Blue Spruce

In Great Britain and/or Ireland:
Foodplant / false gall
crowded pseudothecium of Cucurbitaria piceae causes swelling of characteristically twisted, swollen bud of Picea pungens
Remarks: season: 6-12

Plant / associate
clustered, superficial pycnidium of Megaloseptoria coelomycetous anamorph of Megaloseptoria mirabilis is associated with Gemmamyces infected bud of Picea pungens

Foodplant / saprobe
superficial, clustered, hypophyllous pycnidium of Rhizosphaera coelomycetous anamorph of Rhizosphaera kalkhoffii is saprobic on dead needle of Picea pungens
Remarks: season: late winter to early spring
Other: major host/prey

Foodplant / saprobe
erumpent, shortly stalked apothecium of Tryblidiopsis pinastri is saprobic on dead, attached branch of Picea pungens
Remarks: season: 5-7

Limited hybridization occurs between Picea pungens and P . engelmannii (R.Daubenmire 1972; R.J. Taylor et al. 1975).

Blue spruce ( Picea pungens ) is the state tree of Colorado (as Colorado blue spruce) and Utah.

Trees to 50m; trunk to 1.5m diam.; crown broadly conic. Bark gray-brown. Branches slightly to strongly drooping; twigs not pendent, stout, yellow-brown, usually glabrous. Buds dark orange-brown, 6--12mm, apex rounded to acute. Leaves 1.6--3cm, 4-angled in cross section, rigid, blue-green, bearing stomates on all surfaces, apex spine-tipped. Seed cones (5--)6--11(--12)cm; scales elliptic to diamond-shaped, widest below middle, 15--22 ´ 10--15mm, rather stiff, margin at apex erose, apex extending 8--10mm beyond seed-wing impression. 2 n =24.

Midmontane forests; 1800--3000m; Ariz., Colo., Idaho, N.Mex., Utah, Wyo.

Picea parryana Sargent

Picea pungens, known as blue spruce, Colorado blue spruce, Colorado spruce, silver spruce, and pino real, is a slow- growing, medium-sized, long-lived conifer tree in the Pinaceae (pine family) that is planted extensively as an ornamental because of its symmetric form and attractive color. It is the State Tree of Colorado and Utah. It is not an important timber tree because it is relatively scarce, and the wood is brittle and often full of knots. Blue spruce is a species of the montane zone in the central and southern Rocky Mountains of the western United States, Its range extends from latitude 33° 50' to 48° 54' N. and from longitude 104° 45' to 114° 00' W.; the Rocky Mountain region in high mountains from southern and western Wyoming, eastern Idaho, south to Utah, northern and eastern Arizona, southern New Mexico, to central Colorado. It has been reported in isolated locations in north-central Montana. It is a dominant species in some forests, but is more commonly a minor component of other conifer or mixed conifer-deciduous forests. Over the bulk of its range, blue spruce is most frequently associated with Rocky Mountain douglas-fir (Pseudotsuga menziesii var. glauca), ponderosa pine and (Pinus ponderosa, and with white fir (Abies concolor) on mesic sites in the central Rocky Mountains. Blue spruce is seldom found in large numbers, but on streamside sites it is often the only coniferous species present. Blue spruce is valued mainly for its appearance. Shortly after the species was discovered in 1861, writers described it as "a finely shaped tree" and "the most beautiful species of conifer," alluding to the symmetrical, pyramidal form and the glaucous, bluish or silvery-gray foliage that some trees of the species display. The needle coloration, caused by the presence of surface waxes, apparently intensifies with tree age. These traits of symmetry and blue or silver-gray cast, so common in horticultural plantings, are only occasionally found in natural stands. In nature, trees with similar color tend to occur in small, local populations, suggesting genetic control of the color trait. Blue spruce is widely used as an ornamental, not only in the United States, but in Europe, where it was introduced late in the 19th century. At least 38 cultivars of blue spruce have been named, based primarily on leaf coloration and crown form. Although young blue spruce usually show a pronounced layering of stiff branches, which give it a distinct pyramidal form, the branches begin to droop and the crown becomes thin and irregular as the tree ages. The trunk tapers rapidly, and epicormic shoots commonly develop, giving the tree a ragged appearance. Blue spruce is prized as a Christmas tree, and plantations have been established in its native range as well as in north-central and northeastern United States. Excerpted and edited from Fechner 1990.

blue spruce
Colorado blue spruce
Colorado spruce
silver spruce
pino real

More info for the terms: association, climax, cover, forest, selection, tree

Blue spruce provides good environmental protection for elk, mule deer,
white-tailed deer, small mammals, and small nongame and upland game
birds in Colorado, Utah, and Wyoming. It gives poor cover for pronghorn
in Colorado and Wyoming, and fair to poor cover for waterfowl in Utah
and Wyoming [29].

Blue spruce was one of several species in a commercial conifer nursery
used by white-tailed and mule deer for hiding and thermal cover during a
severe winter in southeastern Wyoming [56]. Moose use blue spruce for
shelter [75]. In Wyoming, moose used the blue spruce climax association
an average of 5 percent over 4 years [63]. Where blue spruce occurred
in a ponderosa pine forest in Colorado, cavity nesting birds showed no
preference in tree species selection for nest sites [100].
Mixed-conifer forests of Arizona and New Mexico that blue spruce occur
in are valuable summer habitat for game and nongame animals and birds
[44,73].

Sensitive and endangered species use mixed-conifer stands in which blue
spruce occurs. Such species include flammulated owls in Colorado, Jemez
Mountain salamander of New Mexico, and northern goshawks in Arizona
[20,94,98,99]. Bald eagle breeding areas at intermediate elevation in
Wyoming are dominated by blue spruce and narrowleaf cottonwood. In the
Snake River Unit, 28 percent of the nests were in blue spruce trees
[114].

More info for the term: tree

Blue spruce is a native evergreen tree with a dense, pyramidal to
spire-shaped crown [75,116,122]. It can be 70 to 115 feet (21-35 m)
tall with a diameter up to 3 feet (0.91 m) [103,104,115,122]. The bark
is 0.75 to 1.5 inches (1.9-3.8 cm) thick [104]. Branches are stout and
horizontal to drooping [65,122]. The leaves are four-angled, stiff with
sharp points, and 1 to 1.25 inches (2.5-3.2 cm) long [37,68]. Cones are
2.5 to 4 inches (6.4-10.2 cm) long with thin, flexible scales [77]. The
seeds are 0.13 inch (0.3 cm) long, about half the length of the wings
[104].

The largest blue spruce recorded was from Colorado at 126 feet (38.4 m)
tall with 60.8 inches (154.4 cm) d.b.h. [38]. The oldest blue spruce
was 600 years [86].

Blue spruce is restricted to the central and southern Rocky Mountains.
Its range extends from scattered populations in eastern Idaho and
western Wyoming to better developed populations in Utah and Colorado.
The range of blue spruce continues southward into Arizona and New Mexico
[22,38,77,103,104]. It occurs rarely in north-central Montana [113].

More info for the terms: fire frequency, fire regime, fire suppression, forest, frequency, succession, tree

Blue spruce is easily killed by fire [67,126]. It has thin bark and
shallow roots which make it susceptible to hot surface fires [14]. Blue
spruce is slow to self-prune lower branches; therefore, surface fires
can crown [19]. Blue spruce foliage has moderately volatile oils [109].
Crowns are dense and highly flammable [106,109]. However, surviving
blue spruce remain windfirm in stands opened by fire [14].

