FIRE EFFECTS
SPECIES: Abies lasiocarpa | Subalpine Fir 



IMMEDIATE FIRE EFFECT ON PLANT : 
Subalpine fir is one of the least fire-resistant western conifers.  It
is very susceptible to fire because it has (1) thin bark that provides
little insulation for the cambium, (2) 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) highly flammable
foliage, and (7) moderate to heavy lichen growth [37,111].

Subalpine fir forests are normally subject to highly destructive crown
fires that occur at 100-year or longer intervals.  Such fires typically
kill all subalpine fir trees.  Subalpine fir 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 [34].


DISCUSSION AND QUALIFICATION OF FIRE EFFECT : 
NO-ENTRY


PLANT RESPONSE TO FIRE : 
Following fire, subalpine fir reestablishes via seeds dispersed by wind
from trees surviving in protected pockets or from trees adjacent to
burned areas.  Subalpine fir readily establishes on burned mineral soil
seedbeds [107].  Ash does not affect germination, but if it is deep, it
can prevent a seedling's roots from reaching mineral soil [85].
Although seedling establishment is often favored by shade, it will
establish in full sunlight following fire [87].

The rate of establishment is quite variable, and depends on the
proximity of the seed source (because the heavy seeds are dispersed over
short distances) and seed production during the year of the fire and
immediate postfire years.  In general, subalpine fir seedling
establishment is very slow in areas suffering large, continuous crown
fires but is relatively rapid on small burned-over areas where a seed
source is nearby [90,124,128].  Three years after a late August wildfire
in northern Colorado, in a dense, overmature stand composed of Engelmann
spruce, subalpine fir, and lodgepole pine, subalpine fir had established
15,200 seedlings per acre (37,500/ha) on small burns that were less than
one-tenth of an acre in size.  But on areas within the middle of the
main burn, subalpine fir had established only 12 seedling per acre
(30/ha) 3 years after the fire [16].  In Colorado, Peet [90] found a
75-year-old burn that had few conifer seedlings even though an
old-growth subalpine fir-Engelmann spruce stand was 218 yards (200 m)
away.

Reinvasion into large burns is slow because much of the seed source is
destroyed.  However, sometimes sporadic survivors provide a limited seed
source so that a small number of seedlings establish quickly following
fire.  When this occurs, large quantities of seeds are dispersed several
decades later as the early invading seedlings mature and reach cone
bearing age [128].

On areas where subalpine fir is abundant and lodgepole pine scarce
before burning, subalpine fir establishes quickly following fire if
sufficient numbers of seed trees survive or are near the burn.  However,
if lodgepole pine is present prior to burning, it usually seeds in
aggressively and assumes a dominant role because it quickly overtops any
fir seeding in at the same time [34].  Subalpine fir can be suppressed
for several decades in seral lodgepole stands which develop following
fire; one-hundred-year-old individuals may be only 3 feet (0.9 m) tall
[90].  It may take 50 to 150 years after a fire for substantial
subalpine fir establishment under dense lodgepole pine stands
[18,109,128].

In the Olympic Mountains, tree seedling establishment following fires in
closed mountain hemlock-subalpine fir forests was higher during wet
growing seasons than during dry growing seasons.  Establishment rates
were higher near the edge of a fire or near survivors than in areas
removed from a seed source [4].  On many burned areas, subalpine fir did
not establish seedlings for several years because of poor seed crops.
On some burns there was a lag time of 40 to 50 years after fire before
there was substantial seedling establishment.  This was a result of
early invading trees maturing and dispersing seeds [4].

High elevation subalpine fir stands that have burned often remain open
for several decades or more [18,31].  The harsh environment near
treeline makes it difficult for tree seedlings to establish and survive
[18].  Grasses and sedges may form a mat in subalpine meadows which
prevents tree seeds from reaching mineral soil [109].


DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : 
NO-ENTRY


FIRE MANAGEMENT CONSIDERATIONS : 
Subalpine fir is very fire sensitive and is often killed even by surface
fires.  Following timber harvest, on sites where subalpine fir is not a
preferred species, light surface fires may be used to kill subalpine
fir and promote the establishment of other conifers [93].  

Fuels remain moist in many high elevation subalpine fir habitat types
during most of the year, leaving only a short time period during certain
years when prescribed burning can take place [63,91].

Subalpine fir seeds germinate poorly in soils under burned slash piles
[130] but readily germinate on mineral soil seedbeds prepared by
broadcast burning [16,107].

Related categories for Species: Abies lasiocarpa | Subalpine Fir