BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Abies lasiocarpa | Subalpine Fir 



GENERAL BOTANICAL CHARACTERISTICS : 
Subalpine fir is a native, coniferous, evergreen tree.  It is the
smallest of the eight species of fir native to the western United
States.  Five growth forms, each apparently an adaptation to a
particular environment, are described below [9,54]:

1.  The typical form is found throughout much of the subalpine zone.
These trees have an extremely narrow and dense crown with short
branches.  Trees growing in openings retain their lower branches, which
often droop and extend down to the ground.  Trees growing in the
overstory may be clear of lower branches for 20 to 30 percent of the
tree's height.

2.  A somewhat broad-crowned, bullet-shaped tree is more typical of
older specimens and drier climates.  

3.  A mature tree with a layered apron is occasionally found in some
areas. 

4.  A flag form tree often occurs at timberline.  These individuals are
characterized by an upright trunk that extends above a krummholzlike
mat.  Branches on the trunk generally grow only along the leeward side
of the trunk, giving the plant a flaglike appearance.

5.  The krummholz form is typical of alpine areas above timberline.  In
these areas, because of cold temperatures and severe winds, subalpine
fir grows in dwarfed, shrubby mats along the ground, and is often much
broader than it is tall.

The typical form often grows to heights of 60 to 100 feet (18-30 m), and
trunk diameters reach 18 to 24 inches (46-61 cm) [39].  Trees up to 130
feet (40 m) tall and 30 inches (76 cm) in diameter have been found but
are rare [39].  Subalpine fir grows very slowly; 150- to 200-year-old
trees are usually only 10 to 20 inches (25-50 cm) in diameter [39].
Trees seldom live more than 250 years because they are very susceptible
to heart rots [9].

Needles are blunt tipped, flattened, and 1 to 1.2 inches (2.5-3 cm) long
[25,57].  Bark on young trees is thin, gray, and smooth, with numerous
resin vesicles; on older trees it is shallowly fissured and scaly [9].
Corkbark fir is generally recognized by its creamy-white, thick, corky
bark [25].  The root system generally is shallow but under favorable
conditions may develop relatively deep laterals [9].

Subalpine fir is monoecious.  Single or small bunches of erect female
cones occur in the upper part of the crown on the upper side of young
branches.  Dense clusters of the smaller male cones occur lower on the
crown on the underside of 1-year-old twigs.  Subalpine fir seeds are
0.23 to 0.28 inch (6-7 mm) long and have broad wings about 0.4 inch (1
cm) long [25,121].  Corkbark fir seeds are about 70 percent larger than
subalpine fir seeds [39].


RAUNKIAER LIFE FORM : 
   Undisturbed State: Phanerophyte (mesophanerophyte)
   Undisturbed State: Phanerophyte (microphanerophyte)
   Undisturbed State: Phanerophyte (nanophanerophyte) Krummholz form 
   Burned or Clipped State: Therophyte


REGENERATION PROCESSES : 
Cone and seed production:  Subalpine fir can begin producing cones when
20 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 [11].  Corkbark fir generally does not produce cones
until about 50 years old [39].  Nearly all cones are produced on the
uppermost part of the crown.  Maximum seed production is by dominant
trees between 150 and 200 years old [39].  Yearly seed production is
very erratic; good seed crops are produced every 3 to 5 years, with
light crops or crop failures in between [39,40,54,86].  Corkbark fir is
also a poor seed producer, having more crop failure years than good seed
crop years [9].  Subalpine fir averages 34,800 seeds per pound
(76,700/kg), while corkbark fir seeds average 22,300 per pound
(49,150/kg) [41].

Seed predation:  Insect pests reduce seed yields by feeding on cones and
seeds; however, the magnitude of loss is variable [11].  Red squirrels
cut and cache large quantities of subalpine fir cones [9].  After
dispersal, numerous small rodents and birds consume seeds from the
ground.

Dispersal:  Mature subalpine and corkbark fir seeds have a large wing
and are dispersed primarily by wind in the fall as cones disintegrate on
the tree.  Seeds travel primarily in the direction of prevailing winds,
but upslope drafts can influence dispersal at low and middle elevations
[9].  Studies in Colorado showed that about one-half of subalpine fir
seeds dispersed into clearcuts fell within 100 feet (30 m) of the
clearcut's windward edge, while the remainder fell within 260 feet (80
m) of the edge [86].  Some seeds are also dispersed by red squirrels
which cut and cache cones before they disintegrate; seeds commonly
germinate from these middens, forming thickets [71].

