Pinus aristata

Pinus aristata, the Rocky Mountain bristlecone pine or Colorado bristlecone pine is a long-lived species of bristlecone pine tree native to the United States. It is found in the Rocky Mountains in Colorado and northern New Mexico, with an isolated population in the San Francisco Peaks of Arizona. It is found at very high altitudes, from Template:Convert in cold, dry subalpine climate conditions, often at the tree line, although it also forms extensive closed-canopy stands at somewhat lower elevations.

Description

Pinus aristata is a medium-size tree, commonly reaching Template:Convert in height and occasionally as much as Template:Cvt in their natural habitat. In favorable conditions they are straight and upright trees, but they become increasingly stunted, short, and twisted the closer they grow to timberline.<ref name="4Corners">Template:Cite book</ref> The crown of the tree is flattened, irregular, or round in shape when fully mature.<ref name="FNA">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The trunk can be very substantial, commonly Template:Cvt and up to Template:Cvt in diameter, and tapers very noticeably towards the top.<ref name="4Corners" /><ref name="FNA" /> The bark is fairly smooth and white-gray on young trees, but becomes dark and cracked with a scaly texture on old trees.<ref name="4Corners" /><ref name="Farjon" /> The color of older bark varies from red-brown to gray.<ref name="FNA" />

Young trees that are not stunted have evenly spaced whorls of branches.<ref name="Krüssmann">Template:Cite book</ref> On older trees the branches are crooked and twisting and may be partially dead.<ref name="Farjon">Template:Cite book</ref> Twigs begin as red-brown, but become gray with age.<ref name="FNA" /> Twigs and very young branches are covered in needles that last for 10 to 17 years, giving them a shaggy bottle brush appearance.<ref name="Farjon" /><ref name="4Corners" /> The needle like leaves are bundles of five and are 2–4 centimeters long, but usually longer than 3 cm.<ref name="FNA" /> The fascicle, the base that holds the needles together, breaks down more quickly in Pinus aristata than in Pinus longaeva, giving a more even appearance to its branches. The resin canals in the needles are closer to the surface and not as sturdy, explaining the noticeable white flecks of resin. The botanist Dana K. Bailey described the needles covered in resin as appearing "dandruffy".<ref name="Garden of Bristlecones" /> The small dried droplets are easily mistaken for scale insects.<ref name="Krüssmann" /> Between the white specks the needles are dark green in color. The buds are egg shaped with a long tapering point (Template:Plantgloss), about 1 cm in size.<ref name="FNA" /> New shoots are light orange and may covered in hairs or hairless.<ref name="Krüssmann" />

Cones

The pollen cone is approximately 1 cm in length and may be blueish to red colored.<ref name="FNA" /> Trees mature enough to produce seed cones are generally about 1.5 meters in height and 20 years of age.<ref name="Whitebark">Template:Cite book</ref> Seed cones are dark purple when immature and turn brown as they ripen. At full size they are 6–11 centimeters in length.<ref name="4Corners" /> A seed cone takes two years to fully ripen. Each scale of the cone is tipped with a thin, brittle pickle 4–10 millimeters long. They fall from the tree soon after releasing their seeds.<ref name="FNA" /> Pinus aristata has seeds that are gray-brown to nearly black in color with darker spots and 5–6 mm long. The seed has an attached papery wing 10–13 mm long.<ref name="FNA" /><ref name="Krüssmann" /> Their mean weight is 25 milligrams, significantly smaller than those of the whitebark pine at 175 mg, but much larger than the 4 mg of lodgepole pine.<ref>Template:Cite book</ref> Large crops of cones are produced only once per century on average.<ref name="Whitebark" />

Seedlings

The seeds of Pinus aristata easily germinate, with as much as 80% of the seeds being viable. Seeds that are mechanically damaged are colonized and killed by fungus. Each new sprout will have between seven and twelve needle-like seed leaves. The seedlings are quite vulnerable to cold temperatures with all being killed if exposed to temperatures of less than Template:Convert.<ref name="Reid">Template:Cite journal</ref>

