FIRE EFFECTS
SPECIES: Picea mariana | Black Spruce 



IMMEDIATE FIRE EFFECT ON PLANT : 
Black spruce is easily killed by fire because it has thin bark and
shallow roots.  Trees are often killed even by low-intensity surface
fires.  Crowning is common in black spruce stands because low-growing,
lichen-draped branches are easily ignited by ground fires.  Crown fires
typically result in extensive mortality.

In interior Alaska, most fires in black spruce stands are a combination
of ground and crown fires that usually kill all black spruce [25].
Hanson [32] found that all black spruce trees were killed following a
low-intensity surface burn (the top 2 to 4 inches [5-10 cm] of the 6 to
14 inch [15-35 cm] organic mat was consumed) in an open black
spruce-tamarack community in interior Alaska.  This site contained 81 to
162 trees per acre (200-400/ha) that ranged from 40 to 178 years old and
1.5 to 3 inches (4-7 cm) in diameter.


DISCUSSION AND QUALIFICATION OF FIRE EFFECT : 
NO-ENTRY


PLANT RESPONSE TO FIRE : 
Closed boreal forests:  Following fire, fire-killed black spruce trees
release large quantities of seeds over a period of 1 to 5 years,
resulting in abundant seedling establishment.  Numerous authors report
that in boreal forests black spruce seeds in promptly following fire.
[25,42,50,63,68].  In interior Alaska, Foote [25] observed an average of
17,954 black spruce seedlings per acre (44,346/ha) on black spruce sites
which had burned 1 to 5 years earlier.  By 50 years after fire, black
spruce stands had naturally thinned to 2,595 stems per acre (6,402/ha);
trees in these stands averaged 2.1 inches (5.4 cm) d.b.h. and were 16.4
to 23 feet (5-7 m) tall.

Open woodlands:  In open black spruce woodlands in the Northwest
Territories, black spruce seed production peaks when stand age reaches
100 to 200 years.  Fires occurring within this time frame have little
effect on black spruce, as it quickly regenerates from seed.  Burning
prepares good seedbeds by removing duff and competing vegetation, and by
altering the thermal regime of the soil, which favors germination
[9,10].  In open woodlands in northern Quebec, black spruce tends to
regenerate quickly after fire, regaining or exceeding prefire density
within 30years [56].  Moving northward from open woodlands to arctic
treeline, the likelihood of successful black spruce seedling
establishment following fire progressively diminishes.

Forest-tundra ecotone:  In the forest-tundra ecotone north of open
spruce woodlands in the Northwest Territories, black spruce seed
production is poor, and generally little or no seed is available for
postfire regeneration.  Where sparse seed production does occur,
short-term climatic changes over a period of only 1 to 10 years could
exhaust the seed population before a fire, or prevent seed germination
after a fire.  Near arctic treeline in the Northwest Territories, black
spruce stands do not regenerate following fire [9,10].  At treeline in
northern Quebec, fires destroy or severely reduce black spruce and cause
a shift toward arctic tundra.  Here, black spruce seedlings are only
occasionally found after fire and are usually in depressions at the edge
of burned areas where nearby living trees contain viable seeds [50].


DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : 
Following fire, black spruce establishes best where severe burning
exposes mineral soils on upland sites or moist peat on lowland sites
[40,72].  Unburned or partially burned sphagnum mosses are also good
seedbeds, but unburned or partially burned feather mosses are poor
seedbeds [2].  In southern Ontario, feather mosses are not wholly
consumed by fire, but rotting logs under the feather mosses are often
exposed and provide excellent seedbeds [45].

After an experimental burn on black spruce/feather moss sites in
interior Alaska, naturally and artifically sown seeds germinated only
where fire had removed part or all of the organic matter.  No seedlings
were found on unburned surfaces or on scorched or charred feather
mosses.  In general, exposed mineral soils provided the best seedbeds.
Although seedlings established in areas where the organic layer was
partially consumed, none survived past 3 years.  However, on sites where
mineral soil was exposed, seedling frequency was 35 percent after 1
year, and 81 percent after 3 years, as a result of continued natural
seedfall [72].  Following broadcast burning on black spruce/feather moss
cut-overs (area thinned from 2,180 to 800 trees per acre
[5,387-1,977/ha]) in southeastern Manitoba, black spruce seedling
establishment and survival were better on moderate-severity than on
light-severity burns [15].  Five years after burning, stocking was 94
percent in areas where burning depth averaged 4 to 7 inches (10-18 cm),
70 percent in areas where burning depth averaged 2 to 3 inches (5-8 cm),
and 35 percent in unburned areas.

