This entry was originally published in Spanish in ¿Cómo ves? magazine, August 2012.
At the foot of the Cerro del Chapulín in Chapultepec Forest there is a fragrant and beautiful park smack in the middle of Mexico City. The park is home to a very Mexican tree species, the ahuehuete, known for its longevity. Some of the ahuehuetes in Chapultepec have their age marked with red paint on the trunk —400 years, 500, 600… The most ancient of these trees were there before the founding of the Aztec city of Tenochtitlan.
I discovered the labels on the trees a few years ago, while strolling in the shade of the old ahuehuetes. I knew that the age of some tree species is determined by counting the growth rings in a cross section of the tree trunk. How could the age of the Chapultepec trees be calculated without cutting them down? I didn’t know it then, but this is the way it is done: you plug a special drill into the trunk and turn a crank until the drill reaches the core of the tree; out of the drill comes a thin, striped cilinder; the stripes are sections of growth rings. You then head back to your laboratory and count stripes under a microscope. The number of stripes gives the approximate age of the tree. To me it was a revelation --and a relief-- to learn that it could be done without killing the tree.
In Search of Time Accumulated
Actually taking the samples, however, can be complicated, as Donald Currey, a graduate student from the University of North Carolina, discovered in 1964. Currey was conducting research on climate change during the period paleoclimatologists call the Little Ice Age, which runs from about 1300 to 1850. During this period world temperatures dipped several degrees. The Little Ice Age had consequences ranging from the biological to the social, but that’s a different story.
Donald Currey needed samples from ancient individuals of the species Pinus aristata, known as brisltecone pine, a tree that dwells in the highest mountains of the southwestern United States. He wanted to do a statistical study of the relationship between the age of the trees and the altitude at which they grow. This would help him tell whether climate changes during the Little Ice Age had modified the altitude of the tree line. If he found very old bristlecones close to the present-day tree line, then Little Ice Age changes could not have been too severe.
Since the 1950s, when Edmund Schulman discovered that bristlecone pines keep very precise and readable registers of climes past in their growth rings, ecologists were convinced that the oldest individuals grew in the White Mountains of California, on the western limit of the species’ habitat. There Schulman found bristlecones more that 4000 years old, which he made famous in an article that appeared in the January, 1958 issue of National Geographic. Schulman died weeks before the article was published.
Schulman’s pines became famous for their eerie beauty. When they reach millennial ages, the gnarled branches of these trees stretch to the sky like pleading arms, and their convoluted trunks of dead, barkless wood seem to fly in the wind like the robes of a Biblical patriarch. The bristlecones of California were also celebrated as the oldest known living organisms.
Donald Currey did not go to California, however, but to Nevada, at the center of the bristlecone habitat. There the young scientist found what he was looking for in a grove of wondrously old-looking pine trees growing at the edge of a deep valley carved out by an ancient glacier in Wheeler Peak. The trees looked as aged as Schulman’s, notwithstanding the dogma that the species only reached extreme ages in California. The young man chose the oldest-looking tree, sank his drill into the trunk, and began to turn the crank. Crick, crick, crick went the drilll as it bit deeper and deeper into the wood of the Methuselah of trees. Crick, crick… CRACK! The crank snapped in Currey’s hand. The device had broken its teeth in the rock-hard wood. Without a spare drill and with the academic calendar against him (he had to turn in a report to the National Science Foundation before the end of the summer), Currey went to the Forest Service for help.
As the first civilization was inventing the plow in Mesopotamia, in a different continent a sapling was growing at the edge of a glacial valley. With the first snows of the alpine winter, at close to 10,000 feet, the little tree entered a phase of lethargic growth as it waited for better times. When the brief summer came, it grew in a desperate spurt to profit from the sunlight and rain. The wood it made during this accelerated growth phase was less dense than the wood produced in the severe conditions of winter. The cycle was repeated through the ages, and the yearly ebb and flow of growth and dormancy was recorded in the stuff of the trunk.
Tree rings represent alternate phases of rapid wood production, when the tree has plentiful sunlight and rain, and slow growth, when sun and nutrients are scarce. Generally, one would expect this cycle to match the cycle of the seasons —in which case each ring would represent a year’s growth—, but if drought strikes in midsummer followed by abundant rains in the fall, the tree will produce two rings. On the other hand, if the whole year is bad —with unseasonable cold, drought and insufficient sunlight—, there simply won’t be a measurable ring to speak of.
Tree rings, then, are not only a proxy for the tree’s age. In their width and other characteristics, nature has written a detailed, year-by-year history of varying weather. Growth rings are like the personal diaries of the tree world. Matching ring sequences from many different trees to average out errors due to double or missing rings, climatologists can build chronologies of past climates. The tecnniques of dendrochronology (dendros means “tree” in Greek), help scientists recognize patterns of climate change with periods as short as one year or as long as several centuries.
Our tree grew old as humanity went from the Bronze Age to the Space Age. Its environment didn’t change much, except for the weather. The land on which it grew remained stable, but for occasional avalanches that deposited two feet of rubble on top of the original ground. The glacier that carved the valley was already long-gone when the tree was a sapling.
But one day in August, 1964…
The Truth and Nothing But?