In riparian areas where blue spruce occurs, intervals between fires are
about 350 to 400 years. Severe fires occur infrequently, and succession
back to the original community is often relatively rapid (15 to 35
years). Depending on the site, blue spruce may be the dominant seral
tree [19].

Successive fires may prevent blue spruce from dominance because it is
fire intolerant. Historical fire frequency in mixed-conifer forests was
about 22 years, based on fire-scarred trees in the White Mountains of
Arizona [27]. Fire suppression during the past 100 years has made the
mixed-conifer forest in which blue spruce occurs more susceptible to
fire; however, blue spruce may be dominant in some areas because of the
longer fire-free intervals.

FIRE REGIMES :
Find fire regime information for the plant communities in which this
species may occur by entering the species name in the FEIS home page under
"Find FIRE REGIMES".

More info for the terms: forest, fuel, fuel loading, natural, prescribed fire

Fire is less frequent in montane mixed-conifer forests at lower
elevations where Douglas-fir is dominant with blue spruce than in
ponderosa pine types. Quaking aspen is seral and present because of
fire in these forests. Prescribed fire here would increase habitat and
browse for wildlife [108].

Blue spruce is not recommended for fire shelterbelts based on studies in
Victoria, Australia. Fuel ladders form from persistent dead low
branches [109].

Fuel prediction is difficult because of the large variation in natural
fuel loadings in the forests where blue spruce occurs [101]. Therefore,
Sackett [102] determined average squared diameters and specific
gravities of blue spruce and seven other conifer species in Arizona and
New Mexico. This established weight and volume of fuels using planar
intersect method. Greatest accumulations on the mixed-conifer forest
floor come from fermentation and humus layers [43]. One fuel loading
estimate was an average of 44 tons per acre (98 t/ha) [128].

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More info for the term: phanerophyte

Phanerophyte

More info for the terms: litter, soil temperature regimes

The shallow roots of blue spruce restrict it to moist sites where water
is close to the surface [75]. Blue spruce occurs on montane
streambanks; well-drained floodplains or cobble flats; first-level
terraces; ravines; intermittent streams; or subirrigated, gentle slopes
[37,60,75,104].

Throughout much of its range, blue spruce grows in cool climates that
are subhumid to humid, characterized by low summer temperatures and low
winter precipitation [37]. In the southern end of its range, it may be
restricted to riparian areas in arid and semiarid climates;
precipitation occurs bimodally with dry springs [92]. Average annual
precipitation in blue spruce habitats varies from 18 to 24 inches
(460-610 mm) [37].

Blue spruce typically occurs at mid-elevations. In Wyoming, blue spruce
is abundant along streams at 6,750 feet (2,057 m) in elevation and
extends up into subalpine zones to 10,499 feet (3,200 m) [37,61]. In
Utah, blue spruce occurs from 6,500 to 8,400 feet (1,981-2,560 m) in
elevation, where often the parent material is limestone or calcareous
sandstone [15,38,65]. In Colorado, blue spruce occurs in canyons from
6,700 to 8,530 feet (2,042-2,600 m) in elevation and on canyon slopes
from 9,800 through 11,500 feet (2,987-3,505 m) in elevation [61,70,74].
Blue spruce occurs from 7,500 to 9,842 feet (2,285-3,000 m) in elevation
in Arizona and New Mexico [1,84,116].

Blue spruce grows on a variety of soil types. Usually, soils are young
and undeveloped; however, soil textures may be deep sandy to gravelly
loams that are well drained [37,61]. Soils are commonly derived from
fluvium, alluvium, and colluvium [60,110]. Soils may have a litter
layer up to 3.5 inches (9 cm) thick [61]. Soil temperature regimes are
frigid in montane canyons to cryic at higher elevations [26,85]. Blue
spruce stands are often associated with areas of cold air drainage
[60,128]. Blue spruce occurs on flat to moderate (12 to 20 percent)
slopes that often are north- to south- or southeast-facing [38,70].

Common associates not mentioned in Distribution and Occurrence are Rocky
Mountain maple (Acer glabrum), thinleaf mountain alder (Alnus incana
ssp. tenuifolia), wax currant (Ribes cereum), Utah honeysuckle (Lonicera
utahensis), Gambel oak (Quercus gambelii), Saskatoon serviceberry
(Amelanchier alnifolia), and common juniper (Juniperus communis)
[3,37,70,88]. Other associated species are hairy goldenaster
(Chrysopsis villosa), Fendler meadowrue (Thalictrum fendleria), Arizona
fescue (Festuca arizonica), bluejoint reedgrass (Calamagrostis
canadensis), and field horsetail (Equisetum arvense) [3,37,115,128].

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

206 Engelmann spruce - subalpine fir
210 Interior Douglas-fir
211 White fir
216 Blue spruce
217 Aspen
218 Lodgepole pine
219 Limber pine
235 Cottonwood - willow
237 Interior ponderosa pine

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

FRES20 Douglas-fir
FRES21 Ponderosa pine
FRES23 Fir - spruce
FRES26 Lodgepole pine
FRES28 Western hardwoods

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

More info for the term: forest

K012 Douglas-fir forest,
K018 Pine - Douglas-fir forest
K019 Arizona pine forest
K020 Spruce - fir - Douglas-fir forest
K021 Southwestern spruce - fir forest
K022 Great Basin pine forest
K025 Alder - ash forest

More info for the term: severity

Fire kills blue spruce. Low severity fires will kill saplings and
seedlings [2]. Slow burning of fine fuels will kill the shallow roots
of blue spruce [14].

More info for the terms: cover, forest

Blue spruce provides cover for a variety of bird and animal species
[29]. Big game forage is good throughout blue spruce habitat types in
northern New Mexico and southern Colorado [26]. Numerous birds eat blue
spruce seeds [122]. Blue spruce cones are cached by red squirrels in
Utah [128].

In a mixed-conifer forest in the White Mountains of Arizona, nongame
birds moderately preferred blue spruce for cover and gleening for
insects. In a comparison of usage in logged and control areas, mountain
chickadee and ruby-crowned kinglet preferred blue spruce in unlogged
areas only; yellow-rumped warbler preferred it in both treatment areas;
and gray-headed junco preferred blue spruce in logged areas only [47].

More info for the terms: codominant, forest, habitat type, series

Blue spruce occurs as dominant or codominant in small stands or as
scattered individuals. In riparian settings, blue spruce is codominant
with cottonwoods such as narrowleaf cottonwood (Populus angustifolia) or
balsam poplar (P. balsamifera) [7,85,117]. Blue spruce is more
important in habitat type series of the central Rocky Mountains. Blue
spruce series are restricted to cool, moist areas thoughout the
southwestern mixed-conifer forests [1,26,120]. Common codominants are
Engelmann spruce, white fir (Abies concolor), and Douglas-fir
(Pseudotsuga menziesii) [3,26,88].

Blue spruce is often a long-lived seral species. It is seral in white
fir, corkbark fir (Abies lasiocarpa var. arizonica), or fir phases of
Engelmann spruce habitat types [3,39]. It infrequently occurs in the
spruce-fir subalpine zone [31].

