32 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. Ill 



west of the Pass although there are individual exceptions. The most 

 striking contrast appears between the trees from the drier sites, group 

 10. and those from the wetter, group ii. 



In summary, it is rather clearly evident, first, that a group is 

 superior to single trees for a record of rainfall variations and, second, 

 that the variations shown among the trees in table i6, especially in the 

 ratios of opposed trends, emphasize the influence of what has pre- 

 viously been referred to as microsite factors. A union of several tree 

 records apparently generalizes the record of response to rainfall. 

 When consideration is given the facts that the trees do dififer from 

 each other by an amount to be expected over a short term, in view of 

 the variations among different rainfall records themselves ; that the 

 trees are several miles from Chacon ; that rainfall is but one growth 

 factor in a complex ; and that rainfall itself is rather remote from 

 its incorporation into the hydrostatic system of the plant, the correla- 

 tions not only between rainfall and tree groups but also between 

 rainfall and individual trees are surprisingly high for the period 1909- 

 1941. 



Tree growth (groups) and the rainfall of other stations. — Certain 

 groups were correlated with the rainfall of the stations at Black Lake, 

 Taos Canyon, Taos, and Albuquerque. The results for four of the 

 groups are shown in table 17. Before continuing it should be mentioned 

 that these particular correlations were not included to demonstrate that 

 tree growth can be compared to distant rainfall with significant re- 

 sults or to indicate favor for such correlations. They are shown 

 rather because they appear to indicate that detailed influence of 

 specific rainfall subsides with distance and only general variations 

 common to the region remain. With ratios of opposed trends ranging 

 from 0.22 to 0.50, tree growth in one locality gives a poor picture 

 of rainfall variations at a distance. 



On the one hand, correlations with March- July rainfall, the best 

 in the case of Chacon, are mixed and poor ; it is difficult to read any 

 significance into them. On the other hand, correlations with the more 

 general interval of January- August rainfall are higher and more 

 consistent and emphasize the regional regime. Even so, the number 

 of instances in which the trees respond in a direction opposite to the 

 rainfall trends militates against the use of tree growth, as exemplified 

 by the Holman Pass collection, for an accurate gauge of regional 

 rainfall variations from season to season. This is not to say that 

 smoothing would not bring out general trends if the influence of other 



