26 



BULLETIN 1170, U. S. DEPARTMENT OF AGRICULTURE. 



plants do not have a chance to make much growth, they do not use 

 much of the soil moisture. Therefore, because A. frigida is left un- 

 disturbed until late in the season it has the advantage of nearly all 

 the moisture available in the soil. It has increased in extent until 

 the cattle will not clean up all of it before they lose weight. In the 

 unit closed in 1918 the competition of other species had not been 

 greatly reduced and the plants of A. frigida are in about a normal 

 condition of growth. The competitive influence of other species has 

 not been of much consequence in the units closed in J.920 and 1921. 

 The increase in the number and the size of the individual plants has 

 enlarged the area occupied by A. frigida, in the 30-acre pasture about 

 10 times. It can thus be readily seen how this one plant can ma- 

 terially reduce the grazing capacity of a pasture. 



Table 7. — Average height, number of stalks per plant, and number of plants 

 of Artemisia frigida per square meter in the units closed to grazing each 

 year in the isolation transect in the 30-acre pasture. 



[Measurements made in the autumn of 1921.] 





Average of 2 square-meter quadrats. 



Year closed to grazing. 



Height of 

 plants. 1 



Stalks per 

 plant. 



Plants per 

 square 

 meter. 



1918 



Millimeters. 

 177.5 

 196.4 

 289.6 

 295.9 



Number. 

 5.9 

 7.9 

 8.0 



8.7 



Number. 

 5 



1919" 



16 



1920 



18 



1921 



23 







Plants less than 50 millimeters in height were not included. 



In 1920 the difference in the size of the plants of A. frigida was 

 noted in the various pastures. Measurements were made of all the 

 plants over 25 millimeters in height in the list quadrats. The results 

 obtained are presented in Table 8. 



Table 8. 



-Average height, diameter, and number of stalks per plant of Arte- 

 misia frigida in the different pastures in 1920. 





Artemisia frigida. 







Pastures. 







100 acres. 



70 acres. 



50 acres. 



30 acres. 



Height of plants 



Diameter of stalks. . 

 Number of stalks . . . 





millimeters.. 



do.... 



ner nlant.. 



133.9 

 15.2 



127.3 

 15.4 

 5.3 



115.1 

 13.4 

 ,2 



150.2 

 18.1 

 7.4 







It will be noted that the plants in the 30-acre pasture are the 

 largest in all cases, while those in the 50-acre pasture are the smallest, 

 no doubt because the cattle in the latter pasture have so far been 

 able to graze this plant enough to retard its most active stage of 

 development. Therefore, it does not have the advantage over other 

 species that it has attained in the 30-acre pasture. The cattle have 

 remained on the 50-acre pasture longer during the season, and 

 this fact has allowed them sufficient time to remove the plants 

 gradually. The intensity of grazing also has its effect upon these 

 plants, as the cattle have more feed before them. Therefore, the 



