Control of Tundra Plant Allocation Patterns and Growth 179 



TABLE 5-7 Effect of Simulated Grazing upon Dry 



Weight of Shoot Regrowth and Number of 

 Newly Initiated (VO) Rhizomes of Dupontia 

 fisher i Growing in Moist Meadow Tundra 



Note: Treatments involved clipping all leaves of the tiller at the moss surface (clip- 

 ping) and/or severing all rhizome connections between the treated tiller and the rest 

 of the tiller system (ringing). Tillers were clipped or ringed and clipped on 25 July, 

 leaves were reclipped on 4 August, and shoots and rhizomes were harvested on 16 

 August 1973 (n = 10). 

 Source: Mattheis et al. (1976). 



average numbers of newly initiated (VO) tillers are recruited into the pop- 

 ulation in the year of a lemming high. Computer simulations suggest that 

 the differential mortality and reduced competition due to grazing are not 

 responsible for change in age structure (Lawrence et al. 1978). Hence, 

 grazing by moderate lemming populations influences population struc- 

 ture more by increasing recruitment of new tillers than by increasing 

 mortality. 



The maximum stress that lemmings are likely to exert upon the nu- 

 trient reserves of the wet meadow vegetation is simulated and shown in 

 Figure 5-19. Simulations suggest that grazing depletes nitrogen and phos- 

 phorus reserves more rapidly than carbohydrate reserves which, in turn, 

 are depleted more rapidly than are calcium reserves. The strain on below- 

 ground nitrogen or phosphorus reserves may not differ significantly in 

 grazed or ungrazed situations until after four or five defoliations, be- 

 cause the early part of the growing season is characterized by rapid up- 

 ward nutrient translocation regardless of whether grazing occurs or not. 

 Grazing would, however, prevent downward translocation of nutrients 

 lost to herbivores and would likely affect growth primarily in subsequent 

 years. In fact, detailed studies (Tieszen and Archer 1979) of various 

 growth forms at Atkasook, Alaska, have not only shown that seasonal 

 carbon balance is seriously affected (Chapter 3) but also that a single 

 grazing event can reduce reserves in a manner which influences growth 



