FIRE EFFECTS
SPECIES: Betula papyrifera | Paper Birch 



IMMEDIATE FIRE EFFECT ON PLANT : 
Fire generally kills or top-kills most paper birch trees; the thin,
flammable bark makes the bole highly susceptible to girdling even by
light surface fires [17,21,31].  Although the bark of older trees is
thicker, it is also more flammable once it begins to exfoliate [39].

Paper birch seeds on the ground are destroyed by fire.  Summer fires do
not necessarily consume the catkins, but immature seeds will not ripen
on killed or top-killed trees [63].  


DISCUSSION AND QUALIFICATION OF FIRE EFFECT : 
On the Chippewa National Forest in Minnesota, prescribed burning in
mid-May in aspen slash top-killed all 4- to 15-inch-diameter (10-38 cm)
paper birch trees.  These sprouted within a few weeks of the fire, but
sprout mortality over the next few years resulted in 11 percent of the
original trees dead by postfire year 5 [49].

Low-intensity prescribed surface fires (mean flame length > 1 foot [0.3
m], mean rate of spread of 10.8 feet [3.3 m] per minute) in a
30-year-old mixed hardwood stand in central Wisconsin did not kill or
top-kill any paper birch trees greater than 4 inches (10 cm) in trunk
diameter.  Most of the saplings less than 4 inches in trunk diameter,
however, were top-killed [54].

On the Kenai Peninsula, Alaska, 22 percent of paper birch trees were
unaffected, while 78 percent had dead or partially dead aerial crowns 2
years after a light surface fire [69].  Forty-two percent of top-killed
trees produced sprouts.

Prescribed burning in a northern Wisconsin bracken fern (Pteridium
aquilinum)-grassland killed 31 percent of paper birch trees present.
The rest were top-killed but later sprouted.  Basal area was reduced by
90 percent [68].


PLANT RESPONSE TO FIRE : 
Paper birch rapidly revegetates burned areas.  Sprouts, and seedlings if
seed trees are nearby, appear within the first postfire year.

Sprout production:  Young paper birch trees up to about 50 years old
sprout prolifically and vigorously after fire.  Sprouts appear a few
weeks to 2 months after spring or summer fires but not until the
following spring after late fall fires [35,50,61].  They grow rapidly
and are often 20 to 40 inches (50-100 cm) tall after one growing season
[1,35].  In Minnesota, 5-year-old postfire paper birch sprouts averaged
10 feet (3 m) in height [50].  Following prescribed spring fires at
5-year intervals in Idaho, paper birch averaged 31 to 58 basal sprouts
per plant after each fire [35]. Sprout mortality is high in the first 5
postfire years, leaving a few to several sprouts per clump [50].

Seedling establishment:  Mineral soils exposed by fire provide excellent
paper birch seedbeds, but charred or partially removed organic layers
prevent establishment.  In Alaska, germination and subsequent seedling
survival of artifically sown paper birch seed was abundant, practically
nil, and nil on severely, moderately, and lightly burned test plots,
respectively [73].

Undamaged trees within a burn or trees in nearby unburned stands are
necessary for postfire seedling establishment.  Where there are abundant
seed trees, paper birch can easily establish 10's of thousands of
seedlings per acre after fire [19,39,69].  In northern Saskatchewan,
undamaged paper birch trees released 1 and 0.4 million seeds per acre
(2.48 & 1 million/ha) in the first and second fall, respectively,
following an April wildfire [4].

Because seed dispersal occurs in the fall, seedling establishment does
not begin until the second postfire year [46].  Seedling establishment
is generally greatest from postfire years 2 to 5 [3,46].  In Labrador,
paper birch established by seed dated to within 15 years of fire, with
subsequent seedling establishment lacking [21].


DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : 
In white spruce forest types in interior Alaska, paper birch establishes
thousands of seedlings and sprouts shortly after fire.  Sampling
fire-origin paper birch stands in Alaska, Lutz [39] observed an average
of 8,000 seedlings and saplings per acre (19,760/ha) 1 year after fire.
Four years afer fire, Foote [19] observed an average of 12,000 stems per
acre (30,000/ha) of both seed and sprout origin that were 3 to 6 feet
(1-2 m) tall.  Between 26 and 45 years after the fire, these thinned to
a few thousand per acre.

Three years after a prescribed light surface fire in south-central
Alaska, on a site stocked primarily with white spruce and paper birch,
there were about 8,000 and 1,000 paper birch seedlings and sprouts,
respectively, per acre (19,760 and 2,470/ha) [69].  Seedlings averaged 6
inches (15 cm) and sprouts 14 inches (35 cm) in height.


FIRE MANAGEMENT CONSIDERATIONS : 
Prescribed fire can be used to prepare cut-over sites for paper birch
seed regeneration.  In Maine, prescribed burning following winter
logging favored paper birch establishment more than other treatments
did.  Burning or disking following logging exposed mineral soils on more
than 70 percent of the logged area, while logging alone during the
summer or winter, resulted in only 5 percent mineral soil exposure.
Fourteen seed trees per acre (35/ha) were left on each treatment site.
Paper birch seedling establishment was as follows [78]:


Treatment                Posttreatment year 1     Posttreatment year 10
                          #/acre    #/ha           #/acre     #/ha

winter logging/disked    245,400   605,200         3,300      8,200
winter logging/burned     50,100   123,700         4,800     11,900 
summer logging only       65,700   162,300         1,700      4,200
winter logging only       33,700    83,200         1,900      4,700

Prescribed fire can be used to enhance deer and moose winter habitat by
killing late successional conifers and promoting early successional
browse species such as paper birch [69].  It generally takes 3 to 5
years after fire for paper birch sprout and seedling growth to provide
adequate browse for deer and moose [57].  Peak browse production is
generally between 10 and 16 years after fire [57].

Related categories for Species: Betula papyrifera | Paper Birch