Picea engelmannii

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.

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.

General: Pine Family (Pinaceae). These are native trees growing to 60 meters tall, the crown dense and narrowly conic or spire-like. Branches spreading horizontally to somewhat drooping, the lower often persistent (not strongly self-pruning); twigs not pendent, rather stout, yellow-brown. Bark usually reddish- to purplish-brown and thin scaly. Needles are evergreen, borne singly from all sides of the twig, 1.6-3 (-3.5) cm long, 4-angled, stiff and sharp-pointed, blue-green. Seed cones are violet to deep purple, ripening buff-brown, ellipsoid, pendent, mostly 3-6 cm long, the cone scales relatively small, papery, and flexible, remaining intact after cones fall from the tree. Ssp. mexicana differs from the typical ssp. in its lighter (gray) bark, narrower needles (1-1.2 mm wide) and its narrower and slightly larger cones (4.5-8 cm long) and longer cone scales (4-6 mm), although the measurements are overlapping. Named for physician and botanist George Engelmann.

Variation within the species: a primarily Mexican segment of Engelmann spruce is formally distinguished

Picea engelmannii ssp. engelmannii

Picea engelmannii ssp. mexicana (Martínez) P.

Schmidt

These populations also have been recognized as P. mexicana Martínez, P. engelmannii var. mexicana (Martínez) Taylor & Patterson (illegitimate name), and P. engelmannii var. mexicana (Martínez) Silba.

Variation in seed dormancy and hardiness has been documented over the broad geographic range of the typical subspecies, but no other varieties are generally recognized. In the northern part of its range, Engelmann spruce hybridizes freely and intergrades with white spruce (P. glauca). In the Chilliwack River Valley of British Columbia, it apparently hybridizes with Sitka spruce (P. sitchensis).

Alberta and British Columbia southward through Nevada, Utah, and Colorado, into Arizona and New Mexico; the southernmost populations in Arizona (Chiricahua Mountains) and New Mexico (Sierra Blanca) are ssp. mexicana, which otherwise extends southward into both the eastern and western sierras of northern Mexico. For current distribution, please consult the Plant Profile page for this species on the PLANTS Web site.

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 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

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

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.

Picea engelmannii Parry ex Engelm.:
United States (North America)
Canada (North America)
Mexico (Mesoamerica)

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

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

More info for the terms: density, monoecious, natural, 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].

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.

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

More info for the term: association

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 for the terms: climax, codominant, series

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 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 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 association with the following plant community types (as classified by Küchler 1964):

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

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 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).

Systems

• Terrestrial

Adaptation: In montane and subalpine forests, occurring as krummholz at timberline, sometimes growing down into the fir-aspen belt on moist, north facing slopes and in canyons; at 1000-3000 meters elevation. Engelmann spruce and subalpine firs form one of the most common forest associations in the Rocky Mountains.

Planting: Open-grown trees of Engelmann spruce begin cone production at 15-40 years of age but the best seed production is between 150 and 250 years. Good seed crops are generally borne every 2-5 years

Although Engelmann spruce will germinate in all light intensities found in nature, seedlings do not establish readily in the open – 40 to 60 percent of full shade is most favorable for seedling establishment at high elevations. Germination and establishment in undisturbed forest occur on duff, litter, partially decomposed humus, decaying wood, and mounds of mineral soil upturned by wind thrown trees. 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 throughout the Rocky Mountains during the first 5 years of seedling development, especially during prolonged summer dry periods. Once established (at least 5 years old), the ability to survive is favored by adequate soil moisture, cool temperature, and shade. The strong shade tolerance of Engelmann spruce allows it to occur both as a persistent long-lived seral species and as a major climax species.

Engelmann spruce will grow steadily for 300 years, long after the growth of most associated tree species slows down. Dominant spruces are often 250-450 years old and trees 500-600 years old are not uncommon. Trees reaching 760-850 years are known.

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

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 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).

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 for the terms: cover, duff, 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.

More info for the terms: 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 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: secondary colonizer

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: 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 on this topic.

More info for the terms: climax, duff, series, severity, 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]

More info for the terms: duff, layering, litter, natural

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.

More info for the terms: phanerophyte, therophyte

Undisturbed State: Phanerophyte (megaphanerophyte)
Burned or Clipped State: Therophyte

More info for the term: tree

Tree

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).

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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

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).

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

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).

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).

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.

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).

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

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 5
Specimens with Barcodes: 6
Species With Barcodes: 1

Year Assessed

• Needs updating

Assessor/s

Reviewer/s

Canada

Rounded National Status Rank: N5 - Secure

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: G5 - Secure

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

More info for the terms: natural, 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].

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

The shallow root system of Engelmann spruce makes it susceptible to windthrow, particularly after cutting opens a stand. Downed wood from windthrow also makes a site vulnerable to attack from the spruce beetle, which has periodically caused severe damage. The western spruce budworm is another potentially damaging insect that attacks both Engelmann spruce and subalpine fir.

Complete removal of a spruce-fir 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. 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.

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.

The wood of Engelmann spruce is light-colored, relatively soft, low in resin, and sometimes contains many knots and is more valuable for pulp than for high-grade lumber. It has been used for home construction, pre-fabricated wood products, and plywood manufacture. Less commonly it is used for specialty items such as food containers, and sounding boards for violins, pianos, and guitars. Engelmann spruce is widely used for Christmas trees. Spruce beer was sometimes made from its needles and twigs and taken to prevent scurvy. The Engelmann spruce–subalpine fir forest association occupies the greatest water-yielding areas in the Rocky Mountains and the natural adaptations of these trees are important in maintaining stable vegetation.