FIRE EFFECTS
SPECIES: Picea glauca | White Spruce 



IMMEDIATE FIRE EFFECT ON PLANT : 
White spruce is easily killed by fire.  Its thin bark provides little
insulation for the cambium, and the shallow roots are susceptible to
soil heating.  Surface fires can burn deep into litter and duff,
charring or sometimes consuming roots up to 8 to 9 inches (20-23 cm) in
diameter [41].  Surface fires often spread to white spruce crowns
because the highly flammable fine fuels concentrated under the trees
often produce flames that reach the low-growing, flammable,
lichen-draped branches [1,37].

White spruce seeds on the ground are usually killed by fire because they
have little or no endosperm to protect the embryo from high temperatures
[55].  Cones are not necessarily destroyed by summer fires, but immature
seeds will not ripen on fire-killed trees.


DISCUSSION AND QUALIFICATION OF FIRE EFFECT : 
Viereck and Schandelmeier [61] reported that most fires in spruce stands
in interior Alaska are either crown fires or ground fires intense enough
to kill overstory trees.  The needles of white spruce trees often remain
green following ground fires, but the boles are usually scorched to the
extent that most trees die [24].  In interior Alaska, 100 percent of 40-
to 140-year-old white spruce were killed by a high-severity,
low-intensity surface burn that consumed the entire organic mat,
estimated to be 1 to 5 inches (3-13 cm) thick [31].

Following a late May-early June wildfire in Interior Alaska, Zasada
[66] observed that fire effects on white spruce varied considerably
depending upon fire intensity and severity.  This fire occurred when
white spruce flowering was complete, but fertilization was not.  Fire
effects varied as follows:  

Crowns destroyed - within the zone of the highest fire intensity, crowns
were completely destroyed by fire.

Crowns scorched - near the intense zone tree crowns were scorched by the
heat of the fire.  All these trees were killed.  Small cones did not
develop any further.

Boles scorched or girdled - where underburning consumed most of the
forest floor, tree crowns were hardly affected, but trees received so
much damage to the bole that most died by the end of the first or second
summer after the fire.  Although these trees were severely injured, the
cones and seeds continued to develop.  When seed matured, viability was
about equal to seed from adjacent unburned stands.


PLANT RESPONSE TO FIRE : 
Following fire, white spruce reestablishes via wind-dispersed seeds from
surviving trees in protected pockets or from trees in adjacent unburned
areas.  Within a few years after a fire, white spruce reproduction is
often localized and centered around areas of surviving trees.
Establishment is quite variable, depending on the proximity of surviving
cone-producing trees, seed production during the year of the fire and
immediate postfire years, and amount of mineral soil exposed by the
fire.  Under most circumstances, it can rapidly invade burned sites only
when (1) fire consumes the organic mat and exposes mineral soil and (2)
surviving trees provide a seed source.  When these conditions are met,
white spruce begins to establish seedlings 1 or 2 years after fire.


DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : 
White spruce seedling establishment is rapid following fall wildfires
that expose mineral soil but do not burn into the tree crowns.  These
hot surface fires usually kill the trees, but the mature seeds are not
harmed and soon begin dispersing onto the mineral soil.  One year
following a late-August wildfire of this type in interior Alaska, white
spruce frequency was 100 percent, and seedling density was 12,150 per
acre (30,000/ha) [31].  White spruce is less likely to regenerate
following high-severity, low-intensity surface fires in the spring or
summer, because seeds will not develop on the fire-killed trees.
However, if not all trees are killed, some seed will develop over the
summer.  This occurred on portions of a late May-early June burn in
interior Alaska.  One year following this fire, white spruce seedlings
were numerous on portions of the burn where underburning consumed most
of the forest floor, but crowning did not occur.  Although the trees
were severely injured, seeds matured within the cones, so that by fall
1,100 viable seeds were dispersed per square meter.  Seedling frequency
was 100 percent, and density 290 per square meter one growing season
after the fire [66].

In British Columbia and Alberta, in areas where white spruce or white
spruce x Engelmann spruce hybrids are abundant and lodgepole pine
scarce, spruce will establish quickly following fire if sufficient
numbers of seed trees survive or are near the burn.  If lodgepole pine
is present before burning, it usually seeds in aggressively and assumes
a dominant role, quickly overtopping any spruce seedlings [16,35].
However, because of its shade tolerance, white spruce can establish
under a developing pine canopy.  Day [16] sampled lodgepole pine-white
spruce x Engelmann spruce hybrid stands in southern Alberta that
initiated from fires that occurred 29 and 56 years before sampling.  He
found that both pine and spruce initiated large numbers of seedlings
immediately after the fire.  Pine, however, established greater numbers
of seedlings, which rapidly outgrew the spruce and formed a canopy that
was 3 to 4 times the height of the spruce.  Pine seedling establishment
ceased about 30 years after fire, but the shade-tolerant spruce
continued to establish.  Given a sufficient disturbance-free interval,
white spruce will eventually dominate sites where spruce and pine seed
in together following fire.


FIRE MANAGEMENT CONSIDERATIONS : 
Broadcast burning can be used for fuel reduction and site preparation
following logging of white spruce [68].  Survival and early growth of
planted white spruce is enhanced by burning.  Four years after
outplanting of container-grown stock in northeastern British Columbia,
leader length was 36 percent longer on burned versus unburned sites;
however, foliar nutrient content was much lower.  Improvements in growth
on burned sites have been observed for 15 years [5].

Frequent fires can eliminate white spruce from an area because it does
not produce seed in quantity until it is 30 years old or older.  

Related categories for Species: Picea glauca | White Spruce