Pinaceae -- Pine family

    Frank Ronco, Jr.

    Pinyon (Pinus edulis) is a small, drought-hardy, long-lived tree  widespread in the southwestern United States. Its common name is derived  from the Spanish piñon which refers to the large seed of  pino (pine). For this reason the tree is known in the Southwest  and throughout its range by this Spanish equivalent (49). Other common  names are Colorado pinyon, nut pine, two-needle pinyon, and two-leaf  pinyon (50). Its heavy, yellow wood is used primarily for fuel. Because of  their delicate flavor its seeds are in much demand, making them its most  valuable product.

General: Pine Family (Pinaceae). Native shrubs or trees growing 5-12(-21) meters tall, with a strongly tapering trunk, single-stemmed and tallest at higher elevations, multi-stemmed, bushy and sprawling on lower sites, the crown usually compact, rounded and spreading. Bark is reddish-brown, shallowly and irregularly furrowed. Needles are evergreen, 2 per bundle, less commonly 1 or 3, 2-4 cm long, upcurved, yellow-green to blue-green, mostly 2-3-sided, all surfaces with pale stomatal bands, the margins smooth or finely toothed. Seed cones about (3.5) 4(5) cm long at maturity, ovoid before opening, depressed-ovoid to nearly globose when open, short-stalked to nearly sessile. Seeds mostly ellipsoid to obovoid 10-15 mm long, light brown, wingless. The seeds rest in a deep depression on each cone scale and a flap of tissue holds them in place, so the seeds are readily available to birds. The common name represents a species of pinyon pine producing two needles per bundle. The Spanish “piñon” refers to the large seed (pine in Spanish is “pino”).

Variation within the species: the California outlier of two-needle pinyon has been considered a distinct species, California Pine (Pinus californiarum) (Bailey 1987), or a population of 2-needled trees of single-leaf pinyon (Pinus monophylla var. californiarum). Pinus edulis var. fallax is seen by some to combine features of P. edulis and P. monophylla – but it has most recently been treated as part of other species (P. californiarum subsp. fallax; P. monophylla var. fallax). The differences in opinion regarding these species of pinyon pine are further reflected in the observation that even the typical form of P. edulis has been treated as a variety of both P. monophylla and P. cembroides. Naturally occurring hybrids have been reported between two-needle pinyon and single-leaf pinyon in several areas.

Pinyon, common pinyon, New Mexico pinyon, Colorado pinyon, mesa pinyon, two-leaf pinyon, nut pine, twoneedle pinyon. Spanish spellings are piñon and piñón.

Colorado pinyon is primarily a species of the southwestern United States and Colorado Plateau, extending to the eastern rim of the Great Basin [98,167]. It occurs abundantly in Utah, Arizona, Colorado, and New Mexico [26,73,84,85,109,120,133,164,166,167], though its range extends to extreme southern Wyoming, eastern Nevada and California, western Oklahoma, the Trans-Pecos region of Texas, and northern Mexico [98,109,120,126,133,147,164,167]. Colorado pinyon occurrence is generally rare or localized on the edges of its distribution [73,84,120,133,149,164]. The Flora of North America provides a distributional map of Colorado pinyon.

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This species can be found in the following regions of the western United States (according to the Bureau of Land Management classification of Physiographic Regions of the western United States):

BLM PHYSIOGRAPHIC REGIONS [12]:

4 Sierra Mountains

7 Lower Basin and Range

10 Wyoming Basin

11 Southern Rocky Mountains

12 Colorado Plateau

13 Rocky Mountain Piedmont

AZ	CA	CO	NM	NV
OK	TX	UT	WY

MEXICO

As a codominant with juniper species (Juniperus spp.), pinyon  trees predominate in pinyon-juniper woodlands of the semidesert zone,  which cover nearly 24.7 million ha (61 million acres), extending from  Texas to California (9). Woodlands in which pinyon is the major pine  species cover about 14.9 million ha (36.9 million acres) in Arizona,  Colorado, New Mexico, and Utah. Outliers in California, Oklahoma, Texas,  and Wyoming contribute a relatively insignificant acreage to the total  (48). However, the outlier in California has been considered a population  of 2-needled individuals of single-leaf pinyon (Pinus monophylla),  and more recently, a new species, California single-needle pinyon (Pinus  californiarum) (5,44).

     
- The native range of pinyon.

Pinus edulis Engelm.:
Mexico (Mesoamerica)
United States (North America)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Southwestern United States, in southern California (rare), the intermountain region (Wyoming, Utah, Colorado, Arizona, New Mexico), to western Oklahoma (rare) and western Texas, and south into Chihuahua, Mexico. For current distribution, please consult the Plant Profile page for this species on the PLANTS Web site.

Shrubs or trees to 21m; trunk to 0.6m diam., strongly tapering, erect; crown conic, rounded, dense. Bark red-brown, shallowly and irregularly furrowed, ridges scaly, rounded. Branches persistent to near trunk base; twigs pale red-brown to tan, rarely glaucous, aging gray-brown to gray, glabrous to papillose-puberulent. Buds ovoid to ellipsoid, red-brown, 0.5--1cm, resinous. Leaves (1--)2(--3) per fascicle, upcurved, persisting 4--6 years, 2--4cm ´ (0.9--)1--1.5mm, connivent, 2-sided (1-leaved fascicles with leaves 2-grooved, 3-leaved fascicles with leaves 3-sided), blue-green, all surfaces marked with pale stomatal bands, particularly the adaxial, margins entire or finely serrulate, apex narrowly acute to subulate; sheath 0.5--0.7cm, scales soon recurved, forming rosette, shed early. Pollen cones ellipsoid, ca. 7mm, yellowish to red-brown. Seed cones maturing in 2 years, shedding seeds and falling soon thereafter, spreading, symmetric, ovoid before opening, depressed-ovoid to nearly globose when open, ca. (3.5--)4(--5)cm, pale yellow- to pale red-brown, resinous, nearly sessile to short-stalked; apophyses thickened, raised, angulate; umbo subcentral, slightly raised or depressed, truncate or umbilicate. Seeds mostly ellipsoid to obovoid; body 10--15mm, brown, wingless. 2 n =24.

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Colorado pinyon often grows as a low, bushy tree [166] with an irregularly rounded, spreading crown [26,85,109,133]. Crowns of young trees are broadly conical, and those of old trees are spreading or flat-topped [5,64]. The trunk is generally short and crooked [26,64,85,109,133], with several large, crooked branches [64]. It may grow to 40 inches (1 m) in diameter [5,26,64,126]. Height is typically 26 to 56 feet (8-17 m) [5,26,64,85,109,133,147,164].

The needles are 2.7 to 4.3 inches (6-11 cm) long [167] and in fascicles of 2 [126]. Needles remain on the tree for approximately 9 years. Bark thickness of Colorado pinyon ranges from 0.5 to 0.87 inch (1.3-2.2 cm) [64], with young trees having smoother and thinner bark than older trees. Cones are 1.5 to 2 inches (3.5-5) cm long and are borne singly or in groups of 2 to 4 [126]. The average cone contains 10 to 20 soft-shelled seeds [59,61,108,133,139]. The Flora of North America provides a morphological description and identification key for Colorado pinyon.

Colorado pinyon's root system consists of a taproot and shallow lateral roots occurring more than 1 inch (3 cm) below the soil surface [59,71]. Taproots extend to soil depths of at least 20 feet (6 m) [50]. Laterals are generally found at depths of 6 to 16 inches (15-40 cm) and can extend from the tree up to twice the crown radius [59,139,159].

Colorado pinyon is a slow-growing, long-lived tree [59,64,105]. It can survive more than 500 years [9,32,44,64,155] and may reach 800 to 1,000 years of age [118,139]. The density of Colorado pinyon in woodland communities ranges from none or few to several hundred stems per hectare [139].

Tree, Shrub, Evergreen, Monoecious, Habit erect, Trees without or rarely having knees, Tree with bark rough or scaly, Young shoots 3-dimensional, Buds resinous, Leaves needle-like, Leaves alternate, Needle-like leaf margins entire (use magnification), Needle-like leaf margins finely serrulate (use magnification or slide your finger along the leaf), Leaf apex acute, Leaves < 5 cm long, Leaves < 10 cm long, Leaves blue-green, Needle-like leaves somewhat rounded, Needle-like leaves not twisted, Needle-like leaf habit erect, Needle-like leaves per fascicle mostly 2, Needle-like leaf sheath early deciduous, Twigs glabrous, Twigs pubescent, Twigs viscid, Twigs not viscid, Twigs without peg-like projections or large fascicles after needles fall, Berry-like cones orange, Woody seed cones < 5 cm long, Seed cones bearing a scarlike umbo, Umbo with obvious prickle, Bracts of seed cone included, Seeds brown, Seeds wingless, Seed wings narrower than body.

