Engelmann Spruce

Foodplant / false gall
crowded pseudothecium of Cucurbitaria piceae causes swelling of characteristically twisted, swollen bud of Picea engelmannii
Remarks: season: 6-12

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

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

Varieties 2 (1 in the flora): North America, Mexico.

Picea engelmannii, Engelmann spruce, is a large coniferous tree in the Pinaceae (pine family) native to North America. Also known as Columbian spruce, mountain spruce, white spruce, silver spruce, and pino real, it is one of seven spruce species native to the United States. It is widely distributed in and a major component of high-elevation forests in the Rocky Mountains extending from British Columbia and Alberta, Canada, south New Mexico and Arizona in the United States. It is also a minor component of high-elevation forests in the Cascades and the Coast Range, in the Pacific Northwest. Engelmann spruce is generally restricted to cold, humid habitats because of its low tolerance to high temperature and drought. Engelmann spruce-subalpine fir forests occupy the greatest water yielding areas in the Rocky Mountains, so they are important for watershed protection. They also provide timber, habitats for a wide variety of game and nongame wildlife, forage for livestock, and recreational opportunities and scenic beauty. Engelmann spruce timber tends to be knotty, so it yields relatively little select-grade lumber, but a high proportion of the common grades. In the past, spruce was used principally for mine timbers, railroad ties, and poles. Today, much of the lumber is used in home construction where great strength is not required, and for prefabricated wood products. In recent years, rotary-cut spruce veneer has been used in plywood manufacture. Other uses of spruce include specialty items such as violins, pianos and aircraft parts. The pulping properties of Engelmann spruce are excellent. Long fibers, light color, and absence of resins permit trees to be pulped readily by the sulfite, sulfate, or groundwood processes. The species has been used for pulp in the northern Rocky Mountains but not in the central or southern Rocky Mountains. Excerpted and edited from Alexander and Shepperd 1990.

More info for the terms: cover, duff, forest, herbaceous, prescribed fire, shrub, wildfire

Postfire Engelmann spruce seedling establishment is best on moist
surfaces where fire has consumed most or all of the duff leaving bare
mineral soil. Seedlings do require some shade to survive; thus
regeneration after fire is best on sites where standing dead trees,
logs, or developing vegetation is present [73]. Engelmann spruce
postfire regeneration is poor on sites subjected to high light
intensities. A 26,000 acre (64,200 ha) burn on a high-elevation site in
southwestern Colorado showed poor conifer regeneration 100 years after
the fire. This was attributed to intense solar radiation which
inhibited photosynthesis, causing a high percentage of spruce seedlings
to die [75]. Postfire spruce regeneration is also poor where shrub and
herbaceous cover is dense, where exposed mineral soil is subject to
excessive evaporation, and where fire has only charred the duff [10].
Ash does not affect germination, but if it is deep, it can prevent a
seedling's roots from reaching mineral soil [62].

In northern Colorado, 3 years after a late August wildfire in a dense,
mature stand composed of Engelmann spruce, subalpine fir, and
lodgepole pine, Engelmann spruce established 1,000 seedlings per acre
(2,470/ha) in burned areas that were than less than 0.1 acre (0.05 ha).
However, in the middle of the main burn, no Engelmann spruce seedlings
had established by 3 years after the fire [10]. In Colorado, Peet [66]
reported a 75-year-old burn that had good spruce regeneration near the
burn boundary, but only 218 yards (200 m) inside the burn edge, few
seedlings had established, and the area was still fairly open.

Day [24] sampled lodgepole pine-Engelmann spruce x white spruce hybrid
stands in southern Alberta that had established after fires that had
occurred 29 and 56 years prior to sampling. He found that both pine and
spruce had initiated large numbers of seedlings immediately after the
fire. Pine, however, had established more seedlings and rapidly outgrew
the spruce, forming a canopy that was three to four times taller than
the spruce canopy. Pine seedling establishment had ceased by 30 years
after the fire, but spruce continued to establish seedlings. Engelmann
spruce eventually dominates sites where spruce and pine come in together
after fire.

The Research Project Summary Revegetation in a subalpine fir forest after logging
and fire in central British Columbia provides information on prescribed fire
and postfire response of plant community species, including Engelmann spruce,
that was not available when this species review was originally written.

Engelmann spruce
Columbian spruce
mountain spruce

More info for the terms: cover, habitat type

Big game: Engelmann spruce provides excellent hiding and thermal cover
for deer, elk, moose, bighorn sheep, and bear [40,50,98]. Dense stands
of this species can provide cool summertime shade for big game.
High-elevation stands provide bedding sites and protection from storms
for bighorn sheep, mule deer, and elk [59].

Small mammals and birds: Small Engelmann spruce trees provide good
year-round hiding cover for small animals. Blue grouse, which
overwinter in conifers at high elevations, use spruce trees for
protective cover and roosting sites [50,80]. Spruce trees in the
Engelmann spruce/soft leaved sedge (Carex disperma) habitat type in
central Idaho provide important nesting sites for the MacGillivray's
warbler, American robin, and warbling vireo [89]. Engelmann spruce
snags are used by numerous cavity-nesting birds. Snags greater than 11
inches (28 cm) d.b.h. are most often used [82].

More info for the terms: density, monoecious, natural, seed, tree

Engelmann spruce is a long-lived, native, coniferous, evergreen tree.
It is one of the largest of the high-elevation mountain conifers.
Mature trees have a narrow, pyramid form and short, compact branches.
Within natural stands, mature trees average 15 to 30 inches (38-76 cm)
in diameter; the average dominant height varies from 45 to 130 feet
(14-40 m), depending on site quality and density. Larger individuals
are not uncommon and may exceed 40 inches (102 cm) in diameter and 160
feet (49 m) in height. Engelmann spruce is long-lived; dominant trees
are often 350 to 450 years old, and 500- to 600-year-old trees are not
uncommon [7]. The crowns of trees within a stand normally make up 50 to
70 percent of the total height of the tree [4]. Dead lower limbs tend
to be persistent. The crowns of open-grown trees often extend down to
the ground. In alpine areas just above treeline, Engelmann spruce often
forms a krummholz. At treeline in northern Idaho, mature Engelmann
spruce generally do not exceed 65 feet (20 m) in height, and
progressively become more stunted as elevation increases, forming
krummholz at the most severe, high-elevation sites [17].

The four-sided, acute-tipped needles are not particularly sharp, are
deep bluish-green, and are 0.8 to 1.2 inches (2-3 cm) long [21,41]. The
young twigs are finely pubescent, a characteristic which differentiates
this spruce from white spruce, which has glabrous twigs. The bark is
very thin, grayish-brown on young trees but at maturity becomes purplish
brown to russet and is broken into loosely attached scales. Engelmann
spruce is generally shallow rooted, but laterals may penetrate to a
depth of 8 feet (2.4 m) in deep, porous, well-drained soils [4].

Engelmann spruce is monoecious. Female cones are light brown, 1.5 to
2.4 inches (4-6 cm) long, and occur in the upper part of the crown [21].
Male cones are usually found lower in the crown than female cones.
Engelmann spruce seeds are about 0.12 inch (3 mm) long and have a
single, well-developed wing about twice as long as the seed [21,77].

Engelmann spruce is widely distributed throughout the mountains of
the western United States and Canada. It occurs from central British
Columbia and Alberta as far south as New Mexico and Arizona [6]. It is
cultivated in Hawaii [101].

In the Pacific Coast region, Engelmann spruce is only a minor component
of high-elevation forests. It grows from the Coastal Range in
west-central British Columbia, south along the east slope of the
Cascades through Washington and Oregon to Mount Shasta in northern
California [6].

In the Rocky Mountains Engelmann spruce is a major component of
high-elevation forests. It grows from southwestern Alberta, south
through the mountains of eastern Washington, Idaho, and western Montana
to the high mountains of southern Arizona and New Mexico [6].

More info for the terms: fuel, litter, tree

Plant adaptations to fire: Engelmann spruce is very fire sensitive and
is generally killed even by low-intensity fires. Postfire
reestablishment is via wind-dispersed seeds which readily germinate on
fire-prepared seedbeds. The occasional mature tree which survives fire,
those escaping fire in small, unburned pockets, and trees adjacent to
burned areas provide seeds to colonize burned sites. Large trees
occasionally survive light fires [31].

Scattered individuals or pockets of Engelmann spruce trees commonly
escape burning because they occur in wet locations where fire spread is
hampered. In subalpine habitats, scattered Engelmann spruce trees often
escape fire because of discontinuous fuels, broken and rocky terrain,
and the moist and cool environment [67,88].

Fire regime: Engelmann spruce-subalpine fir forests usually develop in
cool, moist locations and experience fire-free intervals averaging 150
years or more [8]. Many Engelmann spruce stands are even aged,
suggesting that they developed after fire [54].

Fuels and fire behavior: The fuel structure in stands dominated by
Engelmann spruce and subalpine fir promotes highly destructive
stand-destroying fires. Fuel loads are higher than in lower elevation
montane stands, and the fuel beds tend to be irregular and have large
amounts of needle litter accumulating under the narrow crowned trees
[31,91]. The needles are small and fine, and form a compact fuel bed in
which fire spreads slowly [28]. These concentrated, slow-burning fuels
commonly produce flames high enough to reach Engelmann spruce's
low-growing, lichen-draped branches and start crown fires [20,91].

More info for the terms: cover, duff, natural

After clearcutting Engelmann spruce stands, broadcast burning can be
used to prepare seedbeds for natural regeneration.  Broadcast burns
which remove most of the duff or organic matter and burn hot enough to
destroy some or all of the competing vegetation favor spruce seedling
establishment [72].  However, seedling establishment is poor or
nonexistent in areas where hot fires leave deep layers of ash or
generate such intense heat that rocks are fractured, such as under slash
pile fires [72,94].  For this reason, where large amounts of slash must
be burned, windrows or piles should be kept small and cover a minimal
portion of the area [3].  Engelmann spruce often occurs in cool and
moist locations which restricts the time of year when effective
broadcast burning can take place.  Prior to burning, duff must be dry
enough to ensure that it will be consumed.  Seedling establishment will
be inhibited on burns that only blacken the organic matter.  Some cull
logs and slash should be left in place to provide shade and protection
for developing seedlings [72].

