Bristlecone Pine Tree

Il termine pino di bristlecone comprende tre specie di alberi di pino ....

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 Pinus longaeva is more than 5,000 years old, making it the oldest known individual of any species.

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. In gardens, they succumb quickly to root rot. They do very well, however, where most other plants cannot even grow, such as in rocky dolomitic soils in areas with virtually no rainfall.

Bristlecone pines grow in scattered subalpine groves at high altitude in arid regions of the Western United States. Bristlecones, along with all related species in class Pinopsida, are cone-bearing seed plants commonly known as conifers; the name comes from the prickles on the female cones

Species and range

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 and, unlike the other two, is commonly 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 160-mile (260 km) gap between the ranges of P. longaeva and P. aristata and the northern Owens Valley provides a 20-mile (30 km) gap between the ranges of P. longaeva and P. balfouriana.

Description

Bristlecone pines grow in isolated groves just below the tree line, between 5,600 and 11,200 ft (1,700 and 3,400 m) 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.[8] 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 wood is very dense and resinous, and thus resistant to invasion by insects, fungi, and other potential pests. The tree's longevity is due in part to the wood's extreme durability. While other species of trees that grow nearby suffer rot, bare bristlecone pines can endure, even after death, often still standing on their roots, for many centuries. Rather than rot, exposed wood, on living and dead trees, erodes like stone due to wind, rain, and freezing, which creates unusual forms and shapes.