Schulman • Tree-rings and History in the Western United States 



183 



Leonardo da Vinci near a.d. 1500 to 

 this effect is the earliest only because 

 far earlier ones were not recorded or 

 have been lost, perhaps in the disap- 

 pearance of the Alexandrian Library! 



Despite this ancient recognition of 

 tree-rings as an historical index, mod- 

 ern scientific research on ring-growth 

 at first quite properly emphasized bo- 

 tanical and ecological aspects. By the 

 end of the nineteenth century a truly 

 vast amount of work had been done on 

 the nature of such growth layers and 

 their complex relationships to climatic 

 and other factors. 



In recent decades, however, many 

 investigators in this country and abroad 

 have sampled various forest stands and 

 have measured several millions of an- 

 nual rings in an effort to develop long 

 chronologies which might represent, to 

 some extent, histories of past rainfall, 

 temperature, river flow and other cli- 

 matic variables. The stimulus for this 

 activity arose, in good part, in an as- 

 tronomical objective! 



Quite independently, it occurred to 

 a Dutch astronomer, later renowned 

 for his contributions on stellar statis- 

 tics, and to an American astronomer, 

 studying variations such as those of the 

 markings on Mars, that the rings of 

 trees might directly or indirectly re- 

 cord year-by-year changes in the sun. 



Julius C. Kapteyn, about 1880, ex- 

 amined oak sections from western 

 Germany and Holland and derived a 

 240-year ring chronology. The later dec- 

 ades of this history corresponded well 

 with rainfall data, and a strong, but 

 quite unexplainable, cyclic variation 

 of 12.4 years was present throughout. 

 Fortunately for astronomy, Kapteyn 

 evidently felt this work to be strictly 

 extra-curicular, for he carried it no fur- 

 ther. But his single paper on the sub- 

 ject, a published lecture in Pasadena 

 in 1908, is a delight to read for its sim- 

 ple presentation of essentials and its 

 humility. 



In contrast to this somewhat abor- 

 tive effort, the program of research ini- 

 tiated by A. E. Douglass at Flagstaff, 

 Arizona, in 1904, has been carried on 

 for almost half of a century at the 

 University of Arizona, at Tucson, and 

 has led to important developments in 

 quite unexpected directions. The most 

 spectacular development was a method 

 which made it possible to precisely date 

 many ruins and thus provide a time- 

 scale for the pre-Spanish cultures of the 

 Southwest. This method is based on 

 detailed matching or cross-dating of 

 the patterns in tree-rings— an applica- 

 tion of the operation of forecast-and- 

 verification, which is such an integral 

 part of the scientific method. It proved 

 to have far-reaching implications in 

 climatic studies as well, for it was the 

 essential key to the development of 

 highly significant tree-ring histories of 

 rainfall and other climatic variables. 



We thus see that modern tech- 

 niques in dendrochronology find their 

 principle application in two fields of 

 research: (a) dendro-climatology, that 

 is, historical climatology based on fluc- 

 tuations in ring-growth, and (b) 

 dendro-archaeology, the dating of pre- 

 historic structures and activities by the 

 precise dating of ancient wood. 



DENDRO-ARCHAEOLOGY 



The method of overlapping patterns 

 by means of which prehistoric beams 

 may be dated is illustrated in highly 

 idealized form in Fig. 1. It is evident 

 that matching the outer rings of an old 

 beam with the inner rings in a living 

 tree serves two purposes, namely, to 

 date the old beam and to extend into 

 earlier times the potential climatic 

 chronology in the living tree. 



Those acquainted with the great 

 range of variability', which seems to be 

 one of the universal properties of bio- 

 logic elements, will recognize that such 

 simple growth and perfect synchrone- 



