Frank P. 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.
Regional Distribution in the Western United States
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 :
4 Sierra Mountains
7 Lower Basin and Range
10 Wyoming Basin
11 Southern Rocky Mountains
12 Colorado Plateau
13 Rocky Mountain Piedmont
Occurrence in North America
- The native range of pinyon.
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.
Colorado pinyon often grows as a low, bushy tree  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 . 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  and in fascicles of 2 . 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) , 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 . 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) . 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 .
Colorado Plateau Shrublands Habitat
This taxon can be found in the Colorado Plateau shrublands, as one of its North American ecoregions of occurrence. The Plateau is an elevated, northward-tilted saucer landform, characterized by its high elevation and arid to semi-arid climate. Known for the Grand Canyon, it exhibits dramatic topographic relief through the erosive action of high-gradient, swift-flowing rivers that have downcut and incised the plateau. Approximately 90 percent of the plateau is drained by the Colorado River and its tributaries, notably the lower catchment of the Green River.
A pinyon-juniper zone is extensive, dominated by a pygmy forest of Pinyon pine (Pinus edulis) and several species of juniper (Juniperus spp). Between the trees the ground is sparsely covered by grama, other grasses, herbs, and various shrubs, such as Big sagebrush (Artemisia tridentata) and Alder-leaf cercocarpus (Cercocarpus montanus).
A montane zone extends over large areas on the high plateaus and mountains, but is much smaller than the pinyon-juniper zone. The montane vegetation varies considerably, from Ponderosa pine in the south to Lodgepole pine and Aspen further north. Northern Arizona contains four distinct Douglas-fir habitat types. The lowest zone has arid grasslands but with many bare areas, as well as xeric shrubs and sagebrush. Several species of cacti and yucca are common at low elevations in the south.
Numerous mammalian species are found within the Colorado Plateau shrublands ecoregion, including the Black-tailed prairie dog (Cynomys ludovicianus); Long-eared chipmunk (Tamias quadrimaculatus); Utah prairie dog (Cynomys parvidens EN); Yellow-bellied marmot (Marmota flaviventris); and the Uinta chipmunk (Tamias umbrinus), a burrowing omnivore.
A large number of birds are seen in the ecoregion, with representative taxa: Chestnut-collared longspur (Calcarius ornatus NT); Greater sage grouse (Centrocercus urophasianus NT); Northern pygmy owl (Glaucidium gnoma); Cactus wren (Campylorhynchus brunneicapillus).
There are various snakes occurring within the Colorado Plateau, including: Black-necked garter snake (Thamnophis cyrtopsis), usually found in riparian zones; Plains Blackhead snake (Tantilla nigriceps); Black-tailed rattlesnake (Crotalus molossus), who seeks inactivity refuge in rock crevices, animal burrows and even woodrat houses. Other reptiles found here include the Common checkered whiptail (Cnemidophorus tesselatus).
There are only a limited number of anuran taxa on the Colorado Plateau; in fact, the comprehensive occcurrence list for the ecoregion is: Red-spotted toad (Anaxyrus punctatus); Canyon treefrog (Hyla arenicolor); Woodhouse's toad (Anaxyrus woodhousii); Couch's spadefoot toad (Scaphiopus couchii); Northern leopard frog (Lithobates pipiens); Plains spadefoot toad (Spea bombifrons); and Southwestern toad (Anaxyrus microscaphus). The Tiger salamander (Ambystoma tigrinum) is the sole salamander found on the Colorado Plateau shrublands.
The Colorado River fish fauna display distinctive adaptive radiations. The Humpback chub (Gila cypha), for example, is a highly specialized minnow that lives in the upper Colorado. It adapted to the water’s fast current and its extremes of temperature and flow rate. Dams and water diversion, however, have created a series of placid, stillwater lakes and side streams, and the Humpback chub may not be able to adapt to these altered conditions. The species, along with other native Colorado River fishes including the Bonytail (Gila elegans), Squawfish (Ptychocheilus lucius), and the Flannelmouth sucker (Catostomus latipinnis), may not survive much further in time.
