NO. l8 TREE GROWTH AND RAINFALL CLOCK 



15 



Correlations between groups (table 2) east of Pass, on Pass, and 

 west of Pass are only fair. They show a mixed influence of site and 

 distance. Groups 4 and 5 are relatively close together but have dis- 

 similar sites— they have the highest correlation ; groups 4 and 9 are 

 far apart but have somewhat similar sites— they have correlation of 

 intermediate value ; and groups 5 and 9 are far apart and have very 

 dissimilar sites — they have the lowest correlation. 



Table 2 suggests something much more surprising than the dominant 

 influence of local site factors. The correlation among different trees 

 and among different groups as shown not only by the trend coeffi- 

 cients but also by the trend ratios are distinctly less for the period 

 1850-1897 than for the period 1898-1941. In fact, a few of the 

 trends, and trend ratios, are of such poor quality as to indicate little 

 relationship. Growth factors from 1850-1897 apparently must have 

 had a localized variability which to a certain extent became less 

 localized after 1897. 



For further comparisons among the trees the trends were plotted 

 for each tree against every other tree for the total years of record. 

 A comparison of ponderosa pine with other ponderosa pines, of 

 ponderosa with other species, and of other species among themselves 

 shows that species has no bearing upon the trend agreements. A 

 comparison of sequence types, such as variable with variable, variable 

 with uniform, and the like, shows that the type of sequence being 

 correlated is not an important factor. In general terms, however, 

 the closer two trees are together the greater the number of parallel 

 trends. During the period of 44 years from 1898 to 1941, where all 

 nine trees are in the record, there are 15 years with parallel trends. 

 Agreements are concentrated in the lO-year period, 1920- 1929, which 

 has 6 parallel trends. Back of 1898, the period of 48 years adds only 

 9 parallel trends to the 15 of the later period in spite of the fact 

 that the record of the earlier period contains from one to three fewer 

 trees. The striking lack of agreement prior to 1898 appears to fit 

 in with the lack of correlation mentioned in the paragraph above. 

 Again it seems that the microsite factors may have contrasted more 

 acutely from tree to tree or that an over-all factor exerting a general 

 influence on tree growth may have been more areally variable than 

 later. 



