Index of Species Information
SPECIES: Pteridium aquilinum
Introductory
SPECIES: Pteridium aquilinum
AUTHORSHIP AND CITATION :
Crane, M. F. 1990. Pteridium aquilinum.
In: Fire Effects Information System, [Online].
U.S. Department of Agriculture, Forest Service,
Rocky Mountain Research Station, Fire Sciences Laboratory (Producer).
Available: http://www.fs.fed.us/database/feis/ [].
ABBREVIATION :
PTEAQU
SYNONYMS :
Pteris aquilina
Asplenium aquilinum
Allosorus aquilinus
Ornithopteris aquilina
Filix aquilina
Filix-foemina aquilina
Pteridium aquilinum var. lanuginosum
Pteris latiuscula
Pteridium aquilinum var. champlainese
SCS PLANT CODE :
PTAQ
COMMON NAMES :
western bracken fern
bracken
brake fern
brake
hog-brake
grande fougere
fougere d'aigle
warabi
eagle fern
western bracken
eastern bracken
TAXONOMY :
The currently accepted scientific name of western bracken fern is Pteridium
aquilinum (L.) Kuhn. At this time western bracken fern is considered a single,
worldwide species, although some disagree [42,73,189,232]. There are
two recognized subspecies: aquilinum (formerly typicum) in the Northern
Hemisphere and caudatum in the Southern Hemisphere. Of the four
varieties of subspecies caudatum, one, var. caudatum, grows as far north
as southern Florida. Of the eight varieties in subspecies aquilinum,
three grow in North America and one in Hawaii [189,232].
In this report the main emphasis will be given to subspecies aquilinum
and the three main North American varieties of this subspecies:
P. a. var. pubescens
P. a. var. pseudocaudatum
P. a. var. latiusculum
Western bracken fern is used for all varieties. Var. aquilinum is very
closely related to the three North American varieties listed above [42,
232] and has been studied more intensely. Where information concerning
it or other non-North American western bracken fern is included, either the
varietal name or the location is given.
Where varieties of western bracken fern overlap, intergradation between them
occurs. Intermediates between P. a. var. pubescens and P. a. var. latiusculum occur
along the eastern edge of var. pubescens' range in Wyoming and Colorado
and perhaps in Michigan and Wisconsin. Likewise, where the ranges of
P. a. var. latiusculum and P. a. var. pseudocaudatum overlap, intermediates may be
found [73,189,232].
LIFE FORM :
Fern or Fern Ally
FEDERAL LEGAL STATUS :
No special status
OTHER STATUS :
NO-ENTRY
DISTRIBUTION AND OCCURRENCE
SPECIES: Pteridium aquilinum
GENERAL DISTRIBUTION :
Western bracken fern occurs throughout the world with the exception of hot and
cold deserts [189]. Subspecies aquilinum is mostly north temperate in
distribution; subspecies caudatum is found primarily in the Southern
Hemisphere [189]. The distribution of subspecies and varieties found in
the United States and Canada is as follows [72,90,119,174,189,232]:
P. a. var. pubescens is found in western North America and ranges south
from southern Alaska through California and into Mexico and east into
Alberta, Montana, western South Dakota, Wyoming, Colorado, and western
Texas. There are outlier populations in Quebec, Ontario, and northern
Michigan.
P. a. var. pseudocaudatum is primarily along the eastern coastal plain of
the United States from Cape Cod to Florida. It is less frequent to the
west but extends across the southern states to Texas, southeastern
Kansas, and as far north as Illinois.
P. a. var. latiusculum is basically circumboreal in range, growing across
northern Europe, northern Asia and Japan, and much of North America, but
it has not been found in western North America. It grows from
Newfoundland west to northeastern North Dakota, and south to North
Carolina, Oklahoma, and Tennessee. There are occasional outlier
populations in Mississippi, Wyoming, South Dakota, and Colorado.
P. a. var. decompositum is restricted to the Hawaiian Islands.
P. a. var. caudatum is present in Bermuda, southern Florida, the West
Indies, Central America, and into northern South America.
