124 CLIMATIC CYCLES AND TREE GROWTH 



places the larger maximum directly at the sunspot maximum; the minimum 

 crest nearly disappears. The extended curve was reproduced in volume I, 

 just mentioned, page 75. Its correlation coefficient with the sunspot numbers 

 is + 0.62 ± 0.06. Its cyclogram is shown in Plate 22c. 



In the important group of thirteen trees from Eberswalde, Germany, 1100 

 measures, between 1825 and 1907, the crest at minimum has practically gone, 

 except in a very few cases, leaving a massive crest at sunspot maximum, as 

 is shown in figure 51 : 10(d) and Plate 22d. The extended curve has been re- 

 produced in the same volume, page 75. Its correlation coefficient with the 

 sunspot numbers is + 0.51 ± 0.07. 



Six groups, 57 trees, of the nine North Europe groups collected in 1912, 

 when integrated at 11.4 years, show between 1830 and 1910 practical identity 

 with the sunspot cycle similarly integrated, as can be seen in figure 51: 11(e) 

 and Plate 22e. This includes about 4500 measures. The minimum crest 

 occurs rarely and disappears in the average. The extended curve has been 

 reproduced in the same volume, page 77. Its correlation coefficient with the 

 sunspot numbers is + 0.56 ±0.05. 



In the United States, a Vermont curve from eleven trees and some 600 

 measures, 1852 to 1911, shows a strong 11-year cycle with one crest much 

 more prominent than the other, and two or three years phase displacement. 

 The total range between maximum and minimum is about 28 per cent of 

 the mean value. The correlation coefficient is + 0.53 ± 0.06, after allowing 

 for lag of —3 years applied to the solar data. Seventeen Douglas firs on 

 the Oregon coast, 900 rings measured, 1854 to 1910, reach a single-crested 

 cycle with a range of about 10 per cent. There is also a slight lag. The 

 correlation coefficient is -f 0.45 ± 0.07, after allowing for a lag of —2 years 

 applied to the solar data. 



The largest American groups come from California and Arizona. These 

 are perhaps best introduced by curves of the southern California rainfall, 

 using "Lynch's Rainfall Indices," as shown in figure 51: 5(f), extending back 

 to 1770, a very important and useful compilation verified by the San Bernar- 

 dino Mountain tree record. These indices since 1850, of course, became 

 actual rainfall records. Smoothed curves of this rainfall have an obvious 

 resemblance to the Hellmann cycle. Cyclogram analysis, 1855-1901, showed 

 interference by a double-crested 14-year cycle and a high amplitude short 

 variation, apparently a little more or less than two years, which causes an 

 apparent scattering of yearly values. Without these the Hellmann cycle 

 becomes an excellent cycle with more than 30 per cent range. See Plate 

 22f. A study is being made of this two-year cycle. 



Figure 51: 6(g) shows the Hellmann cycle in the sequoias. This comes 

 from the tabulated means of eleven trees, about 600 measures, published by 

 the Carnegie Institution in 1919. The data originally covering 1810 to 

 1914 have been extended to 1930 by collections in the Sequoia National Park. 

 The trees are complacent and the range is small; namely, about 8 per cent. 

 But the maxima are clean-cut and the crests are very stable as there is little 



