114 



CLIMATIC CYCLES AND TREE GROWTH 



Yellowstone Fossil Trees — Concluded 



species today, the coast redwood, they are cross-dated with difficulty, for 

 there are no distinctive drought rings to serve as guides, such as aid so greatly 

 in the giant sequoias and the pines of drier regions. The counting therefore 

 lacks the precision of cross-dated material, but many duplicate radials were 

 counted and measured and it is thought unlikely that important errors have 

 entered the results. Over 11,000 rings were measured, plotted, and given pre- 

 liminary analysis by Mr. H. F. Davis in 1932. These analyses were checked 

 and recently repeated in great detail by Mr. Schulman in order to find various 

 statistical characters of the cycles. We all agree on cycle maxima near 

 8.5, 10, 11$, 14, 17, and 19 years. Some of the sequences gave groups of 

 cycles so closely alike that it may be possible to cross-date by that means. 



It was noted that the frequency periodogram of the Yellowstone fossil 

 trees shows great sensitivity; on the whole the cycles in it seem more precise 

 and follow more consistently one configuration than do the cycles in either 

 the 42 Western Groups, the Arizona and California long chronologies, or 

 the California coast redwoods. The newly derived periodogram from the 

 fossil trees shows the 10 and the 14-year cycles to be fully as important as 

 the 11 ^-year cycle. 



It is highly interesting to make comparisons between frequency periodo- 

 grams from the fossil and the coast redwood. A periodogram of cycles in 

 the latter trees recomputed in accordance with the present reduction meth- 

 ods 1 shows at once a pronounced agreement with the Yellowstone periodo- 

 gram. Due to the short average length of curves in the Yellowstone 

 group, its periodogram has little weight for cycles longer than about 18 

 years. 



The suggestion is strong in the coast redwoods of a liberal sprinkling of 

 random effects in the cycle configurations, which have averaged out in the 



1 Using the rings in upper levels of the trees because such rings were found to be 

 much less erratic. 