ECOSYSTEMS :
FRES10 White - red - jack pine
FRES11 Spruce - fir
FRES12 Longleaf - slash pine
FRES13 Loblolly - shortleaf pine
FRES14 Oak - pine
FRES15 Oak - hickory
FRES18 Maple - beech - birch
FRES19 Aspen - birch
FRES20 Douglas-fir
FRES21 Ponderosa pine
FRES22 Western white pine
FRES23 Fir - spruce
FRES24 Hemlock - Sitka spruce
FRES25 Larch
FRES26 Lodgepole pine
FRES27 Redwood
FRES28 Western hardwoods
FRES34 Chaparral - mountain shrub
FRES36 Mountain grasslands
STATES :
AL AK AZ AR CA CO CT DE FL GA
HI ID IL IN IA KS KY LA ME MD
MA MI MN MS MO MT NE NV NH NJ
NM NY NC ND OH OK OR PA RI SC
SD TN TX UT VT VA WA WV WI WY
AB BC MB NB NF NS ON PE PQ YT
MEXICO
BLM PHYSIOGRAPHIC REGIONS :
1 Northern Pacific Border
2 Cascade Mountains
3 Southern Pacific Border
4 Sierra Mountains
5 Columbia Plateau
6 Upper Basin and Range
8 Northern Rocky Mountains
9 Middle Rocky Mountains
11 Southern Rocky Mountains
12 Colorado Plateau
13 Rocky Mountain Piedmont
14 Great Plains
15 Black Hills Uplift
16 Upper Missouri Basin and Broken Lands
KUCHLER PLANT ASSOCIATIONS :
K001 Spruce - cedar - hemlock forest
K002 Cedar - hemlock - Douglas-fir forest
K003 Silver fir - Douglas-fir forest
K005 Mixed conifer forest
K006 Redwood forest
K007 Red fir forest
K008 Lodgepole pine - subalpine forest
K009 Pine - cypress forest
K011 Western ponderosa forest
K012 Douglas-fir forest
K013 Cedar - hemlock - pine forest
K014 Grand fir - Douglas-fir forest
K015 Western spruce - fir forest
K017 Black Hills pine forest
K018 Pine - Douglas-fir forest
K019 Arizona pine forest
K020 Spruce - fir - Douglas-fir forest
K021 Southwestern spruce - fir forest
K023 Juniper - pinyon woodland
K025 Alder - ash forest
K026 Oregon oakwoods
K028 Mosaic of K002 and K026
K029 California mixed evergreen forest
K030 California oakwoods
K033 Chaparral
K047 Fescue - oatgrass
K093 Great Lakes spruce - fir forest
K095 Great Lakes pine forest
K096 Northeastern spruce - fir forest
K100 Oak - hickory forest
K106 Northern hardwoods
K107 Northern hardwoods - fir forest
K108 Northern hardwoods - spruce forest
K110 Northeastern oak -pine forest
K111 Oak - hickory - pine forest
K112 Southern mixed forest
K114 Pocosin
K115 Sand pine scrub
K116 Subtropical pine forest
SAF COVER TYPES :
1 Jack pine
5 Balsam fir
14 Northern pin oak
15 Red pine
16 Aspen
17 Pin cherry
18 Paper birch
19 Gray birch - red maple
20 White pine - northern red oak - red maple
21 Eastern white pine
22 White pine - hemlock
23 Eastern hemlock
25 Sugar maple - beech - yellow birch
30 Red spruce - yellow birch
31 Red spruce - sugar maple - beech
32 Red spruce
33 Red spruce - balsam fir
35 Paper birch - red spruce - balsam fir
42 Bur oak
43 Bear oak
44 Chestnut oak
45 Pitch pine
51 White pine - chestnut oak
70 Longleaf pine
71 Longleaf pine - scrub oak
72 Southern scrub oak
73 Southern redcedar
74 Cabbage palmetto
75 Shortleaf pine
76 Shortleaf pine - oak
80 Loblolly pine - shortleaf pine
81 Loblolly pine
82 Loblolly pine - hardwood
83 Longleaf pine - slash pine
98 Pond pine
110 Black oak
206 Engelmann spruce - subalpine fir
210 Interior Douglas-fir
211 White fir
212 Western larch
213 Grand fir
215 Western white pine
216 Blue spruce
217 Aspen
218 Lodgepole pine
221 Red alder
223 Sitka spruce
224 Western hemlock
225 Western hemlock - Sitka spruce
226 Coastal true fir - hemlock
227 Western redcedar - western hemlock
229 Pacific Douglas-fir
230 Douglas-fir - western hemlock
232 Redwood
233 Oregon white oak
234 Douglas-fir - tanoak - Pacific madrone
236 Bur oak
237 Interior ponderosa pine
243 Sierra Nevada mixed conifer
244 Pacific ponderosa pine - Douglas-fir
245 Pacific ponderosa pine
249 Canyon live oak
250 Blue oak - Digger pine
255 California coast live oak
SRM (RANGELAND) COVER TYPES :
NO-ENTRY
HABITAT TYPES AND PLANT COMMUNITIES :
Western bracken fern does not persist in forests beyond about 200 years [169].
It is a useful indicator of seral forest communities in western Oregon
[60]. In northwestern Colorado aspen (Populus tremuloides) communities,
western bracken fern indicates site deterioration [121]. Published
classification schemes listing western bracken fern as an indicator species or
as a dominant part of vegetation in community types (cts), habitat types
(hts), plant associations (pas), and ecosystem associations (eas) are
presented below:
Area Classification Authority
s CA general veg pas, cts Paysen and others 1980
CA: s Monterey forest cts Borchert and others 1988
County
nw CO: Routt NF forest hts Hoffman and Alexander 1980
w CO: White forest hts Hoffman and Alexander 1983
River NF
CO general veg, cts, pas Baker 1984a
CO forest hts, cts Alexander 1987
c ID seral cts Steele and Geier-Hayes 1989b
MI and WI forest hts Coffman and others 1980
s OR: Cascade Mtns forest pas Atzet and McCrimmon 1990
nw OR post-burn veg. cts Bailey and Poulton 1968
OR, WA general veg. cts Franklin and Dyrness 1973
SD, WY: Black forest and shrubland Steinauer 1981
Hills NF hts, cts
SD, WY: Black forest and shrubland Hoffman and Alexander 1987
Hills NF hts
UT aspen cts Mueggler and Campbell 1986
WA: Gifford forest pas Topik and others 1986
Pinchot N. F.
