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Bracken

[brak-uhn]

Brackens (Pteridium) are a genus of about ten species of large, coarse ferns, in the family Dennstaedtiaceae. The genus has probably the widest distribution of any fern genus in the world, being found on all continents except Antarctica and in all environments except for hot and cold deserts. Therefore it is considered to have a cosmopolitan distribution. In the past, the genus was commonly treated as having only one species, Pteridium aquilinum, but the recent trend is to subdivide it into several species.

It can also have a major impact on archaeological remains, by disturbing or destroying below-ground archaeological interest. It also obscures archaeological sites which could lead to their inadvertent damage.

The word bracken is of Old Norse origin, related to the Swedish word bräken, meaning fern.

Description and Biology

Evolutionarily, bracken may be considered to be one of the most successful ferns. It is also one of the oldest, with fossil records of over 55 million years old having been found. The plant sends up large, triangular fronds from a wide-creeping underground rootstock, and may form dense thickets. This rootstock may travel a metre or more underground between fronds. The fronds may grow up to 2.5 m (8 ft) long or longer with support, but typically are in the range of 0.6-2 m (2-6 feet) high. In cold environments bracken is winter-deciduous, and, as it requires well-drained soil, is generally found growing on the sides of hills.

It is a herbaceous perennial plant, deciduous in winter. The fronds are produced singly from an underground rhizome, and grow to 1-3 m tall; the main stem is up to 1 cm diameter at the base. The rhizomes typically grow to a depth of 50cm, although in some soils this may extend to more than a metre.

The spores used in reproduction are produced on the underneath of the leaf in structures found on the edges of the leaf called sorus. The linear pattern of these is different to other ferns which are circular and towards the centre.

Distribution

Pteridium aquilinum (Bracken or Common Bracken) is the most common species with a cosmopolitan distribution, occurring in temperate and subtropical regions throughout much of the world, including most of Europe, Asia, and North America in the Northern Hemisphere, and Australia, New Zealand and northern South America in the Southern Hemisphere. It is a prolific and abundant plant in the highlands of Great Britain. It is limited to altitudes of below 600 metres in the UK, does not like extreme cold temperatures, poorly drained Marshes or Fen. It causes such a problem of invading pastureland that at one time the British government had an eradication program. Special filters have even been used on some British water supplies to filter out the bracken spores.. NBN distribution map for the United Kingdom

It has been observered growing in soils from pH 2.8 to 8.6. Exposure to cold or high pH inhibits its growth.

Fungi associations

Woodland fungi can be found growing under the bracken canopy, for example Mycena epipterygia. Camarographium stephensii is host specific to the dead stems.

Other Plant Associations

Allelopathy: Bracken fern is known to produce and release allelopathic chemicals, which is an important factor in its ability to dominate other vegetation, particularly in regrowth after fire. Herb and tree seedling growth may be inhibited even after bracken fern is removed, apparently because active plant toxins remain in the soil.

Brackens substitute the characteristics of a woodland canopy, and are important for giving shade to european plants such as common bluebell and wood anemone, where the woodland does not exist. These plants are intolerant to stock trampling. Dead bracken provides a warm microclimate for development of the immature stages. Climbing corydalis,wild gladiolus and chickweed wintergreen also seem to benefit from the conditions found under bracken stands.

The high humidity helps mosses survive underneath including Campylopus flexuosus, Hypnum cupressiforme, Polytrichum commune, Pseudoscelopodium purum and Rhytidiadelphus squarrosus.

Animal species that use Bracken

Brackens of the northern hemisphere are used as food plants by the larvae of some Lepidoptera species including Dark Green Fritillary, Dot Moth, High Brown Fritillary, Gold Swift, Map-winged Swift, Pearl-bordered Fritillary, Orange Swift, Small Angle Shades, Small Pearl-bordered Fritillary. They also form an important ecological partnership with plants such as violet and cow-wheat (Melampyrum pratense) for various Boloria Fritillary species.

It is also a favoured haunt of the sheep tick Ixodes ricinus which can carry Lyme Disease.

Between 27 to 40 invertebrates (including nine moths) in the UK feed on bracken. These include the sawfly, a plant hopper (Dytroptis pteridis), the map-winged swift moth caterpillar, brown silver-line moth caterpillar (Petrophora chlorosata) and Paltodora cytisella. The numbers feeding on the bracken increase as the season progresses due to the decreasing levels of toxin, and the production of nectaries in the spring, food for ants which in turn may kill any herbivorous insects in the vicinity.

Some birds such as the whinchat and the nightjar use bracken as their preferred habitats. The nightjar may lay its eggs on the bare ground under the bracken. The skylark often nests in bracken and uses it for cover. Other birds known to nest in or beneath bracken include the willow warbler (it will also use bracken to construct its nest), the tree pipit, the yellowhammer, the ring ouzel, the woodcock and the twite.

