1 8 TREE GROWTH AND RAINFALL CLOCK 



43 



within the Transition Zone up into the Canadian ; the number of trees 

 sampled was Hmited to nine; the collection contained trees of four 

 different species and comprised three groups geographically and 

 hypsometrically ; the trees, in the field, divided themselves ecologically 

 into two groups, the one (group lo) representing normal water 

 relationships without excess drainage to or from the trees, and the 

 other (group ii) representing slightly above-normal water relation- 

 ships for the general locality ; the samples consisted of increment cores 

 — essentially one radius to represent the entire volume growth of a 

 tree; site factors were judged solely by inspection on the spot; the 

 terrain was mountainous; the nearest rainfall station, Chacon, was 

 7 miles distant at an elevation intermediate between the highest and 

 lowest trees; and analyses were based on raw (i.e., unsmoothed) data. 



The present study brings out many points in summary which are 

 distinctly secondary to the main objectives. In the present stage of 

 investigations of this type, all points, secondary as well as primary, are 

 highly suggestive only. It remains to be determined if the principles 

 and methods here used in the field and in the laboratory are of more 

 general application. Only then can growth-layer sequences be inter- 

 preted in the absence of nearby rainfall stations. Obviously, we must 

 know how trees reveal their ecologic information before we can 

 determine what they tell. 



Study of grozuth layers. — i. Cross-dating of high quality is not a 

 necessary prerequisite to the correlation of growth-layer thicknesses 

 and rainfall, and its nearly total absence does not indicate a lack of 

 significant response on the part of the trees to rainfall variations. 



2. The presence or absence of high-quality cross-dating does not 

 necessarily constitute the criterion whereby a tree record is included 

 in a group average or excluded from it. Some other criterion should 

 be applied for the elimination of certain growth-layer sequences after 

 the collection is brought to the laboratory, if such elimination is at- 

 tempted with justification. 



3. Partial disagreement among the various trees, growth layer 

 to growth layer, emphasizes a definite localization of site factors to 

 each tree. 



4. Disagreement among the trees increased with increasing distance, 

 distance measured in yards rather than in miles. 



5. Intergroup correlations (of groups 4, 5, and 9) were merely fair, 

 not at all striking. They show a dual influence of site and distance. 



6. In so far as the collection from Holman Pass is concerned, the 

 nature of the species is clearly subordinate to the influence of site. 