Some of the many publications that list blue spruce as an indicator or
dominant in habitat or community types are:

(1) Classification of the forest vegetation on the National Forests of
Arizona and New Mexico [3]
(2) Classification of riparian vegetation of the montane and subalpine
zones in western Colorado [7]
(3) Aspen community types of Utah [88]
(4) A physical and biological characterization of riparian habitat and
its importance to wildlife in Wyoming [91].

More info for the term: tree

Tree

More info for the terms: basal area, cone, cover, forest, layering, natural, seed, seed tree, selection, series, tree

Silviculture: Blue spruce has an intermediate tolerance for single-tree
selection harvesting [55]. Single-tree selection and diameter-limit
harvest methods were compared on a Southwestern old-growth mixed-conifer
stand in which blue spruce occurred. The single-tree selection method
left the stand satisfactorily stocked with 54 percent damage to advance
regeneration. Diameter-limit method left the stand understocked with 71
percent loss of advance regeneration [51]. Conifer regeneration by
small patch clearcutting was also recommended for these forests [42,52].
Effective seeding distance to obtain adequate natural regeneration of
blue spruce is about 3 to 4 times the height of the tree [80]. Because
blue spruce is considered a late successional species, it is not
suitable as a seed tree in clearcuts [53,106]. Silvicultural practices
for mixed-conifer stands are reviewed in detail [67].

Blue spruce ranged from 2 to 28 inches (5.1-71.1 cm) d.b.h. with most
trees at 2 inches (5.1 cm) in stand inventories of virgin mixed-conifer
forest; no blue spruce died during the 5 years of monitoring. Initial
blue spruce volume was 360 board feet per acre; final volume was 391
board feet per acre. Average annual growth of blue spruce was less than
0.2 inch (0.5 cm) [50]. In east-central Arizona, blue spruce were 3.05
square feet per acre (0.7 sq m/ha) basal area in a total 177.7 square
feet per acre (40.8 sq m/ha) for the mixed-conifer forest. Blue spruce
annual basal growth of 2.9 percent was the highest growth rate for all
tree species present [33]. In blue spruce habitat series in central
Colorado, total basal areas ranged from 169 to 300 square feet per acre
(49-83 sq m/ha) with all size classes of blue spruce present [60,61].

Other Uses: In wet sites with well-developed soil, blue spruce timber
potential is high; however, the timber value may be low. Blue spruce is
often more valuable for wildlife habitat and food and for recreation
[70].

Blue spruce is a component of mixed-conifer forests that have been a
part of browse studies [41]. Equations exist for predicting forage
production [12,40,76]. Forage production estimates include hiding and
thermal cover for wildlife management. Since these mixed-conifer
clearcuts require 50 to 100 years to regenerate, clearcut areas are a
long-term forage resource for deer and elk [118]. Quaking aspen
(Populus tremuloides) is often associated with blue spruce on upland
sites. Treatment of conifers in these systems depends on whether aspen
is to be maintained for livestock forage or wildlife habitat [25].

Blue spruce is a part of mixed-conifer stands that are managed for
watershed [52]. Clearcuts in these forests increase water yield almost
in proportion to the area cleared [24].

Artificial vegetative propagation of blue spruce is possible using short
cuttings, grafting, and air layering [28,38,123]. Breeding commercial
stock has been successful; however, interspecific crosses rarely yield
viable hybrids [34,46,90,105]. Blue spruce pollen used in artificial
crosses is viable for almost 3 years when stored at cold temperatures
[36]. Methods for cone harvesting and seed extraction are discussed in
detail [32,103].

Blue spruce have been planted in a wide range of environments. It has
been a part of state nursery programs to stock oldfields in Ohio [93].
Blue spruce nursery stock is more drought resistant than other spruce
species, and it can withstand temperatures to -40 degrees Fahrenheit
(-40 deg C) [38]. It can tolerate some flooding. Forty percent of
3-year-old blue spruce seedlings survived 21 days under aerated,
submerged conditions; all died after 28 days [82].

Blue spruce was included in a 30-year shelterbelt project in the
northern Great Plains. Blue spruce was 13 feet (4 m) tall at 20 years
with 32 percent of the original trees surviving [49]. It has been
successfully used in shelterbelts in Montana, North Dakota, and South
Dakota [9,119]. Planting recommendations have been discussed in detail
[4,107].

Damaging Agents: Insects and disease reduce growth, viability, and
vigor of blue spruce [37,124]. Heart and root rots, cone rusts,
nematodes, snow molds, canker, and tip blight have an impact on blue
spruce [38,89]. Silvicultural methods that minimize pathologic and
insect problems are discussed in detail [2,45,106]. Calibrated
ecosystem models that correlate microclimate with blue spruce stand
information are useful for predicting the behavior of forest pathogens
[83]. Tree ring patterns of blue spruce have been used to construct
past occurrence of insect attacts [69].

Blue spruce is a host of western spruce budworm (Choristoneura
occidentalis); outbreaks and symptoms are discussed in detail [16,78].
Blue spruce is an infrequent host of mountain pine beetle (Dendroctonus
ponderosae) and spruce beetle (D. rufipennis), which kill other conifers
[5,62]. Trees surviving infestation are more susceptible to other
pathogens, insects, and windthrow [45,57].

Blue spruce is the principal host of western spruce dwarf mistletoe
(Arceuthobium microcarpum) and minor host of other dwarf mistletoe
species [58,59,124]. Infected blue spruce seedling mortality under a
heavily infested canopy was twice that of the control [79].

The protein value of blue spruce is rated as poor, and its energy value
is fair [29].

AZ CO HI ID MT NM UT WY

More info for the term: tree

Blue spruce is planted extensively as an ornamental in North America and
Europe [13,77,104,]. Blue spruce are used as Christmas trees [38,65].
It is the state tree of Colorado and Utah [77,65].

Blue spruce is not a highly preferred food for either wildlife or
domestic animals [10,103]. Deer browse blue spruce infrequently [122].
In mixed-conifer forests, blue spruce is the least desired browse
species by elk and deer [67]. White-tailed deer in Conneticut browsed
ornamental blue spruce an average of 0.5 percent throughout the summer
[18]. Blue spruce can be used an an index of mule deer population size;
young blue spruce are severely damaged by browsing during times of
overpopulation [64].

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Reproductive buds of blue spruce form on shoots of the previous year
[103]. Pollen is shed from April to June, depending on altitude. Cones
mature during August or September of their first year; seeds disperse in
fall and winter [37,103]. Some cones drop the first winter; however,
most are retained 2 to 3 years [37]. Seeds germinate in the spring or
summer after dispersal [38].

More info for the term: seed

Blue spruce does not sprout after fire [109]. Rates of establishment
will vary depending on proximity of seed trees and moisture. Seed must
be transported from off-site. Blue spruce will establish by
wind-dispersed seed that readily germinates on the mineral soil exposed
by fire. Small mammals and birds may also carry cones or seeds into a
burn.

More info for the terms: root crown, secondary colonizer

Tree without adventitious-bud root crown
Secondary colonizer - off-site seed

More info for the terms: cone, natural, seed, stratification, tree

Blue spruce reproduces sexually. Natural vegetative reproduction does
not occur, although epicormic shoots sometimes sprout on the trunks
[38].