WA: Mt.Rainier NP forest cts, hts Moir and others 1976
WY forest hts Alexander 1986
Intermountain aspen cts Mueggler 1988
Region: ID,NV,
UT,WY
Pacific general veg. pas Hall 1984
Northwest
Region 2: CO,NE, general veg. pas Johnston 1987
KS,SD,WY
MANAGEMENT CONSIDERATIONS
SPECIES: Pteridium aquilinum
IMPORTANCE TO LIVESTOCK AND WILDLIFE :
In Montana, elk eat western bracken fern only in June when new fronds are
unfurling [247]. Likewise New Jersey deer use is restricted to spring
fiddleheads [227]. In the southern states western bracken fern is ranked as a
low-use forage for deer which eat it only in the spring [92].
White-tailed deer eat western bracken fern in trace amounts only in the summer
and fall [132] or not at all [116]. However, western bracken fern foliage
accumulated high concentrations of nutrients and was heavily used by
deer in Pennsylvania during the first spring following fire [99].
Rabbits occasionally eat the fronds and rhizomes [181].
Goats are the only livestock that normally eat western bracken fern [79].
Cattle feeding on lush grass may eat western bracken fern for roughage or if it
is mixed in hay [33,62]. In the Pacific Northwest sheep avoid mature
fronds of western bracken fern so it increases in cutover areas grazed by sheep
[128]. The fronds may release hydrogen cyanide (HCN) when they are
damaged (cyanogenesis), particularly the younger fronds [42,96].
Herbivores, including sheep, selectively graze young fronds that are
acyanogenic (without HCN) [43,96].
Despite western bracken fern's production of bitter-tasting compounds, chemicals
that interfere with insect growth, and toxic chemicals, western bracken fern
hosts a relatively large number and variety of herbivorous insects
[141,142]. In Great Britain 27 to 35 insect species eat western bracken fern.
The number and diversity of insect species increase toward the end of
the season, possibly because of declining levels of toxic chemicals
[141]. A study in the southwestern United States found only five to
seven insect species feeding primarily on bracken; however, in the
Southwest western bracken fern grows in a very restricted area [142]. Some
North American sawflies feed on western bracken fern [141].
PALATABILITY :
Western bracken fern's palatability is usually nil to poor, although
occasionally it is eaten by livestock after autumn frosts [234]. In the
southern and northeastern United States, newly emerging fronds of
western bracken fern are most palatable to deer and livestock [92,227]. Cattle
sometimes eat it for roughage [62]. A study using captive mule deer
gave western bracken fern a low preference rating, since the deer only consumed
it in July [210].
NUTRITIONAL VALUE :
The crude protein content of western bracken fern decreases during the growing
season, from 20 to 25 percent to 5 to 10 percent in fronds and from 10
to 15 percent to 2 or 3 percent in petioles (stems) [141]. Frond
carbohydrate levels are highest early in the summer and begin to drop by
mid-July [243]. Lignin, tannin, and silicate levels tend to increase
through the growing season making the plants less palatable [141].
Cyanide (HCN) levels fall during the season as do the levels of a
thiaminase which prevents utilization of B vitamins [141]. Tannin
production may be related to edaphic conditions; water stress may reduce
the amount produced [226].
Toxicity: Western bracken fern is known to be poisonous to livestock throughout
the United States, Canada, and Europe [92,234]. Losses are greatest
when livestock is fed hay mixed with western bracken fern [234].
Simple-stomached animals like horses, pigs, and rats develop a thiamine
deficiency within a month. Vitamin B1 is effective in curing the animal
if it is administered early [67]. Acute bracken poisoning affects the
bone-marrow of both cattle and sheep and causes anemia and hemorrhaging
which is often fatal [67,104]. Bright blindness and tumors of the jaws,
rumen, intestine, and liver are also found in sheep feeding on bracken
fern [104]. Sheep and cattle are most often poisoned by western bracken fern
when young animals are moved from an area without western bracken fern to a
field containing the fern. Cumulative poisoning may occur in older
sheep that have ingested small amounts of western bracken fern over a period of
years [104].
COVER VALUE :
Western bracken fern clumps are used for cover by deer in England [43]. Birds,
including pheasants, meadow pipits, and grouse, may use it for escape
cover. In England, woodcocks, chats, and wrens nest in western bracken fern
[172,181], and small animals such as foxes, rabbits, voles, shrews, and
mice find cover in it [181]. Sheep ticks and other insects are often
found in the decomposing litter of western bracken fern [23,77,104].
VALUE FOR REHABILITATION OF DISTURBED SITES :
Nonnative grasses are often seeded onto disturbed sites in some areas of
the West to control erosion. Sites with predisturbance cover of bracken
fern do not normally need seeding and should be low in priority for such
activities [229].
OTHER USES AND VALUES :
Western bracken fern was considered so valuable during the Middle Ages that it
was used to pay rents [202]. Western bracken fern was used as thatch for
roofing and as a fuel when a quick hot fire was desired. The ash was
used as a source of the potash used in the soap and glass industry until
1860 and for making soap and bleach. The rhizomes were used to dye wool
yellow and in tanning leathers [202]. Western bracken fern is still used for
winter livestock bedding in parts of Wales since it is more absorbent,
warmer, and easier to handle than straw [77,125]. It is also used as a
green mulch and compost [70,183,202].