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Longevity

Though they do not obtain the extreme age of the Great Basin bristlecone pines, Colorado bristlecones still reach quite advanced ages. There are 13 trees that are known to be older than 1600 years by reliable dating, including one on Mount Goliath dated to the year 403. Four of these trees exceed 2100 years of age and one is Template:Age years old (see Notable trees). Based on size and appearance scientists estimate there are 30 more trees in the same general area older than 1600 years that have not yet had core samples taken.<ref name="Brunstein" /> The botanist Aljos Farjon thinks that there may be trees that are older 3000 years of age that have yet to be scientifically scrutinized.<ref name="Farjon" /> At lower elevations in montane habitats where they grow with grasses, ages generally do not exceed 300 years.<ref name="FEIS">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

The Rocky Mountain bristlecone is known both for having stripes of dead wood on the trunks of older trees and for the extreme lengths of time that dead trees will remain sound. In this it is very much like the Great Basin bristlecone.<ref>Template:Cite journal</ref>

Taxonomy

File:Pinus aristata - Charles Edward Faxon.png

The branches and cones of Pinus aristata as illustrated by Charles Edward Faxon in The Silva of North America<ref>Template:Cite book</ref>

Pinus aristata was scientifically described in 1862 by George Engelmann with its present scientific name.<ref name="POWO" /> The botanical samples used to describe and name the species were collected in 1861 by Charles Christopher Parry, however the earliest known scientific collection was by Frederick Creuzefeldt in 1853.<ref name="Garden of Bristlecones" /> In 1878 Englemann worked on a reclassification of the taxon as a variety of Pinus balfouriana and in 1880 as a subspecies.<ref name="POWO" /> This reassessment was initially accepted by botanists such as Charles Sprague Sargent,<ref>Template:Cite book</ref> but was rejected by others such as Edward James Ravenscroft.<ref>Template:Cite book</ref> It is listed as an accepted species with no subspecies by Plants of the World Online,<ref name="POWO" /> World Flora Online,<ref>Template:Cite WFO</ref> and World Plants.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Prior to work by Dana K. Bailey published in 1971, Pinus longaeva trees growing in California, Nevada, and Utah were not identified as a separate species or subspecies.<ref>Template:Cite POWO</ref><ref name="PineTreeBook">Template:Cite book</ref> A distance of Template:Convert separates the populations of P. aristata from the closest groves of P. longaeva.<ref name="Sierra Club" />

Names

The species name aristata means "bristle" in botanical Latin, a reference to the long points on the ends of the scales of its cones.<ref name="Garden of Bristlecones">Template:Cite book</ref> As the first bristlecone identified, Pinus aristata is still occasionally referred to simply as bristlecone pine,<ref>Template:Cite book</ref> however Pinus longaeva is also sometimes called bristlecone pine in English.<ref name="Grandtner">Template:Cite book</ref> To distinguish it from its relative the name Rocky Mountain bristlecone pine has been used since at least 1971 and the similar Colorado bristlecone has been in use since at least 1976.<ref name="Gates">Template:Cite journal</ref><ref>Template:Cite book</ref> The common name hickory pine is used, most often in Colorado, due to the hardness and density of the wood being like that of a hickory.<ref name="Garden of Bristlecones" /> It is additionally known as foxtail pine and wind timber,<ref name="Grandtner" /> but the first of these names is more often applied to Pinus balfouriana.<ref>Template:Cite book</ref>

Range and habitat

The Colorado bristlecone grows in three western US states, Colorado, New Mexico, and Arizona.<ref name="USDA">Template:Cite usda plants</ref> The Rocky Mountain bristle cone reaches its northern limit at approximately 40 degrees north latitude.<ref name="Sierra Club">Template:Cite book</ref> They are widely distributed in the Southern Rocky Mountains, but are limited to small areas within its range.<ref name="Elmore">Template:Cite book</ref> The elevation range where it grows is widest, from Template:Convert, in the state of Colorado. The Arizona population is only found above 2900 m and only as high as 3700 m. In New Mexico the trees start at a similarly high elevation of 3000 m and have the same maximum as in Arizona.<ref name="White Pines">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Rocky Mountain bristlecone will grow in krummholz habitat at the edge of the alpine tundra, where it has the typical dwarfed and gnarled growth of these "crooked woods".<ref name="SouthwesternNP">Template:Cite book</ref> Its habitat extends downward into the subalpine forests and even lower in the driest parts of the middle elevations.<ref name="Arno">Template:Cite book</ref> The bristlecones and limber pines (Pinus flexilis) will grow into full trees at elevations where silver spruces (Picea engelmannii) and subalpine firs (Abies lasiocarpa) are reduced to stunted, ground hugging shrubs. Their greater tolerance of dry conditions is what enables them to grow more successfully in challenging mountain habitats.<ref>Template:Cite book</ref>