Seed production begins at about 20 years and peaks at 50 to 150 years
[38,122]. Blue spruce is a good to prolific seed producer, producing
full cone crops every 2 to 3 years [32,38,122]. Cones mature in August
of the first year and have 85 to 195 seeds per cone [37]. Seeds are
wind disseminated, falling within 300 feet (90 m) of the upwind timber
edge [38].

Most germination occurs on exposed mineral soil; however, seeds
germinate on a variety of substrates [37]. Natural germination rates
usually are low; however, one study reported 80 percent germination
[28,38]. Seeds germinate without stratification under a wide range of
temperature and light conditions [38,103]. Blue spruce seedlings will
establish beneath parent or other conifer canopies if understory
vegetation is lacking or sparse [71].

Overall tree growth is slow [65]. In a nursery, blue spruce were 19.1
to 23.3 inches (48.5 to 59.2 cm) tall after 5 years [38]. Seedlings are
susceptible to frost heaving and may be susceptible to drought due to
shallow roots [2,66]. Blue spruce transplanted into the ponderosa pine
(Pinus ponderosa) zone in the southern Rocky Mountains all died due to
drought conditions [21]. Blue spruce was collected throughout its range
and grown in a Michigan nursery. Growth rates slightly decreased as
latitude of origin increased [13]. In a study in North Dakota, 73.6
percent of all blue spruce roots were in the top 2 feet (0.61 m) of the
Fargo clay soil [127]. Despite its shallow roots, blue spruce is
windfirm [122].

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

6 Upper Basin and Range
7 Lower Basin and Range
9 Middle Rocky Mountains
10 Wyoming Basin
11 Southern Rocky Mountains
12 Colorado Plateau
13 Rocky Mountain Piedmont

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More info for the term: climax

Facultative Seral Species

Blue spruce occurs in various seral stages from pioneer to climax. Its
successional status depends on location and associated species [38].

Blue spruce is a pioneer species in riparian communities that are
subject to periodic disturbances, such as scouring and flooding
[8,38,116]. It is present in all size classes along the riparian
systems and on the lower slopes in the southwestern United States, where
it may be a topoedaphic climax species [37].

Blue spruce is an intermediate to late, long-lived seral or climax
species in montane or subalpine zones [6,38,106]. Blue spruce is
intermediate in shade tolerance [38,111]. It may be seral to or climax
with any of the conifer species in the mixed-conifer forests [30,37].
Quaking aspen and lodgepole pine (Pinus contorta) can be seral to blue
spruce [87].

Picea parryana Sarg.
Picea commutata Horton

More info for the terms: natural, seed

The currently accepted scientific name of blue spruce is Picea pungens
Engelm. [68,125]. It is a member of the pine family (Pinaceae). There
are no recognized subspecies, varieties, or forms.

Blue spruce does not readily hybridize with other conifers [105].
Throughout its range, it occurs with Engelmann spruce (Picea engelmannii
Parry), but few if any natural hybrids are ever produced [22,105].
Artificial crosses have produced small amounts of seed with low (0.3
percent) germination [34,46]. Blue spruce, Engelmann spruce, and white
spruce (Picea glauca) are sympatric in the Sweetgrass Hills of
north-central Montana. Putative hybrids among all three spruce species
have been reported [113].

Approximately 38 horticultural varieties of blue spruce have been
developed [37,122].

More info for the terms: cover, reclamation

Blue spruce has been included in roadside reclamation on U.S. Highway 89
south of Afton, Wyoming. One year after grasses had been planted,
container-grown blue spruce were planted [23]. Data on establishment
success were not given.

Blue spruce was chosen as one of several species to provide cover and
foraging area for wildlife. This reclamation planting mediated habitat
loss due to increased water levels in Rufus Woods Lake, Washington [17].
No data on establishment success were given.

Blue spruce was planted in Canada as a part of shelterbelts to prevent
wind erosion [54].

More info for the term: tree

Blue spruce is not an important timber tree because it occurs
infrequently, and the wood is brittle with many knots [38,65]. The wood
is light, soft with numerous resin canals, close-grained, and weak
[104,122]. When it is harvested, it is often cut and marketed with
Engelmann spruce [77].

Blue spruce is a species of the montane zone in the central and southern Rocky Mountains, where it is the principal species of the Blue Spruce forest cover type (Society of American Foresters Type 216) (27). Blue spruce is also named as a minor associate in four other types: Engelmann Spruce-Subalpine Fir (Type 206), Interior Douglas-Fir (Type 210), Cottonwood-Willow (Type 235), and Interior Ponderosa Pine (Type 237).

Over the bulk of its range, blue spruce is most frequently associated with Rocky Mountain Douglas-fir (Pseudotsuga menziesii var. glauca) and Rocky Mountain ponderosa pine and with white fir (Abies concolor) on mesic sites in the central Rocky Mountains. Blue spruce is seldom found in large numbers, but on streamside sites it is often the only coniferous species present.

Hardwoods associated with blue spruce are most commonly narrowleaf cottonwood (Populus angustifolia), quaking aspen (P. tremuloides), and occasionally balsam poplar (P. balsamifera). Smaller streamside trees and common shrub associates are water birch (Betula occidentalis), mountain alder (Alnus tenuifolia), shrubby cinquefoil (Potentilla fruticosa), common snowberry (Symphoricarpos albus), chokecherry (Prunus virginiana), and species of willow (Salix).

On north-facing slopes, blue spruce, rarely found more than 9 to 12 m (30 to 40 ft) above the drainage bottoms, mixed with Douglas-fir or lodgepole pine (Pinus contorta var. latifolia) (24). At higher elevations, above 2590 m (8,500 ft), blue spruce may mingle with Engelmann spruce, subalpine fir, and quaking aspen on moist sites, or lodgepole pine on drier sites (49).

In its southern range (southwestern Colorado, Arizona, and New Mexico) blue spruce is part of the widespread mixed conifer forest as a component of several diverse habitat types constituting topoedaphic climaxes in stream bottoms and meadow borders. In general, blue spruce dominates habitats that are too warm for Engelmann spruce and subalpine fir and that are wetter than those typically occupied by ponderosa pine. Shrub associates include Rocky Mountain maple (Acer glabrum), western serviceberry (Amelanchier alnifolia), common juniper (Juniperus communis), and Gambel oak (Quercus gambelii), as well as alders and willows on the moister sites (50,65).

In its northern range (northern Wyoming, Idaho, and Montana), blue spruce is found only in scattered locations under established stands of narrowleaf cottonwood and among scattered ponderosa pine, with Engelmann spruce and white spruce (Picea glauca) associated with the species in the extreme north (64,84).

Blue spruce grows in a climatic zone that is generally cool and humid, with most of the annual precipitation occurring in the summer.

Mean annual temperatures where blue spruce is most commonly found in Colorado and the Southwest range from 3.9° to 6.1° C (39° to 43° F), with a January mean of -3.9° to -2.8° C (25° to 27° F) and a July mean of 13.9° to 15.0° C (57° to 59° F). Mean minimum January temperatures range from -11.1° to 8.9° C (12° to 16° F) and mean maximum July temperatures range from 21.1° to 22.2° C (70° to 72° F). The frost-free period from June to August is about 55 to 60 days (5,69).