Germination and viability:  Seeds overwinter under or in snow.  This
cold, moist stratification is required for germination [41].
Germination begins in the spring a few days after snowmelt and is
usually completed within a few weeks [9,106].  Percent germination is
low due to unsound seed; about 31 to 38 percent for subalpine fir and 26
to 33 percent for corkbark fir [39,41].  Under natural conditions seeds
remain viable for 1 year [41].  Stratification procedures for stored
seeds have been described in detail [41,74].

Seedling establishment and survival:  Seedlings establish best on
mineral soil seedbeds but will also establish on other surfaces
including litter, duff, and decaying wood [11].  Because Engelmann
spruce requires a mineral soil seedbed, subalpine fir seedlings usually
outnumber spruce seedlings in the understory of spruce-fir stands.
Thus, even though it is short-lived, many ecologists consider subalpine
fir better able to regenerate under climax conditions than Engelmann
spruce.  Subalpine fir is very shade tolerant and easily establishes
under a closed canopy.  Throughout the Rocky Mountains subalpine fir is
reproducing abundantly under conditions of dense shade and is often
abundant as seedlings and saplings in spruce-fir forests, even where
Engelmann spruce dominates the overstory [11,67].

At higher elevations, seedling survival is sometimes greater on duff
seedbeds because the duff helps protect seedlings from high-intensity
summer rain storms and frost heaving [35].  At lower elevations,
seedling densities are often greater on mineral soils [35].  In a
spruce-fir forest in southeastern Wyoming, Knapp and Smith [67] found
that 42 percent of subalpine fir seedlings were on litter deeper than 1
inch (2.5 cm), compared with only 5 percent of Engelmann spruce
seedlings.  Subalpine fir is able to establish in duff because of its
rapid root growth.  Comparing seedlings grown in a greenhouse, subalpine
fir's taproot length (29 mm) 2 weeks after germination was over 200
percent greater than the taproot length of Engelmann spruce (9.4 mm)
[67].

Growth:  Subalpine fir seedlings grow very slowly.  One-year-old
seedlings are frequently less than 1 inch (2.5 cm) tall [11].  One study
found 15-year-old seedlings averaged only 11 inches (28 cm) in height on
burned-over slopes, 10 inches (25 cm) on cut-over dry slopes, and 6
inches (15 cm) on cut-over wet flats [11].  Under favorable conditions
trees reach a height of 4 to 5 feet (1.2-1.5 m) in 20 to 40 years [11].
Under a closed canopy, trees 4 to 6 feet tall (1.2-1.8 m) are often 35
to 50 years old.

Vegetative reproduction:  Near timberline subalpine fir frequently
reproduces by layering, probably as a result of heavy snow, wind, and
cold temperatures which restrict growth away from the ground.  Layering
often results in clusters of sublapine fir growing near timberline [13].
Under closed forest canopy, reproduction by layering is negligible.


SITE CHARACTERISTICS : 
Subalpine fir is a middle to upper elevation mountain conifer.  It
generally occupies sites with a short growing season caused by cold
winters, cool summers, frequent summer frosts, and heavy snowpack.  It
forms extensive forests between warm and dry lower elevation forests of
Douglas-fir, white fir (Abies concolor), grand fir, lodgepole pine, or
blue spruce (Picea pungens) and higher elevation alpine tundra
[23,29,112,125].  At its lower elevational limits, subalpine fir is
often restricted to streambottoms, ravines, frosty basins, or north
exposures.  It increasingly occupies westerly and easterly aspects with
increasing elevation and may occupy all aspects at upper timberline
[23,91].

Stand condition and associated conifers:  Throughout its range,
subalpine fir is most commonly associated with Engelmann spruce.  These
two 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, with subalpine fir
dominating the understory [9].  Within spruce-fir forests of this
region, Engelmann spruce tends to be more important at higher elevations
and on wetter sites, while subalpine fir is more abundant on drier lower
elevation sites [9].  In the northern Rocky Mountains, subalpine fir
typically dominates climax stands, but Englemann spruce becomes
increasingly important on moist, cool sites [23,91].  Other associates
which vary by latitude and elevation are listed below [39]:

Location              Elevation   Associates

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

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.

Elevation:  Alexander and others [11] described the following
elevational ranges for subalpine fir:

Coast Range of southeastern Alaska - subalpine fir is found from sea
level to 3,500 feet (0-1,067 m).  

Coast Range and interior plateaus of Yukon Territory and British
Columbia - subalpine fir is found from 2,000 to 5,000 feet (610-1,524
m). 

Olympic and Cascade Mountains of Washington and Oregon - subalpine fir
is generally found from 4,000 to 6,000 feet (1,219-1,829 m), but may be
found as low as 2,000 feet (610 m) along cold streambottoms and on lava
flows, and as high as 8,000 feet (2,438 m) on sheltered slopes. 

