Bracken (or Pteridium aquilinum) is the largest (approx. 6ft) and most commonly found fern in the U.K. Its widespread distribution is indicated by its occurrence in dozens of the NVC communities. Bracken is found in a wide range of habitats (though it does not ‘like’ wet and is only found at sites below 600M.)
Bracken ‘prefers’ dry, somewhat acid soils though it can grow in a fairly wide pH range. It spreads by means of its underground rhizomes (modified underground stems), sometimes at a rate of one metre per year. On bare ground (for example, after burning), it can establish itself by spores, produced in sori (reproductive structures) on the underside of the leaves / fronds. Often bracken is a pioneer species. It has been described as 'the perfect weed'.
Bracken spores may be found in the cores taken for pollen analysis; these indicate that bracken has a long history in the U.K. landscape. Peaks of bracken spores are associated with loss of woodland cover in the last 2000 years, though there is some evidence for a decline in bracken in the 14th Century – which featured a number of cold (and wet) decades (the Black Death was rampaging across Europe).
In the past, bracken had a number of uses – animal bedding (later composted to give a nutrient-rich mulch), thatching, a source of potash (pot ash = plant ashes soaked in water in a pot giving a soluble form of potassium K+). The harvesting of bracken in historical times probably limited its spread. However, it is now spreading and its dominance in some areas / habitats is a concern.
Due to its height and large spread leaves / fronds, it can deprive other species of light and it produces a deep litter of its own dead, rusty-brown leaves. Bracken also produces allelopathic chemicals, that is, substances that inhibit seed germination and seedling growth of other plants. Thus, dense strands of bracken offer few opportunities for other plant species though bluebell may be found, and, in the New Forest – wild gladiolus. Various mosses find a home underneath bracken.
Some insects feed on bracken – sawflies and moths, and it is also a habitat for the sheep tick (Ixodes ricinus – lyme disease) and some important Fritillary butterflies. If eaten, bracken can induce poisoning in cattle and sheep – it contains a toxin Ptaquiloside and the young leaves when crushed or eaten release hydrogen cyanide.
- Regular cutting (twice a year for some years)
- Crushing / rolling regular – again for several years
- Treading by livestock – they trample the fronds and also expose the rhizomes to frosts etc. nb. It is important that there are other plants for the animals to eat application of herbicides (e.g. Asulam – selective for ferns but use now limited) – effects are soon seen
- Burning and ploughing.
So, how is the advance of this ‘perfect’ weed affecting our woodlands and their capacity to regenerate? Where there are plenty of seed-bearing trees and, therefore, a good seed bank in the soil, regeneration and replacement of mature trees (removed for timber or fallen through old age) will normally come from seedlings emerging through the ground layer. A healthy woodland has trees of all age classes, but bracken can stop this regeneration. Planting 'whips' will have little success in a bracken-dominated ground layer.