FIRE EFFECTS
SPECIES: Populus grandidentata | Bigtooth Aspen 



IMMEDIATE FIRE EFFECT ON PLANT : 
Bigtooth aspen trees are very susceptible to fire, although bigtooth
aspen roots are very fire resistant.  Bigtooth aspen bark is thin and
does not protect the cambium from heat damage [29].  If there is
sufficient fuel in a young sapling stand for a fire to burn, the fire
will kill the saplings [44].  An average scorch height of 0.6 feet (0.2
m) will kill most aspen stems smaller than 6 inches (15 cm) in dbh [55].

Since most fires in aspen are of low severity, mature trees do not
always succumb to fire.  However, basal wounds caused by low-severity
fire serve as entry points for disease organisms [29,44].

Prolonged drought and large amounts of slash are required to raise the
soil temperature high enough to kill the roots of aspen [25].  Bigtooth
aspen roots are deeper in the soil than quaking aspen roots, making root
damage from fire highly unlikely in bigtooth aspen [40].



DISCUSSION AND QUALIFICATION OF FIRE EFFECT : 
NO-ENTRY


PLANT RESPONSE TO FIRE : 
A fire-killed aspen stand regenerates from surviving roots [25,29,44],
which are stimulated to produce suckers when apical dominance is removed
[44,64].

Roots must have a high cytokinin to auxin ratio to initiate sucker
growth.  If a low-intensity fire girdles aspen such that the downward
movement of auxin in the phloem is interrupted but the upward movement
of cytokinin continues in the xylem, the tree may survive for several
years.  Since the cytokinin continues to move out of the roots, it does
not accumulate, and suckers do not develop [64].

Roots are stimulated to sprout if the soil is heated [25,29].  The soil
is heated not only by the fire, but also by blackening of the soil
surface and removal of overstory and duff [48].

The density and growth of suckers is dependent in part on fire severity.
A low-severity fire that does not kill all of the overstory does not
result in suckers as dense or vigorous as those produced after a
moderate-severity fire [25].

Fire also prepares a favorable seedbed for bigtooth aspen.  Seeds from
off-site sources may blow onto burned sites and establish if there is
sufficient moisture and if the competition is not severe [14,56].

Most shrub species in the understory of aspen forests are able to sprout
after fire [13], as are many hardwood associates [38].


DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : 
NO-ENTRY


FIRE MANAGEMENT CONSIDERATIONS : 
Prescribed fire is used as a management tool to regenerate aspen stands
[41].  Moderate-severity fire which kills all remaining canopy stems and
removes duff is recommended following harvest to maximize the number of
suckers [25]. A low-severity fire does not always induce sufficiently
dense and vigorous suckers to regenerate an aspen stand [25].

Soil nutrient concentrations increased after wildfire on both clearcut
and wholetree harvested sites that had formerly supported adjacent
northern red oak-bigtooth aspen forests [73].

A mature aspen stand that is clearcut will generally have enough slash
for fire to kill any residual standing trees.  Fuel loadings of at least
10 tons per acre (22 t/ha) of slash less than 3 inches (8 cm)
in diameter are recommended [41].  Refer to Beyerhelm and Sando [72] for
fuel loading estimation techniques for aspen-northern hardwood stands.

The recommended weather conditions needed to burn a harvested aspen site
are reported for those stands with less than 25 percent conifers,
greater than 25 percent conifers, and with little slash [41].

In northern lower Michigan, Scheiner and others [52] studied the
vegetational response to clearcutting followed 1 year later by burning.
Prior to cutting, bigtooth aspen dominated the site with 153 stems per
acre (378 stems/ha).  One year postcut, but prefire, the vegetation was
dominated by red maple, northern red oak, and paper birch (Betula
papyrifera) sprouts.  However, in postfire year 1, bigtooth aspen was
again the most abundant species with 9,911 sucker stems per acre (24,481
stems/ha).  Although declining in number, bigtooth aspen continued to
dominate the site for the duration of the study (5 years).

Weber [64] studied the response of a quaking aspen and bigtooth aspen
stand to four different treatments:  surface burning before and after
spring leaf flush and clearcutting before and after leaf flush.  Three
years after treatment, the preflush cut had the greatest stem density,
average height, and basal diameter.  Both cut treatments had greater
stem densities than the burn treatments.  The preflush cut treatment
probably had more stems than the postflush cut treatment because
carbohydrate root reserves were not depleted.

One reason for low rates of suckering after prescribed burning was that
the fires did not completely kill the overstory.  The existing trees
survived one to two postfire growing seasons and continued to show
apical dominance, thereby preventing sucker development.  The postflush
fire resulted in more suckers than the preflush fire, probably because
it was a hotter fire and killed more overstory trees [64].

Simard and others [55] developed equations for using postfire
observations to predict fire-caused injury to and mortality in aspen.

The National Fire-Danger Rating System uses the total ash and
silica-free ash content of fuels as one of its variables.  Ash is a
noncombustible constituent of organic material and reduces the
combustion rate of fuel.  In a study in Michigan, the total ash content
of dead bigtooth aspen litter fuels was 3.7 percent in the fall, 5.4
percent in the spring, and 6.2 percent in early summer.  The silica-free
ash content was 2.0, 2.8, and 3.5 percent for fall, spring, and early
summer, respectively [31].

Ambrosia beetle (Xyleborus saxesceni) attacks fire-damaged bigtooth
aspen [58].

Because of its low flammability, bigtooth aspen has been recommended for
use in fire breaks, especially on droughty, sandy sites [27].

Related categories for Species: Populus grandidentata | Bigtooth Aspen