Habitat and Ecology
Colorado pinyon is found on level or gently rolling uplands  to moderately steep and very steep slopes (27-75%) . It also occurs in riparian areas in the Southwest  and on slopes adjacent to river drainages . 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 . Moisture is likely the most critical factor controlling the distribution, composition, and density of pinyon-juniper woodlands , though the distribution of Colorado pinyon may also be affected by soil characteristics .
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:
|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)|||
|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) . 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 , and precipitation generally exceeds evapotranspiration only during December, January, and February . 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 .
Temperature and precipitation in the pinyon-juniper zone vary in relation to elevation and geographic location . 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 . 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 .
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 .
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 . 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 . 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 . Colorado pinyon litter is specifically associated with a reduction of blue grama production .
Habitat: Rangeland Cover Types
This species is known to occur in association with the following Rangeland Cover Types (as classified by the Society for Range Management, SRM):
More info for the terms: cover, shrub, vine
SRM (RANGELAND) COVER TYPES :
411 Aspen woodland
412 Juniper-pinyon woodland
413 Gambel oak
415 Curlleaf mountain-mahogany
416 True mountain-mahogany
417 Littleleaf mountain-mahogany
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
Habitat: Cover Types
This species is known to occur in association with the following cover types (as classified by the Society of American Foresters):
More info for the term: cover
SAF COVER TYPES :
210 Interior Douglas-fir
216 Blue spruce
220 Rocky Mountain juniper
237 Interior ponderosa pine
240 Arizona cypress
241 Western live oak
Habitat: Plant Associations
This species is known to occur in association with the following plant community types (as classified by Küchler 1964):
More info for the term: shrub
KUCHLER  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
K059 Trans-Pecos shrub savanna
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):
FRES21 Ponderosa pine
FRES30 Desert shrub
FRES33 Southwestern shrubsteppe
FRES34 Chaparral-mountain shrub
FRES38 Plains grasslands
FRES40 Desert grasslands
Key Plant Community Associations
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 . 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
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
Gambel oak (Quercus gambelii) [51,64,72,74,102,153], gray oak (Q. grisea) , wavyleaf oak
(Q. undulata) [102,153], blackbrush (Coleogyne ramosissima) [102,153], Nevada
ephedra (Ephedra nevadensis), broom snakeweed (Gutierrezia
sarothrae) , and plains prickly-pear (Opuntia polyacantha) . 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) ,
New Mexico muhly (M. pauciflora) , mutton grass (Poa
fendleriana) [102,153], galleta (Pleuraphis jamesii) , Columbia needlegrass
(Achnatherum nelsonii) [102,153], and sand bluestem (Andropogon
gerardii var. paucipilus) .
Classifications identifying Colorado pinyon as a plant community dominant are
New Mexico [11,51,52,74,83,102,104,153]
Soils and Topography
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).
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
Habitat & Distribution
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.
Associated Forest Cover
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.).
Diseases and Parasites
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.
Broad-scale Impacts of 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 . Young Colorado pinyon are generally killed by fire [86,172]. Research in New Mexico  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 .
Immediate Effect of Fire
POSTFIRE REGENERATION STRATEGY :
Tree without adventitious bud/root crown
Secondary colonizer (on-site or off-site seed sources)
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 .
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 . 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 , though presettlement fire regimes were likely a mixture of surface and crown fires with intensities and frequencies dependent on site productivity . 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  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  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 . 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 . 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 . Gottfried and others  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 . 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 . 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 . 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 . 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 . 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 .
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 . 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 .
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]|
|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 |
|galleta-threeawn shrubsteppe||Pleuraphis jamesii-Aristida purpurea||125]|
|Rocky Mountain Douglas-fir*||Pseudotsuga menziesii var. glauca||25-100 |
|oak-juniper woodland (Southwest)||Quercus-Juniperus spp.||125]|
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 . Successional pathways of pinyon-juniper stands are indeterminate, and conditions after disturbance are generally less stable than the late seral, tree-dominant communities . 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 , 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 . 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 . "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 .
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 .
Colorado pinyon regenerates solely from seed; asexual regeneration has not been documented . 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 .
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 . 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 . 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 . 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 .
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 . 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 .
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 .
