TREE RINGS AND HISTORY — SCHTJLMAN 473 



It is of no little interest to find, in the over-age conifers, a strong 

 suggestion that a century of great drought in the Southwest was 

 followed during the 1300-s by a century of seldom-interrupted rainy 

 years. This very wet interval was perhaps the greatest in two thousand 

 years in this region, as the supplementary evidence in the archeo- 

 logical chronologies suggests. 



A gi-eat deal of attention has been devoted to the attractive hypoth- 

 esis that tree-ring series contain a history of solar or other extra- 

 terrestrial variations, especially cyclic ones. Some instances of direct 

 parallelism which have been noted between sunspot variation and 

 the ring growth of certain trees are often cited and indeed may not 

 be entirely due to chance. In general, however, extraterrestrial vari- 

 ations, if they are recorded by trees, must be in very complex form 

 and are largely obscured by what seem to be random cyclic variations, 

 for no aid toward the solution of the problem of long-range climatic 

 forecasting is as yet established in growth cycles. Nevertheless, the 

 very great importance of the problem and the strong evidence that 

 real, if hidden, nonterrestrial effects are, in fact, present in such 

 growth cycles, would seem to justify contmued scientific inquiry. 



Geographic distribution of drought conifers. — Do over-age conifers 

 providing significant rainfall clironologies exist on other continents ? 

 It now seems quite certain that they do. 



Along the foothills of the Patagonian Andes of Argentina, between 

 latitudes 38" S. and about 43° S., dry sites comparable to the semi- 

 arid Rocky Mountain margins were sampled in early 1950 by the 

 writer. In two coniferous species, Araucaria imbricata Prav. and 

 Lihocedrus chilensis Endl., the ring records showed the characters of 

 sensitivity and cross-dating which are essential for the derivation of 

 climatic chronologies. Since these conifers are developed only in 

 scattered stands in a very thin and short belt between the line of the 

 Andes and the plains, little area is available for development of long- 

 lived strains. Yet the same inverse relation between mean growth 

 rate and age was found for the two Patagonian species as for the 

 conifers of the Rockies. When the analysis of these collections and 

 others in southern Chile is completed, some hundreds of years of 

 climatic chronology for Patagonia should be available. 



Xerophytic conifers, and possibly some hardwood species, exist in 

 apparently suitable environments in a number of other regions, par- 

 ticularly in Asia, and will probably be found to provide significant 

 rainfall chronologies ; little exploration seems yet to have been made 

 of the extensive Siberian forests as sources of temperature chronol- 

 ogies. In the light of present knowledge, hov/ever, it appears that the 

 combination of factors which makes possible long tree-ring histories 

 of climate is particularly favorable and widespread in western North 

 America. 