Caryopitys edulis (Engelmann) Small; Pinus cembroides Zuccarini var. edulis (Engelmann) Voss

More info for the terms: competition, density, litter, shrub, tree, xeric

Colorado pinyon is found on level or gently rolling uplands [39] to moderately steep and very steep slopes (27-75%) [72]. It also occurs in riparian areas in the Southwest [42] and on slopes adjacent to river drainages [72]. Colorado pinyon sites include dry foothills, plateaus, mesas, mountain slopes, and canyon sides [2,64,72,98,112,166]. The distribution of Colorado pinyon in pinyon-juniper woodlands may be limited by Colorado pinyon's lack of tolerance for water stress on low elevational, xeric sites [8,174]. At high elevations, distribution may be limited by low temperatures or competition with ponderosa pine [8]. Moisture is likely the most critical factor controlling the distribution, composition, and density of pinyon-juniper woodlands [58], though the distribution of Colorado pinyon may also be affected by soil characteristics [174].

Elevation: Pinyon-juniper woodlands occur in the foothills above desert shrub or grassland vegetation but below ponderosa pine forest [25,101,127]. Colorado pinyon occurrence ranges from 4,500 to 9,000 feet (1,400-2,700 m) elevation [26,64,112,127,139]. In pinyon-juniper woodland, Colorado pinyon tends to increase in abundance with increasing elevation, while junipers decrease [25,34,123,127]. Colorado pinyon is not generally affected by topographic position (aspect or steepness of slope), other than its prevalence relative to juniper [129,131]. The following table presents information on the elevational distribution of Colorado pinyon by state:

State	Elevation range	References
Arizona	4,000-7,500 feet (1,220-2,280 m); upper limit of 6,500 feet  (1,980 m) on north-facing slopes	[38,39,69,85,96,115,174]
California	4,200-8,850 feet (1,280-2,700 m)	[73,156]
Colorado	Occurs from 5,200 to 9,000 feet (1,580-2,750 m); abundant from 7,000 to 7,900 feet (2,100-2,400 m)	[72,96,166,166,174]
New Mexico	5,000-8,850 feet (1,520-2,700 m)	[2,109]
Texas	>6000 feet (1,830 m)	[147]
Utah	5,000-8,400 feet (1,520-2,560 m) in Utah; upper limit of 8,400 feet (2,560 m) on south-facing slopes	[82,107,174]

Climate: Colorado pinyon occurs in the warm, semiarid climate of the Southwest (Arizona, New Mexico) and in the cold, semiarid climate of the mountainous west (Nevada, Utah, Colorado) [34]. Summers in the pinyon-juniper zone are hot and winters relatively cold. A high percentage of clear days, intense solar radiation, and windy conditions favor high evapotranspiration rates [139], and precipitation generally exceeds evapotranspiration only during December, January, and February [39]. Growth is limited primarily by low precipitation in the Southwest, while in the mountainous west it is limited by both freezing temperatures and low precipitation [34].

Temperature and precipitation in the pinyon-juniper zone vary in relation to elevation and geographic location [131]. Colorado pinyon occurs on sites experiencing approximately 120 frost-free days and 4 to 20 inches (102-520 mm) of annual precipitation, with variable seasonal distribution [39,108,139,168,176]. In the southern portion of the pinyon-juniper woodland distribution, precipitation peaks occur during the summer fed by moisture from the Gulf of Mexico. In the more northern areas, precipitation from convection storms occurs in July and August, and winter storms from the Pacific coast provide moisture during the cool season [131,139,176]. Colorado pinyon is mostly dependent on soil moisture stored from winter precipitation. Much of summer rainfall is ineffective due to runoff after heavy thunderstorms and high evaporation [159]. Colorado pinyon occurs in zones that are generally 6 degrees warmer than in the vegetation zone above and 5 degrees cooler than the zone below [39].

Colorado pinyon is tolerant of cold and drought [101,176]. According to field studies using simulated rainfall events, Colorado pinyon can respond effectively to both monsoon precipitation and small rainfall events [170].

Soils: Colorado pinyon occurs on a wide range of soil types and is not limited by the character or geologic origin of soils [139,176]. Soils of these communities may be shallow to moderately deep and are often rocky, well drained, and low in fertility [34,64,72,127]. Colorado pinyon growing in deeper soils generally grow faster than those in shallow soils [159]. Colorado pinyon occurs on a range of parent materials, including sandstone, limestone, shale, basalt, granite, and mixed alluvium [34,39,69,127,147].

Soils under well-developed pinyon-juniper stands are completely occupied by tree roots, limiting understory growth [112,139]. The lateral roots of the tree species efficiently access interspaces in these communities for soil water and nutrients, further impacting herbaceous species [15,90]. In addition, understory vegetation is reduced by shading and potentially by allelopathic effects [35]. Colorado pinyon accumulates nutrients beneath the tree canopy [34,157]. Organic carbon and nitrogen are greater under pinyon-juniper canopies than in interspaces, especially under mature canopies as compared to younger or more recently disturbed stands [89,90,123]. In addition to accumulations of organic matter, concentrations of soluble salts (Na, Ca, Mg, and K) are significantly higher (p<0.05) under Colorado pinyon canopies than in adjacent shrub-dominated areas. Accrual of nitrate and sulfate is also evident under Colorado pinyon trees, as is higher average concentration of phosphorus and boron, which may be phytotoxic to some herbaceous species [9]. Colorado pinyon litter is specifically associated with a reduction of blue grama production [79].

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This species is known to occur in association with the following Rangeland Cover Types (as classified by the Society for Range Management, SRM):

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SRM (RANGELAND) COVER TYPES [146]:

411 Aspen woodland

412 Juniper-pinyon woodland

413 Gambel oak

415 Curlleaf mountain-mahogany

416 True mountain-mahogany

417 Littleleaf mountain-mahogany

420 Snowbrush

421 Chokecherry-serviceberry-rose

422 Riparian

501 Saltbush-greasewood

503 Arizona chaparral

504 Juniper-pinyon pine woodland

505 Grama-tobosa shrub

509 Transition between oak-juniper woodland and mahogany-oak association

724 Sideoats grama-New Mexico feathergrass-winterfat

725 Vine mesquite-alkali sacaton

735 Sideoats grama-sumac-juniper

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This species is known to occur in association with the following cover types (as classified by the Society of American Foresters):

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SAF COVER TYPES [36]:

210 Interior Douglas-fir

216 Blue spruce

217 Aspen

220 Rocky Mountain juniper

237 Interior ponderosa pine

239 Pinyon-juniper

240 Arizona cypress

241 Western live oak

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This species is known to occur in association with the following plant community types (as classified by Küchler 1964):

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KUCHLER [93] PLANT ASSOCIATIONS:

K018 Pine-Douglas-fir forest

K019 Arizona pine forest

K021 Southwestern spruce-fir forest

K023 Juniper-pinyon woodland

K031 Oak-juniper woodland

K032 Transition between K031 and K037

K037 Mountain-mahogany-oak scrub

K038 Great Basin sagebrush

K040 Saltbush-greasewood

K059 Trans-Pecos shrub savanna

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This species is known to occur in the following ecosystem types (as named by the U.S. Forest Service in their Forest and Range Ecosystem [FRES] Type classification):

ECOSYSTEMS [53]:

FRES21 Ponderosa pine

FRES23 Fir-spruce

FRES29 Sagebrush

FRES30 Desert shrub

FRES33 Southwestern shrubsteppe

FRES34 Chaparral-mountain shrub

FRES35 Pinyon-juniper

FRES38 Plains grasslands

FRES40 Desert grasslands

Colorado pinyon forms a characteristic woodland community with Utah juniper (Juniperus
osteosperma) known as the pinyon-juniper woodland
[26,73,98,104,167]. In this community, Utah juniper often extends to lower elevations without the Colorado pinyon component, while
Colorado pinyon grows at elevations above Utah juniper. The pinyon-juniper woodland often forms large
continuous stands, as for example in the western part of the Uinta Basin [26]. Other pinyon (Pinus spp.) and juniper (Juniperus spp.)
species occurring in these woodlands
include singleleaf pinyon (P. monophylla), Parry pinyon (P.
quadrifolia), Mexican pinyon (P. cembroides), alligator juniper (J. deppeana), Rocky Mountain juniper (J.
scopulorum), and California juniper (J. californica) [74,104,153,156,163].
Colorado pinyon is generally replaced by singleleaf pinyon in pinyon-juniper woodlands on the western edge of its
distribution [167].