Average annual precipitation varies from 460 to 610 mm (18 to 24 in). Winter is usually precipitation-deficient, with less than 20 percent of the annual moisture falling from December through March. Fifty percent of the annual precipitation is rain that falls during the growing season (5,69).

Although blue spruce grows best with abundant moisture, this species can withstand drought better than any other spruce (36). It can also withstand extremely low temperatures (-40° C; -40° F), and it is more resistant to high insolation and frost damage than other associated species.

Several insects are known to attack developing cones and seeds of blue spruce, but damage caused by insects is not heavy (55). The spruce seed chalcid (Megastigmus piceae) is found throughout the range of the host. Larvae of the spruce seed moth (Laspeyresia youngana) and the cone cochylid (Henricus fuscodorsana) bore through cone scales near the axis of the cones, destroying both scales and up to 10 percent of the seeds. Larvae of the spruce coneworm (Dioryctria reniculelloides) mine young cones in addition to feeding on tender terminal growth and its foliage (34,45,54).

In addition to those attacking developing cones and seeds, other insects occasionally damage blue spruce (34). The larvae of the western spruce budworm (Choristoneura occidentalis) feed on old needles in late April, then mine developing buds and defoliate new tree growth (59). Heavy, repeated attacks kill the tree.

Less serious damage can be caused by the spruce needle miner (Taniva abolineana), and another needle miner, Coleotechnites piceaella (34,43,54). The Cooley spruce gall aphid (Adelges cooleyi) and the pine leaf aphids (Pineus pinifoliae and Pineus similis) cause the formation of cone-shaped galls. The former may be of consequence on seedlings and saplings.

Other insects that attack blue spruce are the green spruce aphid, Cinara fornacula, and the related Cinara coloradensis, which feed on terminal twigs, as does the white pine weevil (Pissodes strobi). Twig beetles, Pityophthorus spp., may attack injured trees. Dendroctonus rufipennis, the spruce beetle, is also found on blue spruce. Ips pilifrons, an engraver beetle which attacks recently downed trees, may deprive the spruce beetle of favorable breeding places, thereby reducing the threat of a spruce beetle outbreak (34,72). Secondary insects are Dryocoetes affaber and the four-eyed spruce beetle (Polygraphus rufipennis). Ambrosia beetles, Gnathotrichus sulcatus, and Trypodendron bivattatum, and the golden buprestid (Buprestis aurulenta), a flatheaded borer, attack the wood.

The rust Chrysomyxa pirolata infects the cones of blue spruce. Seed production is not greatly affected by this disease, however, although malformation of the cones may interfere with seed dispersal (67). Seed viability in rust-infected cones may be reduced, but seeds are not totally destroyed.

A variety of diseases also attack seedlings, leaves, stems, and roots of blue spruce. Damping-off, caused by Phytophthora cinnamomi, kills new seedlings, as does the cylindrocladium root rot, caused by Cylindrocladium scoparium (11,48). Nematodes may reduce root growth of seedlings in nurseries (30,37). Low seedling vigor is also caused by the root lesion nematode, Pratylenchus penetrans (48), and snow molds may cause nursery losses during seasons of heavy snow (82).

Leucocytospora kunzei (Syn.: Cytospora kunzei) is widespread in northeastern United States and may cause cankers on one-fourth to one-half of the branches of blue spruce. Although usually not fatal, branch loss dramatically reduces the aesthetic value of landscape trees (35,73). Phomopsis occulta causes a tip blight on blue spruce; it is characterized by downward curling and necrosis of expanding shoots, where stem cankers and sap exudate commonly occur (78). Western spruce dwarf mistletoe (Arceuthobium microcarpum) causes mortality in infected stands two to five times greater than in healthy stands, and heavily infected trees may show a 10-year volume loss of up to 40 percent (61).

Three species of Chrysomyxa cause needle rusts and moderate amounts of shedding of new needles on blue spruce. Another needle cast fungus, Rhizosphaera kalkhoffii, damages Christmas tree plantations of blue spruce in the Midwest and the East. Serious damage is not associated with natural stands of this species although the disease was first reported on blue spruce in its native range in Arizona (44,68,89). Chrysomyxa arctostaphyli causes the perennial yellow witches' broom on blue spruce branches; Arctostaphylos uva-ursi, the common kinnikinnik, serves as host of stage 3 of the fungus (70). Armillaria mellea and Inonotus tomentosus both cause root rot, and Phellinus pini, Fomitopsis pinicola, Climacocystis borealis' and Polyporus caesius are common heart rots (48).

Blue spruce is monoecious. Male strobili develop throughout the living crown of the tree, although they are usually more frequent in the upper one-half of the crown. They commonly develop in whorls of three to five at the base of the current vegetative growth, or singly in subterminal positions (25). Female strobili develop in the upper 10 to 25 percent of the live crown of mature trees. They usually occupy terminal positions on lateral branchlets.

Most male strobili of blue spruce are rose red when they emerge from the buds, but on occasional trees they appear yellowish-green. A single male strobilus, containing 100 sporophylls, may produce about 370,000 pollen grains. The female strobili consist of 175 to 225 scales and thus have a potential to produce 350 to 450 seeds per cone. Pollen is shed in May or June, depending upon altitude.

For a short period of time following emergence from the bud, the scales of the female strobili are a pale greenish color. As peak receptivity is reached, however, the scales of the strobili on most trees become red and are reflexed 90 degrees or more toward the base of the strobilus, which assumes an erect position on the twig. Occasional trees produce yellowish-green strobili. Approximately 2 weeks following initial receptivity, the female strobilus moves from this erect position to about 45 degrees above horizontal. In another week, 50 percent of the cones on a tree are 45 degrees below horizontal to pendent. During the fourth week, all cones become pendent and reach their full size (24,26,28).

Population Differences In a study of seven blue spruce provenances from Arizona, Colorado, Utah, and Wyoming, grown in North Dakota, 5-year survival varied from 22 percent for the Targee National Forest, WY, source to 96 percent for an Ashley National Forest, UT, source (18). In the same study, height differed significantly among the sources; the two sources from Ashley National Forest represented the tallest (57.3 cm; 22.6 in) and the shortest (37.5 cm; 14.8 in). No latitudinal or altitudinal pattern of survival, growth, or frost resistance seemed apparent.

In a Michigan nursery study of progenies from 50 populations collected throughout its range, 2-year-old blue spruce seedlings from Colorado, New Mexico, and Arizona grew more rapidly than those from Utah, Wyoming, or Montana. The average heights of the 10 tallest populations ranged from 18.8 to 16.1 cm (7.4 to 6.3 in) (40).

Variation in foliage color is apparently under strong genetic control (15), although the mechanism of inheritance is not presently known. Because there is no consistency in blue color from any one source, color variation is a characteristic to expect with seed-produced trees (47). Two-year-old progenies from Arizona and New Mexico seed sources show a much higher incidence of "blueness" than those from other areas (40). However, little or no difference has been detected between seedlings with glaucous (bluish) or non-glaucous (greenish) needles in photosynthetic rate, transpiration rate, and moisture retention (75). These studies suggest that genetic variation in natural populations of blue spruce does not conform to a clinal pattern. Rather, the pattern appears to be ecotypic, with considerable stand-to-stand variation and individual tree variation.

