FIRE EFFECTS
SPECIES: Pteridium aquilinum | Bracken Fern 



IMMEDIATE FIRE EFFECT ON PLANT : 
Bracken fern is a survivor [220,221].  The fronds of plants are
generally killed by fire, but some rhizomes survive [1,74,75].  The
rhizomes are sensitive to elevated temperatures.  Except in the spring,
sprouting is less vigorous when rhizomes are exposed to temperatures of
113 degrees F (45 degrees C), and they die when exposed to temperatures
above 131 degrees F (55 degrees C) [74].  During fires the rhizome
system is insulated by mineral soil [74,75].  Depth of the main rhizome
system is normally between 3.5 and 12 inches (8 and 30 cm); short
rhizomes may be within 1.5 inches (3.7 cm) of the surface and some
rhizomes may be as deep as 39.4 inches (1 m) [37,68,74,75,79,87,113].


DISCUSSION AND QUALIFICATION OF FIRE EFFECT : 



PLANT RESPONSE TO FIRE : 
Bracken fern is well known as a postfire colonizer in western
coniferous forests and eastern pine and oak forests [17,156].  Fire
benefits bracken fern by removing its competition while it sprouts
profusely from surviving rhizomes [97,192,229].  New sprouts are more
vigorous following fire, and bracken fern becomes more fertile,
producing far more spores than it does in the shade [191].  Sprouting is
slower following summer burns than following spring and fall burns [76].

Bracken fern spores germinate well on alkaline soils, allowing them to
establish in the basic conditions created by fire [85,191,192].  In a
moist tropical habitat in Costa Rica, bracken fern gametophyte plants
were observed covering the burned surface of bare ground and ash, but no
plants were observed on unburned sites [85].  In North America
establishment of new plants from spores on recently burned areas appears
to be most likely in the moister conditions near either coastline
[99,128].


DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : 
All varieties of bracken fern are well adapted to fire, but there are
differences in rhizome growth rates and their response to disturbance
[73,189,192,232].  Among the most important North American varieties,
var. latiusculum and var. pseudocaudatum are slower growing and
considered less weedy [232,239].  This along with factors such as
season, fire severity and intensity, and site characteristics may
explain some reported differences in response following fire.

var. pubescens:  Bracken fern invades recently logged and burned areas
in the Oregon Cascades, sometimes in the first year and sometimes after
several years [100,173,214,246].  Repeated fires or burns that are
delayed following logging favor a rapid increase in cover and
encroachment of bracken fern [82].  Along the Pacific coast bracken fern
invades recent burns by windborne spores and also spreads from its
buried rhizome [128].  After spring fires in northern Idaho, bracken
fern production dropped somewhat in the first year and then increased in
the second and third years [148].  Bracken fern increased following
single or multiple broadcast fires in northern Idaho [175].  After
logging or fire in Arizona ponderosa pine communities, bracken fern may
cover up to 30 percent of the area for 10 or more years [27,187,188].

var. latiusculum:  It is generally agreed that the bracken-grasslands
[47] of Wisconsin originated as a result of fires [233].  However,
following early spring prescribed fires in these areas, bracken fern's
relative frequency decreased the year after the fire [233].  In New York
oak woods, Swan [223] also found a decrease in frequency following
spring fires; however, bracken fern increased in abundance at the same
time.  He suggested that existing clumps became denser.  Studies in
Great Lakes area jack pine forests show that bracken fern sprouts, and
its cover and biomass usually remain fairly stable, either decreasing or
increasing slightly after burning [4,5,163,184,185].  In red and white
pine (Pinus resinosa and P. strobus) forests of Ontario, bracken fern
decreased slightly after logging without burning but increased strongly
following logging and early summer burning [207,208].  Increased bracken
fern following a spring fire in a Pennsylvania scrub oak community was
attributable to both spore germination and rhizome sprouts [99].  In
northeastern hardwood stands bracken fern sprouts rapidly following fire
and repeated fires may lead to its domination [152,209].  In oak-pine
forests of the Pine Barrens region of New Jersey, bracken fern thrives
following severe fires [17,161].  It increases moderately in canopy gaps
in these forests following surface fires.

var. pseudocaudatum:  Bracken fern is well adapted to fires and
increases its cover greatly when it is burned repeatedly in longleaf
pine and slash pine forests [138].  After two successive wintertime
prescribed underburns, bracken fern increased its frequency from 16.7 to
20.6 percent and doubled its biomass in a Florida slash and longleaf
pine forest [171].  Bracken fern is common following fire in the
pocosins of the Southern Coastal Plain [32].  Its regrowth following a
severe July wildfire in mixed pine (Pinus taeda or P. palustris) and oak
(Quercus virginiana and Q. laurifolia) was vigorous, and cover increased
each of the first 2 years [51].  In South Carolina loblolly pine stands
that have been repeatedly burned for 20 years, bracken fern is found
only in areas burned during the summer and not on winter-burned areas
[152].  In the southeastern United States, prescribed fire has been used
extensively since 1960, favoring bracken fern and allowing it to
dominate other understory species, including wiregrass (Aristida
stricta) which had been prominant [224].


FIRE MANAGEMENT CONSIDERATIONS : 
Fire can facilitate the spread of bracken fern [23,70].  The least
favorable time for prescribed burning is just after the new fronds have
fully expanded and starch reserves in the rhizomes are at their lowest
level [31,136,154, 155,160,196,218,243].  A fire at this time can reduce
bracken fern for up to 2 years [195].  Although more fronds may be
produced, total frond weight and rhizome starch are greatly reduced
[196].  If a prescribed fire at this time is followed with a second
treatment, the rhizome system will be further depleted and fewer dormant
buds may sprout.  Since there are more fronds, a herbicide would have
more entry points to the rhizome system [196].

Fine fuel loading in areas dominated by bracken fern can be quite high
[2,128,95,162,234].  Brown and Marsden [1976] have developed a formula
to estimate fuel loading using the relationship between fuel loading and
the ground cover and height of bracken fern.

Related categories for Species: Pteridium aquilinum | Bracken Fern