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SPECIES:  Pteridium aquilinum
Western brackenfern. Public domain image by Ansel Adams from the series "Ansel Adams Photographs of National Parks and Monuments", compiled from 1941-1942.


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: []. Revisions: Images were added on 22 March 2018. 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 NRCS PLANT CODE : PTAQ COMMON NAMES : western brackenfern bracken brake fern TAXONOMY : The scientific name of western brackenfern is Pteridium aquilinum (L.) Kuhn. At this time western brackenfern 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, hairy brackenfern P. a. var. pseudocaudatum, western brackenfern P. a. var. latiusculum, decomposition brackenfern In this review, the name "western brackenfern" 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 brackenfern is included, either the varietal name or the location is given. Where varieties of western brackenfern 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


SPECIES: Pteridium aquilinum
GENERAL DISTRIBUTION : Western brackenfern 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]:
Distribution of western brackenfern. Map courtesy of USDA, NRCS. 2018. The PLANTS Database. National Plant Data Team, Greensboro, NC [2018, March 22].

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

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.

   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

     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

    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

   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

     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


Western brackenfern 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 brackenfern indicates site deterioration [121].  Published
classification schemes listing western brackenfern 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

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,

Pacific            general veg. pas         Hall 1984

Region 2: CO,NE,   general veg. pas         Johnston 1987


SPECIES: Pteridium aquilinum
IMPORTANCE TO LIVESTOCK AND WILDLIFE : In Montana, elk eat western brackenfern 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 brackenfern is ranked as a low-use forage for deer which eat it only in the spring [92]. White-tailed deer eat western brackenfern in trace amounts only in the summer and fall [132] or not at all [116].  However, western brackenfern 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 brackenfern [79]. Cattle feeding on lush grass may eat western brackenfern for roughage or if it is mixed in hay [33,62]. In the Pacific Northwest sheep avoid mature fronds of western brackenfern 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 brackenfern's production of bitter-tasting compounds, chemicals that interfere with insect growth, and toxic chemicals, western brackenfern hosts a relatively large number and variety of herbivorous insects [141,142].  In Great Britain 27 to 35 insect species eat western brackenfern. 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 brackenfern grows in a very restricted area [142].  Some North American sawflies feed on western brackenfern [141]. PALATABILITY : Western brackenfern'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 brackenfern are most palatable to deer and livestock [92,227].  Cattle sometimes eat it for roughage [62].  A study using captive mule deer gave western brackenfern a low preference rating, since the deer only consumed it in July [210]. NUTRITIONAL VALUE : The crude protein content of western brackenfern 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 brackenfern 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 brackenfern [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 brackenfern [104].  Sheep and cattle are most often poisoned by western brackenfern when young animals are moved from an area without western brackenfern to a field containing the fern.  Cumulative poisoning may occur in older sheep that have ingested small amounts of western brackenfern over a period of years [104]. COVER VALUE : Western brackenfern 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 brackenfern [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 brackenfern [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 brackenfern do not normally need seeding and should be low in priority for such activities [229]. OTHER USES AND VALUES : Western brackenfern was considered so valuable during the Middle Ages that it was used to pay rents [202].  Western brackenfern 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 brackenfern 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 brackenfern 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].  Western brackenfern 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 brackenfern 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 brackenfern 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 brackenfern is a potential source of insecticides and it has potential as a biofuel [140].  Western brackenfern 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 brackenfern fronds are particularly sensitive to acid rain which also reduces gamete fertilization.  Both effects signal the amount of pollutants in rain water making western brackenfern a useful indicator [64,65,66]. OTHER MANAGEMENT CONSIDERATIONS : Competition:  Western brackenfern 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 brackenfern protected planted Douglas-fir seedlings from snowshoe hare and black-tailed deer browsing until the trees overtopped the western brackenfern; tree growth, however, was slower than normal [54,55].  Control may be needed until tree seedlings are taller than the western brackenfern and sturdy enough to withstand the weight of dead fronds [112].  Scots pine (Pinus sylvestris) has successfully invaded stands of dense western brackenfern (var. aquilinum) [159]. Allelopathy:  Western brackenfern'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 brackenfern.  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 brackenfern fronds affected thimbleberry (Rubus parviflorus) and salmonberry (R. spectabilis) germination but did not affect Douglas-fir (Pseudotsuga menziesii).  Western brackenfern 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 brackenfern, most of the new germinants died before shedding seed coats [71].  Herbs may be inhibited for a full growing season after western brackenfern is removed, apparently because active phytotoxins remain in the soil [124,87]. Western brackenfern control:  Timing is important in any treatment of brackenfern [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 brackenfern 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 brackenfern amounts remained fairly steady and did not increase to harmful levels [35]. Biological control:  Biological methods for control of western brackenfern 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 brackenfern control [26,118,129,160,197].  Asulam is more effective if the western brackenfern 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 brackenfern expansion [182,219].


