Associated Forest Cover
provided by Silvics of North America
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.).
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Climate
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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
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Damaging Agents
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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.
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Flowering and Fruiting
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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.
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Genetics
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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).
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Growth and Yield
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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.
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Reaction to Competition
provided by Silvics of North America
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).
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Rooting Habit
provided by Silvics of North America
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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Seed Production and Dissemination
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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).
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Seedling Development
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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).
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Soils and Topography
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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).
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Special Uses
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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).
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Vegetative Reproduction
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Pinyon is not known to reproduce
vegetatively.
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Distribution
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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.
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Brief Summary
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Pinaceae -- Pine family
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.
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