Bracken

Bracken (Pteridium) is a genus of large, cosmopolitan, coarse ferns in the family Dennstaedtiaceae. Brackens are noted for their large, highly divided fronds and are found on all continents except Antarctica; their typical habitat is moorland.The word bracken is of Old Norse origin, related to Swedish bräken and Danish bregne, both meaning fern. In the past, the genus was commonly treated as having only one species, Pteridium aquilinum, but the current trend is to subdivide it into about ten species. Like other ferns, brackens reproduce by spores rather than seeds or fruit. The immature fronds, known as fiddleheads, are sometimes eaten, although some contain carcinogenic compounds.

Description

thumb|Sori (paler green) along outer edge on underside of leaves

Bracken is one of the oldest ferns, with fossil records from the Eocene period 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 long or longer with support, but typically are in the range of high. In cold environments, bracken is deciduous and, as it requires well-drained soil, is generally found growing on the sides of hills.

Fern spores are contained in structures found on the underside of the leaf called sori. The sori of bracken are located in a line next to the leaf-edge and are distinctly different from those in most other ferns, where the sori are circular and occur towards the centre of the leaf.

Species

As of this date, the following is a list of recognised Pteridium species:

Distribution and habitat

Pteridium aquilinum (bracken or common bracken) is the most common species of this plant type with a cosmopolitan distribution (occurring in suitable habitats in temperate and subtropical regions throughout much of the world).

It is a prolific and abundant plant in the moorlands of Ireland, where it is limited to altitudes of below 600 metres. It does not like poorly drained marshes or fen. It has been observed growing in soils from pH 2.8 to 8.6. Exposure to cold or high pH inhibits its growth.

As of the mid-1990s, the problem of the expansive growth of the range of bracken was an acute issue in Great Britain; as Malcolm Smith noted in reporting for The Independent in September 1996,<blockquote>The area covered by [bracken, as of that date] in Britain is equivalent to the size of Yorkshire, 2.5 [million] acres... [and] it is still spreading, in places by up to three per cent a year That expert, Roy Brown, noted bracken to be "particularly bad in eastern Scotland, Cumbria, in the North York Moors, parts of Wales and southwest England", and "spreading on many lowland roadside verges, sometimes into pastures", noting that "In the uplands, if heather moorland is burnt too often, or grazed too heavily, bracken takes over... spread[ing] very quickly, especially on deeper soils, by its underground rhizomes", noting that once it becomes established, its eradication is difficult.)

Bracken is a characteristic moorland plant in Ireland, which over the last decades has increasingly out-competed characteristic ground-cover plants such as moor grasses, cowberry, bilberry, and heathers. It now covers a considerable part of upland moorland. It causes problems in its invading pasturelands.

left|thumb|Bahamian Pineyards with Southern Bracken Fern at The Lucayan National Park of the Bahamas

Once valued and gathered for use in animal bedding, tanning, soap and glass making, and as a fertiliser, bracken is now seen as a pernicious, invasive, and opportunistic plant, taking over from the plants traditionally associated with open moorland and reducing easy access by humans. It is toxic to cattle, dogs, sheep, pigs, and horses, and is also linked to cancers in humans. In the United Kingdom, concern over the ptaquiloside-class of oncogenic natural products has led to application of special filters in processing British water supplies, to filter out bracken spores. Some of these are natural but others can be formed via fires created by humans.

Ecology

Evolutionarily, bracken may be considered one of the most successful ferns. It is considered highly invasive, and can survive in acid soils.

Fungal associations

Woodland fungi such as Mycena epipterygia can be found growing under the bracken canopy. Both Camarographium stephensii and Typhula quisquiliaris grow primarily from dead bracken stems.

Other plant associations

thumb|Young bracken fronds curled

Bracken 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. Its chemical emissions, shady canopy, and thick litter inhibit other plant species from establishing themselves – with the occasional exception of plants which support rare butterflies. Herb and tree seedling growth may be inhibited even after bracken is removed, apparently because active plant toxins remain in the soil.

Bracken substitutes the characteristics of a woodland canopy, and is 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 in the stands helps mosses survive underneath, including Campylopus flexuosus, Hypnum cupressiforme, Polytrichum commune, Pseudoscelopodium purum and Rhytidiadelphus squarrosus.

Control

Some small level of scattered cover can provide beneficial habitats for some wildlife, at least in the UK (as given above). However, on balance, removing bracken encourages primary habitats to re-establish, which are of greater importance for wildlife. Control is a complex question with complex answers, which need to form part of a wider approach. Management can be difficult and expensive; plans may need to be about cost-effective, practical limitation and control rather than give an expectation for eradication.

All methods need follow-up over time, starting with the advancing areas first. Given the decades elapsed to arrive at the current levels of coverage on many sites, slowing or reversing the process will be also of necessity long-term, with consistency and persistence from all parties being key.

Various techniques are recommended by Natural England and the RSPB to control bracken either individually or in combination  RSPB Bracken management in the uplands.

Cutting — Once or twice a year, repeatedly cutting back the fronds for at least 3 years.
Crushing/rolling — Using 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. In May and June, temporary close grazing or mob stocking on small areas away from nests, particularly using cattle, horses, pigs, or ponies may crush emerging bracken fronds resulting in reduced bracken cover. Sufficient fodder will be required to prevent livestock eating the bracken. This may suit steep areas where human access is difficult and herbicide undesirable.
Herbicide — Asulam (also known as Asulox) is selective for ferns; glyphosate is not; but the latter 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. Rare ferns such as adder's tongue (Ophioglossum vulgatum), killarney (Trichomanes speciosum) and lemon-scented ferns can also be found in similar habitats and it is important that these are not destroyed in the process of bracken control.

