Ancient Bristlecone Pine Natural History

Standing as ancient sentinels high atop the White Mountains of the Inyo National Forest, the Great Basin bristlecone pines rank as the oldest trees in the world and have achieved immense scientific, cultural and scenic importance. These trees (Pinus longaeva) are found in the mountains of eastern California, scattered throughout the high mountain regions of Nevada and to a lesser extent, Utah. A cousin, the Rocky Mountain bristlecone pine (Pinus aristata), is located throughout the eastern Rocky Mountain region in Colorado and New Mexico. An isolated population of P. aristata is also located near Flagstaff, Arizona. A third member of the bristlecone pine family, the Sierra foxtail pine (Pinus balfouriana) is located in the southern Sierra range and in isolated groves in northern California.

Classification

Originally classified as a foxtail pine because of the needle arrangement (like a cat or fox's tail), these trees were redesignated in the late 1800s and named bristlecone due to the long prickly "bristle" on the immature cone. In 1963, Dr. Dana K. Bailey determined that there were significant genetic and physical differences between the bristlecones in the Great Basin and those in the Rocky Mountains. His research efforts resulted in another redesignation into two separate species named bristlecone: the Rocky Mountain bristlecone pine and the Great Basin bristlecone pine.

Habitat

In the White Mountains, the ancient bristlecone pines seem to show a preference for growing on the white, rocky soil that gives the name to this mountain range.

This is dolomite, a type of limestone created under the warm, shallow, inland sea that once covered this area. This dolomite is very alkaline in soil chemistry and thus makes for very challenging growing conditions: precisely why the oldest trees are found here. The bristlecone pines don't actually prefer this soil type. Other plant species have a very difficult time growing in it and the bristlecones, because they have adapted to this high alkalinity, have a chance to get established and grow in a near competition-free environment. In other areas, such as the Great Basin National Park, bristlecones have established themselves on soil types that are equally inhospitable to all but the most hearty of survivors.

Life History

Every year, trees produce a new layer of wood just under the bark. During a dormant period, or time of slower growth, a narrow band of dark wood is produced which when added to the lighter colored "summer growth", produces what we see as a distinguishable tree ring. In wet years, the width of this layer of new wood is usually wider than in years of drought. The bristlecone pines are known as great recorders of these climatic variances due to their high sensitivity to changes in annual precipitation. Scientists who study and research tree-ring patterns are known as dendrochronologists; they are called dendroclimatologists if they specialize in climate research through tree-ring records.

Aging/Dating Bristlecones

Researchers use a device called an increment borer to extract a small cross-section of a tree. This sample provides a look at each tree ring and enables scientists to determine both the age of the tree and the pattern of its growth. There are many trees in the bristlecone pine forest of the White Mountains that exceed 4000 years of age, and are still growing. Recent research indicates there is a living tree older than 5,000 years.

Bristlecone pine wood that has fallen to the ground can remain intact for thousands of years in the cold, dry climate of the White Mountains. Using a cross-dating technique that overlaps tree-ring patterns of living trees with the still intact patterns of dead wood, scientists have assembled a continuous tree-ring chronology extending nearly 10,000 years. This bristlecone pine chronology, developed here in the White Mountains by University of Arizona researchers and Dr. Henry Michael of the University of Pennsylvania is the longest in the world and provides an unequaled look into past climatic and environmental conditions.

For many years now, scientists, archeologists, and historians have relied on a dating system known as radiocarbon dating. It was discovered back in the 1960s that this process was flawed and needed to be calibrated. The wood from bristlecone pines helped correct this process by providing samples that could be precisely dated. Scientists dated these samples by counting their growth rings; they then measured the amount of carbon-14 (C-14) in those same samples. They discovered that the radiocarbon dating process was providing dates that were "too young" and established a calibration factor to correct the dating process.

Faulty C-14 data obtained before the bristlecone pine calibration was then re-examined and corrected. Archeologists found that some artifacts discovered in Europe were actually 1000 years or older than previously thought. This revision of archeological site dates led historians to a reinterpretation of cultural diffusion throughout the Mediterranean and European areas. Because the bristlecone pines of this grove provided the wood to recalibrate the radiocarbon dating method, they have become known as the trees that rewrote history.