File:Summit - 1926 (5375570467).jpg

Bristlecone pine (Pinus aristata) at timberline, the summit of the San Francisco Peaks, 1926

In Arizona this species of bristlecone pine is only found on the San Francisco Peaks,<ref name="Sierra Club" /> four volcanic cinder cones in north-central Arizona.<ref name="Arno" /> Their alpine trees and flora resemble those of the Southern Rocky Mountains more than that of Nevada or California, including having Colorado bristlecone pines rather than Great Basin bristlecones. There they grow on south facing slopes together with limber pines. This isolated island of mountain habitat is Template:Convert from the closest alpine habitat in southern Colorado.<ref name="Arno" />

In the Southern Rocky Mountains they, like the limber pine, may grow in extensive stands on some sites without other species of tree or may be found intermixed with them. In the southerly parts of the Sangre de Cristo Range they replace the limber pines at higher elevations on very dry sites. It becomes more common in more northerly portions of the range, especially in habitats above Template:Convert.<ref name="Sierra Club" /> A very large bristlecone pine wood of Template:Convert grows in the Valle Vidal within the Carson National Forest.<ref name="Sierra Club" /><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> In both New Mexico and Colorado they mostly grow on steep, south-facing slopes that are quite dry.<ref name="Ranne et al">Template:Cite journal</ref>

In Colorado there are more than 50 areas with notable populations of bristlecone pine found in the southern and central mountain ranges of the state. On the Spanish Peaks in southern Colorado bristlecone pines grow together with ponderosa pines and Rocky Mountain white oaks at relative low elevations, an unusual habitat type. Though they also grow in nearly pure stands higher up in the subalpine zone of the Spanish Peaks.<ref name="Sierra Club" /> A forest of Template:Convert growing on the southeastern flank of Mount Bross in the Pike National Forest is named the Windy Ridge Bristlecone Pine Scenic Area.<ref name="Windy Ridge" /> Further north, they grow on the mountains of the Front Range south of James Peak.<ref>Template:Cite journal</ref> In the southern part of the range around Pikes Peak they occur on the south facing slopes while limber pines grow on the north facing areas. In areas around Mount Blue Sky bristlecone pines more often mix with limber pines, though bristlecones tend to be more common on fine textured soils while rocky ridges have more limber pines.<ref name="Sierra Club" /> The rocks and soils derived from them along the Front Range are Precambrian granite.<ref name="Ranne et al" /> The small Template:Convert grove in the Mount Goliath Natural area is notable both for the age of one of its trees (see Notable trees) as well as for the ease of public access from the Mount Blue Sky Scenic Byway.<ref name="Sierra Club" />

The typical habitat of high altitude groves is quite cool, even in summer. In the Front Range it was measured to have a mean annual temperature of Template:Convert in the 1970s. The winds are also quite severe with speeds of Template:Convert common.<ref name="Ranne et al" />

Conservation

The International Union for Conservation of Nature last evaluated Pinus aristata in 2012 and listed it as one of their species of "least concern". The evaluation found its population was stable without a continuing decline of mature individuals, but with a naturally very fragmented habitat.<ref name="IUCN" /> In contrast, when NatureServe evaluated it in 1999 they listed it as "vulnerable" (G3) due to its small distribution. They additionally found it to be "imperiled" (S2) in Arizona.<ref name="NatureServe" /> In Arizona the state lists it as a salvage resiricted native plant, one that requires a permit for removal including on private land.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Ecology

The seeds of the Rocky Mountain bristlecone are eaten by Clark's nutcracker (Nucifraga columbiana) and may also be stored by them in years where crops of seeds are particularly large. Unlike the seeds of the Colorado pinyon (Pinus edulis) the seeds of show the same speckled patterns for camouflage on soil as other species and are not adapted to be primarily animal dispersed.<ref>Template:Cite journal</ref>

