SOME TOPOGRAPHIC AND CLIMATIC CHARACTERS IN 



THE ANNUAL RINGS OF THE YELLOW PINES 



AND SEQUOIAS OF THE SOUTHWEST. 



By a. E. DOUGLASS. 

 (Read April 21, 1922.) 



The material here presented is part of a long-continued investi- 

 gation of historical data contained in the annual rings of trees. Such 

 data naturally are impressed by the environment, and the factor of the 

 latter which interests us most is the climate. In this study as a 

 whole, some 500 trees have been used, scattered in groups from Cali- 

 fornia to Austria. About 110,000 rings have been dated and meas- 

 ured. The conclusion hitherto reached may be stated in a few sen- 

 tences. First : the rings in the groups studied may be dated with 

 practical certainty. This is not intended as a general statement for 

 all trees in the world, because the identification of rings seems to 

 increase in difficulty as the snowfall of winter decreases. Second : 

 the yellow pines in the dry climate of northern Arizona give in their 

 rings a rainfall record of considerable accuracy, namely, 70 per cent, 

 in groups of trees near the rainfall record station. This is increased 

 to an accuracy of some 85 per cent, by the application of a simple 

 formula for conservation. Third : certain groups of wet-climate 

 trees, especially about the Baltic Sea, give a very exact record of 

 solar activity, as indicated by the relative sunspot numbers. Fourth : 

 the rings in certain wooden beams used in prehistoric construction 

 can be made to give us certain chronological facts. For example, it 

 has been shown by this means that the old ruin of Pueblo Bonito in 

 northwest New Mexico is forty to forty-five years older than that of 

 Aztec, some fifty miles north of it. Fifth : three mechanical aids 

 have been developed, a tubular borer for securing a core extending 

 from the outside to the center of a beam or a tree, a recording micro- 

 scope slide or micrometer for measuring ring widths, and a cycloscope 

 for rapidly determining periodic effects in a plotted curve. By this 



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