SUMMARY 137 



8. Mean sensitivity is a good indicator of climatic correlation, but 

 it is strongly affected by injuries to the tree. 



9. Average ring-size, doubling, changing, and other characters of 

 rings can be used as indicators in judging the surroundings, and 

 especially the climates, of prehistoric and geologic times. 



10. The Prescott correlation between rainfall and tree-growth is 

 continued and a similar correlation is found between the Flagstaff 

 trees and the winter rainfall recorded there, which, in turn, closely 

 resembles California precipitation. A close correlation is also found 

 between carefully selected (dry ground) sequoias and San Francisco 

 rainfall. 



11. By comparison of smoothed curves, three western centers 

 appear; Pike's Peak, Flagstaff, and Sierra Nevada. The Pike's Peak 

 area as worked out covers the eastern slope of the mountain; the Flag- 

 staff area extends from the Grand Canyon to the Rim and Cibecue, 

 175 miles; the Sierra Nevada area extends from the Calaveras Grove 

 and even farther north to Mount Wilson and farther south, 500 miles. 

 In each of these the curves of growth are homogeneous, and at points 

 between these major centers, such as Charleston Mountain or Aztec, 

 mixed effects are found. 



12. Dating comparisons of cycles in 200-year curves show 75 per 

 cent resemblance in local curves of individual trees, and 50 per cent 

 resemblance between Arizona pines and California sequoias, by large 

 groups of trees. Practical identity of cycles in yellow-pine groups is 

 found across 200 miles between Flagstaff and northwest New Mexico. 



13. The cycles found in the yellow pines of the western zones 

 emphasize the approximate simple fractions of 34 or 35 years, with 11 

 and 14 years dominating on the coast, 14 and 21 years in Arizona, and 

 10 and 11 (or 23) in the Rockies; the coast is deficient in the 20-year 

 variations (the separation of 19, 20, and 21 is not yet fully determined 

 in these zones); Arizona has less of the 11, 23 year cycles and the 

 Rockies are short in the 14, 28 year cycles; they, however, show the 

 8.6- and 17.5-year cycles better than the other zones. 



14. A sequoia arcigram (cycle summary over an area) shows a 

 little more of the Arizona character in the sequoias than in the yellow 

 pines of that region. 



15. The long Flagstaff record, from 1300 to 1925, perhaps the 

 best in the three zones for rainfall history, gives cycles which check 

 with the known solar record. From them we get a solar period of 

 11.30 years lasting for 600 years, but with an interruption from 1630 

 to 1850; we get also a group of 7, 14, and 21 year cycles beginning 

 near 1660 and well established after 1700. The 21-year cycle has 

 dominated Arizona tree-growth for 200 years. A 9.4-year cycle 

 shows in the late 1700 's, when the sunspot cycle was of that length. 

 The 7-year cycle was less active from 1880 to 1905 (in the Flagstaff 

 area mean curve). Growth maxima occur at observed sunspot minima. 



16. Wet and dry climate effects in trees in relation to the solar 

 cycle are confirmed. 