Significant variation exists among populations in the concentration of terpenes derived from cortical tissue. Five populations, each consisting of 10 selected seed trees, differed significantly in the concentration of each of eight monoterpenes in a Michigan study. Although the total percentages of the eight monoterpenes were similar among the populations, the Utah, Colorado, and Wyoming populations were distinct from the New Mexico and Arizona populations due to percentages of specific monoterpenes. For example, the average percentage of a-pinene was 14.3 for the three northern populations and 8.5 for the two southern ones, whereas b-phellandrene averaged 0.58 percent for the northern populations and 0.89 percent for the southern populations (39).

Large differences in monoterpene yield exist in xylem, bark, and needles of individual blue spruce trees, and variation in terpene yield among trees is significant. The concentration of the terpenes in the needles and xylem varies with crown position, the yield increasing with tree height in the xylem and decreasing with tree height in the needles. These yields are correlated with the proportions of resin canals in the respective tissues (66).

Several investigators have reported different results in blue spruce seedlings grown under accelerated greenhouse conditions (20,39,40,41). In a recent study, height growth of 75 single-tree Colorado sources, grown under accelerated greenhouse conditions, varied significantly among six seed zones but not among families within a seed zone. Seed zone averages ranged from 22.2 cm for the tallest to 14.2 cm for the shortest during the 140-day test period (20).

In their reports of a rangewide provenance study of blue spruce conducted in Michigan, investigators noted that the southern sources of blue spruce did not grow as well under accelerated greenhouse conditions as did the northern sources (6,8,41). In contrast, in the Colorado study, southern Colorado sources generally outgrew the northern Colorado sources.

It is interesting to note that in field plantations subsequently established in several midwestern states and Quebec with their blue spruce sources, the Michigan investigators observed a reversal of the variation patterns that they had observed in the greenhouse. In the field plantations, the southern sources outgrew the northern sources (9,10,87). Thus, growth of the seedlings studied in Colorado in the greenhouse followed much the same patterns as the seedlings that were grown outdoors in the Michigan studies.

In only a single study has the date of bud set been recorded in blue spruce. Within latitudinal groups in Colorado, bud set varied with elevation of the seedling seed source, the high-elevation sources setting bud much sooner than the low-elevation sources (20). Some investigators (6,87) have found no consistent pattern or date of bud break in the 400 widely distributed sources of blue spruce studied. And others (10) found that bud break was variously related to longitude but not to elevation. Yet the results of the Colorado study, based on relatively intensive elevational sampling, show a relationship between latitude and elevation of seed origin and the date of bud set.

Thus, whereas research results support the notion that natural variation of most parameters that have been studied in blue spruce conforms to a discontinuous pattern geographically (18,20,39,40,87), variation in date of bud set conforms to a local altitudinal clinal pattern (20).

Hybrids From studies of morphological features of blue spruce and Engelmann spruce, it has been concluded that these two species do not hybridize in nature, although no morphological character absolutely separates the two (16). Considerable overlap in cone size has been found; Engelmann spruce cones vary from 2.8 to 5.8 cm (1.1 to 2.3 in) and blue spruce cones vary from 4.5 to 10.7 cm (1.8 to 4.2 in) in neighboring populations measured in northern Colorado (33). Cone and seed characteristics are often found to be indistinguishable (40).

Controlled crosses between blue spruce and Engelmann spruce obtained up to 2 percent sound seed set when Engelmann spruce was the female parent (29). The reciprocal cross was also successful. Only occasional embryos developed following crosses between the two species, but, more frequently, reproductive failure occurred prior to embryo formation (57).

Much overlap between blue spruce and Engelmann spruce in cortical monoterpene content has also been observed, although species differences in the quantity of several of the compounds are statistically significant. Oleoresins of blue spruce contain higher levels of tricyclene, (a-pinene, camphene, and bornyl acetate, whereas Engelmann spruce oleoresins contain higher levels of b-pinene, 3-carene, terpinolene, and several unknown compounds (80).

These and other results (42) indicate that hybridization between blue spruce and Engelmann spruce is possible. This might account for the various intergrades between blue spruce, white spruce, and Engelmann spruce that have been reported in Montana (83).

Information on inheritance patterns for certain characteristics of blue spruce, although somewhat inconclusive, is provided by results of half-sib and full-sib progeny studies involving that species. For example, in a Canadian study (13,14), inheritance of needle coloration was investigated using such controlled crosses. A qualitative rating scale of one (green) to four (silvery blue) was used for comparison. Although the proportion of blue seedlings was not significantly related to the blue color ratings of their open-pollinated parents, the needle-color ratings of 10-year progeny were related to those of their self-pollinated parents (r = 0.83). One selfed tree produced 94 percent blue progeny.

As is true for certain other coniferous species, albinism in blue spruce is apparently controlled by a single gene. The proportion of normal (green) to albino seedlings derived from self-pollinated seeds of two different trees produce a good fit to a 3:1 ratio, suggesting heterozygosity for a simple lethal factor (12).

In Michigan studies, hybrid progeny from crosses between white spruce and blue spruce showed a slight, but nonsignificant, increase in germination rate over the parental half-sib progeny, and at 42 weeks, needle length was intermediate between those of the parental progeny. Although the hybrid progeny as a group displayed intermediacy in 3-carene biosynthesis ability between the two parents, individual-tree values showed genetic segregation in the open-pollinated (half-sib) blue spruce progeny and uniformity in the open-pollinated (half-sib) white spruce progeny (42). Yet, the range of values for 3-carene biosynthesis ability is controlled by a single pair of alleles, as had been shown for western white pine (Pinus monticola) (38). However, when natural populations of blue spruce were studied for this characteristic, allele frequencies for the 3-carene gene did not conform to expected values in Colorado and New Mexico populations, although they did conform to expected single-gene frequencies in the Utah, Arizona, and Wyoming populations (39). These apparent discrepancies could be artifacts of sample size or other unknown factors.

Whereas the initiation date of germination of hybrid seed has been found to be intermediate between parental (half-sib) seed of blue spruce and Engelmann spruce, cotyledon number, mean day of total germination, and hypocotyl color tend to be similar to those of female parent (29). That cotyledon number is under strong maternal control, as it also is in white spruce (31), is supported by a recent study, in which cotyledon number differed significantly (P = .001) between half-sib Colorado families but not within those families (20).

From studies of controlled crosses among white spruce, blue spruce, and red spruce (Picea rubens), F2 progeny of white spruce x blue spruce crosses were found to be much stunted in height and in needle length (7). Further results of findings among these species are summarized in table 3.

Table 3- Summary of inheritance of various traits from crosses among red, white, and blue spruces. Adapted from Bongarten and Hanover, 1982 (7). Spruce combination Character response (White x blue) x white (backcross) - Similar to white spruce in all measured characters. (White x blue) x blue (backcross) - Similar to blue in 6-month, height, needle curvature, and         3-carene concentration. - Similar to white in needle serrations. - Intermediate in b-pinene concentration (White x blue) x red (trihybrid)

- Similar to red in needle serrations, limonene concentration,      and needle curvature. - Similar to white x red in needle color. - Similar to white x blue in 3-carene and b-pinene    concentrations. In summary, it would appear that for most needle, chemical synthesis, and germination characteristics that have been studied in blue spruce, the gene action is quantitative. Exceptions to this seem manifest in the biosynthetic ability of 3-carene and in the production of albino seedlings, which may be single-gene controlled, and cotyledon number, hypocotyl color, and mean germination date, which may be under strong maternal influence in that species.

