In my other blog (flowertropes.com) I just wrote about the tallest tree (coast redwood) and the largest tree (giant sequoia), both of which live on the west-facing slopes of the California Coast Range and the Sierra Nevada, respectively. The oldest living trees live on the east side of the Sierra Nevada and in subalpine environments scattered across the Great Basin of Nevada into Utah and down into Arizona and New Mexico.
The bristlecone pine is the common name applied to three species of conifer: Pinus longaeva, P. aristata, and P. balfouriana. They aren’t particularly common, but their timberline populations seem to be growing in response to warmer conditions there, where they are sometimes the only tree species present because of the challenges presented by the environment. In other altitudes and other parts of their range, their inherently low reproduction rate has caused a steady erosion of their numbers.
P. longaeva (Great Basin bristlecone) shows a distinct preference for carbonate soils, derived from limestone, marble, but especially dolomite. The latter are rich in calcium and magnesium, but poor in phosphorus. This limits the growth of many plants, which reduces competition for the pines, allowing them to form groves. When these groves are just below the treeline additional challenges are presented, including low temperatures, low rainfall, and high winds. Consequently the trees grow very, very slowly in these conditions.
The wood of these pines is very resinous and their slow growth makes it very dense. This combination makes the wood resistant to insects, fungi, and other pathogens, as well as the physical elements.
The above factors conspire to cause the bristlecone pine to live for thousands of years. The oldest known living specimen is over 5,000 years old, which makes it as old as the pyramids at Giza. This tree is growing in the White Mountains of California and its location is kept secret. It was discovered in the 1950s by Edmund Schulman, a pioneer in the study of these trees, but its age was not determined until 2012, when it was found to be 5,060 years old.
This is not the “Methuselah” tree that was the oldest known living bristlecone until 2012. That tree was also discovered by Schulman and was dated 4,789 years old in the late 1950s. It is now 4,847 years old and reportedly quite healthy and still growing.
A tree is Wheeler Peak, Nevada was cut down in order to determine its age. This story is found in numerous places on the Internet. There is a lengthy version of it here. In 1964 a geography student doing research on the glacial history of the Great Basin. He and a partner were coring bristlecone pines on Wheeler Peak to determine their ages and found that several were over 4,000 years old. Toward the end of their field season, their coring tool broke and they asked the U.S. Forest Service for permission to cut down a tree in order to count the rings.
Through the 1950s a group of conservationists had been attempting establish a Great Basin national park in order to protect the trees. Various other land-use interests conspired against the establishment of the park, but in the process of traveling regularly to Wheeler Peak, the conservationists had given names to individual trees. The one that was cut down was called “Prometheus,” and it had proved to be 4,862 years old. It became a cause celebre and helped bring further protection to the trees. The national park was eventually established in 1986.
Because of its dense resinous nature and the aridity of its habitat, the wood of the bristlecone pine doesn’t decompose when it dies and falls to the ground. Dead trees can also remain standing for centuries. Dendrochronologists, scientists who determine the age of trees, decades ago noticed that tree rings include patterns of thinner and thicker bands that correspond with variations in the regional climate. (Bristlecone pines seems to respond to variations in temperature more than rainfall.) Using statistical analysis these shared patterns can be matched from tree to tree.
The overlaps between tree-ring patterns of living and dead bristlecone pines have been found and then overlaps have been found in the tree-ring patterns of older dead pines. In this way a composite record has been extended back nearly 9,000 years.
Geochemists have sampled the carbon in these rings (which can be dated to an exact year simply by counting) to determine their carbon-14 content. It has been found that the ratio of carbon-14 to carbon-12 has fluctuated over the millennia. The carbon-14 record in the composite tree-ring record has allowed geochronologists to “correct” the radiometric age dates determined from carbon-14, making the method more accurate.