BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Picea engelmannii | Engelmann Spruce 



GENERAL BOTANICAL CHARACTERISTICS : 
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].


RAUNKIAER LIFE FORM : 
   Undisturbed State:  Phanerophyte (megaphanerophyte)
   Burned or Clipped State:  Therophyte


REGENERATION PROCESSES : 
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].


SITE CHARACTERISTICS : 
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)


SUCCESSIONAL STATUS : 
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]


SEASONAL DEVELOPMENT : 
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

Related categories for Species: Picea engelmannii | Engelmann Spruce