Western bracken fern is most commonly used today as a food for humans. The
newly emerging croziers or fiddleheads are picked in spring and may be
consumed fresh or preserved by salting, pickling, or sun drying
[120,202]. Both fronds and rhizomes have been used in brewing beer, and
rhizome starch has been used as a substitute for arrowroot [232]. Bread
can be made out of dried and powered rhizomes alone or with other flour
[202]. American Indians cooked the rhizomes, then peeled and ate them
or pounded the starchy fiber into flour [102,107,149,183]. In Japan
starch from the rhizomes is used to make confections [120,202]. Bracken
fern is grown commercially for use as a food and herbal remedy in
Canada, the United States, Siberia, China, Japan, and Brazil [70] and is
often listed as an edible wild plant [107,120]. Powdered rhizome has
been considered particularly effective against parasitic worms [79,202].
American Indians ate raw rhizomes as a remedy for bronchitis [79,183].
Western bracken fern has been found to be mutagenic and carcinogenic in rats and
mice, usually causing stomach or intestinal cancer [62,63,70,80]. It is
implicated in some leukemias, bladder cancer, and cancer of the
esophagus and stomach in humans [63,80]. All parts of the plant,
including the spores, are carcinogenic, and face masks are recommended
for people working in dense bracken [63]. The toxins in western bracken fern
pass into cow's milk [62,70,80]. The growing tips of the fronds are
more carcinogenic than the stalks [62,141]. If young fronds are boiled
under alkaline conditions, they will be safer to eat and less bitter
[63,70,120].
Western bracken fern is a potential source of insecticides and it has potential
as a biofuel [140]. Western bracken fern increases soil fertility by bringing
larger amounts of phosphate, nitrogen, and potassium into circulation
through litter leaching and stem flow; its rhizomes also mobilize
mineral phosphate [28,140,157,158,242]. Western bracken fern fronds are
particularly sensitive to acid rain which also reduces gamete
fertilization. Both effects signal the amount of pollutants in rain
water making western bracken fern a useful indicator [64,65,66].
OTHER MANAGEMENT CONSIDERATIONS :
Competition: Western bracken fern is competitive plant that invades cultivated
fields and disturbed areas [54,79,129,218,222,234]. It effectively
competes for soil moisture and nutrients. Its rhizomes grow under the
roots of herbs and tree or shrub seedlings, and when the fronds emerge,
they shade the smaller plants. In the winter dead fronds may bury other
plants and press them to the ground [46,117,150,162]. On some sites
shading may protect tree seedlings and increase survival [162]. In a
western Washington study, dense western bracken fern protected planted
Douglas-fir seedlings from snowshoe hare and black-tailed deer browsing
until the trees overtopped the western bracken fern; tree growth, however, was
slower than normal [54,55]. Control may be needed until tree seedlings
are taller than the western bracken fern and sturdy enough to withstand the
weight of dead fronds [112]. Scots pine (Pinus sylvestris) has
successfully invaded stands of dense western bracken fern (var. aquilinum) [159].
Allelopathy: Western bracken fern's production and release of allelopathic
chemicals is an important factor in its ability to dominate other
vegetation [13,84,86]. The release of these toxic chemicals varies by
environment or perhaps by variety of western bracken fern. In tropical areas
rainfall leaches toxins from green fronds. Farther north no
allelopathic chemicals are released from the green fronds but are
readily leached from standing dead fronds [84]. In the Pacific
Northwest, water extracts from green fronds did not inhibit sampled
plants, but extracts from litter did [52].
A Pacific Northwest study found that water-soluble extracts from dead
western bracken fern fronds affected thimbleberry (Rubus parviflorus) and
salmonberry (R. spectabilis) germination but did not affect Douglas-fir
(Pseudotsuga menziesii). Western bracken fern litter reduced the emergence of
all three species [217]. In Pennsylvania, water extracts from green
fronds reduced germination of black cherry (Prunus serotina) [124]. In
an Idaho study, when subalpine fir (Abies lasiocarpa), Engelmann spruce
(Picea engelmannii), Douglas-fir, and grand fir (Abies grandis) seed was
sown under western bracken fern, most of the new germinants died before shedding
seed coats [71]. Herbs may be inhibited for a full growing season after
western bracken fern is removed, apparently because active phytotoxins remain in
the soil [124,87].
Western bracken fern control: Timing is important in any treatment of bracken
fern [68, 154,155,244]. The most effective time for treatment is summer
just after the new fronds have fully expanded and starch reserves in the
rhizome are at their lowest level [31,136,154,155,160,196,218,243]. Two
or more annual treatments and combinations of cutting and herbicide are
more effective than single treatments or even single annual treatments
[154].
Mechanical Treatment: Cutting early in the summer, allowing the
rhizomes to regenerate a second crop of fronds, then recutting will
deplete the resources of the rhizome much faster than a single cutting.
However, single, annual cuttings or deep ploughing can be effective
during midsummer [70,154]. A north Florida slash pine (Pinus elliottii)
site with small amounts of western bracken fern was clearcut in late fall.
Debris and residual vegetation were mechanically chopped the following
April and again in August, followed by mechanical preparation and
planting. Western bracken fern amounts remained fairly steady and did not
increase to harmful levels [35].
Biological control: Biological methods for control of western bracken fern in
Great Britain are being investigated and two South African moths
(Conservula conisigna and Panotima sp. near angularis) appear promising.
Both moths are capable of severely damaging the fronds in the spring,
but no biocontrol agent capable of damaging the rhizomes has yet been
identified [146]. Lawton [143] evaluates potential control insects and
potential problems with their use. The possibility of using disease
fungi, either alone or in conjunction with herbicides, to control
bracken is also being studied [25].