The European adder can be found basking on bracken, the colour of their skin concealing them.

Uses

Bracken fiddleheads (the immature, tightly curled emerging fronds) have been considered edible by many cultures throughout history, and are still commonly used today as a foodstuff. Bracken fiddleheads are either consumed fresh (and cooked) or preserved by salting, pickling, or sun drying. In Korea, where they are called gosari namul (고사리 나물), they are a typical ingredient in the mixed rice dish called bibimbap.

Both fronds and rhizomes have been used to brew beer, and the rhizome starch has been used as a substitute for arrowroot. Bread can be made out of dried and powered rhizomes alone or with other flour. American Indians cooked the rhizomes, then peeled and ate them or pounded the starchy fiber into flour. In Japan, starch from the rhizomes is used to make confections.

Bracken is called wiwnunmí útpas ‘huckleberry’s blanket’ by the Umatilla Indians of the Columbia River in the United States Northwest. The fronds were used to cover a basket full of huckleberries in order to keep them fresh.

The Māori of New Zealand used the rhizomes of P. esculentum (aruhe) as a staple food, especially for exploring or hunting groups away from permanent settlements; much of the widespread distribution of this species in present-day New Zealand is in fact a consequence of prehistoric deforestation and subsequent tending of aruhe stands on rich soils (which produced the best rhizomes). The rhizomes were air-dried so that they could be stored and became lighter; for consumption, they were briefly heated and then softened with a patu aruhe (rhizome pounder); the starch could then be sucked from the fibers by each diner, or collected if it were to be prepared for a larger feast. Patu aruhe were significant items and several distinct styles were developed (McGlone et al. 2005).

Bracken has also been used as a form of herbal remedy. Powdered rhizome has been considered particularly effective against parasitic worms. American Indians ate raw rhizomes as a remedy for bronchitis.

In East Asia, Pteridium aquilinum (fernbrake or bracken fiddleheads) is eaten as a vegetable, called warabi (蕨 / わらび) in Japan, gosari (고사리) in Korea, and juécài (蕨菜) in China and Taiwan. In Korea, a typical banchan (small side dish) is gosari-namul (고사리나물) that consists of prepared fernbrake that has been sauteed. It is a component of the popular dish bibimbap.

Bracken has been shown to be carcinogenic in some animals and is thought to be an important cause of the high incidence of stomach cancer in Japan. It is currently under investigation as a possible source of new insecticides.

Uncooked bracken contains the enzyme thiaminase, which breaks down thiamine. Eating excessive quantities of bracken can cause beriberi, especially in creatures with simple stomachs. Ruminants are less vulnerable because they synthesize thiamine.

It was traditionally used for animal bedding, which later broke down to a rich mulch which could be used as fertiliser.

Other uses were as packing material for products such as earthenware, as a fuel, as a form of thatch. The ash was used for degreasing woolen cloth.

The ash of bracken fern was used in making forest glass in Central Europe from about 1000 to 1700.

Poisoning

The plant is carcinogenic to animals such as mice, rats and cattle when ingested, although they will usually avoid it unless nothing else is available. Young stems are used as a vegetable in Japan, leading some researchers to suggest a link between consumption and higher stomach cancer rates. The spores have also been implicated as a carcinogen. Danish scientist Lars Holm Rasmussen released a study in 2004 showing that the carcinogenic compound in bracken, ptaquiloside or PTQ, can leach from the plant into the water supply, which may explain an increase in the incidence of gastric and oesophageal cancers in bracken-rich areas.

In cattle, bracken poisoning can occur in both an acute and chronic form, acute poisoning being the most common. In pigs and horses bracken poisoning induces vitamin B deficiency. Poisoning usually occurs when there is a shortage of available grasses such as in drought or snowfalls.

It damages blood cells and destroys thiamine (Vitamin B1). This in turn causes beriberi, a disease linked to nutritional deficiency.

Control

Various techniques are recommended by Natural England to control bracken either individually or in combination:

  • Cutting - once or twice a year, for at least 3 years
  • Crushing - using heavy rollers, again for at least 3 years
  • Livestock treading - during winter, encouraging livestock to bracken areas with food. They trample the developing plants and allow frost to penetrate the rhizomes. Livestock should be removed in the spring to prevent them being poisoned.
  • Burning - useful for removing the litter, but may be counter-productive as bracken is considered to be a fire adapted species
  • Ploughing - late in the season followed by sowing seed
  • Herbicide - Asulam is selective for ferns, and Glyphosate is not but has the advantage that the effects can be seen soon after application. They are applied when the fronds are fully unfurled to ensure that the chemical is fully absorbed. Natural England recommends that only Asulam can be sprayed aerially, Glyphosate requires spot-treatment e.g. using a weedwiper or knapsack spray.
  • Allowing plants to grow in its place, e.g., the establishment of woodland, causes shade that inhibits bracken growth

Gallery

See also

References

External links

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