Rocky Mountains of British Columbia and Alberta south of the Peace River
- subalpine fir is found from 3,000 to 7,000 feet (914-2,134 m) but is
more abundant above 5,000 feet (1,524 m).

Rocky Mountains of Montana and Idaho and associated ranges of eastern
Oregon and Washington - subalpine fir grows from 2,000 to 11,000 feet
(610-3,353 m) but is most common at 5,000 to 9,000 feet (1,524-2,743 m).

Rocky Mountains of Wyoming, Utah, and Colorado - subalpine fir occurs
from 8,000 to 11,500 feet (2,438-3,506 m) but is most common at 9,000 to
11,000 feet (2,743-3,353 m).

Rocky Mountains of New Mexico and Arizona - subalpine fir occurs from
8,000 to 12,000 feet (2,438-3,658 m) but is usually found on north
slopes from 9,500 to 11,000 feet (2,896-3,353 m).


SUCCESSIONAL STATUS : 
In the Rocky Mountains, subalpine fir is a shade-tolerant climax species
favored by long fire-free intervals.  Its seedlings outcompete spruces,
lodgepole pine, and Douglas-fir when light intensities are less than 50
percent of full sunlignt, but cannot compete with these conifers under
brighter light [11].  In Montana and Idaho and in the mountains of
eastern Washington and eastern Oregon, subalpine fir often forms pure
stands at climax, but it may also mix with Engelmann spruce, which,
although considered to be seral to subalpine fir, outlives it and
persists to climax.  In the Rocky Mountains north and south of Montana
and Idaho, Engelmann spruce and subalpine fir may codominate at climax
[11].

Throughout much of the Cascade Mountains subalpine fir grows as a
shade-intolerant, seral species and is gradually replaced by more
shade-tolerant associates such as Pacific silver fir, grand fir, and
mountain hemlock [43].  It often invades recently disturbed areas with
lodgepole pine.  It also pioneers harsh sites on raw geologically young
surfaces such as lava flows and talus slopes and on climatically harsh
sites near timberline [43].

In areas where subalpine fir is a climax dominant, succession following
disturbance varies depending upon the severity and type of disturbance,
elevation, and the availability of conifer seeds.  Subalpine fir may
establish immediately following disturbances if mature trees survive to
provide seeds and seral species such as lodgepole pine and aspen are
scarce.  Near treeline, it may take 100 years or more for subalpine fir
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 [18,109].  Aspen and lodgepole
pine are the most common seral species.  They often form pure stands and
completely dominate low and middle elevation stands within the subalpine
fir zone following large fires [5,68].  These species grow rapidly and
quickly overtop any subalpine fir seedlings that may establish at the
same time.  Aspen stands can sometimes persist for decades or even
centuries when conifer seed trees are eliminated [29].  When lodgepole
pine establishes immediately following stand-destroying fires, it often
forms even-aged dense stands that dominate for 100 to 300 years.
Because it is very shade tolerant, subalpine fir eventually establishes
under the pine canopy, usually within 100 years, and attains dominance
as the pine stand begins to break up [90,98].

In many of the warmer and lower elevation subalpine fir habitat types,
subalpine fir has not achieved climax dominance because of repeated
fires which favor shade-intolerant seral conifers.  Many of these
habitat types are in midsuccessional stages.  Lodgepole pine, western
larch, western white pine, or Douglas-fir dominate the overstory, but
subalpine fir seedlings and saplings occur in the understory [93,113].


SEASONAL DEVELOPMENT : 
Subalpine fir requires 2 years to complete its reproductive cycle [115].
Cones are initiated in the spring of the first year as microscopic
primordia within vegetative buds.  Bud differentiation occurs in
midsummer, and separate seed-cone and pollen-cone buds develop until
each becomes dormant in the fall [115].  During the spring of the second
year, cone buds resume growth and conelets are recognizable in the early
spring.  During the second year, reproduction phenology generally
proceeds as follows:

Phenological event  Location      Timing of event           Reference

flowering           sw MT, nw WY   mid-June - early July     
cones full size         "               late August          
seeds dispersed         "         early Sept - early Oct     [41,101]

flowering           nw MT, n ID   mid-June - early July      
cones full size         "         late July - early Aug      
seeds dispersed         "               mid-Sept             [41,101]

flowering               OR         late May - early July     
seed dispersal          "             early Oct               [41]

male bud burst      Linn, OR         early to mid-May        
female bud burst        "            mid to late May         
pollen shed             "                 June               
seed dispersal begins   "              early October          [45]

flowering        AZ, San Fran.Peaks     late June            
cone ripening           "           mid-Sept - early Oct     
seed dispersal          "           late Sept - early Oct     [41]

Related categories for Species: Abies lasiocarpa | Subalpine Fir