30 BULLETIN 1170, U. S. DEPARTMENT OF AGRICULTURE. 



case of the " other plants," which include all other species, the curve 

 is fairly uniform for the season. The diagram plainly shows that 

 the period of most active growth, and therefore greatest production 

 of the vegetation as a whole, is during May and June. This period 

 corresponds to the period of the largest gains of the cattle. 



In Table 9 are presented the average weights (in grams) for the 

 different intensities of clipping. It will be noted that the totals 

 for the 10-day and 20-day quadrats average very close to each other. 

 This will also be observed for the 30-day and 40-day quadrats. 

 Therefore, it would be possible to drop one of each pair and still 

 retain practically the full value of the data. 



The annual quadrats have a lesser total green weight than some 

 of the others but a higher dry weight. This is to be expected, as 

 many of the species are practically dry when cut. Bouteloua and the 

 two species of Carex have produced lesser quantities in the annual 

 quadrats than in any of the others. This may be accounted for in 

 large part because of actual loss through drying. Since the two 

 species of Carex mature early, they are much overripe by September, 

 and part of the stems and leaves is lost by being blown away or 

 dropping to the ground. This fact is only partially true for Bou- 

 teloua. The tips of the leaves dry up and may break off, but they 

 are usually green below at this time. It has been noted from obser- 

 vation, and the clipping data confirm it, that Bouteloua is the one 

 species that is benefited by frequent grazing or by clipping. This 

 does not mean that it is impossible to injure this grass by overgraz- 

 ing, but that it will permit severe grazing longer than any other 

 species and that its growth is stimulated by moderate grazing. The 

 same is true to a lesser degree for the two species of Carex. In the 

 10-day quadrats practically all that is now left are Bouteloua and 

 Carex, and they have been weakened. 



Table 9 shows that Stipa runs low in all quadrats up to the annual 

 ones. From the data and observations of the biennial quadrats as 

 compared with the ones cut annually there are indications that this 

 species is weakened by even the annual cutting. However, as will 

 be noted in Table 9, it is still producing fairly high in the annual 

 quadrats. Stipa has disappeared from the different quadrats in 

 direct relation to their frequency of clipping. The quantity pro- 

 duced was less than before in 1919 in the 10-day and 20-day quad- 

 rats, was practically nothing in 1920, and in 1921 there was none in 

 the 10-day and only a trace in the 20-day quadrats. The 30-day quad- 

 rats in 1919 produced over 19 grams dry weight ; in 1920, 0.65 gram ; 

 and a trace in 1921. The monthly removal of the vegetation by 

 clipping and the weakening effect of it have been observed else- 

 where. 25 In the 40-day quadrats the quantity was greatly reduced in 

 1920 and 1921, but they are still producing a light growth. The 

 clipped quadrats show clearly and support the general observation 

 that Stipa comata is more susceptible to a reduction or complete ex- 

 tinction by intense clipping or grazing than any other important 

 species at this point. As previously noted, this species has been 

 greatly reduced by severe grazing in the 30-acre pasture. Hardly a 

 stalk of this grass has been allowed to mature normally in the 30- 

 acre or the 50-acre pasture since 1916. The closed units of the isola- 



23 Sampson. Arthur W. Range improvement by deferred and rotation grazing-. U. S. 

 Dept Agr. Bui. 34. 16 pp., 5 pis. 11)13. 