Chemical control: Asulam is a relatively specific and environmentally
safe herbicide that is very effective for western bracken fern control
[26,118,129,160,197]. Asulam is more effective if the western bracken fern is
cut first [54]. Dead fronds may need to be cut away from growing trees
after spraying with asulam [212]. Glyphosate (Roundup) is also
effective and reduces carbohydrate reserves of the rhizome
[12,26,48,136,160,241]. Other effective chemical controls include
amitrole-T, dicamba, karbutilate, picloram, 4-CPA, sodium
chlorate/borate, chlorthiamid, and dichlobenil [31,165]. The
effectiveness of these is variable in the Pacific Northwest [26]. Two
applications increases control [222]. Methods and timing of herbicide
application are discussed by Hamel [103], Robinson [201], Miller and
Kidd [166], and Burrill and others [26]. Spraying vegetation with other
herbicides may reduce competition and allow western bracken fern expansion
[182,219].
BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Pteridium aquilinum
GENERAL BOTANICAL CHARACTERISTICS :
The leaves or fronds of western bracken fern are normally from 1 to 10 feet
(3-30 dm) long including a stipe (leaf-stalk) that may be as long as 39
to 59 inches (10-15 dm) but is usually shorter than the leaf blade
[119]. The blades of the fronds are divided into pinnae, the bottom
pair of which are sometimes large enough to give the impression of a
three-part leaf. Each pinna is in turn divided into pinnules. Above
the first division of the stipe into a frond, it is called a rachis. On
fertile fronds the spores are borne in sori beneath the outer margins of
the pinnules. The sori are protected by the inrolled pinnule margins on
one side and a thin membrane called an indusium on the other [119].
Nectaries are found at the base of the pinnae during spring and early
summer [141,232]. The largest nectaries are found near the base of the
frond and the nectaries get progressively smaller going up the rachis
[141]. Ants are attracted by and feed on sugars produced by these
extra-floral nectaries [110,111,227]. It has been suggested but not
proven that an ant-plant mutualism may exist where the ants would attack
other insects feeding on the plants. The ants do attack introduced
caterpillars and they tend an aphid species on western bracken fern in Arizona
[110,111,144,227].
The fronds are killed by frost. In northern climates they are killed
each winter and new fronds grow in spring; in mild areas individual
fronds persist for 2 to 3 years before being replaced [195]. Dead
fronds form a mat of highly flammable litter that insulates the
below-ground rhizomes from frost when there is no snow cover. This
litter also delays the rise in soil temperature and emergence of
frost-sensitive fronds in the spring [237].
Rhizomes are the main carbohydrate storage organs [48,243]. Rhizomes
also store water and are consistently around 87 percent water [211].
Rhizomes can be up to 1 inch (2.5 cm) in diameter [79] and branching is
alternate [236,238,239]. The rhizome system has two components. The
long shoots form the main axis or stem of the plant [239]. They
elongate rapidly, have few lateral buds, do not produce fronds, and
store carbohydrates [48,236,243]. Short shoots, or leaf-bearing lateral
branches, may be closer to the soil surface [33]. They arise from the
long shoots, are slow growing, and produce annual fronds and many
dormant frond buds. Transition shoots start from both short and long
shoots and may develop into either [48]. Thin, black, brittle roots
extend from the rhizome and may extend over 20 inches (50 cm) deeper
into the soil [211,238,239]. Endotrophic mycorrhizae have been found on
the roots of western bracken fern [41,126].
Fossil evidence suggests that western bracken fern has had at least 55 million
years to evolve and perfect antidisease and antiherbivore chemicals
[192]. It produces bitter tasting sesquiterpenes and tannins,
phytosterols that are closely related to the insect molting-hormone,
and cyanogenic glycosides that yield hydrogen cyanide (HCN) when
crushed. It generates simple phenolic acids that reduce grazing, may
act as fungicides, and are implicated in western bracken fern's allelopathic
activity [42]. Severe disease outbreaks are very rare in western bracken fern
[126,192].
Most work describing western bracken fern has been done on var. aquilinum which
is closely related to varieties latiusculum, pseudocaudatum, and
pubescens [232]. Some differences between the varieties are noted below
[90,106,198,205,232,239].
P. a. var. latiusculum - Growth of the long rhizomes is relatively slow with
rates of 4 to 7 inches (10-17 cm) versus 10 to 35 inches (25-90 cm)
annually so it is less weedy than other varieties. The growing tip of the
rhizome has no hairs or a few whitish hairs. The terminal segment of
the frond is not much longer than lateral segments; thus the frond
appears triangular or three-parted. The only pubescence is along the
pinnule margins and midvein.
P. a. var. pseudocaudatum - The frond blade is usually completely glabrous and
rarely ternate. The terminal segment of the frond is much longer than
the lateral segments and between six and fifteen times as long as broad.
The growing tip of the rhizome usually has a tuft of dark hairs.
P. a. var. pubescens - The frond blade is ovate-triangular but not ternate,
while the upper surface of the frond is frequently pubescent and the
lower surface is usually densely pubescent. There is a tuft of dark
hairs on the growing tip of the rhizome.
