METHOD OP ESTIMATING RAINFALL BY GROWTH OF TREES. 



Ill 



indicate clearly that the chief cause of doubling is a deficiency of snowfall in the winter 

 months, December to March. This appears to mean that if the winter precipitation is 

 sufficient to bridge over the usual spring drought, the growth continues evenly through 

 the year, giving a large single ring which ends only in the usual red growth as the severity 

 of winter comes on. If, however, the preceding winter precipitation has not been entirely 

 adequate, the spring drought taxes the resources of the tree and some red tissue is formed 

 because of deficient absorption in the early summer before the rains begin. 



£ 20 

 o. 



o 10 

 ■g 



Year 

 1905 



Sec 6. 



7-=^ 



Sec. 7 



Sec. 3 



Sec. 2 



Sec. 1 



4.0 

 3.0 

 2.0 

 1.0 



1.0 e 



a 



w 



g 



1.5 I 

 1.0 E 



1.0 I 



< 



1.0 



0.5 



0.5 

 0.0 

 0.5 

 0.0 



JuJ>' Oct. Jan. Apr. 



"Solid line=Rainfall producing; 

 big doubles, 1..55 mm. 



luly Oct. Jan. Apr. 



Dotted line=Rainfall producingr 

 big singles. 1.54 mm. 



S. 5.0 



Fig. 13 



Fig. 14 



Fig. 12. — GrowthofIndividu.il 

 Trees compared with Pre- 

 cipitation at Flagstaff. 



Figs. 13 and 14. — Effect of Monthly Distribution of Precipitation on 

 Thickness of Rings of Growth. 



It appears further that if not only the winter snows are lacking, but the spring rains 

 are unusually scantj% then the tree may close up shop for the year and produce its final 

 red tissue in midsummer, gaining no immediate benefit from the summer rains. This 

 appears to be the interpretation of the lower diagram of figure 13. Here the same 6 big 

 doubles mentioned above are plotted, together with a selected list of G small singles par- 

 ticularly deficient in red tissues. They are 1904 (double once in ten), 1902 (double once 

 in ten), 1899 (single), 1895 (single), 1894 (single) and 1880 (double once in ten). In these 

 it is evident that drought in the spring stops the growth of the tree. The double ring 

 therefore seems to be an intermediate form between the large, normal, single ring, growing 

 through the j'ear, and the small, deficient ring, ending its growth by midsummer. This 

 probably explains why the Prescott trees do not show an agreement of more than about 

 70 per cent between growth and rainfall. It .suggests also that the Flagstaff trees which 

 grow under the conditions of more rainfall, and which have very few double rings, give a 

 more accurate record than those of Prescott. Consistent with this view of the doubling is 

 the condition of the outer rings in the various Prescott groups collected by Mr. Hinderer. 

 These trees were cut during various months from May to November. Naturally those cut 