Engelmann spruce stocking was greater than 50 percent and averaged 573
seedlings per acre (1415/ha) 5 years after broadcast burning in
clearcuts in northern Idaho where the uncut stand composition was 56
percent western larch, 22 percent Engelmann spruce, 15 percent mountain
hemlock, and 7 percent subalpine fir.  This broadcast burn exposed
mineral soil on 53 percent of the area [14].  In northwestern Montana,
Engelmann spruce seedling establishment was much greater on broadcast
burned clearcuts where burning exposed mineral soil than on unburned
clearcuts.  Eleven years after burning, stocking of Engelmann spruce
seedlings was 23 percent on burned cuts but only 1 percent on unburned
cuts.  Seventeen years after burning, stocking was 56 percent on burned
cuts but only 2 percent on unburned cuts [84].

Broadcast burning is generally not recommended following partial cutting
because residual Engelmann spruce trees are very fire sensitive.

More info on this topic.

More info for the term: phanerophyte

Phanerophyte

More info for the terms: association, forest, habitat type

Engelmann spruce is found in some of the highest and coldest forest
environments in the western United States, characterized by long, cold
winters with heavy snowpack and short, cool summers [7]. It extends
down to lower elevations along stream bottoms where cold air flows down
the valley and collects in localized frost pockets [22]. It is
generally found on moist and cool sites, but at timberline it may occur
on somewhat dry sites. At middle elevations, pure stands are usually
found on alluvial terraces, wet benches, bottomlands, slopes with seeps
or cold north or east aspects [67,88]. It occurs on all aspects at
timberline.

Stand condition and associated conifers: Engelmann spruce forms pure
stands but is more commonly associated with subalpine fir. These
species frequently occur as codominants forming widespread subalpine
forests. In the central and southern Rocky Mountains, Engelmann spruce
commonly makes up 70 percent of overstory trees, and subalpine fir
dominates the understory. Within Engelmann spruce-subalpine fir forests
in this region, the spruce tends to be more important at higher
elevations and on wetter sites, while subalpine fir is more abundant on
drier lower elevation sites [4]. In Montana, pure Engelmann spruce
stands are often found in cool ravines at lower elevations than
subalpine fir [67]. Other associated conifers, which vary by latitude
and elevation, are listed below [6]:

Location Elevation Associates

northern Rocky Mtns low and western white pine (Pinus monticola),
and Cascade Mtns middle western redcedar (Thuja plicata),
western hemlock (Tsuga heterophylla),
Douglas-fir, grand fir (Abies grandis),
lodgepole pine
high Pacific silver fir (A. amabilis),
mountain hemlock (Tsuga mertensiana),
subalpine larch (Larix lyallii),
whitebark pine (Pinus albicaulis)
central and southern low and lodgepole pine, Douglas-fir, blue
Rocky Mtns middle spruce, white fir, aspen (Populus
tremuloides)
high corkbark fir (Abies lasiocarpa var.
arizonica), bristlecone pine (Pinus
aristata), limber pine (P. flexilis)

Understory associates: Understory vegetation is extremely variable,
changing with elevation, exposure, and soil moisture. Habitat type and
plant association guides describe characteristic understory plants for
differing sites.

Soil: Engelmann spruce grows best on moderately deep, well-drained,
loamy sands and silts, and silt and clay loam soils developed from
volcanic lava flows and sedimentary rock. It also grows well on
alluvial soils where the underlying water table is readily accessible.
It grows poorly on shallow, dry, coarse-textured sands; gravels
developed primarily from granitic and schistic rock; coarse sandstones
and conglomerates; rocky glacial till; heavy clay surface soils; and
saturated soils [6].

Elevation: Elevational ranges for Engelmann spruce are described below
[6]:

Cascade Mountains -- generally between 4,000 and 6,000 feet (1,219 and
1,829 m); at 8,000 feet (2,438 m) on sheltered
slopes and at 2,000 feet (610 m) in cold pockets
along streams and valley bottoms

Rocky Mountains:

ID, MT,
adjacent mtns
eastern WA and OR -- between 2,000 and 9,000 feet (610 and 2,743 m);
above 6,000 to 7,500 feet (1,829-2,286 m) a
minor component of the stand; below 5,000 feet
(1,676 m) confined to moist, lower slopes and
cold valley bottoms

UT, WY, and CO -- generally 9,000 to 11,000 feet (2,743-3,354 m); as
low as 8,000 feet (2,438 m) along cold stream bottoms
and sometimes as high as 11,500 (3,506 m)

AZ and NM;
plateaus of s UT -- between 8,000 and 12,000 feet (2,438 and 3,658 m);
most common between 9,500 and 11,000 feet (2,896
and 3,354 m)

More info on this topic.

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

201 White spruce
203 Balsam poplar
205 Mountain hemlock
206 Engelmann spruce - subalpine fir
208 Whitebark pine
209 Bristlecone pine
210 Interior Douglas-fir
212 Western larch
213 Grand fir
215 Western white pine
216 Blue spruce
217 Aspen
218 Lodgepole pine
219 Limber pine
224 Western hemlock
226 Coastal true fir - hemlock
227 Western redcedar - western hemlock
228 Western redcedar

More info on this topic.

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
FRES22 Western white pine
FRES23 Fir - spruce
FRES24 Hemlock - Sitka spruce
FRES25 Larch
FRES26 Lodgepole pine
FRES28 Western hardwoods
FRES44 Alpine

More info on this topic.

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

K004 Fir - hemlock forest
K012 Douglas-fir forest
K014 Grand fir - Douglas-fir forest
K015 Western spruce - fir forest
K018 Pine - Douglas-fir forest
K020 Spruce - fir - Douglas-fir forest
K021 Southwestern spruce - fir forest
K052 Alpine meadows and barren

More info for the term: lichen

Engelmann spruce is easily killed by fire. It is very susceptible to
fire because it has (1) thin bark that provides little insulation for
the cambium, (2) a moderate amount of resin in the bark which ignites
readily, (3) shallow roots which are susceptible to soil heating, (4)
low-growing branches, (5) a tendency to grow in dense stands, (6)
moderately flammable foliage, and (7) heavy lichen growth [87].

Crown fires typically kill Engelmann spruce trees. Engelmann spruce is
also very susceptible to surface fires because fine fuels which are
often concentrated under mature trees burn slowly and girdle the
thin-barked bole or char the shallow roots [20,31]. Some large
Engelmann spruce may survive light, surface fires, but these often die
later due to infection by wood-rotting fungi that enter through fire
scars [31].

More info for the term: woodland

Livestock: Livestock generally do not browse Engelmann spruce [4,89].

Wildlife habitat: Engelmann spruce-subalpine fir forests provide forage
and habitat for a wide variety of small and large wildlife species
[4,7,57,58]. However, these properties are characteristic of where
spruce grows and the understory species associated with it rather than
to the species itself. Animals that inhabit Engelmann spruce stands
include moose, elk, mule deer, woodland caribou, porcupine, snowshoe
hare, red squirrel, chipmunks, and voles. A partial list of birds that
nest and feed in Engelmann spruce trees includes the mountain chickadee,
Williamson's sapsucker, red-breasted nuthatch, brown creeper, and owls
and woodpeckers [82].

Wildlife food: The young growth of Engelmann spruce is occasionally
browsed by ungulates, but it is not an important food item and is
probably only taken as a last resort [4]. Spruce grouse and blue grouse
may feed extensively on buds and needles [56,80]. Squirrels sometimes
clip and eat twigs and buds [77].

Engelmann spruce seeds are eaten by several species of small mammals and
birds. Red squirrels, chickarees, and chipmunks eat seeds from cached
cones [6,98]. Engelmann spruce seeds are also eaten off the ground or
snow by chipmunks, mice, and voles [4]. Numerous species of birds,
including chickadees, nuthatches, crossbills, and the pine siskin,
remove and eat seeds from spruce cones [36,56]. Small birds may make
considerable use of spruce seeds, but their foraging is scattered and
sporadic throughout subalpine forests [36].

More info for the terms: climax, codominant, forest, series, woodland

Climax stands consisting entirely of Engelmann spruce are somewhat
scattered and often restricted to wet or cold habitats [4,88]. The
Engelmann spruce series is generally recognized by the absence or scant
representation of subalpine fir. This is because many ecologists,
especially those working in the northern Rocky Mountains, believe that
only in the absence of subalpine fir does Engelmann spruce dominate at
climax [22,67,98].

Throughout the Rocky Mountains, Engelmann spruce occurs in widespread
forests within the subalpine fir or white fir (Abies concolor)
habitat-type series either as a climax codominant or long-lived seral
species [4,98]. In the northern Rocky Mountains, Engelmann spruce is
considered a long-lived seral species in fir habitat types. In the
central and southern Rocky Mountains, Engelmann spruce and subalpine fir
often codominate at climax; however, these forests are classified under
the subalpine fir series to be consistent with habitat-type usage
elsewhere [40,47].

Published classification schemes listing Engelmann spruce as an
indicator or dominant in habitat types (hts), community types (cts),
plant associations (pas), ecosystem associations (eas), site types
(sts), riparian zone associations (rzas), or dominance types (dts) are
presented below:

Area Classification Authority

AZ, NM: ----- forest & woodland hts Layser & Schubert 1979
----- forest hts Moir & Ludwig 1979
Apache, Gila,
Cibola NFs forest hts Fitzhugh & others 1987
s of Mogollon
n AZ: San Fransisco general veg. cts, hts Rominger & Paulik 1983
n AZ, n NM forest hts Larson & Moir 1987

CO: Arapaho &
Roosevelt NFs forest hts Hess & Alexander 1986
Gunnison &
Uncompahgre NFs forest hts Komarkova & others 1988
Routt NF forest hts Hoffman & Alexander 1980
White River NF forest hts Hoffman & Alexander 1983
w CO riparian pas Baker 1989a

ID: Sawtooth, White
Cloud, Boulder,
& Pioneer Mtns general veg. cts Schlatterer 1972
c ID forest hts Steele & others 1981
n ID forest hts Cooper & others 1987
e ID, w WY forest hts Steele & others 1983
riparian cts Youngblood & others 1985a

MT forest hts Pfister & others 1977
riparian dts Hansen & others 1988
c, e MT riparian cts, hts Hansen & others 1990
nw MT riparian hts, cts Boggs & others 1990
sw MT riparian sts, cts, hts Hansen & others 1989
NM: Cibola NF forest hts Alexander & others 1987
Lincoln NF forest hts Alexander & others 1984
n NM, s CO forest hts Develice & others 1986

