The normal frequency ratio is useful in many kinds of studies 

 in testing the uniformity of the vegetation, the most essential 

 point being that class E should be larger than class D. This ob- 

 jective method can be quickly applied in the field, before pro- 

 ceeding with more detailed analysis. For example, in a 

 representative stand of the Stipa comata-Bouteloua gracilis-B. curti- 

 pendula type in the lower foothills of Colorado, the number of 

 species in 20-m2 quadrats was ^, 24; 5, 6; C, 3; A 2; and E, 5. 

 In a nearby Artemisiafngida-weed stand on similar soil in a prairie- 

 dog town the distribution was A, 10; B, 6; C, 4; D, 2; and E, 1, 

 the difference between the two ratios indicating considerable dis- 

 turbance. 



The ratio may be affected by the intensity of grazing, as shown 

 in an analysis of Agropyron smithii range land in Colorado 

 where the ratio was 62, 14, 7, 7, and 10 in a deferred-rotation 

 pasture to 59, 13, 13, 11, and 4 in an adjoining, continuously 

 grazed pasture. ^"^ These ratios indicate that palatable species of 

 low frequency tended to disappear under continuous grazing, while 

 unpalatable species of low frequency tended to increase under the 

 same conditions. This was exemplified by Eurotia lanata, a palat- 

 able shrub, which had a frequency of 56 per cent under deferred- 

 rotation grazing but per cent under continuous grazing, while 

 the unpalatable Artemisia frigida on the other hand, had frequen- 

 cies of 16 and 52, respectively, under the two grazing conditions. 

 When the total number of species in a stand is small they often 

 tend to be confined to classes A and E, and, obviously, in almost 

 pure stands they are almost exclusively in class E. The number 

 and size of sample areas influence the ratios; if too large or too 

 small, the ratios tend to be obscured. The square meter has been 

 widely employed in grassland research, so that data from many 

 areas are comparable, but smaller sizes have also been extensively 



used.^^ 



The frequency index has been employed to reveal differences 

 between grasslands subjected to various conditions. The effects of 

 grazing upon the frequency of prairie species in Missouri^ ^ are 

 shown in the following table. The data indicate that competition 

 between species, especially in the case of Andropogon gerardi in 



114 • THe ComMtiunity 