On sloping sites, Colorado pinyon seeds may be washed "some distance away" by runoff .
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 .
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 . Floyd  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% . Cold stratification may result in more rapid seed germination . Floyd  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 .
Seedling establishment/growth: Reproduction of Colorado pinyon is generally sparse and scattered due to removal of seeds by birds and mammals , and seedling establishment is dependent on chance dispersal to favorable sites and ample rainfall . 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 . 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 ; 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 . 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 . 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 .
Growth Form (according to Raunkiær Life-form classification)
More info for the term: phanerophyte
RAUNKIAER  LIFE FORM:
Plant Response to Fire
Reaction to Competition
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).
Life History and Behavior
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 .
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).
Seed Production and Dissemination
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).
Flowering and Fruiting
Growth and Yield
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.
Molecular Biology and Genetics
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).
Barcode data: Pinus edulis
Statistics of barcoding coverage: Pinus edulis
Public Records: 13
Specimens with Barcodes: 19
Species With Barcodes: 1
IUCN Red List Assessment
Red List Category
Red List Criteria
National NatureServe Conservation Status
Rounded National Status Rank: N5 - Secure
NatureServe Conservation Status
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.
Cultivars, improved and selected materials (and area of origin)
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.
Relevance to Humans and Ecosystems
Other uses and values
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 .
Wood Products: The wood of Colorado pinyon is narrow-ringed, hard, and very brittle . 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].
Importance to Livestock and Wildlife
Livestock grazing is an important use of pinyon-juniper woodlands . 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 , and are important winter habitat for goshawks .
Pinyon-juniper woodlands are important winter ranges for mule deer [34,98], providing cover, shelter, and understory forage . 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 .
The seeds of Colorado pinyon are an important food source for birds, particularly Clark's nutcracker [18,21], scrub jays, and pinyon jays . 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 . Seeds are an important food for small mammals, primarily chipmunks and squirrels .
Palatability/nutritional value: Colorado pinyon browse is unpalatable to domestic cattle, sheep, and, horses . 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 .
Value for rehabilitation of disturbed sites
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].
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.
|This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. (September 2009)|
Pinus edulis, the Colorado pinyon, two-needle pinyon, or piñon pine, is a pine in the pinyon pine group whose ancestor was a member of the Madro-Tertiary Geoflora[a] (a group of drought resistant trees) and is native to the United States.
Distribution and habitat
The range is in Colorado, southern Wyoming, eastern and central Utah, northern Arizona, New Mexico, and the Guadalupe Mountains in westernmost Texas. It occurs at moderate altitudes of 1,600–2,400 metres (5,200–7,900 ft), rarely as low as 1,400 m (4,600 ft) and as high as 3,000 m (9,800 ft). It is widespread and often abundant in this region, forming extensive open woodlands, usually mixed with junipers in the pinyon-juniper woodland plant community. The Colorado pinyon (piñon) grows as the dominant species on 4.8 million acres (19,000 km2 or 7,300 sq mi) in Colorado, making up 22% of the state's forests. The Colorado pinyon has cultural meaning to agriculture, as strong piñon wood "plow heads" were used to break soil for crop planting at the state's earliest known agricultural settlements.
There is one known example of a Colorado pinyon growing amongst Engelmann spruce (Picea engelmannii) and limber pine (Pinus flexilis) at nearly 3,170 metres (10,400 ft) on Kendrick Peak in the Kaibab National Forest of northern Arizona.
The piñon pine (Pinus edulis) is a small to medium size tree, reaching 10–20 metres (33–66 ft) tall and with a trunk diameter of up to 80 centimetres (31 in), rarely more. The bark is irregularly furrowed and scaly. The leaves ('needles') are in pairs, moderately stout, 3–5.5 cm (1.2–2.2 in) long, and green, with stomata on both inner and outer surfaces but distinctly more on the inner surface forming a whitish band.
