Associated Forest Cover
(
الإنجليزية
)
المقدمة من Silvics of North America
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).
- ترخيص
- cc-by-nc
- حقوق النشر
- USDA, Forest Service
Climate
(
الإنجليزية
)
المقدمة من Silvics of North America
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).
- ترخيص
- cc-by-nc
- حقوق النشر
- USDA, Forest Service
Damaging Agents
(
الإنجليزية
)
المقدمة من Silvics of North America
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).
- ترخيص
- cc-by-nc
- حقوق النشر
- USDA, Forest Service
Flowering and Fruiting
(
الإنجليزية
)
المقدمة من Silvics of North America
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).
- ترخيص
- cc-by-nc
- حقوق النشر
- USDA, Forest Service
Genetics
(
الإنجليزية
)
المقدمة من Silvics of North America
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).
- ترخيص
- cc-by-nc
- حقوق النشر
- USDA, Forest Service
Growth and Yield
(
الإنجليزية
)
المقدمة من Silvics of North America
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.
- ترخيص
- cc-by-nc
- حقوق النشر
- USDA, Forest Service
Reaction to Competition
(
الإنجليزية
)
المقدمة من Silvics of North America
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).
- ترخيص
- cc-by-nc
- حقوق النشر
- USDA, Forest Service
Rooting Habit
(
الإنجليزية
)
المقدمة من Silvics of North America
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).
- ترخيص
- cc-by-nc
- حقوق النشر
- USDA, Forest Service
Seed Production and Dissemination
(
الإنجليزية
)
المقدمة من Silvics of North America
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).
- ترخيص
- cc-by-nc
- حقوق النشر
- USDA, Forest Service
Seedling Development
(
الإنجليزية
)
المقدمة من Silvics of North America
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
- ترخيص
- cc-by-nc
- حقوق النشر
- USDA, Forest Service
Soils and Topography
(
الإنجليزية
)
المقدمة من Silvics of North America
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).
- ترخيص
- cc-by-nc
- حقوق النشر
- USDA, Forest Service
Special Uses
(
الإنجليزية
)
المقدمة من Silvics of North America
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.
- ترخيص
- cc-by-nc
- حقوق النشر
- USDA, Forest Service
Vegetative Reproduction
(
الإنجليزية
)
المقدمة من Silvics of North America
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).
- ترخيص
- cc-by-nc
- حقوق النشر
- USDA, Forest Service
Distribution
(
الإنجليزية
)
المقدمة من Silvics of North America
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.
- ترخيص
- cc-by-nc
- حقوق النشر
- USDA, Forest Service
Brief Summary
(
الإنجليزية
)
المقدمة من Silvics of North America
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.
- ترخيص
- cc-by-nc
- حقوق النشر
- USDA, Forest Service