Shrub species occurring as understory dominants with Colorado pinyon are pointleaf
manzanita (Arctostaphylos pungens) [102,153], big sagebrush (Artemisia
tridentata) [102,153,169], true mountain-mahogany (Cercocarpus montanus) [11,72,74,102,153,169], rubber
rabbitbrush (Chrysothamnus nauseosus) [11,102,153], Stansbury cliffrose (Purshia
mexicana var. stansburiana), antelope bitterbrush (Purshia
tridentata) [102,153],
Gambel oak (Quercus gambelii) [51,64,72,74,102,153], gray oak (Q. grisea) [74], wavyleaf oak
(Q. undulata) [102,153], blackbrush (Coleogyne ramosissima) [102,153], Nevada
ephedra (Ephedra nevadensis), broom snakeweed (Gutierrezia
sarothrae) [169], and plains prickly-pear (Opuntia polyacantha) [51]. Herbaceous
species occurring as understory dominants with Colorado pinyon include blue grama
(Bouteloua gracilis) [51,74,102,153], Arizona fescue (Festuca arizonica) [102,153],
mountain muhly (Muhlenbergia montana) [74],
New Mexico muhly (M. pauciflora) [153], mutton grass (Poa
fendleriana) [102,153], galleta (Pleuraphis jamesii) [51], Columbia needlegrass
(Achnatherum nelsonii) [102,153], and sand bluestem (Andropogon
gerardii var. paucipilus) [102].
Classifications identifying Colorado pinyon as a plant community dominant are
listed below:
Arizona [11,69,83,102,104,153]

California [156]
Colorado [1,72,83]

Nevada [169]
New Mexico [11,51,52,74,83,102,104,153]
Utah [83,169]

Pinyon-juniper woodlands are located mainly on the more rocky plateaus,  mesas, foothill terraces, and lower mountain slopes; shrubs or grasses  grow on finer soils in intervening valleys, canyons, or shallow washes.  Such discontinuities have been attributed to fire history and soil-related  differences. The oldest pinyons are frequently found on steep, rocky sites  where fire occurrence and severity are probably lower than in intervening  areas, and consequently less damaging to trees (37,41,67,73).

    Discontinuities ascribed to soil differences may in fact be related to  the greater amounts of water that coarser soils make available to the  tree, as the different soils are adjacent and there are no obvious  differences in climatic factors. Furthermore, pinyon-juniper woodlands are  found on a wide variety of soil depths and textures that range from  coarse, rocky gravels to fine, compacted clays, indicating little if any  correlation between these conditions and the presence of pinyon. Depth and  texture, however, could affect productivity (37,45,62,67).

    Woodlands also are associated with a broad range of soil Great Groups,  of which Haplustalfs of the order Alfisols, Ustochrepts of the order  Inceptisols, and Ustorthents of the order Entisols are the most common  (37,52,76). Parent materials are equally varied. Sedimentary sandstones,  limestones, and shales are most common, but materials of igneous origin,  such as cinders and basalt, and those from metamorphic sources, also are  found (40,62,67). In some soils, carbonates may accumulate and form a  petrocalcic horizon (hardpan) that may extend as deep as 1.5 m (5 ft), but  is usually much shallower. Upper layers of woodland soils generally  exhibit pH values ranging from about 7 to 8.4, but at higher and wetter  elevations, soils tend to be slightly acid in reaction, approaching 6.5  (31,37,43,45,69).

    Pinyon-juniper woodlands are found between the low plains covered by  grassland, desert shrub, or chaparral vegetation and the high mountains  just below the zone dominated by either submontane shrubs or ponderosa  pine (Pinus ponderosa). The lower limit of growth is probably  related more to the inability of pinyon trees- especially seedlings- to  tolerate water stress arising from decreasing precipitation and subsequent  reduction of total moisture, rather than to soil or temperature factors.  In contrast, the upper limit appears to be a function of greater biotic  competition resulting from increased moisture (10,67).

    In elevation, the woodlands lie mostly between 1370 and 2440 m (4,500  and 8,000 ft) (67). Individual pinyons, however, may extend up to 3200 m  (10,500 ft) on south- and west-facing slopes in the mixed conifer forests  of Arizona (70), while scattered juniper trees may descend to 910 m (3,000  ft) (41). Although the range in any given locality is considerably  narrower, the elevational band occupied by woodlands is a rather uniform  span of about 610 m (2,000 ft). There is a tendency, however, for the  entire band to decrease in elevation in a southeasterly direction (72). In  Arizona, the majority of the type is found between 1370 and 1980 m (4,500  and 6,500 ft), whereas in Colorado, the band extends from 1830 to 2440 m  (6,000 to 8,000 ft). The bulk of the woodland in New Mexico and Utah  occupies a zone from 1520 to 2130 m (5,000 to 7,000 ft).

The pinyon-juniper type occupies the lowest and warmest forested zone in  the United States, with a climate generally characterized as semiarid, and  locally as dry subhumid (65). Summers are hot and winters relatively cold,  especially in northern locations and at high elevations. A high percentage  of clear days, intense solar radiation, and windy conditions favor high  evapotranspiration rates (67).

    Annual precipitation, which varies widely throughout the type because of  differences in elevation, topography, and geography, ranges from 250 mm  (10 in) at low elevations where the type adjoins the desert or grassland  vegetation to 560 mm (22 in) or higher at the upper reaches (62,67,73).  Locally, amounts as high as 690 mm (27 in) have been recorded, as along  the Mogollon Rim in northern Arizona (15).

    Seasonal distribution, which also varies considerably, is related to  prevailing storm patterns. In eastern New Mexico, for example,  approximately 75 percent of the annual precipitation occurs during the  warm season (April through September) from storms originating in the Gulf  of Mexico, whereas the percentage decreases as these summer storms lose  intensity during their northwesterly movement (62). Nevertheless, summer  precipitation throughout much of northern Arizona and the south-central  and eastern portions of Utah is still about equal to, or slightly greater  than, winter moisture (14,42). Furthermore, as much as one-third of the  rainfall may occur during July and August (67). In contrast, woodlands of  Nevada and northern Utah receive more precipitation during the cool season  (October through March), primarily from Pacific winter and spring storms  (13,14). Snow depths are not great, except at higher elevations and more  northerly latitudes, but even then, melt generally occurs within a few  days, especially on south-facing slopes (62).

    The mean annual temperature in pinyon-juniper woodlands varies from 4°  to 16° C (40° to 61° F); extremes may fall to -35° C  (-31° F) and reach 44° C (112° F). January means may be as  low as -10° C (14° F) in the more northerly portion of the type,  and about 6' C (430 F) near the southern limits. Mean July temperatures  are less variable, ranging from 20° to 27° C (68° to 81°  F). The frost-free period ranges from about 90 to 205 days, the shorter  period typifying more northerly latitudes and higher elevations  (59,67,73).

    Because of wide variation in temperature and the amount and distribution  of precipitation, the following classification has been proposed to better  characterize the climate of pinyon-juniper woodlands in Arizona and New  Mexico (62):

        Precipitation              Climate  Winter  Summer        mm      Cool, moist  230 to 280  180 to 230      Warm, moist  250 to 330  150 to 230      Cool, winter dry  130 to 180  180 to 230      Warm, winter dry  100 to 180  200 to 280      Cold, winter dry  100 to 150  200 to 250      Cold, summer dry  180 to 230  100 to 150      Warm, summer dry  180 to 230  100 to 150        in      Cool, moist    9 to 11  7 to 9      Warm, moist  10 to 13  6 to 9      Cool, winter dry  5 to 7  7 to 9      Warm, winter dry  4 to 7    8 to 11      Cold, winter dry  4 to 6    8 to 10      Cold, summer dry  7 to 9  4 to 6      Warm, summer dry  7 to 9  4 to 6

Dry mountain slopes, mesas, plateaus, and pinyon-juniper woodland; 1500--2100(--2700)m; Ariz., Calif., Colo., N.Mex., Okla., Tex., Utah, Wyo.; Mexico in Chihuahua.

Systems

• Terrestrial

Adaptation: Dry mountain slopes, mesas, plateaus, growing scattered in open woodlands at 1200-2450 (-2700) meters elevation, in pure stands, or commonly mixed with one or more of several species of juniper. Two-needle pinyon is one of the most slow-growing and drought-resistant species of pines, requiring only 12-18 inches of rainfall a year, but it grows best on the higher, wetter sites, just below the zone of ponderosa pine.

Planting: Trees may begin producing cones when 25 years of age but produce significant quantities of seed only after reaching 75-100 years old. Good seed crops occur every 4 to 7 years (on average) or more frequently on better sites, and cone bearing tends to be synchronous over large geographical areas. Germination is generally above 80%.

A relationship of mutual benefit exists between two-needle pinyon and four species of corvid birds: Clark’s nutcracker, Steller’s jay, scrub jay, and pinyon jay. These birds are the primary agents of dispersal of this pine, which provides a large portion of their diet and subsistence, but only the scrub jay and pinyon jay cache seeds in the pinyon-juniper zone and are responsible for its regeneration.

Seed germination and establishment of the two-needle pinyon are best in the shade of trees or shrubs and probably depend on an adequate moisture supply during the first summer. Growth through all stages is extremely slow. Dominant trees in a stand are often 400 years old, and individuals 800-1000 years old have been found.

Pinyon is a minor component of the following forest cover types (61):  Bristlecone Pine (Society of American Foresters (Type 209), Interior  Douglas-Fir (Type 210), Rocky Mountain Juniper (Type 220), Interior  Ponderosa Pine (Type 237), Arizona Cypress (Type 240), and Western Live  Oak (Type 241). It is an integral component in Pinyon-Juniper (Type 239)  over a large area. However, as the type extends westward, pinyon is  replaced by singleleaf pinyon (Pinus monophylla) in Nevada and  some localities in western Utah and northwestern Arizona (4,67). Southward  along the Mexican border, Mexican pinyon (P. cembroides var. bicolor),  recently given separate species status as border pinyon (P.  discolor), becomes the dominant tree in the woodlands (6,48,49).

