364 CARNEGIE INSTITUTION OF WASHINGTON. 



This condition is rare except in pastures, where overgrazing reaches its 

 extreme. 



A basic discovery has been made to the effect that all dominants 

 and subdominants in a group are indicators of competition wdth each 

 other to varying degrees. Under optimum conditions, with competi- 

 tion lacking, it has been found that the dominant grasses of the true 

 and mixed prairie will grow to heights two and even three times 

 greater than the usual height in the community. Thus, in areas of 

 similar water-content or regions of the same rainfall, height and spread 

 may be used as fanly exact indicators of the degree of competition. 



Grazing Research, hy F. E. Clements, Edith Clements, and G. V. Loftfield. 



Grazing research has been continued throughout the year, and 

 informal cooperation has been entered into with several additional 

 State experiment stations. The generally abundant rains over the 

 Great Plains and the Southwest produced an exceptional development 

 of grass and permitted a close comparison with grazing conditions in 

 the two preceding years of drought. The abundance of grass forage 

 reacted upon the herbaceous population more or less favorably, as 

 the herbs were less grazed and increased correspondingly. The 

 fenced inclosures on the Santa Rita Range Reserve showed less 

 striking differences than were expected, and clearly demonstrated the 

 remarkable capacity of grasses to recover after severe drought. It is 

 assumed that the explanation of this is to be found in the storage in 

 rootstock or crown, and this possibility is being studied. 



The grass quadrats of the inclosures were charted m the fall, and 

 those of whiter annuals in the spring. Some quadrats are used to 

 study the relation between the two, and these were charted at both 

 times. The grass quadrats in rodent-mfested areas in northern 

 Arizona were charted in the fall. At this time the grasses showed the 

 most strikmg differences under protection, and these differences were 

 measured and photographed. 



Land Classification and Settlement, hy F. E. Clements and E. S. Clements. 



Further studies have been made of the causes underlying the abandon- 

 ment of farms and ranches over the Great Plains and in the Southwest. 

 These abandoned farms are more numerous than for a long time, 

 in consequence of the critical droughts of 1916-1918. Since the dry 

 years of 1907 and 1908 there had been extensive settlement in the arid 

 regions of the West, stimulated first by the enlargement of the home- 

 stead to 320 and then recently to 640 acres. These enlarged home- 

 steads did not increase the certainty of producing crops, except in so 

 far as they permitted successful dry-farming, and they were still quite 

 too small to make stock-raising profitable. As a consequence, the 

 drought produced much the same effect as the earlier ones of 1871- 