The cones are globose, 3–5 cm (1.2–2.0 in) long and broad when closed, green at first, ripening yellow-buff when 18–20 months old, with only a small number of thick scales, with typically 5–10 fertile scales. The cones open to 4–6 cm (1.6–2.4 in) broad when mature, holding the seeds on the scales after opening. The seeds are 10–14 millimetres (0.39–0.55 in) long, with a thin shell, a white endosperm, and a vestigial 1–2 mm (0.039–0.079 in) wing; they are dispersed by the Pinyon Jay, which plucks the seeds out of the open cones. The jay, which uses the seeds as a food resource, stores many of the seeds for later use, and some of these stored seeds are not used and are able to grow into new trees.
The species intermixes with Pinus monophylla sbsp. fallax (see description under Pinus monophylla) for several hundred kilometers along the Mogollon Rim of central Arizona and the Grand Canyon resulting in trees with both single- and two-needled fascicles on each branch. The frequency of two-needled fascicles increases following wet years and decreases following dry years. The internal anatomy of both these needle types are identical except for the number of needles in each fascicle suggesting that Little's 1968 designation of this tree as a variety of Pinus edulis is more likely than its subsequent designation as a subspecies of Pinus monophylla based entirely upon its single needle fascicle.
It is most closely related to the single-leaf pinyon, which hybridises with it occasionally where their ranges meet in western Arizona and Utah. It is also closely related to the Texas Pinyon, but is separated from it by a gap of about 100 kilometres (62 mi) so does not hybridise with it.
An isolated population of trees in the New York Mountains of southeast California, previously thought to be Colorado pinyons, have recently been shown to be a two-needled variant of single-leaf pinyon from chemical and genetic evidence. Occasional two-needled pinyons in northern Baja California, Mexico have sometimes been referred to Colorado pinyon in the past, but are now known to be hybrids between single-leaf pinyon and Parry pinyon.
The edible seeds, pine nuts, are extensively collected throughout its range; in many areas, the seed harvest rights are owned by Native American tribes, for whom the species is of immense cultural and economic importance. One early legend asserts that the "tree of life" is a pinyon pine, rooted in ancient cultural sites found within areas of pinyon (piñon) Canyon, Colorado.
The habitat destruction by deforestation of large areas of pinyon forests in the interests of cattle ranching, for habitat conversion to grazing rangeland, is seen by many as an act of major ecological and cultural vandalism.
Colorado pinyon is also occasionally planted as an ornamental tree and sometimes used as a Christmas tree.
- A. Farjon (2013). "Pinus edulis". IUCN Red List of Threatened Species. Version 2014.3. International Union for Conservation of Nature. Retrieved 21 March 2015.
- "New Mexico Secretary of State: KID'S Corner". Retrieved 2009-05-09.
- Axelrod, Daniel I. (July 1958). "Evolution of the madro-tertiary geoflora". The Botanical Review 24 (7): 433–509. doi:10.1007/BF02872570.
- Ogg, James G.; Gradstein, F. M; Gradstein, Felix M. (2004). A geologic time scale 2004. Cambridge, UK: Cambridge University Press. ISBN 0-521-78142-6.
- Moore, Gerry; Kershner, Bruce; Craig Tufts; Daniel Mathews; Gil Nelson; Spellenberg, Richard; Thieret, John W.; Terry Purinton; Block, Andrew (2008). National Wildlife Federation Field Guide to Trees of North America. New York: Sterling. p. 92. ISBN 1-4027-3875-7.
- Cole, Ken; Fisher, Jessica; Arundel, Samantha; Canella, John; Swift, Sandra (2008). "Geographical and climatic limits of needle types of one- and two-needled pinyon pines". Journal of Biogeography 35: 357–369.
- Little, Elbert (1968). "Two new pinyon varieties from Arizona". Phytologica 17: 329–342.
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.
Names and Taxonomy
Comments: Pinus edulis as treated in Kartesz (1999) does not include the variety 'fallax.'
Engelm. (Pinaceae) [26,41,73,84,85,109,133,166,167].
Where the ranges of both species overlap, Colorado pinyon frequently
hybridizes with singleleaf pinyon (P. monophylla)
[27,95,96,98,99,100,106]. The eastern edge of the Great Basin is the rough boundary
between Colorado and singleleaf pinyons, and forms a "zone of
hybridization" . Colorado pinyon also hybridizes
with Mexican pinyon (P. cembroides) .
Rocky Mountain pinyon