OR: Wallowa-Whitman NF steppe & forest pas Johnson & Simon 1987
Deschutes, Ochoco,
Fremont &
Winema NF's riparian rzas Kovalchik 1987
OR, WA: Blue Mtns forest & nonforest cts Hall 1973

c, s UT forest hts Youngblood & Mauk 1985
n UT forest hts Mauk & Henderson 1984
UT, se ID riparian cts Padgett & others 1989

WA: Okanogan NF forest pas Williams & Lillybridge 1983

WY: ----- riparian cts Olson & Gerhart 1982
Medicine Bow NF forest hts Alexander & others 1986
Bighorn Mtns forest hts Hoffman & Alexander 1976
Wind River Mtns forest hts Reed 1976

USFS R-4 aspen cts Mueggler 1988

AB general veg. cts Moss 1955
w-c AB forest cts Corns 1983
general veg. eas Corns & Annas 1986
BC: Prince Rupert
Forest Region general veg. eas Pojar & others 1984

More info for the term: tree

Tree

More info for the terms: natural, scarification, seed, seed tree, selection, tree

Timber harvest: Clearcutting and group selection silvicultural methods
favor Engelmann spruce over true firs (Abies) and hemlocks (Tsuga) but
increase the proportion of intolerant associates such as lodgepole pine
(Pinus contorta) and Douglas-fir (Pseudotsuga menziesii) [6].
Shelterwood and individual tree selection tend to favor more tolerant
associates. The seed tree method is generally not used because of the
susceptibility of Engelmann spruce to windthrow. In the Rocky
Mountains, clearcutting and shelterwood cutting have been the most
commonly used harvesting methods in old-growth Engelmann
spruce-subalpine fir stands because these stands tend to be even aged
and overmature [3]. Successful natural regeneration of Engelmann spruce
following logging is usually accomplished through mechanical
scarification or broadcast burns which expose at least 40 percent of the
mineral-soil seedbed [3]. Silvicultural systems and cutting methods for
managing Engelmann spruce are described in detail in the literature
[3,6].

Disease: The most common disease of Engelmann spruce is caused by
wood-rotting fungi which results in root or butt decay. Spruce broom
rust is also common in spruce-fir forests and causes bole deformation
and spike tops, increases susceptibility to wind breakage, and provides
entry points for decay fungi in spruce [7]. Dwarf mistletoe
(Arceuthobium microcarpum) causes heavy mortality of spruce trees in
Arizona and New Mexico [7].

Insects: The spruce beetle is the most serious insect pest of Engelmann
spruce. Outbreaks are associated with extensive windthrow because
downed trees provide a good food supply, causing a rapid expansion of
beetle populations. Unabated logging slash has been responsible for
past outbreaks [7].

Engelmann spruce is low in protein but fair in energy value [26]. A
study in Montana found the following concentration of elements in
Engelmann spruce needles and twigs [86]:

1-yr-old green needles twigs less than .25 inch in diameter
Calcium (mg/g [mean]) 6809 4028
Copper 7 9
Iron 57 237
Potassium 6914 7034
Magnesium 810 747
Manganese 669 323
Nitrogen 10911 4621
Sodium 100 128
Phosphorus 1841 1264
Zinc 69 72
Ash (percent [mean]) 5 3

AZ CA CO HI ID MT NV NM OR UT
WA WY AB BC

More info for the term: tree

Engelmann spruce is sometimes used as an ornamental landscape plant. It
has been used for screenings, windbreaks, and as a specimen tree [90].

Native Americans used Engelmann spruce for numerous purposes. The bark
was often peeled into sheets and used for making canoes, baskets, and
roofing. The fibrous roots were used to make rope, and the boughs and
needles to make incense, body scents, and cleansing agents. Various
teas and poultices were made from Engelmann spruce for medicinal
purposes. Native Americans occasionally ate the inner bark [92].

The palatability of Engelmann spruce to livestock and big game is low
[26]. The seeds are palatable to small mammals and birds.

More info on this topic.

More info for the term: seed

Pollen is generally shed from late May to early June at lower elevations
and from late June to early July at higher elevations. Cones develop
rapidly and are full size by August. Cones open and seeds are shed in
late September and October, but some continue to fall throughout the
winter. After seed dispersal, most cones fall during the winter, but
some may persist for longer periods [4].

Phenological observations of Engelmann spruce in Montana, Idaho, and
Wyoming made from 1928 to 1937 are presented below [79]:

Buds Pollen shed Winter Cones Cones
burst begins ends buds formed full size open

(east of Continental Divide in Montana, and in Yellowstone NP)
avg date June 16 June 17 July 3 Aug 3 Aug 17 Aug 30
earliest May 21 May 18 May 30 June 26 July 19 Aug 18
latest July 14 July 3 July 20 Sept 17 Sept 5 Sept 21

(west of Continental Divide in western Montana and northern Idaho)
avg date May 27 June 1 June 7 Aug 23 Aug 6 Sept 8
earliest May 5 Apr 26 May 12 June 14 June 20 Aug 11
latest July 10 June 11 May 12? Oct 11 Sept 24 Oct 5

More info for the terms: forest, seed, succession, tree, tundra

Following fire, Engelmann spruce reestablishes via seeds dispersed by
wind from trees surviving in protected pockets or from trees adjacent to
burned areas. The rate of reestablishment is variable and depends on
the proximity of surviving cone-producing trees and seed production
during the year of the fire and immediate postfire years. In general,
Engelmann spruce seedling establishment is very slow in areas burned by
large, continuous crown fires because much of the seed source is
destroyed. However, on small burns or near pockets of surviving trees
within a large burn, Engelmann spruce usually establishes numerous
seedlings within 5 to 10 years [42,44].

In areas where Engelmann spruce is abundant and lodgepole pine scarce
before burning, Engelmann spruce establishes rapidly after fire if
sufficient numbers of seed trees survive or are near the burn. If
lodgepole pine is present in the preburn community, it usually seeds in
aggressively, assuming a dominant role as it overtops any spruce
seedlings establishing on the site [24,28,42]. However, Engelmann
spruce seedlings usually survive under the developing pine canopy
because of its shade tolerance.

Above 9,850 feet (3,000 m), lodgepole pine does not regenerate, and
burned areas remain open for several decades or longer. Postfire
succession in this harsh, high-elevation zone (9,850 to 10,850 feet
[3,000-3,300 m]) proceeds very slowly. Spruce slowly becomes
established as scattered seedlings [12]. It may take 100 to 200 years
before young spruce-fir forest covers the area. However, conditions in
the upper parts of this zone sometimes make it difficult for tree
seedlings to establish and survive at all. Here, grasses and sedges may
form a mat which prevents tree seeds from reaching mineral soil [85].
Burned fir-spruce forest is replaced by alpine tundra which can persist
for long periods of time [12].

More info for the terms: secondary colonizer, seed

crown-stored residual colonizer; short-viability seed in on-site cones
off-site colonizer; seed carried by wind; postfire years 1 and 2
secondary colonizer; off-site seed carried to site after year 2

More info for the terms: climax, cone, duff, forest, layering, litter, natural, seed

Cone and seed production: Engelmann spruce can begin producing cones
when 15 to 40 years old and 4 or 5 feet (1.2-1.5 m) tall, but under
closed forest conditions seed production is generally not significant
until trees are older and taller [6]. Within natural stands, most seed
is produced by dominant trees greater than 15 inches (38 cm) d.b.h.
Although yearly production is erratic, Engelmann spruce is considered a
moderate to good seed producer. Good to bumper crops are produced every
2 to 5 years [4,6]. The seeds are light, averaging 135,000 per pound
(297,500/kg) [77].

Seed predation: Cone and seed insects, especially the spruce seed worm,
reduce seed yields. Seed production in Colorado was reduced an average
of 28 percent by insects over a 4-year period [4]. Small mammals
consume considerable amounts of freshly fallen seed off the forest
floor, but the extent of loss is not known [6].

Dispersal: Engelmann spruce seed is generally shed by the end of
October, but some may continue to fall throughout the winter. The
winged seeds are wind dispersed. Seeds travel primarily with the
prevailing winds, but upslope drafts can influence dispersal at low and
middle elevations. Seed is generally dispersed within 300 feet (91 m)
of a windward source; when bumper seed crops occur, about 5 to 10
percent of the seed may be dispersed as far as 600 feet (183 m) [6,63].
Seed dispersed during winter can travel great distances by skidding over
glazed snow [58].

Viability and germination: The viability of Engelmann spruce seed is
rated as good [7]. Germination averages 69 percent, which is much
higher than that of associated species [7,77]. Under natural
conditions, seeds overwinter under snow and germinate 2 to 3 weeks
following snowmelt [6,83]. Occasionally germination may occur after
summer rains or be delayed until the second year [4].

Seedling establishment and survival: Seedlings establish best on
mineral soil. Decayed wood, duff, and litter are poor seedbeds because
they dry out rapidly [6]. In general, seedlings that establish on
organic matter deeper than 2 inches (5 cm) soon die because their
shallow roots cannot penetrate to mineral soil before the surface
organic layer dries out [4]. At middle to upper elevations, seedling
survival may be greater on duff because the duff helps protect seedlings
from high-intensity summer rain storms and from frost heaving [29]. In
the central and southern Rocky Mountains, seedlings do not establish
well in the open. Intense light on open slopes can inhibit
photosynthesis, which eventually kills the seedling [63]. Direct
sunlight also dries out seedbeds. Seedlings survive best under
conditions of shade, cool temperatures, and adequate soil moisture [6].

Engelmann spruce requires a mineral soil seedbed; subalpine fir,
however, is able to establish in duff because of its rapid root growth.
Consequently, subalpine fir seedlings usually outnumber spruce seedlings
in the understory of spruce-fir stands, even where Engelmann spruce
dominates the overstory. Thus, even though it is short-lived, many
ecologists consider subalpine fir better able to regenerate under climax
conditions than Engelmann spruce.

Growth: Engelmann spruce seedlings grow very slowly. One-year-old
seedlings are seldom over 1 inch (2.5 cm) tall, and 5-year-old seedlings
are usually 1 to 4 inches (2.5-10 cm) tall. Ten-year-old seedlings may
be only 6 to 8 inches (15-20 cm) tall under heavy shade and 10 to 12
inches (25-30 cm) tall under partial shade. Under a dense overstory,
seedlings may be severely suppressed; 3- to 5-foot-tall trees may be 100
years old. In light shade or full sun trees may grow to 4 or 5 feet
(1.2-1.5 m) in height in about 20 years [6].