Blue spruce is apparently a long-lived tree, surviving up to 600 years or more. Diameter growth is slow; trees 10 to 13 cm (4 to 5 in) in d.b.h. may be 125 to 135 years old; at 46 to 56 cm (18 to 22 in), they may be 275 to 350 years of age (84). The "1982 National Register of Big Trees" lists the largest blue spruce as 154.4 cm (60.8 in) in d.b.h. and 38.4 m (126 ft) tall, on the Gunnison National Forest, CO.

Few growth and yield data are available for blue spruce. In one study, in a mixed conifer forest in east-central Arizona, blue spruce was found to constitute a total of 0.7 m²/ha basal area (3.05 ft²/acre) of a total of 40.8 m² (177.7 ft²). The 728-ha (1,800-acre) forest consisted of Douglas-fir (31.4 percent), quaking aspen (15.9 percent), white fir (14.5 percent), ponderosa pine (14.1 percent), Engelmann spruce (13.5 percent), southwestern white pine (Pinus strobiformis) (5.6 percent), corkbark fir (Abies lasiocarpa var. arizonica) (3.3 percent), and blue spruce (1.7 percent). In this study, the annual basal area growth for blue spruce was found to be 2.9 percent, greater than that of any other species except corkbark fir, which was 3.7 percent per year (22). The total basal area growth for blue spruce, 0.008 m² (0.088 ft²) per year, was distributed as shown in table 1.

Table 1- Annual basal area growth for blue spruce in east-central Arizona (22).
D.b.h. class Percent
of stand
Incremental growth m²/ha ft²/acre 0.3 to 17.5 cm
0.1 to 6.9 in
4 0.004


0.0 17.8 to 27.7 cm
7.0 to 10.9 in
18 0.001


0.006 27.9 to 42.9 cm
11.0 to 16.9 in
18 0.001



0.006 43.2 to 58.2 cm
17.0 to 22.9 in
10 0.001


0.004 58.4 cm and larger 23.0 in and larger
5 -


0.002 Total 100 0.007 0.035

Blue spruce is classed as intermediate in tolerance of shade, the middle of five tolerance categories for western conifers. It is less tolerant than subalpine fir, Engelmann spruce, and white fir; it is similar in tolerance to, or slightly more tolerant than, Douglas-fir; it is more tolerant than southwestern white pine, ponderosa pine, lodgepole pine, Rocky Mountain juniper, quaking aspen, or its other moist-site hardwood associates (4,27,52,62).

On cool sites, a dense or moderately dense canopy favors regeneration of subalpine fir, blue spruce, white fir, and Engelmann spruce, to the exclusion of Douglas-fir. On warm sites, an open canopy favors ponderosa pine, whereas a moderate canopy favors Douglas-fir (92).

Blue spruce occurs in various seral stages, from pioneer to climax, in 32 currently recognized habitat types (28). The exact successional status depends on the location within its geographic range and on its immediate associates. For example, in the Southwest, blue spruce represents a topo-edaphic climax, one in which environmental factors compensate for one another (17); here it reproduces and is present in all sizes, along stream banks, in well-watered tributaries, on gentle lower slopes, and in forest borders of grassy meadows. On these sites, ponderosa pine and Douglas-fir may be long-lived seral species, white fir and southwestern white pine may occur as minor seral species, and subalpine fir may be of accidental occurrence (58,65). Blue spruce may also form climax stands with Engelmann spruce on slopes and in drainages at higher elevations and with Douglas-fir and white fir (1) on lower slopes and north aspects at lower elevations (65). Blue spruce may be a minor seral species in white fir- and subalpine fir-dominated forests on cooler sites (58), and it may constitute a pioneer species on wet sites (21).

In Utah, blue spruce is a climax species in three distinct environments: gentle to steep mountain slopes, floodplains and valley bottoms at lower elevations, and montane sites on alluvium or aqueaceous north-aspect deposits (23). Almost exclusively, sites that support climax stands of blue spruce have parent materials of limestone or calcareous sandstone. Thus, blue spruce probably constitutes an edaphic climax on these sites (62,71). On Utah sites, quaking aspen is the prinicipal seral species, except in the Uinta Mountains, where the seral role is assumed by lodgepole pine. At the higher altitudes in Utah, blue spruce becomes a minor seral species to subalpine fir (71).

Young seedlings of blue spruce are shallow rooted, with roots penetrating the soil only about 6.4 cm. (2.5 in) during the first year (50). Although blue spruce tissue is not damaged much by freezing, seedling losses can result from frost heaving. Shade in late spring and early fall minimizes such frost-heaving losses (2,69).

Even in mature trees, the root system of blue spruce is relatively shallow, compared to that of Douglas-fir and ponderosa pine, adapting it to the moist site on which it usually grows. In spite of the shallow root system, blue spruce is decidedly windfirm. (36).

Pruning roots of blue spruce 5 years before transplanting doubles the total root surface area of 2-meter-tall trees at transplanting time. It also increases the concentration of the root system within the dripline from 40 to 60 percent, an advantage in landscape plantings (90).

Blue spruce is generally considered to be from good to prolific in seed production, yielding full crops of cones every 2 or 3 years (77,84). Some intermediate years are complete failures (24). Seed production begins at approximately 20 years, and optimum seed-bearing age is reached between 50 and 150 years (88). Cones mature in August of the first year; seed shed begins from early to late September, depending on altitude, and continues into the winter (26,77). The seed is wind disseminated, seedfall diminishing rapidly as distance from the source increases; most seeds fall within 90 m (300 ft) of the upwind timber edge (2).

It is unlikely that heavy cone crops will occur in successive years on a single blue spruce tree, because the female strobili occupy terminal positions on lateral branchlets. Such terminal positions are at a minimum in the year following one of high seed production, because once a strobilus is differentiated from an apical meristem, only the strobilus develops at that position during the following growing season. If a whorl of new axillary buds is produced on the branchlet at the base of the developing cone, these buds ordinarily produce vegetative shoots for one season before female strobili are again differentiated. Thus, although blue spruce cones occasionally occupy sessile, axillary positions, the likelihood of heavy seed crops occurring more frequently than every 2 years is very remote (24).

Seeds of blue spruce germinate on a variety of media, although natural reproduction is mostly confined to exposed mineral soil with side shade and overhead light in the vicinity of seeding trees. Natural reproduction is scanty, probably because the lightweight seed is prevented from coming into contact with mineral soil by the dense herbage, grass, or other ground-cover vegetation that is usually abundant in the habitat of the species (84).

Seeds of blue spruce were once thought to show embryo dormancy. It is now known, however, that blue spruce seeds germinate promptly and completely without prior stratification, under a wide range of temperatures, with or without light (46). Germination is epigeal (77).

In most parts of the blue spruce range natural germination of seed takes place in the spring or summer following dispersal and is dependent on adequate precipitation (51).

Spring and early summer drought periods occur regularly in the Southwest. Although soils of the mixed conifer forest are wet at the end of winter from melting snows, these drought periods during the growing season create soil moisture deficits that are critical to initial seedling survival. Fall moisture deficits common over the remainder of the range are less limiting to seedling establishment and usually do not kill seedlings established for 2 years or more except on severely affected sites (2,52).

