NO. l8 TREE GROWTH AND RAINFALL CLOCK 



35 



with March-July rainfall slightly exceed those with January-August. 

 They decrease in quality with distance ; that is, correlations of group 4 

 (east of Pass) are highest and those of group 9 (west of Pass) are 

 lowest. 



The most striking feature of the table is the decided increase in 

 correlation of the period 1910-1941 over the period 1893-1941. Dur- 

 mg the later period (1910-1941) the trees follow more closely the 

 variations in rainfall as recorded at Las Vegas. 



Tree growth and Santa Fe rainfall. — Although Santa Fe is distant 

 some 40 miles from Holman Pass it is worth while, because of the 

 length of record, to compare Santa Fe rainfall with tree growth in 

 order to determine if the quality of correlation varied throughout the 

 length of that record. Nine tree groups were correlated with all 

 rainfall intervals for the periods 1850-1897 and 1898-1941 separately. 



Data most pertinent to the study appear in table 19, which gives 

 the trend coefficients and ratios of opposed trends for the periods 

 mentioned above. The remainder of the data, not shown, simply 

 corroborate what the table itself shows. On the whole, tree growth 

 correlates considerably better with March- July than with January- 

 August rainfall. Here, however, in contrast with Chacon rainfall, 

 groups 4, 5, and 7 agree somewhat better with March- June rainfall. 



General correlations are fair; they possess litde value except to 

 show a regional tendency toward similarity during a portion of the 

 years. This appears in table 20 where trend coefficients for the period 

 of 1850-1941 vary from 0.52 to 0.67 and the ratios of opposed trends 

 from 0.24 to 0.37. The values for group 7 are 0.65 for the trend 

 coefficient and 0.35 for the ratio of opposed trends. Thus, a case of 

 35 opposite trends against 65 parallel gives neither high nor depend- 

 able correlation. Surprisingly, the trees from the wetter sites, group 

 II, compare most favorably with Santa Fe rainfall for the period 

 1850-1941. In view of the quality of correlation between Holman 

 Pass tree growth and Chacon rainfall on the one hand and between 

 Chacon and Santa Fe rainfall on the other, the correlation between 

 tree growth and Santa Fe rainfall possesses values consistent with 

 the relative distances. 



Figure 5 shows Santa Fe rainfall for March- July compared with 

 tree growth of the several pertinent groups. Figure 6 shows the 

 correlations in charted form. For the period 1898-1941 the trend of 

 the graph resembles that for the Chacon correlations. It contrasts 

 notably with the graph for the period 1850-1897, where the emphasis 

 seems to be on spring rainfall. 