RAUNKIAER LIFE FORM :
Undisturbed State: Cryptophyte (geophyte)
Burned or Clipped State: Cryptophyte (geophyte)
REGENERATION PROCESSES :
Most regeneration in western bracken fern is vegetative. Many investigators
have searched for young plants growing from spores [186, Stickney 1989,
personal communication], but few have found them. However, spores do
germinate and grow readily in culture [7,33,37,40].
Young western bracken fern plants can produce spores by the end of the second
growing season in cultivation but normally do not produce spores until
the third or fourth growing season [40,97]. A single, fertile frond can
produce 300,000,000 spores annually [38,40]. Spore production varies
from year to year depending on plant age, frond development, weather,
and light exposure [40]. Production decreases with increasing shade
[40,189]. The wind-borne spores are extremely small. Dry spores are
very resistant to extreme physical conditions, although the germination
of western bracken fern spores declines from 95 to 96 percent to around 30 to 35
percent after 3 years storage [190]. The spores germinate without any
dormancy requirement. Under favorable conditions, young plants could be
found 6 to 7 weeks after the spores are shed [37,40]. Under normal
conditions the spores may not germinate until the spring after they are
shed [33,38].
Sufficient moisture and shelter from wind are important factors in fern
spore germination [167]. Western bracken fern spore germination appears to
require soil sterilized by fire [37,186]. On unsterilized soils spores
may germinate, but the new plants are quickly overwhelmed by other
growth [37]. Temperatures between 59 and 86 degrees F (15-30 degrees C)
are generally best for germination, although western bracken fern is capable of
germination at 33 to 36 degrees F (1-2 degrees C). A pH range of 5.5 to
7.5 is optimal for germination [38,167]. Germination of western bracken fern is
indifferent to light quality; it is one of the few ferns that can
germinate in the dark [189,240]. Despite limitations on spore
germination, genotype analysis in the Northeast indicates that many
stands of western bracken fern represent multiple establishment of individuals
from spores [96,250].
When spores germinate, they produce bisexual, gamete-bearing plants
about 0.25 inch (0.6 cm) in diameter and one cell thick. These tiny
plants (gametophytes or prothalli) have no vascular system and require
very moist conditions to survive. The young spore-bearing plant
(sometimes called a sporling) which develops from the fertilized egg is
initially dependent on the gametophyte until it develops its first leaf
and roots. The first fronds are simple and lobed. They develop into
thin, delicate fronds divided into lobed pinnae. They do not look like
adult plants and are frequently not recognized as western bracken fern [37,189].
Cultivated plants of var. aquilinum begin to resemble adult western bracken fern
after 18 weeks. The rhizomes begin to develop after there are a number
(up to 10) of fronds and a well-developed root system or in the
fifteenth week of growth under optimal conditions. In the first year
rhizomes may grow to 86 inches (217 cm) long [20]. By the end of a
second year the rhizome system may exceed 6 feet (18 dm) in diameter
[20,37].
Western bracken fern's aggressive rhizome system gives it the ability to
reproduce vegetatively and reduces the plant's dependence on water for
reproduction [42]. The rhizomatous clones can be hundreds of years old,
and some clones alive today may be over 1,000 years old [186,192,250].
Rhizomes have a high proportion of dormant buds [236]. When disturbed
or broken off, all portions of the rhizome may sprout, and plants
growing from small rhizome fragments revert temporarily to a juvenile
morphology [48, 192]. A recent study of western bracken fern genotypes using
isozyme patterns found individual clones in New England were up to 400
feet (120 m) in diameter, and clones often intermingled in an area
[250].
SITE CHARACTERISTICS :
Western bracken fern grows on a variety of soils with the exception of heavily
waterlogged soils [23]. Its efficient stomatal control allows it to
succeed on sites that would be too dry for most ferns, and its
distribution does not normally seem limited by moisture [230,235].
Western bracken fern grows best on deep well-drained soils with good
water-holding capacity, and it may dominate other vegetation on such
sites [57,68]. Its productivity increases with increasing soil profile
development on Michigan entisols and spodosols [113]. In northern Idaho
the surface soil horizon under western bracken fern is an acidic, dark mineral
layer, while under interspersed conifer stands the surface soil horizon
is an acidic, light mineral layer [59].
Western bracken fern rhizomes are particularly effective at mobilizing
phosphorus from inorganic sources into an available form for plant use
[168]. Western bracken fern contributes to potassium cycling on sites and is
associated with high levels of potassium [28,157,175]. Fertilization of
cultured plants increases frond dry weight; using both nitrogen (N) and
phosphate (P) increases rhizome length, while using N, P, and potassium
(K) increases both rhizome length and rhizome dry weight [49]. Bracken
fern is characteristically found on soils with medium to very rich
nutrients [91,105,235]. In southeastern Alaska western bracken fern prefers a
pH of 5.0 to 6.0 [225]. It is absent from soils contaminated with zinc
[131].
In northern climates western bracken fern is frequently found on uplands and
side slopes, since it is susceptible to spring frost damage [47,150].
Fronds growing in the open or without litter cover are often killed as
crosiers by spring frost damage, since the soil warms earlier and growth
begins sooner [237]. The result is that fronds appear earlier in shaded
habitats [113,204]. Cultivated and shaded plants produce fewer, thinner
but larger fronds than open-grown plants [49]. A New York study found
that fronds growing in the shade were twice as likely as fronds growing
in the open to be cyanogenic [204]. That was also true in Great Britain
[43], however, a New Jersey study found no cyanogenic plants [226].
