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 and Danish , 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
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
, Plants of the World Online accepted 20 species: Image Scientific name DistributionPteridium aquilinum Macaronesia, N. & NE. Tropical Africa, Arabian Peninsula, Europe to Siberia and IranPteridium arachnoideum Mexico to Tropical America Pteridium brownseyi Pakistan to W. Himalaya Pteridium campestre S. Tropical America. Pteridium capense Africa.Pteridium caudatum Tropical & Subtropical America. Pteridium centrali-africanum Gabon to Kenya and S. Tropical AfricaPteridium decompositum HawaiiPteridium esculentum SE. China to Sumatera and S. Pacific Pteridium falcatum China (E. Guangxi) Pteridium feei Mexico to Central America Pteridium japonicum China to Indo-China and Temp. E. AsiaPteridium latiusculum Canada to N. Mexico Pteridium lineare China (W. Yunnan)Pteridium pinetorum Europe to Siberia. Pteridium pseudocaudatum Central & E. U.S.A. Pteridium pubescens Alaska to Mexico (Baja California) Pteridium revolutum Tropical & Subtropical Asia to N. Australia Pteridium rostratum E. Himalaya to W. Malesia, Maluku, NE. Queensland Pteridium yunnanense China (W. Yunnan)
Distribution and habitat
Pteridium aquilinum (bracken or common bracken) is the most common species of this genus 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 . 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,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 citing a Bracken Advisory Commission member and professor of sustainable land use.See also the 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. Brown stated his view, at that time, that "removing the grants that used to be paid to farmers to eradicate bracken has done us no favours". (At one time the British government had an eradication programme, paying farmers to do so—but as of September 1996, such support had ceased, except in Wales.)
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 when it invades pastureland.
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.
Bracken can harbour high levels of sheep ticks, which can pass on Lyme disease. Grazing provided some control by stock trampling, but this has almost ceased since the 2001 foot-and-mouth disease outbreak reduced commercial livestock production.
Bracken is a well-adapted pioneer plant which can colonise land quickly, with the potential to extend its area by as much as 1%–3% per year. This ability to expand rapidly at the expense of other plants and wildlife can cause major problems for land users and managers. It colonises ground with an open vegetation structure, but is slow to colonise healthy, well managed heather stands.
Bracken presents a threat to biodiversity. Many plant species occur only on upland moorland, tied to unique features in the habitat. The loss and degradation of such areas due to the dominance of bracken has caused many species to become rare and isolated.
Bracken is known to form large fern prairies (sometimes known as fern savannahs or the Fernland). Some of these are natural but others can be formed via fires created by humans.Brackens are also key parts of other types of savannah such as Pine savannah and Pineyards.
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
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.
Uses
Food
Bracken fiddleheads have been eaten by many cultures throughout history, either fresh, cooked, or pickled. Pteridium aquilinum is especially common in East Asian cuisine.