    Common associates of pinyon over most of its range are oneseed juniper  (Juniperus monosperma) and Utah juniper (J. osteosperma); redberry  juniper (J. erythrocarpa), also a one-seeded juniper, is confined  to the southern portion. Alligator juniper (J. deppeana) and Rocky  Mountain juniper (J. scopulorum) are also found in some localities  (1,4,67). Oneseed juniper predominates in east-central Arizona and most of  New Mexico, and extends into western Texas and south-central Colorado.  Rocky Mountain juniper is also a common component in northern New Mexico  and the western half of Colorado, but it is found over most of the  woodlands as well. It usually grows at higher elevations and is seldom  dominant in the stand. Utah juniper is the codominant associate in Utah,  northern Arizona, western Colorado, and northwestern New Mexico. At  higher, more mesic elevations in southern and western New Mexico and  westward into central Arizona, alligator juniper commonly forms a  component of stands.

    Although pinyon-juniper woodlands consist of relatively few tree  species, stands exhibit considerable diversity in appearance and  composition (4). Some have nearly closed canopies of a single tree species  with little or no understory vegetation. Others are open, with widely  scattered pines, junipers, or both among grasses and shrubs. A typical  pinyon-juniper woodland, with its many-branched trees resembling shrubs,  has the appearance of a stunted coniferous forest.

    Any particular stand usually contains only a few different plant  species, but because of the wide distribution of the type, the total flora  associated with woodlands is quite varied (4,67,73). Common tree and shrub  associates include: Gambel oak (Quercus gambelii), gray oak (Q.  grisea), shrub live oak (Q. turbinella), true  mountain-mahogany (Cercocarpus montanus), curlleaf  mountain-mahogany (C. ledifolius), antelope bitterbrush (Purshia  tridentata), big sagebrush (Artemisia tridentata), black  sagebrush (A. nova), serviceberry (Amelanchier spp.),  rabbitbrush (Chrysothamnus spp.), Mexican cliffrose  (Cowania mexicana), Apache-plume (Fallugia paradoxa), skunkbush  (Rhus trilobata), Mormon-tea (Ephedra spp.), yucca  (Yucca spp.), opuntia (Opuntia spp.), broom  snakeweed (Gutierrezia sarothrae), and buckwheat (Eriogonum  spp.).

    Some of the more important herbaceous plants are goosefoot (Chenopodium  graveolens), rock goldenrod (Solidago pumila), gilia (Gilia  spp.), penstemon (Penstemon spp.), segolily  (Calochortus nuttallii), globemallow (Sphaeralcea spp.),  white aster (Aster hirtifolius), hymenopappus (Hymenopappus  filifolius var. lugens), Indian ricegrass (Oryzopsis  hymenoides), dropseed (Sporobolus spp.), needle-and-thread  (Stipa comata), squirreltail (Sitanion hystrix), Junegrass  (Koeleria pyramidata), galleta (Hilaria jamesii), blue  grama (Bouteloua gracilis), sideoats grama (B. curtipendula),  ring muhly (Muhlenbergia torreyi), western wheatgrass (Agropyron  smithii), bluebunch wheatgrass (A. spicatum), slender  wheatgrass (A. trachycaulum), downy chess (Bromus tectorum),  and threeawn (Arisitada spp.).

Small pinyons 1 to 2 m (3 to 6 ft) tall are  readily killed by fire, but larger trees appear more resistant. Fire is  generally not a serious problem, however, because stands are open and  understory fuels are sparse. Where vegetation is dense and weather  conditions favorable, fire has been effective as a treatment for  converting woodlands to grasslands (3,18,40).

    Among insects most commonly attacking the vegetative portion of trees  are pinyon pitch nodule moth (Petrova albicapitana arizonensis), tiger  moth (Halisidota ingens), mountain pine beetle (Dendroctonus  ponderosae), pinyon sawfly (Neodiprion edulicolus), adelgid  (Pineus coloradensis), pinyon needle scale (Matsucoccus  acalyptus), pine needle scale (Chionaspis pinifoliae), Arizona  fivespined ips (Ips lecontei), pinyon ips (Ips confusus), pinyon  needle miner (Coleotechnites edulicola), pinyon tip moth (Dioryctria  albovittella), and gallmidges (Pinyonia spp., Janetiella  spp., and Contarinia spp.) (22,24,27,28,63,67). The  most damaging cone and seed insects include cone moths (Eucosma  bobana) and the pinyon cone beetle (Conophthorus edulis). Many  species of nematodes, especially in the Helocotylenchus, Tylenchus,  and Xiphinema genera, are parasitic on pinyon roots, but their  effect on growth in natural stands is unknown (53).

    A number of foliage diseases have been reported on pinyon, including  needle casts (Elytroderma deformans and Bifusella saccata)  and needle rusts (Coleosporium jonesii and C. crowellii)  (36,67). Pinyon blister rust (Cronartium occidentale) and  pinyon dwarf mistletoe (Arceuthobium divaricatum) cause stem  diseases, the latter being considered the major pathogen of pinyon. Verticicladiella  wagenerii, a root rot, is also ranked high as a damaging agent;  principal heart rots are red-ring rot (Phellinus pini) and brown  cubical rot (Fomitopsis pinicola). Armillaria mellea and Phaeolus  schweinitzii are not particularly important diseases, but both cause  root rot and butt rot.

More info for the term: surface fire

Colorado pinyon 6 feet (1.8 m) tall or more may be somewhat resistant to surface fire because foliage is high enough above the ground to avoid damage [29,172]. In communities where Colorado pinyon has reached 4 feet (1 m) or more in height, the tress are often less susceptible to fire due to an absence of fine fuels to carry fire [175]. Young Colorado pinyon are generally killed by fire [86,172]. Research in New Mexico [172] showed that Colorado pinyons less than 4 feet (1.2 m) tall experienced more damage than taller trees after tebuthiuron application and fire, even though saplings were more readily defoliated by herbicide treatments than seedlings [162].

Colorado pinyon is very sensitive to fire and may be killed by even low-severity surface burns [44,110], especially when trees are less than 4 feet (1.2 m) tall [14,25,34,117,172].  Colorado pinyon is particularly susceptible when individuals are >50% defoliated by fire [29]. Fire kill of Colorado pinyon may be more extensive on flat to gently rolling terrain; in rough terrain, islands of unburned trees may be left on ridges and hills [5,6,23]. Crown fires kill Colorado pinyon of all age classes [172].

More info for the terms: adventitious, secondary colonizer, tree

POSTFIRE REGENERATION STRATEGY [152]:
Tree without adventitious bud/root crown
Secondary colonizer (on-site or off-site seed sources)

More info for the terms: competition, cover, crown fire, density, fire frequency, fire interval, fire occurrence, fire-free interval, frequency, fuel, fuel loading, natural, point fire interval, shrub, shrubs, succession, surface fire, tree

Fire opens pinyon-juniper stands, increases diversity and productivity in understory species, and creates a mosaic of stands of different sizes and ages across the landscape. In addition, fire maintains the boundaries between the woodlands and adjacent shrub- or grasslands [14,25].

Fire adaptations: Mature Colorado pinyon trees are short with open crowns, but they do not self-prune their dead branches [14,25,117]. The accumulated fuel in the crowns, thin bark, and the relative flammability of the foliage make individual trees susceptible to fire [14,86,117]. Stand structure also impacts fire susceptibility; open stands of trees with large amounts of fine grass fuel or dense, mature trees capable of carrying crown fire during dry, windy conditions are the most flammable [14,67,117]. With sparse fuels, Colorado pinyon survives fire because it is seldom exposed to lethal heat [67].

Where stand-replacing fires do occur and potential seed sources are removed, dispersal of Colorado pinyon seeds by animals becomes particularly important in the reestablishment of tree seedlings. Birds in particular may cache seeds at "considerable distances" from the seed source [68]. Seeds cached within the shade of shrubs or trees are more likely to germinate and establish seedlings [59,62,71,86]. For more information on seed dispersal and Colorado pinyon succession following fire, please see the "Biological and Ecological Characteristics" section of this FEIS species summary.

FIRE REGIMES: Pinyon-juniper stands can support stand-replacing fires [63], though presettlement fire regimes were likely a mixture of surface and crown fires with intensities and frequencies dependent on site productivity [125]. Natural fires may be infrequent due to a sparseness of vegetation combined with an infrequency of lightning in some areas [25,62,86]. Floyd and others [44] estimated the "natural" fire turnover times of pinyon-juniper woodlands in southern Colorado at approximately 400 years, with fires largely the result of lightning strikes. Keeley [86] estimated the natural fire frequency of pinyon-juniper woodlands at 100 to 300 years. The woodlands are described as "resilient" with a minimum fire-free interval of 100 years and an unlimited maximum fire-free interval [86]. However, of 10 fire-scarred Colorado pinyon trees collected from 3 locations in New Mexico, multiple fire scars reflected a mean point fire interval for the trees of 27.5 years, with a range of intervals from 10 to 49 years [16]. A 208-year fire chronology of an eastern California pinyon-juniper woodland (based on fire scarred trees) suggests that fires burned somewhere within the <100-acre study area every 8 years [67]. Gottfried and others [62] estimate fire intervals ranging from 10 to 50 years for surface fires and >200 years for crown fires in the Middle Rio Grande Basin. Other studies report surface fire intervals of 20 to 30 years, and standwide fires occurring at 15 to 20 year intervals in New Mexico [125]. The variation in fire intervals in Colorado pinyon  is the result of differences in fuel loading and composition; where vegetation is sparse and unable to carry fire, fire-free intervals are much longer than in areas with a well-developed understory or greater tree density.