What happened when Donald Currey went to the Forest Service for help is not clear. One version has it that the scientist asked permission to cut down the tree and take a slab of trunk, which would be more cumbersome than the thin cilinder from the drill, but would certainly simplify the actual counting of the rings. According to another version, it was Donald Cox, from the Forest Service, who suggested that Currey cut the tree, which was, after all, one of many ancient bristlecones in the area. However it happened, Currey went back up the mountain with pack horses and Forest Service personnel armed with chainsaws. The men brought down the ancient tree.
Very satisfied —or perhaps not—, the young researcher took a large wooden slab more than two meters in diameter down the mountain to his hotel in Baker, Nevada. The next day he set the slab on a table outdoors, took out a magnifying glass and some sandpaper to bring out the grain in the wood, and started counting. By the end of the first day he had counted back to the Middle Ages. This did not surprise him, because he already had core samples from 113 trees from Wheeler Peak. He knew they were really old. Currey counted on. The following day he had reached back to the time of the Roman Empire —and he was not even halfway through the counting.
In 1965 Donald Currey published a paper in the journal Ecology. By that time his goal had changed from building a chronology of the Little Ice Age to proving that Schulman had been wrong to believe that the oldest individuals of the species Pinus aristata were to be found only in California. Here is what Currey writes regarding the tree he named WPN-114 (the 114th tree from Wheeler Peak, Nevada): “The tree-ring series contains both distinctively thin (microscopic) rings and difficult-to-count incomplete (locally absent) rings.” This did not daunt the scientist. He went on counting rings for one week. The article continues: “The derived radius measures 2,280 mm to the pith, 100 inches above the original base, and encompasses 4,844 counted rings.” Then, in the same serene, unfathomable monotone, he adds: “Allowing for the likelihood of missing rings and for the 100-inch height of the innermost counted ring, it may be tentatively concluded that WPN-114 began growing about 4,900 years ago.”
The impersonal drone typical of scientific papers conceals what the author must have felt when he discovered that his tree began life before the birth of Greek civilization, and even before the Ancient Empire in Egypt. Schulman’s oldest specimen was 4,600 years old. Currey had found one that was even older… and he had cut it down.
It was Currey’s misfortune that the people of Baker had grown fond of the trees in the old grove on Wheeler Peak. Darwin Lambert, an official with the Forest Service, had formed an association to promote the creation of a national park in the area to protect them. To make things more poignant, Lambert had even named every individual tree. Currey’s was called Prometheus.
In 1966 Darwin Lambert, who by then had nourished the park project for years, heard that a researcher from North Carolina had found in Wheeler Peak the oldest living tree in record. Lambert felt a jolt of excitement at the possibility that it was one of his trees. He procured a copy of the journal where the researcher had published his paper and his heart sank when he understood that the tree in question had been destroyed. Understandably, Lambert flew into a rage and wrote an article in a local newspaper. The media and the public went after Currey, accusing him of killing “the oldest living organism in the world.” Overwhelmed, the young man hid in his university and tried to keep a low profile, as scientists will after a clash with the media.
Now, Currey killed (the term may be too strong in its overtones) the oldest living organism known at the time, which does not necessarily mean that Prometheus was the oldest tree in the world. We do not know the age of every tree in existence. There may be others that are even more ancient. It is misleading to call Prometheus the oldest living organism in the world. And exactly what is an individual organism? Many plants reproduce by a kind of natural cloning mechanism consisting in throwing offshoots that are genetically identical to the original plant. The offshoots form a clonal colony. One can argue that the clonal colony is an organism that lives on even if the individual plants die. There is a clonal colony of creosote bushes which we know for certain to be 11,700 years old. In the state of Utah there is a colony of quaking aspen trees linked by an enormous root system that has lived for some 80,000 years (though not one of the individual trees is more than a couple of centuries old). Prometheus was the oldest living non-clonal organism known in 1965, not simply the longest-lived being on the planet.
One more detail: Currey found on Wheeler Peak the remains of pines of the same species scattered all over the place. The trees had been cut down without consideration by surveying expeditions in the 19th century. Some of those trees were probably older than Prometheus. Currey was “appalled by the destruction.” This was not contrition enough. In the eyes of the public he remained a heartless murderer.
Today bristlecone pines are recognized as useful to science. In 1970 a researcher by the name of D. K. Bailey found variations in the form of the pine cones and needles of bristlecones from different regions. Bailey proposed dividing the species in two: Pinus aristata and Pinus longaeva. Climate chronologies based on the growth rings of this species as well as on pieces of deadwood (dated by radiocarbon) reach almost 9,000 years into the past. The oldest living non-clonal organism known today is one of Schulman’s bristlecones. Named Methuselah, it is 4,844 years old as of 2012 and its location is kept secret.
There is another turn of the screw in the story of Donald Currey and the Prometheus tree. Darwin Lambert, the national park advocate, and his group never could get the US National Park System to approve the recommendation to create a park in the mountains of Nevada. The area’s resources (mining, hunting, pastures) were too rich to give up in the name of tourism and the environment. Powerful lobbies opposed the park. The death of Prometheus gave the project a new edge by focusing attention on the need to protect bristlecone pines. Currey’s error contributed at least a little to tilt the balance and finally, in 1986, the Great Basin National Park was created.
Donald Currey endured as best he could the grief that his mistake caused him. At the time of his death, in 2004, he still was not over it. As for Prometheus, all that remains of the once proud ancient is an inglorious stump.