Vegetative reproduction: Near timberline, where the species assumes a
dwarf or prostrate form, Engelmann spruce frequently reproduces by
layering. Layering also occurs when only a few trees survive fire or
other disturbances, but once numbers have increased enough to improve
germination and establishment, layering decreases. In closed forest
stands layering is negligible [7].

More info on this topic.

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):

2 Cascade Mountains
4 Sierra Mountains
5 Columbia Plateau
6 Upper Basin and Range
7 Lower Basin and Range
8 Northern Rocky Mountains
9 Middle Rocky Mountains
11 Southern Rocky Mountains
12 Colorado Plateau
16 Upper Missouri Basin and Broken Lands

More info on this topic.

More info for the terms: climax, duff, herbaceous, seed, series, severity, succession, tree

In the Rocky Mountains north and south of Montana and Idaho, Engelmann
spruce and subalpine fir often codominate at climax to form extensive
Engelmann spruce-subalpine fir forests [4]. These spruce-fir forests
are usually classified as subalpine fir climax series habitat types. In
the understory of these stands, subalpine fir seedlings usually
outnumber Engelmann spruce seedlings because they are more shade
tolerant and readily establish on duff seedbeds. However, Engelmann
spruce is longer lived and usually the largest tree in the stand. There
is little evidence that Engelmann spruce will ever be replaced by
subalpine fir in these regions [47].

In the Rocky Mountains of Montana and Idaho, and in the mountains of
eastern Washington and eastern Oregon, Engelmann spruce is usually
considered seral to subalpine fir. Subalpine fir may form pure stands
at climax, but Engelmann spruce is also often present because it
outlives subalpine fir and persists to climax [4]. In eastern
Washington and northern Idaho, Engelmann spruce is seral to grand fir,
western redcedar, and western hemlock [22]. However, in Montana,
eastern and central Idaho, and western Wyoming, Engelmann spruce may
attain climax dominance on the wettest habitat types where it appears
more successful than subalpine fir [88]. Farther east, progressing away
from the Pacific maritime influence, the importance of Engelmann spruce
increases and that of subalpine fir decreases [88], and in parts of
central and southwestern Montana, Engelmann spruce may be dominant on
well-drained benches and droughty soils [67].

On sites where Engelmann spruce attains climax dominance or codominance,
succession following disturbance may vary depending on the severity and
type of disturbance, elevation, and availability of seed. Near
treeline, it may take 100 years or more for Engelmann spruce to
establish seedlings following fire because an increase in herbaceous
species prevents seeds from reaching mineral soil, and the harsh climate
kills many seedlings that do establish [12,85]. Within subalpine
stands, Engelmann spruce may establish immediately following disturbance
if mature trees survive to provide seeds, and seral species such as
lodgepole pine and aspen are scarce. Aspen and lodgepole pine are the
most common seral species and often dominate subalpine forests following
fire [6,47,85]. These species grow rapidly and quickly overtop any
Engelmann spruce seedlings that may establish at the same time. Aspen
stands can sometimes persist for decades or even centuries when conifer
seed trees are eliminated [25,89]. When lodgepole pine establishes
immediately following stand-destroying fires, it often forms dense
even-aged stands that dominate for 100 to 300 years. Because it is
shade tolerant, Engelmann spruce eventually establishes under the pine
canopy, usually within 100 years, and attains dominance as the pine
stand begins to break up [24,54].

On some of the lower elevation Engelmann spruce and subalpine fir
habitat types, Engelmann spruce will not achieve climax dominance or
codominance because of repeated fires which favor shade-intolerant seral
conifers. Many of these habitat types are in midsuccessional stages;
Douglas-fir, lodgepole pine, western larch (Larix occidentalis), or
limber pine dominate the overstory [67,88]

Abies engelmannii Parry
Picea engelmannii var. glabra Goodman
Picea glauca var. engelmannii (Parry) Boivin
Picea glauca ssp. engelmannii (Parry) T. M. C. Taylor
Picea columbiana Lemmon

More info for the term: natural

The genus Picea consists of about 30 species of evergreen trees found in
cool, temperate regions of the northern hemisphere. Seven species of
Picea, including Engelmann spruce, are native to North America. The
currently accepted scientific name of Engelmann spruce is Picea
engelmannii Parry ex Engelm. [45,53]. There are no recognized races or
geographic varieties.

Natural hybridization between species of Picea is common. Engelmann
spruce x white spruce (Picea glauca) hybrids are common where the ranges
of these species overlap. Natural crosses between these species occur
from central British Columbia as far south as eastern Washington and
Yellowstone National Park [23]. Within this area, trees at low
elevations closely resemble pure white spruce. Pure Engelmann spruce
tends to dominate at higher elevations [23]. Engelmann spruce x white
spruce hybrids are common throughout low elevations in British Columbia
[32].

Using artificial pollination techniques, Engelmann spruce has been
successfully crossed with white spruce, blue spruce (P. pungens), and
Sitka spruce (P. sitchensis) [32].

More info for the terms: forest, seed

Engelmann spruce can be planted on disturbed sites within forest
vegetation types where it naturally occurs. It is primarily used for
reforestation projects on cool, moist sites below upper timberline. It
has been used to a limited extent for revegetation and long-term
stabilization of high-elevation mine spoils [4,96]. In west-central
Alberta, Engelmann spruce x white spruce hybrids were observed invading
coal mine spoils at high elevations [76].

Planting nursery stock is more successful than direct seeding. Most
commonly, 2- or 3-year-old bareroot or container-grown stock is planted
following snowmelt [4,96]. Since seedlings are sensitive to direct
sunlight, they should be planted in the protective shade of stumps, logs,
or vegetation [4]. Artificial shade also is effective in protecting
seedlings from wind and sun [15]. Two- to 4-foot tall (0.6-1.5 m),
open-grown Engelmann spruce seedlings dug from the wild before breaking
dormancy have shown good survival when transplanted [15]. Methods for
collecting, processing, testing, storing, and planting seed, and for
care and transplanting of bareroot and container-grown Engelmann spruce
seedlings have been described in the literature [4,96].

Engelmann spruce is an important commercial wood in the United States.
The wood is white, odorless, lightweight, straight grained, soft, stiff,
and can be readily air dried. It is easy to work, glues well, holds
nails fairly well but has only average paint-holding properties. The
wood is primarily used for lumber for home construction and for
prefabricated wood products. Less common uses include veneer in plywood
manufacture, poles, and specialty items, such as food containers,
violins, pianos, and aircraft parts. Spruce has not been used much for
pulp and paper, although its pulping properties are excellent [6].

Engelmann spruce most typically grows together with subalpine fir (Abies lasiocarpa) to form the Engelmann Spruce-Subalpine Fir (Type 206) forest cover type. It may also occur in pure or nearly pure stands. Spruce grows in 15 other forest types recognized by the Society of American Foresters, usually as a minor component or in frost pockets (95):

201 White Spruce
205 Mountain Hemlock
208 Whitebark Pine
209 Bristlecone Pine
210 Interior Douglas-Fir
212 Western Larch
213 Grand Fir
215 Western White Pine
216 Blue Spruce
217 Aspen
218 Lodgepole Pine
219 Limber Pine
224 Western Hemlock
226 Coastal True Fir-Hemlock
227 Western Redcedar-Western Hemlock

The composition of the forest in which Engelmann spruce grows is influenced by elevation, exposure, and latitude (30). In the Rocky Mountains and Cascades, subalpine fir is its common associate at all elevations. In the northernmost part of its range along the Coast Range and in the Rocky Mountains of Canada, it mixes with white spruce (Picea glauca), black spruce (Picea mariana), Douglas-fir (Pseudotsuga menziesii), balsam poplar (Populus balsamifera), and paper birch (Betula papyrifera). In the Rocky Mountains of Montana and Idaho, in the Cascades, and in the mountains of eastern Washington and Oregon, associates at lower and middle elevations are western white pine (Pinus monticola), Douglas-fir, western larch (Larix occidentalis), grand fir (Abies grandis), and lodgepole pine (Pinus contorta); associates at higher elevations are Pacific silver fir (Abies amabilis), mountain hemlock (Tsuga mertensiana), alpine larch (Larix lyallii), and whitebark pine (Pinus albicaulis). In the Rocky Mountains south of Montana and Idaho, and in the mountains of Utah, lodgepole pine, interior Douglas-fir (Pseudotsuga menziesii var. glauca), blue spruce (Picea pungens), white-fir (Abies concolor), aspen (Populus tremuloides), and occasionally ponderosa pine (Pinus ponderosa) and southwestern white pine (Pinus strobiformis), are common associates at lower and middle elevations, and corkbark fir (Abies lasiocarpa var. arizonica), limber pine (Pinus flexilis), and bristlecone pine (Pinus aristata) at high elevations. Engelmann spruce extends to timberline in the Rocky Mountains south of Idaho and Montana, and may form pure stands at timberline in the southernmost part of its range. In the Canadian Rockies of southwestern Alberta and adjacent British Columbia and into the Rocky Mountains north of Wyoming and Utah, and the Cascades, spruce usually occupies moist sites below timberline; its high-elevation associates form timberline forests (6,20).

Rocky Mountain maple (Acer glabrum) (warm, moist sites); twinflower (Linnaea borealis), (cool, moist sites); common creeping juniper (Juniperus communis) (warm, dry sites); and grouse whortleberry (Vaccinium scoparium), heartleaf arnica (Arnica cordifolia), boxleaf myrtle (Pachistima myrsinites), elk sedge (Carex geyeri), mountain gooseberry (Ribes montigenum), and fireweed (Epilobium angustifolium) (cool, dry sites) occur as undergrowth throughout much of the range of Engelmann spruce. Undergrowth vegetation is more variable than tree associates, however. Undergrowth characteristically found in the Pacific Northwest Region and the Rocky Mountains and associated ranges north of Utah and Wyoming include: Labrador-tea (Ledum glandulosum), Cascades azalea (Rhododendron albiflorum), rusty skunkbrush (Menziesia ferruginea), woodrush (Luzula hitchcockii), dwarf huckleberry (Vaccinium cespitosum), and blue huckleberry (Vaccinium globulare), (cool, moist sites); false solomons-seal (Smilacina stellata), queenscup beadlily (Clintonia uniflora), twistedstalk (Streptopus amplexifolius), and sweetscented bedstraw (Galium triflorum) (warm, moist sites); pinegrass (Calamagrostis rubescens) and beargrass (Xerophyllum tenax) (cool, dry sites); Oregongrape (Berberis repens), white spires, (Spiraea betulifolia), and big whortleberry (Vaccinium membranaceum) (warm, dry sites); and marsh-marigold (Caltha leptosepala), devilsclub (Oplopanax horridum), and bluejoint reedgrass (Calamagrostis canadensis) (wet sites) (14,39).