The amount of fine fuels varies with habitat type, stand history, and climatic conditions. Fuel loadings of more than 11 tons per acre (25,000 kg/ha) are considered heavy [125]. Fine fuels in many open pinyon-juniper stands range from 600 to 1,000 pounds per acre (635-998 kg/ha), and approximately 600 to 700 pounds per acre (635-726 kg/ha) are required to sustain surface fires [14]. Open pinyon-juniper stands (average canopy cover 12.4 to 21.8%) at Los Alamos, New Mexico, contained an average of 17,666 pounds per acre (20,033 kg/ha) of downed woody fuels and 22,347 pounds per acre (25,342 kg/ha) of total surface fuels [122]. Stands of moderate tree density where overstory competition reduces the herbaceous fuel and the trees are widely spaced are less likely to burn. Closed pinyon-juniper stands do not have understory shrubs to carry a surface fire, and do not burn until conditions are met to carry a crown fire [14]. Key conditions for crown fires include sufficient canopy closure to promote fire spread between trees, abundance of dead woody fuels on the surface and as standing snags, and extreme weather conditions (low humidity and high winds) [62,125].

Fire intervals in Colorado pinyon are difficult to quantify because living fire-scarred trees are rare: Colorado pinyon is often killed directly by fire or indirectly due to increased susceptibility to heart rot [16,125]. Though fire-scarred Colorado pinyon verify fire occurrence in pinyon-juniper communities, they are not a reliable indicator of fire frequency. Localized stand-replacing fires do occur in pinyon-juniper woodlands, and the absence of frequent fire in pinyon-juniper communities likely results in increased tree cover and tree density, encouraging crown fires rather than surface fires [67].

Due to the slow establishment and growth of Colorado pinyon, repeated fires maintain earlier seral stages in these communities [25,31,80,86]. Repeated burning every 20 to 40 years may eventually replace pinyon-juniper woodlands with shrub communities because shrubs colonize areas much faster than trees can re-establish [86,87], while the absence of fire eventually allows Colorado pinyon to replace extensive shrub vegetation [87]. Frequent fire may prevent the expansion of Colorado pinyon into grasslands, based on the perception that periodic fires burned these grasslands often enough to kill tree seedlings while they are most susceptible to fire. In the absence of frequent fire, seedlings become established in the grassland, eventually converting it to a woodland or savanna community. The effectiveness of fire in restricting the spread of Colorado pinyon (and juniper) depends on fire frequency and intensity of the fire, with the time required for seedlings to reach 4 feet (1.2 m) tall a critical determinant of the effective fire interval [130].

FIRE REGIMES for plant communities and ecosystems in which Colorado pinyon occurs are summarized below. For further information regarding FIRE REGIMES and fire ecology of communities and ecosystems where Colorado pinyon is found, see the "Fire Ecology and Adaptations" section of the FEIS species summary for the plant community or ecosystem dominants listed below.

Community or Ecosystem	Dominant Species	Fire Return Interval Range (years)
saltbush-greasewood	Atriplex confertifolia-Sarcobatus vermiculatus
desert grasslands	Bouteloua eriopoda and/or Pleuraphis mutica	5-100
plains grasslands	Bouteloua spp.	125]
curlleaf mountain-mahogany*	Cercocarpus ledifolius	13-1000 [4,142]
mountain-mahogany-Gambel oak scrub	C. ledifolius-Quercus gambelii
Arizona cypress	Cupressus arizonica
Rocky Mountain juniper	Juniperus scopulorum	125]
blue spruce*	Picea pungens	35-200
pine-cypress forest	Pinus-Cupressus spp.	3]
pinyon-juniper	Pinus-Juniperus spp.	125]
Mexican pinyon	P. cembroides	20-70 [119,154]
Colorado pinyon*	P. edulis	10-400+ [44,62,86,125]
interior ponderosa pine*	P. ponderosa var. scopulorum	2-30 [3,7,103]
Arizona pine	P. ponderosa var. arizonica	2-10 [3]
galleta-threeawn shrubsteppe	Pleuraphis jamesii-Aristida purpurea	125]
Rocky Mountain Douglas-fir*	Pseudotsuga menziesii var. glauca	25-100 [3]
oak-juniper woodland (Southwest)	Quercus-Juniperus spp.	125]

*fire return interval varies widely; trends in variation are noted in the species summary

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More info for the terms: climax, cohort, cover, density, fire occurrence, fire severity, presence, severity, shrub, shrubs, succession

Pinyon-juniper stands have slow succession rates [44,80]. Colorado pinyon occurs as an early to late-seral or climax species [31,34,172]. Following a fire in a pinyon-juniper stand in southern Colorado, Colorado pinyon began establishing in postfire year 25 [31]. Successional pathways of pinyon-juniper stands are indeterminate, and conditions after disturbance are generally less stable than the late seral, tree-dominant communities [63]. Factors that influence the pattern of succession after fire include past use history, site factors, moisture regime, stand age when disturbed, fire severity, presence of residual trees, and the presence of animal dispersal agents [14,141]. Seedlings may appear as early as the 1st postfire year [172], potentially the result of effective seed dispersal by animals, a wet moisture regime, and suitable shady sites provided by residual trees.

The general successional recovery after fire in dense stands of pinyon-juniper begins with the establishment of annuals, a stage that may peak in the 2nd and 3rd postfire years. A perennial grass stage follows, in which perennials are more abundant than annuals, with a shrub stage developing soon after. The re-establishment of trees during the shrub stage then leads to the pinyon-juniper climax, presuming no further fire occurrence [5,14,25,32,57,131,141]. The suppression of shrubs by mature trees may take up to 100 years [31,32], and climax stands may require 300 years to develop [25]. Frequent disturbance in these woodlands maintains earlier seral stages (e.g. the open shrub stage) [25,63,80]. As pinyon-juniper crown cover increases, cover, productivity, and density of understory species decrease. The understory is generally most productive, diverse, and responsive to disturbance when pinyon-juniper crown cover is at or below 20%. When crown cover exceeds 20 to 30%, understory thinning accelerates [77]. "Old-growth" stands of pinyon-juniper are fairly open and contain a cohort of dominant old, slow-growing trees with little or no understory of grass or shrubs. Down dead material is common, as is dead material on the live trees [113].

Colorado pinyon is intolerant of shade in all but the seedling stage of its growth [58,64,139,141,159]. "Nurse plants" are required during this stage to protect the seedlings from excessive drying and heating [14].

More info for the terms: competition, dioecious, fresh, litter, monoecious, natural, shrub, shrubs, tree

Colorado pinyon regenerates solely from seed; asexual regeneration has not been documented [5]. The natural reproduction of Colorado pinyon is limited due to unfavorable climate, infertility of the seed, rapidly declining germination of seed produced, and loss of seed to vertebrates and insects [159].

Breeding system: Colorado pinyon is generally monoecious [34,48,59,97,139,167]. The upper crown of Colorado pinyon tends to bear more ovulate than staminate cones and the opposite is true of the lower crown, though there may be broad overlap [97]. Some dioecious individuals do occur [48,59]. Dioecy may be more prevalent in younger age classes, perhaps as an adaptation to arid environments or other stress [47,48,59]. Dioecy may also occur in response to site factors, with male trees potentially predominating on south-facing slopes; however, clear connections between site conditions and Colorado pinyon breeding systems have not been established [46]. In 1 study, monoecious trees produced significantly more (p<0.001) empty seeds than female dioecious trees, and seedlings from monoecious trees were shorter and less vigorous than seedlings from dioecious trees [48]. Laboratory experiments have found 57% survival of self-pollinated cones and 83% survival of outcrossed cones. Outcrossed cones produced more seeds per cone than self-pollinated cones [97].

Pollination: The pollen of Colorado pinyon is carried for miles by the wind [34,97].

Seed production: Colorado pinyon may start bearing cones at 25 years. Good seed production occurs on trees that are 75 to 100 years old, with maximum seed production occurring on trees 160 to 200 years of age [34,59,139,159]. Large seed crops are produced every 3 to 7 years and are adversely impacted by water stress [40,61,112,139]. The periodicity of seed crops is related to the drain of nutrients required to produce a large crop and the time required for nutrients to be replenished [40]. Cones require 3 years to mature [59,61,108,139]. Colorado pinyon cones and seeds are attacked by a variety of insect species, which may destroy large portions of seed crops [121,139].

Seed dispersal: The wingless seeds of Colorado pinyon are dispersed by birds [5,20,34,68,98,101,112,166] and small mammals, primarily squirrels and chipmunks [5,20,21,34,68,112]. Four species of birds cache Colorado pinyon seeds: Clark's nutcrackers, scrub jays, pinyon jays, and Steller's jays [34,68,139]. However, most seeds are cached outside the elevational range of Colorado pinyon by Clark's nutcracker and to some extent, pinyon and Steller's jays. Scrub jays that live permanently in pinyon-juniper woodlands cache substantial numbers of seeds, making these birds locally important in Colorado pinyon regeneration [68].

