EFFECTS OF DIFFERENT SYSTEMS OF GRAZING. 



29 



20 for the 20-day periods, etc. The a annual " is fixed at September 

 1. as there is very little growth after that date.' In no season since 

 these quadrats were started have the 10, 20, and 30 day quadrats 

 made enough growth to afford vegetation for clipping at all possible 

 periods. This has been largely because of drought. 



Figure 10 shows in graphic form the periods of growth for the 

 different species and groups. The 30-day period was selected for 

 this study, as it represents each of the four months of the season and 

 also corresponds to the weighing dates of the cattle. Bouteloua 

 presents the most uniform line, showing that this species produces a 



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Fig. 10. — Diagram showing the average quantity of vegetation produced bv different 

 species and groups of plants at the end of 30-day periods for the period from 1917 to 

 1921, inclusive. The lines represent the green weight of the vegetation in grams per 

 square-meter quadrant. 



fairly uniform growth throughout the season. This is one of the 

 reasons why it is such a valuable grass for grazing. Both Stipa and 

 other grasses also produce fairly uniform lines, but their production 

 is very ligjit toward the close of the season. In the case of the two 

 species of Carex there is a pronounced abundant early growth. 

 C. -fUifolia is one of the earliest plants to mature. It sheds its seeds 

 usually late in May and does not make much growth after that time. 

 C. heliophila is not quite as early in maturing and makes more 

 growth later in the season. The two species are shown together, but 

 beginning in 1919 they were separated for the above reasons. In the 