Undergrowth characteristically found in the Rocky Mountains and associated ranges south of Idaho and Montana include: mountain bluebells (Mertensia ciliata) and heartleaf bittercress (Cardamine cordifolia) (cool, moist sites); thimbleberry (Rubus parviflorus) (warm, moist sites); red buffaloberry (Shepherdia canadensis), Oregongrape, mountain snowberry (Symphoricarpos oreophilus), and Arizona peavine (Lathyrus arizonicus) (warm, dry sites); and Rocky Mountain whortleberry (Vaccinium myrtillus), groundsel (Senecio sanguiosboides), polemonium (Polemonium delicatum), daisy fleabane (Erigeron eximius), prickly currant (Ribes lacustre), sidebells pyrola (Pyrola secunda), and mosses (cool, dry sites) (14).

Engelmann spruce grows in a humid climate with long, cold winters and short, cool summers. It occupies one of the highest and coldest forest environments in the western United States, characterized by heavy snowfall and temperature extremes of more than -45.6° C (-50° F) to above 32.2° C (90° F). Climatic data for four subregions of the United States within the species range are given in table 1 (23,42,65,100).

Table 1- Climatological data for four regional subdivisions within the range of Engelmann spruce Average temperature Frost each period Location Annual July January Annual precip. Annual Snowfall °C °F °C °F °C °F cm in cm in days Pacific Northwest 2 35 10-13 50-55 -9 to -7 15-20 152-406 60-160 1015+ 400+ 45-90 U.S. Rocky Mountains    Northern¹ -1 to 2 30-35 4-13 45-55 -12 to -7 10-20 61-114 24-45+ 635+ 250+ *30-60    Central² -1 to 2 30-35 10-13 50-55 -12 to -9 10-15 61-140 24-55 381-889+ 150-350+ *30-60    Southern³ 2 35 10-16 50-60 -9 to -7 15-20 61-89+ 24-35+ 508 200+ *30-75 ¹Includes the Rocky Mountains of Montana and Idaho and associated mouintains of eastern Washington and Oregon.
²Includes the Rocky Mountians of Wyoming and Colorado and associated mountains of Utah.
³Includes the Rocky Mountains and associated ranges of New Mexico and Arizona and the plateaus of southern Utah.
*Frost may occur any month of the year. The range of mean annual temperatures is narrow considering the wide distribution of the species. Average annual temperatures are near freezing, and frost can occur any month of the year. Average precipitation exceeds 61 cm (24 in) annually, with only moderate or no seasonal deficiency. Summer is the driest season in the Cascades and Rocky Mountains west of the Continental Divide south to southwestern Colorado. The mountains east of the divide, in southwestern Colorado, and in New Mexico and Arizona, receive considerable summer rainfall, while winter snowfall can be light (23,48,64,100). Winds are predominantly from the west and southwest and can be highly destructive to Engelmann spruce (13,20).

Engelmann spruce is susceptible to windthrow, especially after any initial cutting in old-growth forests.

Partial cutting increases the risk because the entire stand is opened up and therefore vulnerable. Windfall is usually less around clearcuts because only the boundaries between cut and leave areas are vulnerable, but losses can be great if no special effort is made to locate windfirm cutting-unit boundaries (1,3). While the tendency of spruce to windthrow is usually attributed to a shallow root system, the development of the root system varies with soil and stand conditions. Trees that have developed together in dense stands over long periods of time mutually protect each other and do not have the roots, boles, or crowns to withstand sudden exposure to wind if opened up too drastically. If the roots and boles are defective, the risk of windthrow is increased. Furthermore, regardless of kind or intensity of cutting, or soil and stand conditions, windthrow is greater on some exposures than others. Alexander (13) has identified spruce windfall risk in relation to exposures in Colorado as follows:

Below Average:

Valley bottoms, except where parallel to the direction of prevailing winds, and flat areas. All lower, and gentle, middle north-east-facing slopes. All lower, and gentle, middle south- and west-facing slopes that are protected from the wind by higher ground not far to windward. Above Average:

Valley bottoms parallel to the direction of prevailing winds. Gentle middle south and west slopes not protected to the windward. Moderate to steep middle, and all upper north- and east-facing slopes. Moderate to steep middle south- and west-facing slopes protected by higher ground not far to windward. Very High:

Ridgetops. Saddles in ridges. Moderate to steep middle south- and west-facing slopes not protected to the windward. All upper south- and west-facing slopes. The risk of windfall in these situations is increased at least one category by such factors as poor drainage, shallow soils, defective roots and boles, and overly dense stands. Conversely, the risk of windfall is reduced if the stand is open-grown or composed of young, vigorous, sound trees. All situations become very high risk if exposed to special topographic situations, such as gaps or saddles in ridges at high elevations to the windward that can funnel winds into the area (1,3,13).

The spruce beetle (Dendroctonus rufipennis) is the most serious insect pest of Engelmann spruce (86). It is restricted largely to, mature and overmature spruce, and epidemics have occurred throughout recorded history. One of the most damaging out breaks was in Colorado from 1939 to 1951, when beetles killed nearly 6 billion board feet of standing spruce (64). Damaging attacks have been largely associated with extensive windthrow, where downed trees have provided an ample food supply for a rapid buildup of beetle populations. Cull material left after logging has also caused outbreaks, and there are examples of large spruce beetle populations developing in scattered trees windthrown after heavy partial cutting. The beetle progeny then emerge to attack living trees, sometimes seriously damaging the residual stand. Occasionally, serious spruce beetle outbreaks have developed in overmature stands with no recent history of cutting or windfall, but losses in uncut stands that have not been subjected to catastrophic wind storms have usually been no greater than normal mortality in old growth (13).

Spruce beetles prefer downed material to standing trees, but if downed material is not available, then standing trees may be attacked. Large, overmature trees are attacked first, but if an infestation persists, beetles will attack and kill smaller trees after the large trees in the stand are killed. In the central Rocky Mountains susceptibility to beetle attack can vary by location; the following sites are arranged from most to least susceptible: (1) trees in creek bottoms, (2) good stands on benches and high ridges, (3) poor stands on benches and high ridges, (4) mixed stands, and (5) immature stands (59,85). Analysis of past infestations suggests the following kinds of stands are susceptible to outbreaks: (1) single- or two-storied stands, (2) high proportions of spruce in the overstory, (3) basal area of 34 m²/ha (150 ft²/acre) or more in older and larger trees, and (4) an average 10-year periodic diameter growth of 1.0 cm (0.4 in) or less (87).

The western spruce budworm (Choristoneura occidentalis) is another potentially dangerous insect attacking Engelmann spruce and subalpine fir (40). Although spruce and fir are among the preferred hosts, budworm. populations have been held in check by combinations of several natural control factors- parasites, predators, diseases, and adverse climatic conditions. The potential for future outbreaks is always present, however. An excellent summary of the ecology, past insecticidal -treatments, and silvicultural practices associated with western spruce budworm in northern Rocky Mountain forests is given by Carlson et al. (28).

The most common diseases of Engelmann spruce are caused by wood-rotting fungi that result in loss of volume and predispose trees to windthrow and windbreak (46). In a recent study of cull indicators and associated decay in Colorado, the major root and butt fungi in mature to overmature Engelmann spruce were identified as Phellinus nigrolimitatus, Flammula alnicola, Polyporus tomentosus var. curnatua, Gloeocystidiellum radiosum, and Coniophora puteana. Trunk rots, which caused 88 percent of the decay, were associated with Phellinus pini, Haematosterceum sanguinolentum, Echinodontium sulcatum, and Amylosterceum chailletii. Spruce broom rust (Chrysomyxa arctostaphyli) is also common in spruce-fir forests. It causes bole deformation, loss of volume, and spiketops; increases susceptibility to windbreak; and provides infection courts for decay fungi in spruce (20,46).

Dwarfmistletoe (Arceuthobium microcarpum) causes heavy mortality in spruce in Arizona and New Mexico, but it has a limited range in the Southwest and is not found elsewhere (44).

Engelmann spruce does not prune well naturally. Thin bark and the persistence of dead lower limbs make it susceptible to destruction or severe injury by fire (fig. 8). Many root and trunk rots in old growth appear to be associated with fire injury. Because of the climate where spruce grows, the risk of fire is less than in warmer and drier climates (20).

Engelmann spruce is monoecious; male and female strobili are formed in the axils of needles of the previous year's shoots after dormancy is broken, usually in late April to early May- Ovulate strobili (new conelets) are usually borne near ends of the shoots in the upper crown and staminate strobili on branchlets in the lower crown (38,102). Separation of male and female strobili within the crown reduces self-fertilization. The dark purple male flowers are ovoid to cylindrical and pendant. Female flowers are scarlet, erect, and cylindrical. Male flowers ripen and pollen is wind disseminated in late May and early June at low elevations, and from mid-June to early July at high elevations. The conelets grow rapidly and soon reach the size of the old cones that may have persisted from previous years. The new cones mature in one season and are 2.5 to 6.3 cm (1 to 2.5 in) long. They ripen in August to early September, open, and shed their seed. The cones may fall during the following winter or may remain attached to the tree for some time (20, 89,102).

Population Differences Available information on population differences of Engelmann spruce is limited to a few studies. For example, spruce trees from high-elevation seed sources and northern latitudes break dormancy first in the spring, and, when grown in low-elevation nurseries with low- and middle-elevation seed sources,

are the first to become dormant in the fall. Conversely, low-elevation and southern latitude seed sources frequently are more resistant to spring frosts, but are less winter-hardy than middle- and high-elevation seed sources (38). In one study that compared seedlings from 20 seed sources, ranging from British Columbia to New Mexico, planted at an elevation of 9,600 feet in Colorado, seedlings from northern latitudes and lower elevations made the best height growth (93). Overall survival from all sources was 73 percent with no significant differences among sources.

