NO. l8 TREE GROWTH AND RAINFALL CLOCK 37 



The most important, perhaps, and certainly the most startling 

 information yielded by tables 19 and 20 is the great increase in the 

 quality of correlation from the period 1850- 1897 to the period 1898- 

 194 1. Table 20 shows this in abbreviated form for March- July rain- 

 fall, which appears to have most influence on tree growth. In addition, 

 table 20 includes the period 1910-1941. It is to be noted that cor- 

 relation is higher for 1910-1941 than for 1898-1941 ; in other words, 

 there is a general increase in correlation toward recent years. Of 

 all the groups, numbers 5 and 11, containing trees from the wetter 

 show not only the greatest increases but also the highest corre- 



sites 



Table 20.— Correlation of tree groups and Santa Fc rainfall 



Trend coeffieients and ratios of opposed trends 

 March-July rainfall 



lations for the periods 1 898-1 941 and 191 0-1941. And of these two 

 groups, number 5, composed of trees on the Pass, exceeds even group 

 II. Group 10, in contrast, containing trees from the drier sites, and 

 group 4 exhibit the least increases. Table 11, giving the March- July 

 rainfall of Santa Fe for the periods 1850-1897, 1898-1941, and 1910- 

 1941, shows the rainfall to have been 6.34, 6.74, and 6.88 inches, 

 respectively, for those periods. Furthermore, the low incidence of 

 parallel trends, growth layer to growth layer, among the trees prior 

 to 1897 as compared with the years following 1897 (as noted above 

 under study of growth layers), and the lower correlations between 

 trees and groups (table 2), suggest emphatically that the above phe- 

 nomena are closelv related. 