The Rocky Mountain bristlecone is quite vulnerable to fire. After forest fires stands show very little regeneration after thirty years and a lower abundance compared with other species tree species that are more able to colonize newly open areas.<ref>Template:Cite journal</ref>

Notable trees

The oldest tree in Colorado is a Rocky Mountain bristlecone that was dated by F. Craig Brunstein and David Yamaguchi to 442 BCE.<ref name="Windy Ridge">Template:Cite book</ref> Designated in the 1992 paper as CB-90-11, it grows on Black Mountain in the Pike National Forest west of Pike's Peak. At the time core samples were taken by researchers the trees showed many signs of old age including dead wood that had been sculpted by wind erosion, crowns that had died back, only strips of living bark, and a radius greater than Template:Convert. Three other trees in the same area were dated to earlier than 100 BCE.<ref name="Brunstein">Template:Cite journal</ref>

The oldest known tree on Mount Goliath was discovered by Dr. Paula Krebs in 1970 while working on her doctoral dissertation. The tree, which she named Great Grandma, was dated to 403 CE making it Template:Age years old.<ref name="Windy Ridge" />

The tallest recorded tree is one Template:Cvt tall that grows in the Carson National Forest, New Mexico. When measured in 1996 it also had a diameter of Template:Cvt and a crown spread of Template:Cvt.<ref name="Conifers">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

The American National Register of Champion Trees records a tree with a very large diameter of Template:Convert Huerfano County, Colorado. This tree also has a height of Template:Cvt and a crown spread of Template:Cvt when it was measured in 2018.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Uses

Formerly it was used for fuel, electric utility poles, signposts, and as support timbers in mines.<ref name="Grandtner" /><ref name="Garden of Bristlecones" />

Cultivation

Rocky Mountain bristlecone the most common of the bristlecone pines in cultivation.<ref name="Jacobson">Template:Cite book</ref> It is a very attractive slow-growing small tree suitable for small gardens in cold climates.<ref name="Xeriscape">Template:Cite book</ref> It was brought into cultivation by Parry at the Arnold Arboretum soon after he collected the materials for its scientific description in 1861.<ref name="Jacobson" /> It has been cultivated since at least 1863 in the United Kingdom, but is a rarely planted tree there.<ref>Template:Cite book</ref> In gardens it will range from Template:Convert high and Template:Convert wide.<ref name="NCEx">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> However, due to its slow growth rare it is rare to see one taller than 10 m in landscaping.<ref name="Small Garden">Template:Cite book</ref> It requires a well drained soil, one that is rocky and poor in organic material being particularly suitable. They also tolerate alkaline soils.<ref name="Xeriscape" />

Trees are tolerant of windy conditions,<ref name="Xeriscape" /> but will show evidence damage from the wind.<ref name="NCEx" /> They have an extreme resistance to cold, being hardy in USDA zones 3–7.<ref name="NCEx" /> They can be encouraged to grow more quickly with supplemental water, but overwatering resulting in deformed growth or death is a frequent problem in landscaping.<ref name="Xeriscape" /><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The Colorado bristlecone is quite flammable and is also susceptible to air pollution.<ref name="NCEx" /><ref name="Xeriscape" /> Though symmetrical and bushy when young, as the trees grow they become more open in structure and irregular in shape.<ref name="Small Garden" />

Cultivars

'Blue Bear'

A thick branched cultivar named for its blue-green foliage. It grows at about Template:Cvt each year.<ref name="NCEx" />

'Formal Form'

A cultivar with a narrower, upright growth habit and blue-green foliage.<ref name="NCEx" />

'Joe's Bess'

A dwarf selection that has a uniform shape and upright habit.<ref name="NCEx" /> It is used in full sun borders or as a specimen plant.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

'Sherwood Compact'

This is a very dwarfed variety. It grows with a somewhat more treelike form when grafted onto Pinus strobus as a rootstock, but remains very small. It was introduced to the horticultural trade in 1983.<ref name="Jacobson" /> It also has shorter needles.<ref name="NCEx" />

External links

• Gymnosperm Database: Pinus aristata
• Flora of North America: Pinus aristata
• High-elevation white pine educational website: Pinus aristata