentage seedling survival, etc., 

 suggest that the carbon cost of producing a new tiller in coastal tundra by 

 sexual reproduction is 10,000 times greater than the cost of tiller produc- 

 tion through vegetative reproduction. The fact that sexual reproduction 

 receives substantial carbohydrate allocation in spite of the low frequency 

 of seedHng establishment points out the necessity of a long-term evolu- 

 tionary framework within which to view growth and allocation pro- 

 cesses. On successional and evolutionary time scales there must be sub- 

 stantial selection for sexual reproduction to maintain genetic variability 

 and flexibihty and to permit dispersal to new areas. The selective advan- 

 tage of dispersal capability results from the heterogeneous nature of the 

 microtopography that limits the expansion of clones, and the occasional 

 creation of new unvegetated areas such as frost scars and drained lake 

 basins that are not effectively colonized by clonal expansion. Population 

 processes and evolutionary strategies deserve attention in future tundra 

 studies. 



EFFECT OF GRAZING ON ALLOCATION 

 AND POPULATION STRUCTURE 



Lemmings periodically graze wet meadow communities to such an 

 extent that maximum aboveground biomass may be decreased from 100 

 g m'^ to as little as 5 g m"^ (Dennis 1968, Tieszen 1972b, Chapter 8). Sim- 

 ulations suggest that the long-term effect of lemming grazing is to reduce 

 total foliage by an average of 33% (Lawrence et al. 1978). Grazing alters 

 graminoid allocation patterns in the tundra at Barrow and affects plant 

 survival and community structure. Certain gross morphological features 

 of Dupontia and other graminoids appear to be adaptive under a grazing 

 regime. The shoot meristem and virtually all the storage and perennial 

 tissues are located below ground, protected from grazing. Tissues that 

 are available to grazers are only weakly lignified and are potentially 

 replaceable at a minimal biochemical cost. Grazing may be a critical fac- 

 tor leading to the dominance of the graminoid growth form at Barrow. 



Clipping experiments on Dupontia indicate that the movement of 

 carbohydrate from one tiller to another is important in allowing Dupon- 

 tia to survive intensive grazing. Dupontia leaves regrow rapidly following 

 grazing because of the abundance of belowground carbohydrate reserves 

 (Mattheis et al. 1976). Light clipping to simulate grazing can even result 

 in a slight increase in the available carbohydrate pool of the rhizome, 

 provided the chpped tiller remains attached to the tiller system (Mattheis 

 et al. 1976), perhaps due to decreased shading and increased photosyn- 

 thesis. After six consecutive clippings in a single season, to simulate the 