Races and Hybrids There are no recognized races or geographical varieties of Engelmann spruce. There is abundant evidence that natural introgressive hybridization between Engelmann and white spruce occurs in sympatric areas, especially around Glacier Park in Montana (32). It has been suggested that Engelmann and Sitka spruces cross in British Columbia, but it seems more likely that the crosses are between Sitka and white spruce. Engelmann spruce has been artificially crossed with several other spruces, but with only limited success (38).

Engelmann spruce is one of the largest of the high-mountain species. Under favorable conditions, average stand diameter will vary from 38.1 to 76.2 cm (15 to 30 in), and average dominant height from 14 to 40 m (45 to 130 ft), depending upon site quality and density (20). Individual trees may exceed 101.6 cm (40 in) in diameter and 49 m (160 ft) in height (60). Engelmann spruce is a long-lived tree, maturing in about 300 years. Dominant spruces are often 250 to 450 years old, and trees 500 to 600 years old are not uncommon (13).

Engelmann spruce has the capacity to grow well at advanced ages. If given sufficient growing space, it will continue to grow steadily in diameter for 300 years, long after the growth of most associated tree species slows down (20,60).

Yields are usually expressed for the total stand. Engelmann spruce does not normally grow in pure stands but in various mixtures with associated species. Average volume per hectare in old-growth (normally 250 to 350 years old) spruce-fir may be practically nothing at timberline, 12,350 to 37,070 fbm/ha (5,000 to 15,000 fbm/acre) on poor sites, and 61,780 to 98,840 fbm/ha (25,000 to 40,000 fbm/acre) on better sites. Volumes as high as 197,680 to 247,100 fbm/ha (80,000 to 100,000 fbm/acre) have been reported for very old stands on exceptional sites (77,99). Average annual growth in virgin spruce-fir forests will vary from a net loss due to mortality to as much as 494 fbm/ha (200 fbm/acre), depending upon age, density, and vigor of the stand (69). Engelmann spruce usually makes up at least 70 percent and often more than 90 percent of the basal area in trees 12.7 cm (5.0 in) and larger at breast height in these stands (76).

With prompt restocking after timber harvest and periodic thinning to control stand density and maintain growth rates, growth of individual spruce trees and yields of spruce-fir stands can be greatly increased and the time required to produce the above volumes and sizes reduced- For example, in stands managed at the growing stock levels (GSL) considered optimum for timber production (GSL 140 to 180) on 140- to 160-year rotations with a 20-year thinning interval, average volumes per hectare will range from 74,100 to 98,800 fbm/ha (30,000 to 40,000 fbm/acre) on poor sites to 222,400 to 259,500 fbm 1 ha (90,000 to 105,000 fbm/acre) on good sites. Volume production declines -on all sites when growing stock level is reduced below the optimum for timber production, and the decline is greater with each successive reduction in GSL. Average annual growth will vary from 445 to 1,606 fbm/ha (180 to 650 fbm/acre) (15). Moreover, since most subalpine fir will be removed in early thinnings, these yields will be largely from Engelmann spruce.

Engelmann spruce is rated tolerant in its ability to endure shade (24). It is definitely more shade-enduring than interior Douglas-fir, western white pine, lodgepole pine, aspen, western larch, or ponderosa pine but less so than subalpine fir (the most common associate throughout much of its range), grand fir, white fir, and mountain hemlock. The Engelmann spruce-subalpine fir type is either a co-climax type or long-lived seral forest vegetation throughout much of its range. In the Rocky Mountains of British Columbia and Alberta, and south of Montana and Idaho, Engelmann spruce and subalpine fir occur as either codominants or in nearly pure stands of one or the other. In the Rocky Mountains of Montana and Idaho, and in the mountains of Utah, eastern Oregon and Washington, subalpine fir is the major climax species. Engelmann spruce may also occur as a major climax species, but more often it is a persistent long-lived seral species. Pure stands of either species can be found, however (6).

Although spruce-fir forests form climax or near climax vegetation associations, they differ from most climax forests in that many stands are not truly all-aged (60). Some stands are clearly single-storied, indicating that desirable spruce forests can be grown under even-aged management. Other stands are two- or three-storied, and multi-storied stands are not uncommon (13,68). These may be the result of either past disturbances, such as fire, insect epidemics, or cutting, or the gradual deterioration of old-growth stands due to normal mortality from wind, insects, and disease. The latter is especially evident in the formation of some multi-storied stands. On the other hand, some multi-storied stands appear to have originated as uneven-aged stands and are successfully perpetuating this age-class structure (16,43,104).

Although climax forests are not easily displaced by other vegetation, fire, logging, and insects have played an important part in the succession and composition of spruce-fir forests. Complete removal of the stand by fire or logging results in such drastic environmental changes that spruce and fir are usually replaced by lodgepole pine, aspen, or shrub and grass communities (80,97). The kind of vegetation initially occupying the site usually determines the length of time it takes to return to a spruce-fir forest. It may vary from a few years, if the site is initially occupied by lodgepole pine or aspen, to as many as 300 years, if grass is the replacement community.

What is known about the utilization of water by Engelmann spruce in Colorado can be summarized as follows: (1) leaf water potential decreases in proportion to the transpiration rate but is influenced by soil temperature and water supply; (2) needle water vapor conductance (directly proportional to stomatal opening) is controlled primarily by visible irradiance and absolute humidity difference from needle to air (evaporative demand), with secondary effects from temperature and water stress; (3) nighttime minimum temperatures below 3.9° C (39° F) retard stomatal opening the next day, but stomata function well from early spring to late fall, and high transpiration rates occur even with snowpack on the ground; (4) leaf water vapor conductance is higher in Engelmann spruce than in subalpine fir, but lower than in lodgepole pine and aspen; (5) Engelmann spruce trees have less total needle area per unit area of sapwood water conducting tissue than subalpine fir but more than lodgepole pine and aspen; and (6) Engelmann spruce trees have a greater needle area per unit of bole or stand basal area than subalpine fir, lodgepole pine, and aspen. At equal basal area, annual canopy transpiration of spruce is about 80 percent greater than lodgepole pine, 50 percent greater than subalpine fir, and 220 percent greater than aspen. These high rates of transpiration cause Engelmann spruce to occur primarily on moist sites (50,51,52,53,54,55,56,57,58).

Both even- and uneven-aged silvicultural systems are appropriate for use in Engelmann spruce forests, but not all cutting methods meet specific management objectives (5,12,17). The even-aged cutting methods include clearcutting, which removes all trees in strips, patches, blocks, or stands with a single cut; and shelterwood cutting, which removes trees in one, two, or three cuts and its modifications. Because of susceptibility to windthrow, the seed-tree method is not a suitable way to regenerate spruce. The seedbed is prepared for regeneration after clearcutting, or after the seed cut with shelterwood cutting, by various methods ranging from burning and mechanical scarification to only that associated with logging activity (5,12,17).

The uneven-aged cutting methods appropriate to spruce are individual tree and group selection cuttings and their modifications, which remove selected trees in all size classes at periodic intervals over the entire area or in groups up to 0.8 hectares (2 acres) in size. Reproduction occurs continuously, but methods of site preparation are limited (12,13).

Shelterwood and individual tree selection cutting methods will favor associated species such as true firs and hemlocks over spruce. Clearcutting, group shelterwood, and group selection cutting methods will favor Engelmann spruce over these more tolerant associates, but will increase the proportion of intolerant associates such as lodgepole pine and Douglas-fir (13).

Engelmann spruce has a shallow root system. The weak taproot of seedlings does not persist beyond the juvenile stage, and when trees grow where the water table is near the surface or on soils underlain by impervious rock or clay hardpans, the weak, superficial lateral root system common to the seedling stage may persist to old age. Under these conditions, most roots are in the first 30 to 46 cm (12 to 18 in) of soil. But, where spruce grows on deep, porous, well drained soils, the lateral root system may penetrate to a depth of 2.4 m (8 ft) or more (20).

Although open-grown Engelmann spruces begin bearing cones when they are 1.2 to 1.5 m (4 to 5 ft) tall and 15 to 40 years old, seed production does not become significant until trees are larger and older. The most abundant crops in natural stands are produced on healthy, vigorous, dominant trees 3.8 dm (15 in) or more in diameter at breast height and 150 to 250 years old. Engelmann spruce is a moderate to good seed producer (11,19,21). Good to bumper seed crops, based on the following criteria, are generally borne every 2 to 5 years, with some seed produced almost every year (19):

Number of sound seeds/hectare Seed crop rating 0-24,700 (0-10,000/acre) Failure 24,700-123,500 (10,000-50,000/acre) Poor 123,500-247,000 (50,000-100,000/acre) Fair 247,000-617,000 (100,000-250,000/acre) Good 617,000-1,235,000 (250,000-500,000/acre) Heavy >1,235,000 (>500,000/acre) Bumper There is great variation in seed production from year to year and from area to area. In one study on the Fraser Experimental Forest in Colorado, annual seed production averaged only 32,100 sound seeds per acre during the period 1956-65 (4). Only one good and two moderate crops were recorded. In more recent studies, spruce seed production has been greater, possibly because the studies were better designed to sample seed production. One such study of seed production on five National Forests, covering 42 area-seed crop years from 1962 to 1971, rated seed crops as 5 bumper, 1 heavy, 6 good, and the remaining 30 fair to failure (74). In the one year, 1967, that a bumper seed crop was produced on all areas, seed production was the highest ever recorded in Colorado (84). In another study on the Fraser Experimental Forest covering 15 years (1970-84) and 13 locations, seed production was rated 2 bumper, 3 heavy, 2 good and 8 fair to failure (21).

In the northern Rocky Mountains, Boe (26) analyzed cone crops in Montana between the years 1908 and 1953. Twenty-two crops observed west of the Continental Divide during the 45-year period were rated: 5 good, 8 fair, and 9 poor. East of the Divide, seed production was poorer: only 2 good, 4 fair, and 15 poor crops were reported for a 21-year period. In other studies in the Northern and Intermountain Regions, seed production was rated as good to bumper in 1 year out of 5, with the other 4 years rated as failures (78,96).