Blue spruce seedlings are more sensitive to day temperatures between 13° and 31° C (55° and 88° F) than to night temperatures between 7° and 25° C (45° and 77° F) (86).

Under greenhouse conditions, blue spruce seedlings are affected by supplemental light. They grow continuously when exposed to photoperiods exceeding 16 hours and enter dormancy within 4 weeks under photoperiods of 12 hours or less. Dormancy is prevented under 12-hour photoperiods by 2-hour light breaks of red light (1.70 µw/cm² @ 650 nm) or high intensity white light (2,164.29 µw/cm² @ 400 to 800 nm) given in the middle of the 12-hour night (94), or by one-minute light breaks every 30 minutes throughout the night (85).

The establishment of blue spruce seedlings under natural conditions is probably benefited by moisture availability and shading, which prolong snow and soil moisture in late spring.

Early growth of blue spruce seedlings is very slow. In a Michigan nursery study, the tallest of 50 populations averaged 15.7 cm (6.2 in) at 2 years (40). In North Dakota, the tallest of seven sources was 58.4 cm (23.0 in), 5 years after outplanting (18). Similarly, in a plantation in the southern range, trees were 48.5 to 59.2 cm (19.1 to 23.3 in) tall after five growing seasons (53).

Basic information on soils and landforms needed for silvicultural decisions for blue spruce is limited. Both soils and landforms are very complex. Soils are young and vary widely in texture and physical and chemical properties according to the bedrock from which they originate. Glacial deposits, alluvium from streams, and material weathered in place from country rock are predominant, however (2). The pH is 6.8 to 7.2, neutral to slightly alkaline (21,62). The soils on which blue spruce grows naturally are in the order Mollisols and, to a lesser extent, in the orders Histosols and Inceptisols.

Blue spruce is found on gentle upland and subirrigated slopes, in well-watered tributary drainages, extending down intermittent streams, and on lower northerly slopes. Sites on which blue spruce grows are more moist than those of Rocky Mountain ponderosa pine (Pinus ponderosa var. scopulorum) and warmer than those of Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa) (2,65). In Utah, blue spruce is considered a pioneer tree species on wet soils (21).

Blue spruce is characteristically found at elevations from 1830 to 2740 m (6,000 to 9,000 ft) in its northern range and from 2130 to 3050 m (7,000 to 10,000 ft) in its southern range (27,65).

Blue spruce is valued mainly for its appearance. Shortly after the species was discovered in 1861, writers described it as "a finely shaped tree" and "the most beautiful species of conifer," alluding to the symmetrical, pyramidal form and the glaucous, bluish or silvery-gray foliage that some trees of the species display. The needle coloration, caused by the presence of surface waxes (76), apparently intensifies with tree age (13,14). These traits of symmetry and blue or silver-gray cast, so common in horticultural plantings, are only occasionally found in natural stands. In nature, trees with similar color tend to occur in small, local populations, suggesting genetic control of the color trait.

Blue spruce is widely used as an ornamental, not only in the United States, but in Europe, where it was introduced late in the 19th century. At least 38 cultivars of blue spruce have been named, based primarily on leaf coloration and crown form (3,19) (table 2). Although young blue spruce usually show a pronounced layering of stiff branches, which give it a distinct pyramidal form, the branches begin to droop and the crown becomes thin and irregular as the tree ages. The trunk tapers rapidly, and epicormic shoots commonly develop, giving the tree a ragged appearance. Blue spruce is prized as a Christmas tree, and plantations have been established in its native range and in north-central and northeastern United States.

Table 2- Some cultivated varieties of blue spruce. Cultivar Characteristics 'Argentea' Rosenthal Silvery white 'Aurea' Niemitz Golden yellow 'Bakeri' Bailey Deep bluish white, long-leaved 'Caerulea' Beissner Bluish white 'Compacta' Rehder Dwarf, compact, densely flat-topped 'Glauca' Beissner
Bluish green; collective name for all glaucous-leaved cultivars 'Glauca Pendula' Koster ex Beissner Pendulous, bluish leaves, strongly sickle-shaped 'Hoopsii' Hoops ex F.J. Grootend Dense, pyramidal; leaves very silvery

'Hunnewelliana' Hornibr.

Dwarf, dense, pyramidal; leaves pale green 'Koster' Boom

Pyramidal, pendulous-branched, with main branches almost horizontal; leaves bluish white to silvery white 'Moerheimi' Ruys
Pyramidal, slender, dense, compact; leaves deep blue 'Thomsen' Thomsen
Pyramidal; leaves whitish to silvery blue, long 'Viridis' Regel Dull green

Natural vegetative reproduction of blue spruce has not been reported. The species does not sprout from the stump or root, but the development of epicormic branches on the trunk is common. Grafting and air-layering have been practiced successfully for many years to perpetuate desired horticultural varieties (32,60,63, 74,91). Success has also been achieved through the rooting of hardwood or greenwood stem cuttings, especially in sand-peat-soil media, or hydroponically (56,79,81,93).

Blue spruce is primarily native to the central and southern Rocky Mountains of the western United States. Its range extends from latitude 33° 50' to 48° 54' N. and from longitude 104° 45' to 114° 00' W.; the Rocky Mountain region in high mountains from southern and western Wyoming, eastern Idaho, south to Utah, northern and eastern Arizona, southern New Mexico, to central Colorado. It has been reported in isolated locations in north-central Montana (83).


- The native range of blue spruce.

Pinaceae -- Pine family

Gilbert H. Fechner

Blue spruce (Picea pungens) is also called Colorado blue spruce, Colorado spruce, silver spruce, and pino real. It is a slow-growing, long-lived tree of medium size that, because of its symmetry and color, is planted extensively as an ornamental. Because blue spruce is relatively scarce and the wood is brittle and often full of knots, it is not an important timber tree.

Tree, Evergreen, Monoecious, Habit erect, Trees without or rarely having knees, Tree with bark rough or scaly, Young shoots 3-dimensional, Buds resinous, Buds not resinous, Leaves needle-like, Leaves alternate, Needle-like leaf margins entire (use magnification), Leaf apex acute, Leaf apex spine tipped or with a differentiated and very sharp tip, Leaves < 5 cm long, Leaves < 10 cm long, Leaves blue-green, Needle-like leaves 4-angled, Needle-like leaves not twisted, Needle-like leaf habit erect, Needle-like leaf habit drooping, Needle-like leaves per fascicle mostly 1, Needle-like leaf sheath early deciduous, Needle-like leaf sheath persistent, Twigs glabrous, Twigs viscid, Twigs not viscid, Twigs with peg-like projections or large fascicles after needles fall, Berry-like cones orange, Woody seed cones > 5 cm long, Bracts of seed cone included, Seeds brown, Seeds winged, Seeds unequally winged, Seed wings prominent, Seed wings equal to or broader than body.

The blue spruce (Picea pungens), also commonly known as green spruce, Colorado spruce, or Colorado blue spruce, is a species of spruce tree. It is native to North America, and is found in USDA growing zones 1 through 7. It is found naturally in Arizona, Colorado, Idaho, New Mexico, Utah and Wyoming. It has been widely introduced elsewhere and is used as an ornamental tree in many places far beyond its native range. The blue spruce has blue-green colored needles and is a coniferous tree.