National Geographic : 1958 Mar
Douglass determined the age of Pueblo Bonito, New Mexico, in what is now Chaco Canyon National Monument. These expeditions pushed back the Southwest's historical horizon to more than 800 years before Columbus.* The Indians naturally preferred tall, straight young trees for building timbers. They rarely bothered with the gnarled vet erans that here and there clung to a dry sand stone ledge. Driven, however, by an 'entirely different need, we began sampling such "worthless" veterans. We were looking for old trees whose growth rings might give us a longer and more sensitive history of past droughts. Underprivileged Trees Live Longest At once it became evident that precisely under such difficult living conditions trees not only showed the expected high sensitivity to rainfall, but were able to live far beyond the normal life span of more "fortunately" located individuals of the species. There came a day when we could point, for example, to an inconspicuous Douglas fir clinging to a narrow ledge near Mesa Verde National Park headquarters and say: "That slender tree only 20 feet high began its life about A. D. 1375. It has seen sev eral generations of Douglas firs, like those now bordering the creek bed below, grow to magnificent size and then rot and die, while it remains sound to the core." And later it was a thrilling experience to find, sample, and date a cliff tree in Navajo Canyon near by with a life span reaching back to the time of the cliff dwellers of Mesa Verde, abandoned forever about A. D. 1290. An 860-year ponderosa pine in Bryce Can yon National Park, a 975-year pifion pine in central Utah, and other grand veterans gave us continuous tree-ring histories of an nual rainfall much longer than we had once thought possible. But after many years of hunting and sampling old trees throughout the semiarid West, it began to seem that we were approaching the absolute age limits for rain-sensitive dwarf trees in this region. Then, at the very end of the summer field season of 1952, an entirely unexpected find opened up new possibilities. Sampling a stand of old Douglas firs above Sun Valley, Idaho, we found an alpine-type limber pine with one side completely dead. The core from this tree could not reach center but seemed to have an unusual number of rings. That night with the aid of a flashlight at our camp below, I cut a surface on the sample 358 and examined it more closely. I was aston ished to find that the 16-inch core contained some 1,400 years of datable growth rings. Later we found that this limber pine was almost exactly 1,650 years old. But it was in the 1953 field season that the dazzling possibilities of new and fantasti cally long records of year-by-year rainfall in alpine trees became apparent. Prof. Frits W. Went, of the Earhart Plant Research Laboratory at the California Insti tute of Technology, joined me on another visit to the unusually old pines of Sun Valley, and we spent most of one day in cutting down, for detailed laboratory analysis, the 1,650 year pine discovered the preceding year. The next day, with the help of the Forest Service, we piled much of it into our truck and took off for Pasadena, where I was working at Caltech on a year's leave from the Univer sity of Arizona. On our homeward drive we detoured into the White Mountains of California, to check on a rumor that old trees existed there. Often such rumors had turned out to be unfounded. But not this one! "Patriarch" a Mere 1,500 Years Old In this portion of the Inyo National Forest a multiple-stemmed bristlecone pine tree some 37 feet in over-all circumference near the base had been reported some years earlier by the local ranger, A. E. Noren, who had named it the Patriarch (page 362). We sampled the Patriarch and found it to be about 1,500 years old, but with the typically insensitive ring growth of upper timberline. More exciting was our discovery that on drier sites near by lived 1,500-year-old bristle cones-upper-timber-zone trees-which were better recorders of drought years than even the Sun Valley limber pines. Sampling the stem of a very old bristlecone pine, however, proved quite a problem, for many of them are completely unorthodox in shape. Instead of the familiar circular cross section, these trees are distorted so greatly that often it is a major puzzle to locate the early portion of the stem. The strip of living tissue in an old, eroded stem may now be growing in a direction at right angles to its direction a millennium ago. How was I to get a complete sample from bark to center in such a tree? The available borers were not designed to go around a bend! * See "Secret of the Southwest Solved by Talka tive Tree Rings," by Andrew Ellicott Douglass, NA TIONAL GEOGRAPHIC MAGAZINE, December, 1929.