The term bristlecone pine covers three species of pine tree (family Pinaceae, genus Pinus, subsection Balfourianae). All three species are long-lived and highly resilient to harsh weather and bad soils. One of the three species, Pinus longaeva, is among the longest-lived life forms on Earth. The oldest of this species is more than 4,800 years old, making it the oldest known individual of any species. Many scientists are curious as to why this tree is able to live so long. In one study, they discovered that Pinus longaeva has higher levels of telomerase activity, which further slows or prevents the attrition rate of telomeres. This potentially contributes to the extended life of the bristlecone pine.

Despite their potential age and low reproductive rate, bristlecone pines, particularly Pinus longaeva, are usually a first-succession species, tending to occupy new open ground. They generally compete poorly in less-than-harsh environments, making them hard to cultivate. They do very well, however, where most other plants cannot even grow, such as in rocky dolomitic soils in areas with virtually no rainfall.

Species and range

thumb|Great Basin bristlecone pines in the [[Ancient Bristlecone Pine Forest of the White Mountains, California]]

There are three closely related species of bristlecone pines:

  • Great Basin bristlecone pine (Pinus longaeva) in Utah, Nevada and eastern California. The famous longest-lived species; often the term bristlecone pine refers to this tree in particular.
  • Rocky Mountain bristlecone pine (Pinus aristata) in Colorado, New Mexico and Arizona. The most populous species; capable of forming closed canopies. Dwarf forms of this pine are sometimes cultivated.
  • Foxtail pine (Pinus balfouriana) with two disjunct populations found in the Klamath Mountains (subspecies balfouriana) and the southern Sierra Nevada (subspecies austrina). A small outlying population was reported in southern Oregon, but was proven to have been misidentified. Forms the thickest groves of the three.

At least some of the three species can hybridize in cultivation, but the ranges of wild populations do not overlap. The Colorado River and Green River produce a gap between the ranges of P. longaeva and P. aristata and the northern Owens Valley provides a gap between the ranges of P. longaeva and P. balfouriana.

Description

Bristlecone pines grow in isolated groves just below the tree line, between elevation on dolomitic soils. The trees grow in soils that are shallow lithosols, usually derived from dolomite and sometimes limestone, and occasionally sandstone or quartzite soils. Dolomitic soils are alkaline, high in calcium and magnesium, and low in phosphorus. Those factors tend to exclude other plant species, allowing bristlecones to thrive. Because of cold temperatures, dry soils, high winds, and short growing seasons, the trees grow very slowly. Even the tree's needles, which grow in bunches of five, can remain on the tree for forty years, which gives the tree's terminal branches the unique appearance of a long bottle brush.

The bristlecone pine's root system is mostly composed of highly branched, shallow roots, while a few large, branching roots provide structural support. The bristlecone pine is extremely drought tolerant due to its branched shallow root system, its waxy needles, and thick needle cuticles that aid in water retention. The species are on the International Union for Conservation of Nature (IUCN) red list. The name bristlecone pine refers to the dark purple female cones that bear incurved prickles on their surface. The dark color of these cones helps to absorb heat. After maturity, which takes about two years, the cones will become brown in color. As the tree ages, much of its vascular cambium layer may die. In very old specimens, often only a narrow strip of living tissue connects the roots to a handful of live branches. Even though the trees' needles may age, they still remain functional in regulating water and by their ability to photosynthesize.

The other two species, Pinus balfouriana and Pinus aristata, are also long-lived, though not to the extreme extent of P. longaeva; specimens of both have been measured or estimated to be up to 3,000 years old. The longevity of the trees is believed to be related to the proportion of dead wood to live wood. This high ratio reduces respiration and water loss, thereby extending the life of the tree. although tree ring samples date individual, above-ground trees at an average of about 130 years.

Bristlecone pines are invaluable to dendroclimatologists, because they provide the longest continual climatically sensitive tree-ring chronologies on Earth. By cross-dating millennia-old bristlecone pine debris, some chronologies reach beyond 9,000 years before present.

The Rocky Mountain population is severely threatened by an introduced fungal disease known as white pine blister rust, and by mountain pine beetles. Climate change may also affect the species as temperatures increased over a 30-year period throughout the southern Rocky Mountain range. These changes in climate would mostly affect trees in higher elevations. With these problems, the genetic diversity within the species has become a concern; old specimens of bristlecone pine, however, have survived previous warmer periods.

See also

  • List of longest-living organisms

References

Further reading

  • Gymnosperm Database – Pinus longaeva, Pinus aristata, Pinus balfouriana
  • Prometheus: The Martyred One