Shaded plants produce fewer spores than plants in full sun [189].
Elevation: Elevational ranges in some western regions are [56,142,179]:
Minimum Maximum
feet meters feet meters
New Mexico 8,000 2,438 9,500 2,896
California sea level 10,000 3,048
Utah 5,500 1,676 8,000 2,438
Colorado 5,300 1,615 10,000 3,048
Wyoming 4,800 1,463 8,500 2,591
Montana 4,300 1,311 5,000 1,524
Var. pubescens is generally found in open forests, pastures, and on open
slopes; it is common following fire [189,232]. In the Pacific Northwest
western bracken fern is found along the coast on stabilized dune meadows and in
coastal prairies. It is found in the forests of western Washington and
northwestern Oregon and it may be a dominant in grassy balds of the
Coast Mountains, subalpine meadows, and on avalanche tracks and
southerly slopes in the Cascades [57,78,169]. Western bracken fern increases
from west to east across the central Washington Cascades [53]. Within
the rain shadow area of the eastern slope of the Olympic Mountains,
western bracken fern is a dominant understory species in Oregon white oak
(Quercus garryana) savanna [50,228]. In the Columbia Basin of eastern
Oregon and Washington western bracken fern grows in riparian communities with
Douglas hawthorn (Crataegus douglasii) [78]. It is more frequent on
south-facing slopes in northern Idaho [175] and north-central Washington
where its cover is greater below 3,800 feet (1,150 m) than at higher
elevations [229]. It grows well on snow chutes in subalpine fir (Abies
lasiocarpa) habitat types in northwestern Montana [248]. In British
Columbia it grows best in areas with a humid climate, mild winters, and
a relatively long growing season [97]. In southeastern Alaska bracken
fern is found in the ecotone between forest and bog [180] or in muskegs
[225]. Western bracken fern is found in the coastal redwood region of
California and on flood plains and gentle slopes under the giant sequoia
(Sequoiadendron giganteum) in California's Sierra Nevada [108,235]. In
Arizona it is an understory species in deciduous, riparian forests [21].
In New Mexico and Arizona western bracken fern is found in the mountains under
blue spruce (Picea pungens) and Douglas-fir, in pinyon-juniper or Gambel
oak (Quercus gambelii) and ponderosa pine (Pinus ponderosa) woodlands,
and in grassy meadows [19,134,142,170,194]. Western bracken fern is found with
aspen in Colorado [15,121,122].
P. a. var. latiusculum: In Wisconsin, northern Michigan, and probably
Minnesota, bracken-grasslands, doubtless initially caused by fire, are
found on soils ranging from loam to fine sand [47]. Some of these
bracken-grasslands occupy depressions with western bracken fern dominant on the
surrounding slopes. Western bracken fern is also a common understory species in
Wisconsin oak (Quercus spp.) openings and barrens [47]. In New England
P. a. var. latiusculum and P. a. var. pseudocaudatum prefer dry woods, clearings,
fields, and thickets. Western bracken fern is not found on limey soil [205].
In White Mountain forests it is most often found on dry areas of shallow
bedrock or outwash [147].
P. a. var. pseudocaudatum: Southern western bracken fern is most common on
well-drained sandy soils under open stands of longleaf pine (Pinus
palustris), shortleaf pine (P. echinata), and mixtures of pine (Pinus
spp.) and oak [35,88,92,135]. It is also associated with pocosin [135].
In West Virginia western bracken fern was found on a high plateau growing among
other vegetation in a heath meadow with scattered small spruce [44]. On
the Alabama piedmont it is associated with upper slopes and ridges with
shallow soils [88]. Along the Atlantic Coastal Ridge of southern
Florida, western bracken fern is found on low hammocks and disturbed sites
[200]. Var. caudatum may also be found in this area on low hammocks and
disturbed sites [200]. On low hammocks western bracken fern is associated with
oaks and cabbage palmetto (Sabal palmetto) [200]. It is also found in
the margins of scrub vegetation where the sandy soil contains more clay
and silt and thus retains water better [178]
SUCCESSIONAL STATUS :
Western bracken fern is basically a shade-intolerant pioneer and seral species
that is sufficiently shade tolerant to survive in light-spots in
old-growth forests [127,192,216]. A study in southwestern Oregon
suggested that western bracken fern is an indicator of light intensity. In this
study western bracken fern cover was 75 percent at 60 to 100 percent of full
sunlight, and dropped to 50 percent between 25 and 60 percent of full
sunlight. When light intensity was under 25 percent of full sunlight,
western bracken fern cover was less than 5 percent [61].
The light, windborne spores of western bracken fern allow it to colonize newly
vacant areas. Western bracken fern has been documented as a pioneer on sterile,
cooled lava slopes [190]. After disturbance in western Washington and
northwestern Oregon forests, western bracken fern often invades sites where it
was not previously present [78,100]. It enters the dry meadow stage of
succession on coastal sand dunes of the Pacific Northwest and was an
early seral species following the eruption of Mount St. Helens where
some plants were observed originating from rhizome fragments
[78,101,164].
In areas unaffected by coastal moisture western bracken fern rarely establishes
from spores [68]. However, solitary plants may expand from rhizomes
following disturbance [220,221]. These plants may depend upon canopy
level removal or openings for establishment of a system of clonal
ramets. Under a canopy of oak and pine in the New Jersey pine barrens,
western bracken fern distribution resembles that of sexually reproducing herbs
rather than that of clones [161].