Observations in spruce forests before seedfall have indicated that part of each seed crop is lost to cone and seed insects (13). In a recently completed study in Colorado, insect-caused loss of Engelmann spruce seed averaged 28 percent of the total seed produced during a 4-year period (1974-1977) (88). The percentage of infested cones was highest during years of poor seed production. The primary seed-eating insects were a spruce seedworm (Cydia youngana = (Laspeyresia youngana) and an unidentified species of fly, possibly a Hylemya, found only in the larval stage.

Some seed is lost from cutting and storing of cones by pine squirrels (Tamiasciurus hudsonicus fremonti), but the actual amount is unknown. After seed is shed, small mammals such as deer mice (Peromyscus maniculatus), red-backed mice (Clethrionomys gapperi), mountain voles (Microtus montanus), and chipmunks (Eutamias minimus) are the principal source of seed loss. Undoubtedly, mammals consume much seed, but the amount is not known and results of studies on protecting seed are conflicting. For example, in western Montana, spruce seedling success was little better on protected than unprotected seed spots (90), but in British Columbia, protection of spruce seed from rodents was essential to spruce regeneration success (94).

Cones begin to open in September. Most seed is shed by the end of October, but some falls throughout the winter. The small, winged seeds are light, averaging about 297,000/kg (135,000/lb) (102). Nearly all of the seed is disseminated by the wind; squirrels, other mammals, and birds are not important in seed dispersal.

Seed is dispersed long distances only in years of bumper seed crops. For example, studies in the Rocky Mountains show that 237,200 to 617,800 sound seeds/ha (96,000 to 250,000/acre) were dispersed 122 to 183 in (400 to 600 ft) from the source into clearcut blocks 183 m to 244 m (600 to 800 ft) wide (74). Seedfall in cut stands ranged from 1,236,000 to 12,355,000 seeds/ha (500,000 to 5,000,000/acre). In years of good to heavy seed crops, seedfall into cleared openings diminished rapidly as distance from seed source increased. Prevailing winds influence the pattern of seedfall in openings 61 to 244 m (200 to 800 ft) across, with about 40 percent of the seeds failing within 31 m (100 ft) of the windward timber edge (4,16,74). Seeffall then diminishes but at a less rapid rate of decline as distance increases to about two-thirds of the way-46 to 183 m (150 to 600 ft)-across the openings. At that distance, the average number of seeds falling is about 25 percent (at 46 m [150 ft]) to less than 5 percent (at 183 m [600 ft]) of the number of released in the uncut stand (4,74,78,80). Beyond this point, seedfall gradually increases toward the leeward timber edge, but is only about 30 percent of the seedfall along the windward edge (13,16). In the openings observed, a U-shaped pattern of seedfall was poorly defined. The "tailing-off' suggests that significant quantities of seed were released during periods of high winds (36).

Viability of Engelmann spruce seed is rated good and the vitality persistent. The average germinative capacity of spruce is higher than for many associated species (102):

Species Average germinative
capacity Engelmann spruce 69 Subalpine fir 31-34 Lodgepole pine 65-80 Western white pine 44 Interior Douglas-fir 60-93 Western larch 57 Grand fir 46-57 Western hemlock 53-56 Pacific silver fir 20-26 White fir 30-37 Viable seeds of spruce that survive over winter normally germinate following snowmelt when seedbeds are moist and air temperature is at least 7° C (45° F). Field germination of spruce over long periods in Colorado have ranged from 0 to 28 percent of the sound seeds dispersed, depending upon the seedbed and environmental factors (9,73).

In the undisturbed forest, spruce seeds germinate and seedlings become established on duff, litter, partially decomposed humus, decaying wood, and mounds of mineral soil upturned by windthrown trees. Any disturbance that removes the overstory produces new microhabitats (80). Under these circumstances, germination and initial establishment are generally better on prepared mineral soil, and disturbed mineral soil and humus seedbeds because moisture conditions are more stable (27,35,41,73,94). However, initial survival of spruce on severe sites at high elevations in the Intermountain Region was higher on duff seedbeds than on mineral soil seedbeds (37). Spruce seedling establishment on burned seedbeds has been variable. Success is related to severity of burn, depth of ash, and amount of exposed mineral soil (29,80,91). Regardless of the seedbed, high initial mortality usually slows establishment of seedlings. Once established (at least 5 years old), the ability to survive is not increased by a mineral soil seedbed, but is favored by adequate soil moisture, cool temperature, and shade.

Engelmann spruce will germinate in all light intensities found in nature, but 40 to 60 percent of full shade is most favorable for seedling establishment at high elevations. Light intensity and solar radiation are high at elevations and latitudes where spruce grows in the central and southern Rocky Mountains, and seedlings do not establish readily in the open. Planted seedlings often develop a chlorotic appearance that has been attributed to solarization-a phenomenon by which light intensity inhibits photosynthesis and which ultimately results in death (82). Mortality can be reduced by shading seedlings. At low elevations and high latitudes in the northern Rocky Mountains, spruce can become established and survive in the open (17). Spruce can establish and survive better in low light intensities than its common, intolerant associates such as lodgepole pine, Rocky Mountain Douglas-fir, and aspen, but at extremely low light intensities it cannot compete favorably with such shade-enduring associates as the true firs and hemlocks (20).

Engelmann spruce is restricted to cold, humid habitats because of its low tolerance to high temperature and drought (25,45). However, solar radiation at high elevations heats soil surfaces [up to 66° C (150° F or more)] and increases water losses from both seedlings and soil by transpiration and evaporation (9,73,80).

Because of its slow initial root penetration and extreme sensitivity to heat in the succulent stage, drought and heat girdling kill many first-year spruce seedlings. Drought losses can continue to be significant during the first 5 years of seedling development, especially during prolonged summer dry periods (9,34,73).

Tree seedlings in the succulent stage are particularly susceptible to stem-girdling. The cortex is killed by a temperature of 54° C (130° F), but prolonged exposures to somewhat lower temperatures may also be lethal. On the Fraser Experimental Forest, heat-girdling caused much early seedling mortality on unshaded seedbeds (9,73). Soil-surface temperature exceeded 65° C (150° F) in the open on a north aspect and 71° C (160° F) on a south aspect at 3200 m (10,500 ft) elevation in June. Maximum air temperature during this period did not exceed 260 C (780 F). In western Montana, at low elevations, soil surface temperatures exceeded 71° C (160° F) on gentle north slopes several times during one summer (80). Early shade protection increased survival of newly germinated spruce seedlings; 30 to 50 percent of the seedlings were lost to heat-girdling on unshaded plots, compared to 10 percent on shaded plots. In southwestern Alberta, when newly germinated spruce seedlings were deprived of water, nearly three-fourths of the mortality on four different unshaded seedbed types was caused by heat-girdling (34). Surface temperatures as low as 45° C (113° F) caused heat girdling, but losses were not high until soil surface temperatures were above 50° C (122° F). Shading reduced heat-girdling on all seedbed types. Soil surface temperatures in excess of lethal levels for spruce seedlings, especially on burned seedbeds, have been reported in British Columbia (94).

Air and soil temperatures (below the surface) are not usually directly responsible for seedling mortality, but they affect growth. In a growth chamber study of Engelmann spruce seedlings under 30 different combinations of day and night temperatures, the greatest height and root growth, and top and root dry matter production was with a diurnal variation of 19° C (66° F) (air and soil) day temperatures and 23° C (73° F) (air and soil) night temperatures (45). Shepperd (92), using the same night temperature regime, raised the day soil temperature to 23° C (72° F) and significantly increased root growth.

Frost can occur any month of the growing season where spruce grows. It is most likely to occur in depressions and cleared openings because of cold air drainage and radiation cooling. Newly germinated spruce seedlings are most susceptible to early fall frosts. In a greenhouse and laboratory study, new seedlings did not survive temperatures as low as -9.5° C (15° F) until about 10 weeks old (71). Terminal bud formation began at 8 weeks; buds were set and needles were mature at 10 to 12 weeks after germination.

After the first year, seedlings are most susceptible to frost early in the growing season when tissues are succulent. Shoots are killed or injured by mechanical damage resulting from tissue freezing and thawing. Frost damage has been recorded in most years in Colorado (81). In light frost years, damage was minor, but heavy frosts either damaged or killed all new shoots of open-grown seedlings.

In early fall, the combination of warm daytime temperatures, nighttime temperatures below freezing, and saturated soil unprotected by snow are conducive to frost-heaving. On the Fraser Experimental Forest, Colorado, these conditions generally occurred about 1 out of 2 years (9,73). Frost-heaving has been one of the principal causes of first-year seedling mortality on scarified seedbeds on north aspects (9). Furthermore, seedlings continue to frost-heave after four growing seasons. Shading has reduced losses by reducing radiation cooling.

The moisture condition of the seedbed during the growing season largely determines first-year seedling survival. On some sites in the central Rocky Mountains, summer drought causes great first-year mortality, especially in years when precipitation is low or irregular. On the Fraser Experimental Forest in the central Rocky Mountains, drought and desiccation caused more than half the first-year seedling mortality on south aspects, and nearly two-thirds of the total after 5 years. On north aspects during the same period, drought accounted for about 40 percent of first-year seedling mortality, and more than half the mortality at the end of 5 years (9).

In the northern Rocky Mountains, late spring and early summer drought is a serious threat most years to first-year seedlings. In western Montana, all seedlings on one area were killed by drought in a 2-week period in late summer when their rate of root penetration could not keep pace with soil drying during a prolonged dry period (80). Late spring and early summer drought is also a serious cause of first-year seedling mortality in the southern Rockies. Drought losses can continue to be significant throughout the Rocky Mountains during the first 5 years of seedling development, especially during prolonged summer dry periods (9,73).

The moisture provided by precipitation during the growing season is particularly critical to seedling survival during the first year. A greenhouse study of the effects of amount and distribution of moisture on seedling survival (simulating common summer precipitation patterns in north-central Colorado) showed that under favorable seedbed and environmental conditions: (1) at least 2.5 cm. (1 inch) of well distributed precipitation is needed monthly before seedlings will survive drought; (2) with this precipitation pattern, more than 3.75 cm (1.5 in) of monthly rainfall is not likely to increase seedling survival; but (3) few seedlings will survive drought with less than 5 cm (2 in) of rainfall monthly when precipitation comes in only one or two storms (18).

Summer precipitation may not always benefit seedling survival and establishment. Summer storms in the Rocky Mountains may be so intense that much of the moisture runs off, especially from bare soil. Moreover, soil movement on unprotected seedbeds buries some seedlings and uncovers others (80).