SPECIES: Pteridium aquilinum
GENERAL BOTANICAL CHARACTERISTICS : The leaves or fronds of western brackenfern 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 brackenfern 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 brackenfern [41,126]. Fossil evidence suggests that western brackenfern 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 brackenfern's allelopathic activity [42].  Severe disease outbreaks are very rare in western brackenfern [126,192]. Most work describing western brackenfern 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 : Cryptophyte Geophyte REGENERATION PROCESSES : Most regeneration in western brackenfern 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 brackenfern 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 brackenfern 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 brackenfern 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 brackenfern 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 brackenfern 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 brackenfern 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 brackenfern [37,189]. Cultivated plants of var. aquilinum begin to resemble adult western brackenfern 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 brackenfern'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 brackenfern 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 brackenfern 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 brackenfern 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 brackenfern is an acidic, dark mineral layer, while under interspersed conifer stands the surface soil horizon is an acidic, light mineral layer [59]. Western brackenfern rhizomes are particularly effective at mobilizing phosphorus from inorganic sources into an available form for plant use [168].  Western brackenfern 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].  Western brackenfern is characteristically found on soils with medium to very rich nutrients [91,105,235].  In southeastern Alaska western brackenfern prefers a pH of 5.0 to 6.0 [225].  It is absent from soils contaminated with zinc [131]. In northern climates western brackenfern 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 brackenfern 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 brackenfern 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 brackenfern is a dominant understory species in Oregon white oak (Quercus garryana) savanna [50,228].  In the Columbia Basin of eastern Oregon and Washington western brackenfern 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, western brackenfern is found in the ecotone between forest and bog [180] or in muskegs [225].  Western brackenfern 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 brackenfern 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 brackenfern 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 brackenfern dominant on the surrounding slopes.  Western brackenfern 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 brackenfern 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 brackenfern 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 brackenfern 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 brackenfern 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 brackenfern 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 brackenfern 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 brackenfern is an indicator of light intensity.  In this study western brackenfern 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 brackenfern cover was less than 5 percent [61]. The light, windborne spores of western brackenfern allow it to colonize newly vacant areas.  Western brackenfern has been documented as a pioneer on sterile, cooled lava slopes [190].  After disturbance in western Washington and northwestern Oregon forests, western brackenfern 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 brackenfern 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 brackenfern distribution resembles that of sexually reproducing herbs rather than that of clones [161]. In western forests very small amounts of western brackenfern persist under a canopy for at least 200 to 400 years [94,133,169].  Following disturbance, western brackenfern 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 brackenfern 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 brackenfern predominantly in mature or late seral stands with low light intensities [36].  Authors of a New Jersey study with similar results suggested that western brackenfern distribution in their area was spotty and showed no real preference for low light [24]. In Southern longleaf pine plantations western brackenfern 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 brackenfern 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 brackenfern invades grasslands and low shrublands, it may exhibit a cyclic succession.  If undisturbed, the dense western brackenfern cover gradually deteriorates into sparse western brackenfern with grass and shrubs. Eventually dense western brackenfern 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 brackenfern 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 brackenfern 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].


SPECIES: Pteridium aquilinum
FIRE ECOLOGY OR ADAPTATIONS : Western brackenfern 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 brackenfern fronds grow to 6 feet, resulting in several tons of flashy fuel per acre [162] and western brackenfern adds to the high fuel loads in northern Idaho brushfields [95].  Repeated fires favor western brackenfern [2,127,128,206]. Most sources agree that western brackenfern'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 brackenfern's windborne spores may disperse over long distances.  Fire removes competition and creates the alkaline soil conditions suitable for its establishment from spores [192]. FIRE REGIMES : Find fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find Fire Regimes". POSTFIRE REGENERATION STRATEGY :    survivor species; on-site surviving rhizomes    off-site colonizer; spores carried by wind; postfire years one and two


SPECIES: Pteridium aquilinum
IMMEDIATE FIRE EFFECT ON PLANT : Western brackenfern 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]. PLANT RESPONSE TO FIRE : Western brackenfern is well known as a postfire colonizer in western coniferous forests and eastern pine and oak forests [17,156].  Fire benefits western brackenfern by removing its competition while it sprouts profusely from surviving rhizomes [97,192,229].  New sprouts are more vigorous following fire, and western brackenfern 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 brackenfern 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 brackenfern 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 brackenfern 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 brackenfern 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 brackenfern [82].  Along the Pacific coast western brackenfern invades recent burns by windborne spores and also spreads from its buried rhizome [128].  After spring fires in northern Idaho, western brackenfern production dropped somewhat in the first year and then increased in the second and third years [148].  Western brackenfern increased following single or multiple broadcast fires in northern Idaho [175].  After logging or fire in Arizona ponderosa pine communities, western brackenfern 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 brackenfern'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 brackenfern 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 brackenfern 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 brackenfern decreased slightly after logging without burning but increased strongly following logging and early summer burning [207,208].  Increased western brackenfern 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 brackenfern 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 brackenfern thrives following severe fires [17,161].  It increases moderately in canopy gaps in these forests following surface fires. P. a. var. pseudocaudatum:  Western brackenfern 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 brackenfern increased its frequency from 16.7 to 20.6 percent and doubled its biomass in a Florida slash and longleaf pine forest [171].  Western brackenfern 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 brackenfern 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 brackenfern 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
brackenfern, that was not available when this species review was originally
Fire can facilitate the spread of western brackenfern [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 brackenfern 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 brackenfern 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 brackenfern.

References for species: Pteridium aquilinum

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