The Wickersham Dome Fire near Fairbanks, Alaska, burned 15,600 acres
(6,300 ha) of mainly black spruce stands ranging in age from 50 to 125
years.  For 3 years after this fire, seedling establishment was quite
variable in both lightly burned areas (<50 percent of ground surface
blackened, litter depth reduced an average of 2.25 inches [5.7 cm], and
40 percent of ground vegetation alive 1 year after fire) and heavily
burned areas (>90 percent of ground surface blackened, litter depth
reduced an average of 4 inches [10.3 cm], and nearly all ground
vegetation consumed).  In one heavily burned area, seedling
establishment was slow, with only 20 percent of plots containing
seedlings 3 years after the fire for a total of 1,113 seedlings per acre
(2,750/ha).  Conversely, another heavily burned area contained 8,500
seedlings per acre (21,000/ha) 3 years after the fire.  In
lightly burned areas, unburned and partially burned sphagnum mosses
provided a good seedbed for black spruce so that by 3 years after the
fire there were 16,200 seedlings per acre (40,000/ha) [62].

Black spruce seeds in quickly after fire on relatively dry uplands where
it occurs with jack, red, or lodgepole pine.  However, the pines also
seed in aggressively and quickly overtop black spruce.  A 35-year-old
burn in northern Minnesota was composed mostly of jack pine and black
spruce.  The jack pine were predominantly 33 to 34 years old and 4 to 6
inches (10-15 cm) in diameter, while the black spruce were 28 to 32
years old and 1 to 3 inches (2.5-3 cm) in diameter [33].  Black spruce
is very shade tolerant and can survive in this suppressed condition for
more than 100 years [33] and, in the absence of fire, will eventually
replace the pines [8,65].

In southern Labrador, black spruce seedling establishment following fire
is slow and progressive over a period of 70 to 100 years, resulting in
uneven-aged stands.  Within spruce stands in this coastal climate, fires
generally consume very little organic matter and leave only charred
humus.  For the first 20 years after fire, seedling establishment is
sporadic and largely restricted to depressions, the edges of water
courses, and exposed mineral soils [26].


FIRE MANAGEMENT CONSIDERATIONS : 
Fire behavior:  In Alaska, Lutz [42] observed that burning in spruce
stands tends to be more intense on ridges than in valleys, and that
slopes with south or west exposures commonly have more mineral soil
exposed after fire than slopes with north or east exposures.  On rocky
slopes or ridges, fires are often unusually severe.

The forest floor under most black spruce stands is made up of a thick
organic mat [18].  Most fires do not consume the entire forest floor,
but produce a mosaic of small patches of exposed mineral soil intermixed
within larger areas of partially consumed organic material [25].  Late
summer fires, however, sometimes consume the entire organic layer and
expose extensive areas of mineral soil [61].  Burning black spruce
stands in Alaska results in increased soil and forest floor temperatures
and nutrient cycling rates.  This results in a warmer, more productive
site for 10 to 20 years after fire [59].

Broadcast burning following timber harvest:  After clearcutting black
spruce on organic sites in the Lake States, slash is often broadcast
burned to aid natural regeneration.  Burning is generally recommended if
there is heavy slash, a feather moss carpet, or abundant tall shrubs,
grasses, or sedges [37].  For natural regeneration to be successful, an
adequate seed supply is necessary, and fuels, including slash, litter,
mosses, and peat, need to be sufficiently dry to allow for reasonably
severe burns [15].  Aksamit and Irving [2] studied black spruce
regeneration on numerous broadcast burned clearcuts in northern
Minnesota.  They found that where the understory was dominated by
sphagnum mosses before cutting, black spruce regenerated well regardless
of the burning treatment.  In fact, adequate regeneration was obtained
even without burning.  On feather-moss-dominated sites, prescribed
burning was necessary to promote black spruce regeneration.  For burns
to be effective on feather moss sites, they should be conducted when
100- and 1000-hour fuel moisture is less than 25 percent.  However,
burning under these conditions may lead to fire control and mop up
problems, and higher costs.  Where speckled alder dominates the
understory before logging, natural regeneration of black spruce after
broadcast burning is quite variable.  Low-intensity burns seem to favor
black spruce regeneration, and more severe burns tend to favor other
tall shrubs which compete fiercely with spruce seedlings.  Johnston [37]
has outlined broadcast burning techniques for lowland black spruce in
the Lake States.

Eastern dwarf mistletoe control:  Prescribed burning can be used to
eradicate eastern dwarf mistletoe in stands of black spruce.  For
mistletoe control to be effective, burning must result in 100 percent
black spruce mortality.  To ensure complete mortality, live trees can be
cut to provide slash where understories are sparse, and/or diesel oil
can be sprayed on slash when surface fuels are too thin or wet [74].

Frequent fires:  Black spruce normally seeds in aggressively following
fire, but it can be eliminated from an area if a second fire occurs
before these young trees reach seed-producing age [1].  Black spruce
regenerated quickly following a 1923 fire in northern Ontario, but 8
years after a second fire in 1929 passed through the area, no black
spruce seedlings were found [46].

Related categories for Species: Picea mariana | Black Spruce