Understory vegetation can be either a benefit or serious constraint to spruce seedling establishment (2,35,83). Spruce seedlings become established more readily on sites protected by willows (Salix spp.), shrubby cinquefoil (Potentilla fruiticosa), fireweed, and dwarf whortleberry than in the open. Because these plants compete less aggressively for available soil moisture than those listed below, the net effect of their shade is beneficial to seedling survival. In contrast, mortality occurs when spruce seedlings start near clumps of grass or sedges or scattered herbaceous plants such as mountain bluebells, currants (Ribes spp.), and Oregongrape that compete severely for moisture and smother seedlings with cured vegetation when compacted by snow cover (83).

The only significant biotic factor affecting spruce regeneration on a long-term study on the Fraser Experimental Forest was birds. About 15 percent to 20 percent of the total mortality resulted from the clipping of cotyledons on newly germinated seedlings by grey-headed juncos (Junco caniceps) (9,73,75).

Damping-off, needlecast, snowmold, insects, rodents, and trampling and browsing by large animals also kill spruce seedlings, but losses are no greater than for any other species (20).

The number of seeds required to produce a first-year seedling and an established seedling (5 years old) and the number of first-year seedlings that produce an established seedling vary greatly, depending upon seed production, distance from source, seedbed, and other environmental conditions. In one study in clearcut openings in Colorado during the period 1961-1975, covering a wide variety of conditions, on the average 665 sound seeds (range 602,066) were required to produce one first-year seedling, and 6,800 (range 926-20,809) to produce a seedling 4 or more years old. An average of 21 first-year seedlings was necessary to produce a single seedling 4 or more years old, although as few as 4 and as many as 24 first-year seedlings survived under different conditions (74).

Aspect and cultural treatments can also affect establishment of Engelmann spruce. In another Colorado study (covering the period 1969-1982), an average of 18 sound seeds was required to produce a single first-year seedling on shaded, mineral soil seedbeds on a north aspect; and 32 sound seeds were needed to produce a 5-year-old seedling. In contrast, 156 seeds were required to produce a first-year seedling on shaded, mineral soil seedbeds on a south aspect, and 341 seeds to produce a 5-year-old seedling (8,9). Shearer (91), studying the effects of prescribed burning and wildfire after clearcutting on regeneration in the western larch type in Montana, also found that natural and planted spruce survived better on the north aspect than on the south aspect.

Environmental conditions favorable and unfavorable to the establishment of Engelmann spruce natural regeneration are summarized in Figure 1.

Favorable Unfavorable Seed crop

More than 600,000 seeds pe hactare (242,800/acre Less than 60,000 seeds per hectare (24,300/acre)
Aspect North South Temperatures




Ambient air more than 0° C (32° F) night and less than 25° C (77° F) day; maximum surface less than 30° C (86° F)
Ambient air less than 0° C (32° F) night and more than 25° C (77° F) day; maximum surface greater than 30° C (86° F) Precipitation

More than 10 mm (0.4 in) per week Less than 10 mm (0.4 in) per week Soil
Light-textured, sandy-loam Heavy-textured, Clay-loam Seedbed




50 percent exposed mineral soil, 40 to 60 percent dead shade, Duff and litter less than 5 cm (2 in), Light vegetative cover 10 percent or less exposed mineral soil, 10 percent or less dead shade, Duff and litter more than 5 cm (2 in), Heavy vegetative cover Survival







Seedlings more than 12 weeks old by mid-September, Low population of birds and rodents that eat seeds and seedlings, Protection from trampling, Snow cover when frost-heaving conditions exist Seedlings less than 12 weeks old by mid-September, High population of birds and rodents that eat seeds and seedlings, No protection from trampling, No snow cover when frost-heaving conditions exist

Information on soils where Engelmann spruce grows is limited. In the Pacific Coast region, soil parent materials are mixed and varied. Country bedrock is composed of a variety of sedimentary, igneous, and metamorphic rock. The most common of the great soil groups are Cryorthods (Podzolic soils), Haplumbrepts (western Brown forest soils), Haplorthods (Brown Podzolic soils), Hapludalfs (Gray-Brown Podzolic soils), and Haploxerults and Haplohumults (Reddish-Brown Lateritic soils); these great soil groups developed from deep glacial and lacustrine deposits, deep residual material weathered in place from country rock, and volcanic lava and ash. Xerochrepts (Regosolic soils), developed from shallow residual material, are also widespread. Xeropsamments (Regosolic soils) and Haplaquolls (Humic Gley soils) are the principal soils derived from alluvium. On the east side of the Cascade crest, soils are largely Haploxeralfs (Non-Calcic Brown soils) and Haploxerolls (Chestnut soils) (39,103).

In the Rocky Mountain subalpine zone, soil materials vary according to the character of the bedrock from which they originated. Crystalline granite rock predominates, but conglomerates, shales, sandstones, basalts, and andesites commonly occur. Glacial deposits and stream alluvial fans are also common along valley bottoms. Of the great soils group, Cryorthods (Podzolic Soils) and Haplorthods (Brown Podzolic Soils) occur extensively on all aspects. Cryochrepts (Thick Cold Soils) occur extensively on the drier aspects. Aquods (Ground-water Podzolic Soils) are found in the poorly drained areas. Cryoboralfs (Gray-Wooded Soils) are found where timber stands are -less dense and parent material finer textured. Haploborolls (Brown Forest Soils) occur mostly in the lower subalpine zone along stream terraces and side slopes. Lithics (Lithosolic Soils) occur wherever bedrock is near the surface. Aquepts (Bog Soils) and Haplaquepts (Humic Gley Soils) occur extensively in poorly drained upper stream valleys (48,103).

Regardless of the parent materials, spruce grows best on moderately deep, well drained, loamy sands and silts, and silt and clay loam soils developed from a variety of volcanic and sedimentary rock. Good growth also is made on glacial and alluvial soils developed from a wide range of parent materials, where an accessible water table is more important than physical properties of the soil. It does not grow well on rocky glacial till, heavy clay surface soils, saturated soils, or on shallow, dry coarse-textured sands and gravels developed primarily from granitic and schistic rock or course sandstones and conglomerates (13,23).

Along the east slope of the Coast Range and interior valleys of southwestern British Columbia, Engelmann spruce grows at 762 to 1067 m (2,500 to 3,500 ft). Farther south in the Cascade Mountains of Washington and Oregon, it generally grows at 1219 to 1829 m (4,000 to 6,000 ft), but it may be found at 2438 m (8,000 ft) on sheltered slopes and at 610 m (2,000 ft) in cold pockets along streams and valley bottoms. In northern California, spruce grows at 1219 to 1524 m (4,000 to 5,000 ft) (16,98).

South of the Peace River Plateau in the Canadian Mountains of British Columbia and Alberta, Engelmann spruce grows at 762 to 1829 m (2,500 to 6,000 ft); in the Rocky Mountains of Idaho and Montana and in the adjacent mountains of eastern Washington and Oregon, at 610 to 2743 m (2,000 to 9,000 ft). But above 1829 to 2286 m (6,000 to 7,500 ft), it is a minor component of the stand, and below 1524 m (5,000 ft) it is confined to moist, low slopes and cold valley bottoms (20).

Engelmann spruce is found at 2743 to 3353 m (9,000 to 11,000 ft) in the Rocky Mountains of Utah, Wyoming, and Colorado, but it may extend as low as 2438 m (8,000 ft) along cold stream bottoms and to timberline at 3505 m (11,500 ft). In the Rocky Mountains of New Mexico and Arizona and on the plateaus of southern Utah, it grows at 2896 to 3353 m (9,500 to 11,000 ft), but it may grow as low as 2438 m (8,000 ft) and as high as 3658 m (12,000 ft) (13,20).

Engelmann spruce-subalpine fir forests occupy the greatest water yielding areas in the Rocky Mountains. They also provide timber, habitats for a wide variety of game and nongame wildlife, forage for livestock, and recreational opportunities and scenic beauty (5). However, these properties are indigenous to where spruce grows rather than to any special properties associated with the species.

The lumber of spruce is likely to contain many small knots. Consequently, it yields only small amounts of select grades of lumber, but a high proportion of the common grades (70). In the past, spruce was used principally for mine timbers, railroad ties, and poles. Today, much of the lumber is used in home construction where great strength is not required, and for prefabricated wood products. In recent years, rotary-cut spruce veneer has been used in plywood manufacture. Other uses of spruce include specialty items such as violins, pianos and aircraft parts (22,63).

The pulping properties of Engelmann spruce are excellent. Long fibers, light color, and absence of resins permit trees to be pulped readily by the sulfite, sulfate, or groundwood processes (22,101). The species has been used for pulp in the northern Rocky Mountains but not in the central or southern Rocky Mountains.

Engelmann spruce can reproduce by layering (47). It most often layers near timberline, where the species assumes a dwarfed or prostrate form. Layering can also occur when only a few trees survive fires or other catastrophes. Once these survivors have increased to the point where their numbers alter the microenvironment enough to improve germination and establishment, layering diminishes. In general, this form of reproduction is insignificant in the establishment and maintenance of closed forest stands (21,76).

Engelmann spruce is widely distributed in the western United States and two provinces in Canada (61). Its range extends from British Columbia and Alberta, Canada, south through all western states to New Mexico and Arizona.

In the Pacific Northwest, Engelmann spruce grows along the east slope of the Coast Range from west central British Columbia, south along the crest and east slope of the Cascades through Washington and Oregon to northern California (6,13,20). It is a minor component of these high-elevation forests.

Engelmann spruce is a major component of the high-elevation Rocky Mountain forests, growing in the Rocky Mountains of southwestern Alberta, south through the high mountains of eastern Washington and Oregon, Idaho, and western Montana to western and central Wyoming, and in the high mountains of southern Wyoming, Colorado, Utah, eastern Nevada, New Mexico, and northern Arizona (6,13,20).


- The native range of Engelmann spruce.

Pinaceae -- Pine family

Robert R. Alexander and Wayne D. Shepperd

Engelmann spruce is one of the seven species of spruce indigenous to the United States (62). Other common names are Columbian spruce, mountain spruce, white spruce, silver spruce, and pino real.

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, 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 pubescent, 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, 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.

Picea engelmannii, with the common names Engelmann spruce, white spruce, mountain spruce, and silver spruce, is a species of spruce native to western North America. It is mostly a high-elevation mountain tree but also appears in watered canyons.