Failure of Colorado pinyon cones to open, possibly due to a wetter spring moisture regime, renders seeds more difficult to access and reduces seed dispersal, particularly dispersal by small mammals [43]. 

On sloping sites, Colorado pinyon seeds may be washed "some distance away" by runoff [64].

Seed banking: In general, Colorado pinyon has short-lived seeds. As a result, seeds form only a temporary seed bank, with most seeds germinating the spring following dispersal. The potential for a large temporary seed bank is high following years of good seed production, while in other years the seed bank is likely sparse [20].

Germination: Colorado pinyon seeds generally germinate in the shade of a tree or shrub rather than in open grassland [34,58,105]. Germination occurs in response to moisture and moderate temperatures of 65 to 75 degrees Fahrenheit (18-24 oC). It occurs in the spring after snowmelt and/or warming temperatures [32,34,58,59,112]. If moisture conditions are not suitable, Colorado pinyon seeds may not germinate until the summer monsoon season [59]. Floyd [47] found that germination of Colorado pinyon occurs optimally at a mean temperature of 68 degrees Fahrenheit (20 oC) and 15 hours of light, with germination rates ranging from 25 to 65% [47]. Cold stratification may result in more rapid seed germination [60]. Floyd [45] found that germination and establishment of Colorado pinyon may be enhanced under a Gambel oak canopy, possibly due to increased moisture retention by litter, shading, decreased evapotranspiration in oak stands, and reduced seed predation. One study found higher Colorado pinyon germination rates when scrub jays cached seeds under junipers or near/under bushes, while very few seeds germinated if cached in the open [68].

Viability of fresh seeds varies between 85 and 95%. Seed viability decreases rapidly in 1 year or less, and the rate of germination is low [34,112].

Seedling establishment/growth: Reproduction of Colorado pinyon is generally sparse and scattered due to removal of seeds by birds and mammals [64], and seedling establishment is dependent on chance dispersal to favorable sites and ample rainfall [86]. More seedlings establish under trees or shrubs than away from them [59,71,86]. Colorado pinyon seedlings require extra moisture or shade until their elongating taproots reach deeper substrates [117]. Taproots of 1-year-old seedlings in northern Arizona averaged 8 inches (20.5 cm) long with a range of 6.7 to 10.6 inches (17-27 cm). Height of 1-year-old Colorado pinyon seedlings averaged 2 inches (5 cm) on northern Arizona sites [71]; growth was estimated at 1 inch per year for the first 10 years [34,105]. Biomass of 1-year-old seedlings is distributed evenly between shoot and root growth [71]. Seedlings growing in partial shade until they reach about 12 inches (30 cm) in height experience better early growth than those in complete shade under mature trees [71,112]. Water is the primary limiting factor in seedling survival and growth [112]. Competition for moisture usually results in the suppression of smaller trees, though they gradually resume normal growth when released from severe competition [59,112]. Saplings grow 4 to 6 inches (10-15 cm) in height annually, and mature trees grow 2 to 4 inches (5-10 cm) annually [59,139]. Mean annual diameter growth of Colorado pinyon is approximately 0.7 inch (1.8 cm) per decade when trees are about 50 years old [139].

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More info for the term: phanerophyte

RAUNKIAER [135] LIFE FORM:
Phanerophyte

More info for the term: tree

Tree

The reestablishment of Colorado pinyon following fire is solely by seed [44]. Seedlings may appear within the 1st year following fire [172], but several decades may be required before many seedlings establish. Following a fire in a pinyon-juniper stand in southern Colorado, Colorado pinyon began establishing at postfire year 25 [31].

Pinyon is a sun-adapted plant and is  classed as intolerant of shade (67). It also appears unable to compete  with grasses for moisture during the seedling stage following germination  (4).

    Secondary succession following fire or other severe disturbance in  pinyon-juniper woodlands appears to follow the general successional model  shown in figure 1 (3). However, the first herbaceous species to become  established after a fire are often those that were present in the stand  before disturbance (19). The shrub stage, often consisting of sagebrush, a  common associate in the woodlands, becomes prominent after about 12 years  (11). Junipers, which appear to have a wider ecological amplitude than  pinyons because of their greater drought resistance, are usually the first  trees to regenerate (10,12,75). They rapidly increase in density after 45  years, and dominate the site at 70 years. Thereafter, pinyons tend to  succeed junipers at rates determined by available seed sources until the  shrub understory is essentially eliminated. If disturbances are less  severe, as when cabling, chaining, or bulldozing is used to remove tree  cover for range improvement, many small surviving pinyons and junipers and  newly established seedlings, reforest the site in about 2 to 3 decades  (55,56,64). Under some conditions, however, natural regeneration can take  much longer (60).

     
Figure 1- Possible series and pathways of secondary  succession 
following disturbance in pinyon-juniper woodlands (3).

    Considerable evidence has accumulated to show that the woodlands,  especially those dominated by singleleaf pinyon, are invading areas below  their historic elevational limits (3,12,17,41). Furthermore, tree density  appears to be increasing in some stands that existed before the invasion  period. Pinyon-juniper woodland expansion since the time of settlement has  been attributed to several factors, including possible climatic changes,  control of fire, increased populations of seed-dispersing birds and  mammals, and reduced competition from grasses resulting from overgrazing  by livestock or the allelopathic influence of juniper foliage and litter  (20,39).

The rooting habit of pinyon is characterized by  both lateral and vertical root systems (67), but roots of pinyons less  than 3 m (10 ft) tall have been traced to depths 6.4 m (21 ft) in  underlying rock (25). Taproots and some laterals that penetrate downward,  however, grow horizontally when they encounter an impenetrable horizon or  bedrock. Laterals develop at a depth of about 15 to 41 cm (6 to 16 in) and  can exceed the crown radius by a factor of two or more. Taproot growth of  seedlings is rapid, averaging 17 to 27 cm (7 to 11 in) in length for  1-year-old seedlings (35). The extensive root system and relatively rapid  rate of root elongation, especially of young seedlings, enhance the  ability of pinyon to survive under and environments.

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More info for the term: natural

Phenology of Colorado pinyon has been studied infrequently, primarily due to the lack of easily observed, periodic phenophases. Observed phases include the emergence of male and female cones, pollination, when cones reach their full size, and when cones begin to open. Both male and female cones emerge in May or June from buds formed the previous year. The growth of these conelets stops around the last week of August -- at the end of the 1st summer their dimensions are only about 1/7 those of ripe cones -- and is resumed the following May. Cones and seeds then reach their full size in July and mature by September of the 2nd year. Cones open in late September and October [5,59,159]. In pinyon pines (P. edulis, P. monophylla, P. cembroides), male and female cones open for pollination during the late spring and early summer. Pollen is only dispersed for a few days and reaches a maximum in the last week of March. Natural germination of Colorado pinyon seed usually takes place the 1st spring following dispersal. Under favorable conditions however, seed may germinate during the summer or early fall [159].

Pinyon is not known to reproduce  vegetatively.

Natural regeneration is difficult to  achieve, primarily because of unfavorable climatic conditions, but seed  predation and heavy grazing pressure, especially by sheep and goats, also  play a role (67). Although pinyon grows best in full sunlight and can  germinate in the open, seedlings must be protected from the harsh  environment (21,31,35,46,49). Regeneration is usually achieved in the  shade of tree canopies, under shrubs such as rabbitbrush,  mountain-mahogany, and sagebrush, or alongside fallen trees.

    Optimum germination temperature for pinyon seed is about 21° C (70°  F). Germination is epigeal (68). Preliminary studies indicate that  germination can be significantly improved by washing seeds for 48 hours in  running tap water. Cold stratification for 30 or 60 days increases speed  of germination but not the percentage. Treatment with hydrogen peroxide to  suppress mold and enhance germination generally is not effective. Seeds  germinate in spring and summer following dispersal, depending on soil  moisture and temperature, with summer germination coinciding with the  onset of the rainy season. Also, seedling establishment probably depends  on an adequate moisture supply during the first summer (29,30,54,66,68).  Growth throughout the seedling stage is extremely slow, often with only  primary needles developing the first year, and subsequent height growth  averaging 2.5 to 5.0 cm (1 to 2 in) per year (67).

Trees reach cone-bearing age  when relatively young: 25 years old and 1.5 to 3.0 m (5 to 10 ft) tall.  Seeds are not produced in quantity, however, until age 75 to 100, but the  long-lived pinyons continue to bear for a few centuries. A mature pinyon  usually has a broad and rounded or irregular crown, which is often almost  as wide as the tree height. Such trees are the heaviest seed producers,  since cones are found mostly in the upper half of the crown near the ends  of branches. Each cone contains about 10 to 20 seeds, which average only  4,190/kg (1,900/lb) because of their large size. A large tree in a good  crop year may yield over 9.1 kg (20 lb) of seed, and better stands will  produce an estimated 336 kg/ha (300 lb/acre). Germinative capacity of  seeds may range between 83 and 96 percent; germinative energy is about 80  percent in 7 days (9,30,67,68).

