178 



F. S. Chapin III et al. 



20 

 10 



h VO 



Leaf Blade 



VI 



V2 



I 2 

 7 20h Sheath and Stem Base 



^ lOh 



9 



E 



o* 



z 







I 2 



2 6 



12 6 



V3 



I 2 



26 0126 0126 



Number of Simulated Grazings 



12 6 



2 6 



FIGURE 5-18. Total nonstructural carbohydrate (TNC) con- 

 tent in various plant compartments and tiller age classes o/Du- 

 pontia fisheri following clipping at various intensities. Plants 

 were clipped at weekly intervals to simulate grazing and were 

 sampled on 20 August in moist meadow tundra. (After Mat- 

 theis et al. 1976.) 



maximum grazing intensity that might be sustained in a lemming high, 

 total nonstructural carbohydrate concentrations still remained high in 

 rhizomes (Figure 5-18), and shoot weight was not affected. However, 

 when a tiller no longer had access to the reserves of the entire tiller 

 system, clipping decreased shoot weight substantially (Table 5-7), as has 

 also been noted by Babb and Bliss (1974). 



Results of clipping experiments suggest that even chronic grazing 

 would have little effect upon survivorship of vegetative tillers, because 

 the tiller meristem is normally not damaged. However, at times of high 

 lemming densities and inadequate food supply, lemmings may grub in 

 the moss layer and remove the shoot meristem, killing the shoot. The im- 

 pact of grazing upon reproduction is most pronounced 1) through the 

 grazing of flowering shoots, since the inflorescence is lost, and 2) 

 through the general lowering of the reserve status of the entire tiller sys- 

 tem so that the chances of successful seed set are diminished. 



The number of new rhizomes produced is curtailed by grazing much 

 less than is shoot production (Table 5-7). Grazing causes not only a de- 

 crease in reserves but also a shift in the allocation pattern from shoot 

 production toward greater rhizome production and vegetative reproduc- 

 tion. Grazing causes a change in age class structure only because above- 



