PRELIMINARY STUDIES ON THE YELLOW PINE. 



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Annual precipitation in inches (dotted lines) 



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NUMBER OF TREES NECESSARY FOR RELIABLE RESULTS. 



In seeking the best curve of tree-growth which a given locality 

 can supply, it might be thought at first that a very large number of 

 trees must be obtained in 

 order to get an average, 

 but experience has shown 

 that the number may be 

 very small. In order to 

 test the accuracy ob- 

 tained from a small num- 

 ber of trees, a comparison 

 was made between large 

 groups and small. Of the 

 original 25 trees in the 

 first Flagstaff group, 19 

 were subjected to very 

 careful cross-identifica- 

 tion. Averages were then 

 obtained of the oldest 5, 

 going back about 400 

 years, the oldest 10 (350 

 years), the oldest 15 (300 

 years), and the entire 19 

 reaching back only 200 

 years. Finally, the record 

 of the oldest 2 was carried 

 back fully 500 years. On 

 plotting the groups of 15, 

 10, and 5 with its exten- 

 sion of 2, it became im- 

 mediately evident that 5 

 trees gave almost the same 

 growth as 15, even to 

 small details. Between 

 these 5 and the oldest 2 

 taken by themselves the 

 agreement was not quite 

 so perfect, yet was so close 

 that errors thus intro- 

 duced would not affect 

 the curves. It must not 

 be taken for granted 

 without test that this re- 

 markable agreement be- 

 tween very small groups 

 of trees is true necessarily 

 for other trees or even for 





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Monthly precipitation in inchest solid lines.) 



FIG. 2. Monthly and yearly precipitation at Prescott and 

 size and character of rings. 