    Cone crops are either good or poor, often with cones practically absent,  but seldom intermediate (67). Although good crops tend to be localized and  occur at irregular and infrequent intervals, some are found nearly every  year somewhere over the widespread range of the species. Furthermore, cone  bearing tends to be synchronous over large geographical areas, a condition  considered to be an evolved mechanism to counteract seed predation (46).  On an average, substantial crops are produced every 4 to 7 years, but  shorter intervals of 2 to 5 years elapse with individual trees or in  certain localities (9). Generally, crops occur more frequently on better  sites over the optimum range of pinyon than at the extreme limits.

    The large, wingless seeds of pinyon are not adapted to wind  dissemination. Instead, seed dispersal beyond tree crowns depends upon the  behavior of four corvid species of birds- Clark's nutcracker, Steller's  jay, scrub jay, and pinyon jay (8). Although these species eat great  quantities of seed during the fall and may be greater predators than  rodents, they also cache large amounts for consumption during ensuing  winter months. Some of these buried seeds are not recovered by the birds,  thus providing a seed source for subsequent germination and seedling  establishment, particularly if caches are located in a suitable  microenvironment, such as alongside shrubs or downed trees (46). Steller's  and scrub jays collect seed only from open cones. In contrast, pinyon jays  and Clark's nutcrackers forage from green cones, from which seeds are  deftly extracted, and then from open cones as the season progresses  (8,71).

    Clark's nutcrackers and Steller's jays probably contribute little  towards regenerating existing woodland sites because their caches are  located at higher elevations in ponderosa pine and mixed conifer forests  or in the ecotone above pinyon-juniper woodlands (8). Thus, these species  tend to expand woodlands to upper elevations. In contrast, scrub jays and  pinyon jays cache seeds in woodland areas, the former in small, local  territories, whereas the latter transport seeds up to 12 kilometers (7.5  mi).

    Pinyon jays live in flocks of 50 to 500 birds, and it has been estimated  that during a substantial seed year in New Mexico, about 4.5 million seeds  were cached by a single flock (46). Even scrub jays, which do not exhibit  flock behavior can be important seed dispersers-a single pair of birds may  harvest and cache about 13,000 seeds from a particular crop. Pinyon jays  can carry an average of up to 56 seeds in an expandable esophagus. Scrub  jays lack this adaption, and the amount of seed that can be transported at  one time is limited to 5 or fewer seeds held in the mouth and bill. The  majority of caches by pinyon and scrub jays are single-seeded, and are  located in the transition zone between mineral soil and the overlying  organic material (8,71).

    Although rodents are known to cache seed, they should not be considered  effective seed dispersers because caches are located in middens or  underground chambers where conditions are not suitable for germination or  seedling establishment. Instead, rodents, such as cliff chipmunks, pinyon  mice, and woodrats, are major predators, caching as much as 35 to 70  liters (1 to 2 bu) of good seed (46,67). Furthermore, limited data  indicate that rodents consume large quantities of seeds taken from bird  caches (32).

    It has been suggested that pinyon trees and seed eating birds have  evolved coadaptive traits that enhance survival of both organisms. The  seed dispersing and caching behavior of birds appears related to certain  traits of the trees: large, thin-coated seeds with high energy values,  different colored seedcoats that aid visually oriented seed harvesters to  distinguish edible from aborted seeds, upward orientation of cone and  scale angle for increased seed visibility, and prolonged seed retention in  open cones because of cone orientation and deep depressions and small  flanges on cone scales (70). Furthermore, the mutual dependence of birds  and trees appears more complex than just their respective roles of seed  dispersing and food providing agents. Gonadal activity of pinyon jays, for  example, is increased before the breeding season by the combined effect of  photoperiod, the appearance of cones, and a diet of seeds (46).

Pinyon is considered monoecious, the  male and female strobili being borne on the same tree (67). However,  dioecy has been observed under certain environmental conditions associated  with moisture stress and insect damage (23,74). Although ovulate cones  require most of three growing seasons to mature, the stages of growth vary  with elevation, weather, and individual trees. In general, winter buds  containing the strobili primordia begin to form in August, and by October   of the first year are fully formed. Bud growth the following year is  resumed near the first of May for staminate cones, and about mid-May for  ovulate cones. By mid-June, staminate cones are mature, and ovulate cones  become visible and receptive to pollen. Pollination is completed by the  end of June when cone scales close, and a period of rapid growth of cones  and seed commences, terminating at the end of August. During the third  year, conelets start growth about the first of May, and fertilization  occurs in early July. Shortly thereafter, cones and seeds reach full size,  and seed coats darken and harden. Seeds mature early in September, and  cone opening begins during mid-month and extends for about a 50-day  period.

Pinyon grows best on the higher, wetter sites  of the woodland zone, just below the ponderosa pine type (40,67). At these  elevations trees reach their tallest heights and tend to develop single  stems. At lower elevations, in contrast, bushy and sprawling crowns are  characteristic. Pinyons may be multistemmed, although to a lesser extent  than junipers. They usually exhibit straight, but short and rapidly  tapering boles, which diverge into many large sinuous branches.

    Growth of pinyon, though maintained with little loss of vigor throughout  the life of the tree, is extremely slow. Height growth of saplings, for  example, is only about 10 to 15 cm (4 to 6 in) yearly, and mature trees  grow even more slowly, averaging 5 to 10 cm (2 to 4 in) per year. Diameter  growth also is slow, especially on poor sites, where 80 to 100 years can  elapse before diameters at breast height reach even 10 to 15 cm (4 to 6  in). On better soils, however, 150-year-old trees may grow to a diameter  of 30 cm (12 in). Mean annual diameter growth of pinyon culminates at  about 1.8 cm (0.7 in) per decade, when trees are approximately 50 years  old. The gross annual increment on sample plots in northern New Mexico  woodlands also reflects the slow growth rate, averaging about 0.42 m³/ha  (6 ft³/acre) for pinyon alone, and 0.66 m³/ha (9.5 ft³/acre)  for all species. Gross cordwood increment for all species was 0.88 m³/ha  (0.14 cord/acre) (38,66,67).

    Pinyon is a long-lived tree, maturing in 75 to 200 years. Dominant trees  in a stand are often 400 years old, and pinyons 800 to 1,000 years old  have been found. Depending on the site, mature trees range between 3.0 and  15.5 m (10 to 51 ft) in height and 15 to over 76 cm (6 to 30 in) in d.b.h.  Although large trees are common, especially in northern New Mexico,  pinyons generally are small trees, usually less than 10.7 m (35 ft) tall  and 46 cm (18 in) in diameter (66,67). The largest living pinyon recorded  grows in New Mexico and measures 172 cm (68 in) in d.b.h., 21.0 m (69 ft)  in height, and has a crown spread of 15.8 m (52 ft) (2).

    Because of the growth habit of woodland species, tree volumes are not  only difficult to measure but can vary more than 300 percent for trees of  the same diameter. There is less variation in well-formed trees, however,  and the gross volume of a representative pinyon with a basal diameter of  30 cm (12 in) and 7.6 m (25 ft) tall is 0.22 m³ (7.7 ft³),  measured to a 10-cm (4-in) top. Woodland volumes vary considerably,  depending on species composition and density. In northern New Mexico and  Arizona, mixed stands may contain cordwood volumes ranging from about 5.0  to 157.4 m³/ha (0.8 to 25 cords/acre), with average volumes of about  69.3 m³/ha (11 cords/acre). Cordwood volumes of nearly pure pinyon  stands average about 75.6 m³/ha (12 cords/acre). Low volumes are a  reflection of the small trees generally associated with woodlands. The  average size tree in many New Mexico stands is only 15 cm (6 in) in  diameter at ground line and about 2.7 m (9 ft) tall (16,67).

    The density of pinyon in woodlands varies considerably, ranging from few  or none to several hundred stems per hectare. Nevertheless, the density in  a typical northeastern Arizona stand averages about 235/ha (95/acre) in  stems less than 7.6 cm (3 in) in d.b.h.; 200/ha (81/acre) from 7.6 to 15  cm (3 to 6 in) in d.b.h.; and 89/ha (36/acre) more than 15 cm (6 in) in  d.b.h. (67). Mixed woodlands are denser and more productive than pure  stands of either pinyon or juniper, and can approach or exceed 3,459  stems/ha (1,400/acre) (9,57). The higher values have been attributed to  differences in rooting habit and drought tolerance of the two species. The  shallower penetrating roots of pinyons limit interspecific root  competition for soil moisture in mixed stands. This, combined with the  lower photosynthetic rate of pinyons compared to that of junipers at  higher water stresses, allows more complete site utilization in mixed  stands (10,25,57). The average number of pinyons suitable for Christmas  trees varies from a few trees per acre to a fairly large number.

Population Differences    A form of pinyon that extends southeastward from northwestern Arizona  into southwestern New Mexico in the mountains south of the Mogollon Rim  has been classified as a taxonomic variety, P. edulis var. fallax  (47). Others considered it a local variant of singleleaf pinyon (44). More  recently, however, it has been recognized as a subspecies of a newly  described species of nut pine- Pinus californiarum subsp. fallax  (Arizona single-needle pinyon) (5).

