4 CLIMATIC CYCLES AND TREE GROWTH 



qualities make them of the highest value. The exact dating of the rings of 

 these giants was obtained by 1919. It is only recently that immensely long 

 chronological sequences have been developed in the Colorado Plateau area, 

 reaching back to A.D. 11. Although the early 80 years of this latter chronol- 

 ogy come from a single tree, it is a Douglas fir and its record may be ac- 

 cepted as valuable, subject to future correction should other tree records be 

 found. 



The value of these two ancient coincident records covering 1900 years, at 

 a distance apart of some 600 miles, becomes very great when we find that in 

 cycle analysis they have a distinct resemblance. Meteorological records go 

 back commonly less than a century and reach the hundred-year mark in only 

 a few accidental spots, but in these trees we find ring records accurately dated 

 reaching back to the beginning of our era, in two well-separated localities of 

 which one maintains its sequence full 1300 years farther into antiquity. 



Need and Function of Cycles — It is well recognized that development of 

 long-range forecasting is highly desirable. This is true in any part of the 

 country, but it is especially true in marginal lands that are subject to strong 

 climatic variations from year to year — variations whose violence and time 

 of coming are of the highest importance, because man's very existence in 

 such places depends upon his power of adaptation to such changes. Changes 

 of this sort become very graphic in the area under consideration. For ex- 

 ample, Mormon Lake, the largest in Arizona, four by six miles in extent, was 

 totally dry in 1901 when crossed by the writer. Now its shores have been a 

 summer resort since 1909 and the lake is advertised for its fishing. What 

 made it go dry, and how can we determine when it will go dry again? In 

 the spring of 1935 the desert was covered with wildflowers, while in 1934 it 

 was not. That is due to great difference in winter precipitation in the two 

 years. What made that difference? 



The problem of drought is more directly human than that. Hundreds 

 of homesteads have been taken up in the semi-arid parts of the Southwest. 

 The owners put in wells by which to pump water from a supposedly inexhaust- 

 ible source below. But that source is not inexhaustible, since it comes from 

 the rains which have fallen on a relatively small area. Too great enlarge- 

 ment of irrigated districts will make demands upon the water resources far 

 beyond their replenishment. It becomes of vital importance, then, to know 

 when the replenishment will take place. 



Everyone who has lived long in this country has seen years of drouth and 

 cattle lying dead beside dried-up water holes. People of early days learned 

 how dangerous it was to travel long distances with horses without full knowl- 

 edge of the technique of obtaining water. 1 They recognized that some years 

 were far more severe than others in respect to drought ; with no knowledge of 

 what would come to pass, they must be prepared for the worst. Obviously 

 our duty is to develop all possible methods of foretelling the future. Increase 



1 In 1896 a young cowboy from Beaver Creek, Arizona, could not believe me when 

 I told him that in New England we did not carry canteens wherever we went. 