In western forests very small amounts of western bracken fern persist under a
canopy for at least 200 to 400 years [94,133,169]. Following
disturbance, western bracken fern is a common seral species that may be dominant
in coastal forests from Oregon to Southern Alaska and in New England
[50,94,114,133]. In the Pacific Northwest annuals may be followed
closely by western bracken fern and other perennials [45,203]. It is seral in
Oregon's interior valleys [89], in California coastal redwoods, and in
valley oak (Quercus lobata), blue oak (Q. douglasii), and digger pine
(Pinus sabiniana) savannas [93,249]. It follows disturbance in grand
fir and cedar hemlock forests of the northern Rocky Mountains [153]. It
occurs in seral brush fields in northern Idaho and southwestern Oregon
[95,109]. In contrast, a study in white fir (Abies concolor) forests of
the Sierra Nevada found western bracken fern predominantly in mature or late
seral stands with low light intensities [36]. Authors of a New Jersey
study with similar results suggested that western bracken fern distribution in
their area was spotty and showed no real preference for low light [24].
In Southern longleaf pine plantations western bracken fern is associated with
disturbance following thinning operations but is absent from patch or
clearcut areas [245]. Following fire in a Pennsylvania scrub oak
(Quercus ilicifolia) community, western bracken fern increased rapidly
immediately after burning but declined sharply after the first year due
to competition from blueberry (Vaccinium spp.) and huckleberry
(Gaylussacia spp.) [99].
Where western bracken fern invades grasslands and low shrublands, it may exhibit
a cyclic succession. If undisturbed, the dense western bracken fern cover
gradually deteriorates into sparse western bracken fern with grass and shrubs.
Eventually dense western bracken fern may reinvade [159,238].
SEASONAL DEVELOPMENT :
In North America, fronds usually begin to emerge between March and early
May. Frost-killed fronds are replaced through mid-July [33]. In a
northern Idaho study, western bracken fern first appeared in early May and
continued growth through mid-July. The fronds began to change color by
mid-August, probably because of limited soil moisture [58]. Spore
maturation and dispersal begins at the base of the frond and proceeds up
to the tip resulting in an extended period of spore dispersal [40]. In
New England and the Carolinas, western bracken fern produces spores from early
July to late September [198,205]. Spore release in Michigan is between
the first of June and mid-August [115] and from July to September on the
Great Plains [90]. In Canada sporulating begins as early as June 24 in
Ontario, June 29 in Quebec, July 16 in Nova Scotia, July 22 in British
Columbia, July 29 in New Brunswick, August 1 on Prince Edward Island,
and August 5 in Manitoba [33].
FIRE ECOLOGY
SPECIES: Pteridium aquilinum
FIRE ECOLOGY OR ADAPTATIONS :
Western bracken fern is considered a fire-adapted species throughout the world
[192]. It is not only well adapted to fire, it promotes fire by
producing a highly flammable layer of dried fronds every fall
[2,79,128,234]. In the Pacific Northwest western bracken fern fronds grow to 6
feet, resulting in several tons of flashy fuel per acre [162] and
western bracken fern adds to the high fuel loads in northern Idaho brushfields
[95]. Repeated fires favor western bracken fern [2,127,128,206].
Most sources agree that western bracken fern's primary fire adaptation is its
deeply buried rhizomes which sprout vigorously following fires before
most competing vegetation is established [6,30,192,209,220,221,224].
Western bracken fern's windborne spores may disperse over long distances. Fire
removes competition and creates the alkaline soil conditions suitable
for its establishment from spores [192].
POSTFIRE REGENERATION STRATEGY :
survivor species; on-site surviving rhizomes
off-site colonizer; spores carried by wind; postfire years one and two
FIRE EFFECTS
SPECIES: Pteridium aquilinum
IMMEDIATE FIRE EFFECT ON PLANT :
Western 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 :
Western bracken fern is well known as a postfire colonizer in western
coniferous forests and eastern pine and oak forests [17,156]. Fire
benefits western bracken fern by removing its competition while it sprouts
profusely from surviving rhizomes [97,192,229]. New sprouts are more
vigorous following fire, and western 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].
Western 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, western 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 western 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,
P. a. var. latiusculum and P. a. 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.
P. a. var. pubescens: Western 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 western bracken fern [82]. Along the Pacific coast western 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]. Western bracken fern increased following
single or multiple broadcast fires in northern Idaho [175]. After
logging or fire in Arizona ponderosa pine communities, western bracken fern may
cover up to 30 percent of the area for 10 or more years [27,187,188].
P. a. 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, western 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, western 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 western 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, western 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 western 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, western bracken fern thrives
following severe fires [17,161]. It increases moderately in canopy gaps
in these forests following surface fires.
P. a. var. pseudocaudatum: Western 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, western 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]. Western 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, western 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 western bracken fern and allowing it to
dominate other understory species, including wiregrass (Aristida
stricta) which had been prominent [224].
The following Research Project Summaries
provide information on prescribed
fire use and postfire response of plant
community species, including western
bracken fern, that was not available when this
species review was originally
written:
FIRE MANAGEMENT CONSIDERATIONS :
Fire can facilitate the spread of western 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
western 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 western 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 western bracken fern.
References for species: Pteridium aquilinum
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