Natural England recommends that only Asulam can be sprayed aerially, Glyphosate requires spot treatment, e.g. using a weedwiper or knapsack spray. The toxicity of Asulam is low and has been generally highly cost-effective but its use is now restricted by the EU after 2012, at least until specific registered uses can be defined.

Selective sprays like Starane, Access, Metsulfuron 600WG, etc. work well but only if sprayed in late autumn so the rhizomes store food for winter and hence absorb the poison.

On archaeological sites, chemical control is usually required as mechanical methods may cause damage.

Allowing plants to grow in its place, e.g., the establishment of woodland, causes shade that inhibits bracken growth. In the UK, trees, notably rowan, have done well since grazing reduced greatly after the foot-and-mouth epidemic in 2000 but young saplings struggle in high bracken. In decades to come and if permitted, tree shade cover may increase and so may reduce bracken growth, but this is both long-term and in some cases is contentious in the change it would bring to traditionally open heath or moorland, both aesthetically and as a valuable habitat.
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.

Any bracken control programme must be completed, or bracken will re-establish.

Image:Adelaarsvaren planten Pteridium aquilinum.jpg|Pteridium aquilinum

Image:Tylerfinvold023 bracken ferns.jpg|Fronds of bracken

Image:The Dingle Peninsula, County Kerry, Ireland as seen from the south 05.jpg|Bracken fronds emerging from uncultivated land that was recently burned of heather

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Uses

thumb|Dried bracken bundles (P. aquilinum) at a food market in [[South Korea]]

Food

thumb|[[Warabimochi bracken jelly, a traditional Japanese dessert. The darker jelly on the left is made from pure bracken powder, while the lighter jelly on the right uses other starches as well.]]

Bracken fiddleheads have been eaten by many cultures throughout history, either fresh, cooked, or pickled. Pteridium aquilinum is especially common in East Asian cuisine.

In Korea, bracken (sometimes referred to as 'fernbrake' in Korean recipes) is known as gosari (), and is a typical ingredient in bibimbap, a popular mixed rice dish. Stir-fried bracken (gosari namul) is also a common side dish (banchan) in Korea.

In Japan, bracken is known as (ja), and is steamed, boiled, or cooked in soups. Warabimochi bracken jelly, named after its resemblance to mochi rice cakes, is a popular traditional dessert, although commercial variants are often made with cheaper potato starch instead. The fiddleheads are also preserved in salt, sake, or miso.

In China, bracken is known as juecai (), and is eaten like vegetables or preserved by drying. Also called "fernbrake", it is used as a vegetable in soups and stews.

Bracken rhizomes can be ground into flour to make bread. In the Canary Islands, the rhizome was historically used to make a porridge called gofio.

Bracken leaves are used in the Mediterranean region to filter sheep's milk, and to store freshly made ricotta cheese. after which the starch could be sucked from the fibres. Patu aruhe were important ritual items, and several distinct styles were developed. It has advantages over other sources of plant ash, such as hardwood, due to its high potash yield as a percentage of both dry and fresh mass, abundance, growth rate, and ease of harvesting. Bracken has been recognized as a source of potash since at least the 10th century AD, with numerous references in European texts, typically in relation to its use for soap and glass making. It is also used as a winter mulch, which has been shown to reduce the loss of potassium and nitrogen in the soil, and to lower soil pH. Foraging animals may ingest the plant when other sources of food are unavailable, such as during droughts or after snowfalls. In cattle, bracken poisoning can occur in acute and chronic forms, acute poisoning being the most common; milk from cows that have eaten bracken may also contain ptaquiloside, which is especially concentrated in buttermilk. Ptaquilosides have been shown to leach from wild bracken plants into the water supply, which has been implicated in high rates of stomach and oesophageal cancers in areas with high bracken growth, such as Wales and South America. Consumption of ptaquiloside-contaminated milk is thought to contribute to human gastric cancer in the Andean states of Venezuela.  (High stomach cancer rates are found in Japan and North Wales, where bracken is often eaten, but it is unclear whether bracken plays a role.)

The ptaquilosides are water-soluble and destroyed in heat (by cooking) and alkaline conditions (by soaking). Korean and Japanese cooks have traditionally soaked the shoots in water and ash to detoxify the plant before eating.

The British Royal Horticultural Society recommends against consumption of bracken altogether, by both humans and livestock. Moderation of consumption is recommended by some popular, non-expert publications (to reduce chances of cancer formation). In pigs and horses, bracken poisoning induces vitamin B1 deficiency.

In insects

Hydrogen cyanide is released by the young fronds of bracken when eaten by mammals or insects. Two major insect moulting hormones, alpha ecdysone and 20-hydroxyecdysone, are found in bracken. These cause uncontrollable, repeated moulting in insects ingesting the fronds, leading to rapid death. As of 2008, bracken was under investigation as a possible source of new insecticides.

Archaeology

thumb|200px|Bracken in Ireland with a linear pattern running across the hillside, a possible indication of past cultivation.

Many sites have archaeological remains dating from the Neolithic and Bronze Ages through to the Industrial Revolution. The root systems of established bracken stands degrade archaeological sites by disrupting the strata and other physical evidence. These rhizomes may travel a metre or more underground between fronds and form 90% of the plant, with only the remainder being visible.

In culture

Bracken is commonly referred to by local populations in the north of England as 'Moorland Scrub'.

The creature 'Bracken' from the 2023 video game Lethal Company is named after the plant.

References

External links

World fern species list — Pteridium
Independent page devoted to bracken (uses older classification scheme)
RSPB: Bracken management in the uplands
Bracken for Butterflies by Butterfly Conservation
Edibility of Bracken: Identification and edible parts of bracken