BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Picea pungens | Blue Spruce 



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

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


RAUNKIAER LIFE FORM : 
   Phanerophyte


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

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

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

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


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

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

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

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

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


SUCCESSIONAL STATUS : 
Facultative Seral Species

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

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

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


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

Related categories for Species: Picea pungens | Blue Spruce