    Practically no information is available regarding population differences  of pinyon. Considering the wide range of the species and the different  environmental conditions under which it grows, differences would be  expected. It has been reported that seed size is relatively consistent  from year to year in individual trees but varies among trees (67). Also,  some trees generally produce more cones than others, and some bear larger  cones with more seeds per cone.

    Races and Hybrids    No races of pinyon have been recorded. Natural hybridization has been  reported between pinyon and singleleaf pinyon in three zones common to the  species-the eastern edge of the Great Basin, the mountains south of the  Colorado Plateau, and areas adjacent to the Colorado River and its major  drainages (44). The two species also have been artificially crossed.  Pinyon and the newly described Arizona single-needle pinyon also are known  to hybridize (5).

The following is a representative barcode sequence, the centroid of all available sequences for this species.


No available public DNA sequences.

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Barcode of Life Data Systems (BOLDS) Stats
Public Records: 13
Specimens with Barcodes: 19
Species With Barcodes: 1

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: G5 - Secure

Reasons: Widely distributed in the southwestern United States and possibly in the northwestern corner of Chihuahua, Mexico, on dry, rocky slopes at altitudes of 1,600-2,400 m.

Please consult the PLANTS Web site and your State Department of Natural Resources for this plant’s current status, such as, state noxious status and wetland indicator values.

These plant materials are readily available from commercial sources. Contact your local Natural Resources Conservation Service (formerly Soil Conservation Service) office for more information. Look in the phone book under ”United States Government.” The Natural Resources Conservation Service will be listed under the subheading “Department of Agriculture.”

Grazing pressure by sheep and goats greatly reduces the regenerative capacity of the two-needle pinyon, and huge areas of pinyon-juniper woodlands have been extensively cattle-grazed. Range improvement practices to increase forage for wildlife and livestock have removed the trees over large areas. Woodland watersheds also have been mechanically cleared or chemically treated in the past, but future treatments may be limited to specific areas, because the possibility of generally increasing water yield does not appear promising.

Compared to pinyon pines, junipers have deeper root penetration and drought resistance and will dominate regeneration for up to 70 years after severe disturbance at a site. If small junipers and pines survive a less severe disturbance, the site may be naturally reforested after 2-3 decades.

The edible seeds of Colorado pinyon are gathered from native stands and marketed commercially [26,34,49,105,112,133,147,167]. Traditionally, these seeds were an important dietary supplement for Native Americans in the Southwest [19,30,81,98,116]. Traditional Native American uses for Colorado pinyon pitch include medicinal purposes and waterproofing of baskets and clay water bottles [30,81,116]. Colorado pinyon is used for Christmas trees [34,40,49,105] and landscaping [49].

Wood Products: The wood of Colorado pinyon is narrow-ringed, hard, and very brittle [64]. Wood products from Colorado pinyon include fuelwood, charcoal, mine timbers, railroad crossties, lumber, fenceposts, and pulpwood [30,34,49,64,98,105,112,116,167].

More info for the term: cover

Livestock grazing is an important use of pinyon-juniper woodlands [34]. Pinyon-juniper communities provide food and shelter for deer, elk, pronghorn, wild horses, small mammals, and both game and nongame bird species [112,134]. They also provide habitat for coyotes, mountain lions, and bobcats [134], and are important winter habitat for goshawks [63].

Pinyon-juniper woodlands are important winter ranges for mule deer [34,98], providing cover, shelter, and understory forage [34]. Colorado pinyon provides browse for mule deer, though it is not substantially utilized [10,17,94]. It may constitute 1 to 5% of mule deer winter diets [91].

The seeds of Colorado pinyon are an important food source for birds, particularly Clark's nutcracker [18,21], scrub jays, and pinyon jays [21]. Clark's nutcracker  preferentially harvest seed from trees with large cone crops. Cones chosen for seed removal also tend to have more seeds as well as more viable seeds, potentially resulting in differential reproductive success of Colorado pinyon [22]. Seeds are an important food for small mammals, primarily chipmunks and squirrels [21].

Palatability/nutritional value: Colorado pinyon browse is unpalatable to domestic cattle, sheep, and, horses [28]. The seeds are rich in protein and unsaturated fats, containing essential amino acids, carbohydrates, fats, vitamins, and minerals [81,98].

Cover value: Colorado pinyon provides good cover for elk, mule deer, white-tailed deer, pronghorn, upland game birds, small nongame birds, and small mammals [28,39]. Pinyon-juniper woodlands also provide important cover for coyotes [54].

Colorado pinyon is used to rehabilitate mined areas and critical habitats that have been damaged by fire [61,173].

Artificial regeneration: Dormancy of Colorado pinyon seeds is broken by soaking the seed for 1 to 2 days, followed by cold stratification at temperatures between 33 and 41 degrees Fahrenheit for 0 to 60 days [61,92].

Firewood is the product derived from pinyon-juniper woodlands that has  been used most widely and for the longest time and it continues to be the  primary energy source for the rural population of small communities in  much of the Southwest (9,60). Pinyon is preferred for fuelwood since it  has a higher heat value than any of its associates except the oaks and  burns with a pleasing and distinctive aroma.

    Although pinyon has physical properties similar to those of ponderosa  pine and is suitable for processing, it is not extensively used for sawn  products because of poor growth form and small size (9,51). Specialized  woodworking shops use pinyon for novelties, and small sawmills produce  mine timbers and railroad ties. The ties are used primarily in open pit  mines because of their toughness and resistance to breakage during  frequent rail line shifts. Pinyon has been used for pulping in the  Southwest, but only to alleviate shortages of normally used mill-residue  chips and pulpwood of other species. It is also occasionally processed for  charcoal.

    The edible nuts of pinyon are probably the most valuable product of the  species and are in great demand because of their delicate flavor (9,67).  Annual nut crops have been estimated to average between 454 000 and 907  000 kg (1 to 2 million lb), reaching 3.6 million kg (8 million lb) in an  exceptionally productive year. Commercial crops are practically  nonexistent in some years, however. Nuts are commonly sold and consumed  after roasting in the shell, but small quantities are sold raw. A limited  retail market exists for shelled nuts, which have also been used in  candies and other confections.

    Pinyons have been cut for private use for Christmas trees for many years  and have recently appeared on commercial lots (9). In states with large  acreages of pinyon-juniper woodlands, up to 40 percent of the yearly  harvest in the past has been reported as pinyon. Demand has decreased  since 1960, however, when 294,000 trees were harvested, ranking pinyon as  13th nationally. The decline has been attributed to an increasing supply  of other plantation-grown species and the scarcity of high-quality trees  in easily accessible stands.

    Pinyon-juniper woodlands over the past 400 years have been, and will  continue to be, grazed extensively (62). Furthermore, range improvement  practices to increase forage for wildlife and livestock have removed the  woodland trees over large areas. Woodland watersheds also have been  mechanically cleared or chemically treated in the past, but future  treatments may be limited to specific areas, because the possibility of  generally increasing water yield does not appear promising (7,9,15).

    Pinyon-juniper woodlands provide a habitat for a varied wildlife  population (26). Mule deer, white-tailed deer, elk, desert cottontail,  mountain cottontail, and wild turkey provide increasing hunter recreation.  Pinyon nuts are a preferred food for turkeys, but in poor seed years,  juniper mast is extensively consumed (58). Similarly, deer subsist on  browse species, but pinyon is a common food particularly during harsh  winters with deep snows (33,34).

The edible nuts of pinyon and are in demand because of their delicate flavor and are probably the most commercially valuable product of the species. Pinyon ranks first among the native nut trees that are not also cultivated. The nuts are commonly sold and eaten after roasting in the shell, but small quantities are sold raw. They were once a staple food of Southwestern Indians. Local residents now harvest quantities for the local and gourmet market, but they are in competition with many wild animals that also seek the nuts as food.

Pinyon nuts are a preferred food for turkeys, pinyon jays, woodrats, bears, and other wildlife, and they are a common food for deer, particularly during harsh winters with deep snows. Pinyon-juniper woodlands provide habitat for a varied wildlife population, including mule deer, white-tailed deer, elk, desert cottontail, mountain cottontail, and wild turkey.

Poor growth form and small size of two-needle pinyon has limited its use for sawn products. Specialized woodworking shops use the wood for novelties, and small sawmills produce mine timbers and railroad ties. Two-needle pinyon has been used for pulping in the Southwest, but only to alleviate shortages of normally used mill-residue chips and pulpwood of other species. It has been widely used for fuel since the pitchy wood has a higher heat value than any of its associates except the oaks and burns with a pleasing aroma. It is also occasionally processed for charcoal.

Pinyons have been cut for private and commercial use for Christmas trees. These beautiful little trees are slow growing but should be more widely used for ornamental purposes. Two-needle pinyon is the state tree of New Mexico.

Pinus edulis var. fallax Little ( P . californiarum subsp. fallax (Little) D.K.Bailey) appears to combine features of P . edulis and P . monophylla . More study is needed. 

 Seeds of Pinus edulis , the commonest southwestern United States pinyon, are much eaten and traded by Native Americans.

Pinyon ( Pinus edulis ) is the state tree of New Mexico.

Comments: Pinus edulis as treated in Kartesz (1999) does not include the variety 'fallax.'