70 CLIMATIC CYCLES AND TREE-GROWTH. 



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3. From A n an approximate R n is found by the formula 



R n = M+A n -A n _ l 



4. This series of approximate rainfall R n is smoothed and becomes 

 the S n of the formula. 



5. Final values are then found by the proportion 



0.90M +M, . q , T 1P 



' ' . O J. n . -fin 



250 



It should be emphasized that the above formula for conservation 

 is the one found to apply under dry climatic conditions. In moist 

 climates the trees, so far as observed, seem to depend on other meteoro- 

 logical elements or combinations of elements. 



The Prescott trees, as we have seen, even without correction give a 

 record of rainfall with an accuracy of about 70 per cent. It is possible 

 that the Flagstaff trees with their higher elevation, more certain rain- 

 fall, and more central location in the zone occupied by this species give 

 somewhat more accurate records. They are probably much less often 

 subjected to extremes of dryness, which throw the tree out of its 

 equilibrium and cause it to produce an abnormally small set of rings. 

 It seems likely, also, that the less compact soil, combined with a more 

 abundant precipitation, produces a yearly growth more nearly pro- 

 portional to the rainfall than at Prescott. 



Summary. In considering this reduction it seems fairly clear that 



(1) there is a strong correlation between rainfall and tree-growth; 



(2) the accuracy may be increased by introducing a conservation cor- 

 rection; (3) in dry soils this factor enters as a coefficient; (4) this co- 

 efficient depends on the state of activity of the tree ; (5) in the Prescott 

 trees this state of activity follows the curve of accumulated moisture. 



Although the moisture-content of apparently dry ground may be a 

 most important item, it is by no means certain that the observed ac- 

 cumulated moisture effects consist in actual moisture in the ground. 

 It may be that they represent some vital condition of the tree. The 

 matter is a very interesting one for future study. 



Sequoia correlation with rainfall. On his return from the big trees 

 in 1912, Professor Huntington supplied me with a curve of sequoia 

 growth obtained from many comparatively young trees which had been 

 cut in the lower edge of Redwood Basin near Camp 6. On comparing 

 these with his curve of rainfall in the San Joaquin Valley, compiled 

 from records at Fresno and San Francisco, a close relation was not 

 evident, but an additive formula 



rp _fc R n -\-R n -i+R n -?> 



Rn + Rn-l + Rn-2 



was used with encouraging results. This formula was designed to 

 allow for strong conservation in the soil, not of the static type as in a 



