250 



AGRICULTURAL INDICATORS. 



for seed-production. In the special study of grazing during the past five 

 years a large amount of material has been collected which shows the critical 

 effect of the wet and dry phases upon growth and reproduction. As is well 

 known, field crops also exhibit a striking response to years of abundant rain- 

 fall as well as to those of drought. While methods of tillage influence crop 

 production profoundly, the latter clearly reflects the wet and dry phases of 

 the climatic cycle at those stations in the arid regions where the record is 

 suflBciently long. The effect of the 11-year cycle upon animals is most strik- 

 ingly seen in the case of range cattle, which live under semi-natural condi- 

 tions, but it is also readily discovered in all animal populations which are 

 directly dependent upon the natural vegetation of arid regions for their food- 

 supply. 



Periods of drought. While both wet and dry phases have a marked effect 

 upon the annual production of natural and cultural crops, the periods of 

 drought stand out with especial vividness. While this is particularly true of 

 arid regions, it holds likewise for semi-arid ones during the period of early 

 settlement, when economic resources are at a minimum. The consequences 

 are sufficiently disastrous even in such cases, as the history of settlement in 

 the Middle West proves. In the case of a native a^icultural population held 

 more or less rigidly within its own boundaries by the pressure of other tribes, 

 they led to famine with attendant wars and revolts. As a result, there is much 

 historical evidence of the periods of drought and famine in the Southwest, 

 and this makes it possible to discover how closely these correspond with the 

 phases of the 11-year cycle. As would be expected, there is frequent mention 

 of droughts in the chronicles of Mexico and the Southwest from 1600 to 1850. 

 A much smaller number of these were accompanied by famine, and appear to 

 represent drought periods. Of more than a dozen such periods, all but two 

 occurred at the sun-spot maximum, or within a year or two of it, and furnish 

 a record of agreement comparable to that of the last half-century (fig. 14). 



noo 



nso 



itso 



Fro. 14.- 



1000 

 Ytars 

 -Double and triple sun-spot cycle in yellow pine from 1700 to 1900 A. D. 

 After Douglass. 



The agricultural development of the West began with the passage of the 

 homestead act in 1862, and the consequent inrush of settlers. Since that time 

 the drought periods are known with certainty, and their correlation can be 

 made without question. In this connection it is essential to distinguish be- 

 tween drought periods and drought years. The former consist of two to three 

 or even four years and are felt generally throughout the West. In the Great 

 Basin, as well as in the Southwest, a single year of drought for a particular 

 r^on or locality may occur at almost any time, since the normal rainfall is so 



