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]. 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

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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