NO. l8 TREE GROWTH AND RAINFALL CLOCK 45 



5. If tree growth shows high correlation with a certain rainfall 

 interval, as March- July, and if that interval has high correlation with 

 a second one, as January-August, then tree growth may be expected 

 to show high correlation with the second interval even though part 

 of the rainfall of the longer interval may not influence growth. 



6. Within limits, maximum correlation combined with minimum- 

 length month-intervals should be the focus of critical information on 

 the response of trees to rainfall. 



7. The average March-July rainfall at Santa Fe was higher during 

 the period 1 898-1 941 than during the period 1850- 1897 and higher 

 during the period 1909-1941 than during the period 1898-1941. 



8. Average year-to-year variation, average departure, and average 

 departure from mean variation of March-July rainfall at Santa Fe 

 was less during the period 1898-1941 than during the period 1850-1897. 



9. For the contrasted periods 1850- 1897 and 1 898-1 941, the char- 

 acteristics of the dry-site trees ran counter to those of rainfall whereas 

 those of the wet-site trees ran parallel. 



10. When a criterion of conformity, based on average departure, 

 was applied and the two trees not conforming were eliminated, the 

 characteristics of the resultant group 7 (restricted) followed those 

 of rainfall. 



Correlation between free groivth and rainfall. — i. Correlations 

 between tree growth and rainfall of Chacon, the nearest station, were 

 highest for the rainfall of the March-July interval of the same year. 

 This is consistent with the principle of maximum correlation with 

 minimum-length month-interval. The next best correlation, with 

 January- August, was also high, but the reason was held to be the 

 rather high correlation between that interval and March- July. 



2. The growth of the trees composing the Holman Pass collection 

 correlated directly with the precipitation which fell immediately before 

 and during the season of greatest growth. 



3. Correlation between the Holman Pass trees and Chacon March- 

 July rainfall, based on raw (unsmoothed) data, attained the following 

 remarkably high values: a trend coefficient of 0.965 and a ratio 

 of opposed trends of 0.12. 



4. The accumulated evidence points rather clearly to the conclu- 

 sion that the trees respond very nearly 100 percent to fluctuations of 

 rainfall at the immediate site. 



5. Correlations between individual trees and Chacon rainfall were 

 lower than those for groups. A few were surprisingly high. 



6. The nature of the species appeared to make little difference in 

 the quality of correlations. 



