FIRE ECOLOGY
SPECIES: Abies lasiocarpa | Subalpine Fir 



FIRE ECOLOGY OR ADAPTATIONS : 
Plant adaptations to fire:  Subalpine fir is very fire sensitive and
generally suffers high mortality even from low intensity fires.  It
relies on wind-dispersed seeds which readily germinate on fire-prepared
seedbeds to colonize burned areas.  The occasional mature tree which
survives fire, those escaping fire in small, unburned pockets, and trees
adjacent to burned areas provide seeds to colonize burned sites.  In
subalpine habitats, scattered subalpine fir trees often escape fire
because of discontinuous fuels, broken and rocky terrain, and the moist
and cool environment [78,87,91].

Fire regime:  Subalpine fir habitat types vary from cold and wet at
higher elevations to warm and moist or cool and dry at lower elevations.
This environmental gradient influences the mean fire return interval
(MFRI).  Relatively dry lower elevation subalpine fir habitat types have
more frequent and less intense fires than moist middle and upper
elevation subalpine fir habitat types [12,91].  Such forests in the
Bitterroot National Forest in Montana have a MFRI of 17 to 28 years
[14].  Fires at this frequency kill subalpine fir and keep these forests
dominated by seral conifers such as lodgepole pine, Douglas-fir, or
western larch.  Moist, middle and upper elevation subalpine fir habitat
types, however, generally experience high intensity stand-replacing
fires at intervals of 100 years or more.  Mean fire return intervals for
middle and upper elevation subalpine fir habitat types in several areas
are presented below:

Location                  Community dominants           MFRI    Reference
                                                       (years)
Kananaskis Park, AB      subalpine fir, spruce,          90       [12]
                         lodgepole pine         
northern Cascades, WA    subalpine fir                 154        [2]
northern Cascades, WA    subalpine fir-lodgepole pine  109        [2]
Olympic NP, WA           subalpine fir                 150        [116]
Yellowstone NP, WY       subalpine fir                 300-350    [98]
Coram Exp. Forest, nw MT western larch, Douglas-fir,   117-146    [129]
                         lodgepole pine, subalpine fir

Fuels and fire behavior:  The fuel structure in subalpine-fir-dominated
stands promotes highly destructive stand-destroying fires.  Fuel loads
in subalpine fir stands are greater than in lower elevation montane
stands because the cool and moist environment slows the decomposition of
organic matter allowing fuels to accumulate more rapidly [1].  Fuel beds
tend to be irregular, with over twice as much fuel accumulating under
the narrow-crowned trees as between them [116].  The needles are small
and fine and form a compact fuel bed in which fire spreads slowly [34].
These concentrated, slow burning fuels frequently produce flames high
enough to reach subalpine fir's low-growing dead branches [116].  Thus
crowning is common in subalpine fir stands.

Once a crown fire begins, it spreads easily because subalpine fir has a
tendency to grow in dense stands and has highly flammable foliage.  A
lightning strike on May 7, 1987, in a subalpine fir-mountain hemlock
stand in Mount Rainier National Park started a crown fire even though
the ground was still partially snow covered.  The fire spread slowly
through the tree crowns by (1) igniting lichens draped along the fine
branches, (2) preheating and igniting the foliage, and (3) spreading to
a nearby tree by igniting its lichens [62].


POSTFIRE REGENERATION STRATEGY : 
   crown-stored residual colonizer; short-viability seed in on-site cones
   secondary colonizer; off-site seed carried to site after year 2
   off-site colonizer; seed carried by wind; postfire years 1 and 2

Related categories for Species: Abies lasiocarpa | Subalpine Fir