Bracken, Pteridium aquilinum, is one of the world’s oldest and most successful plants. It occurs on every continent except Antarctica. It is found in every part of Scotland, in a wide variety of habitats, and has been recorded growing at elevations up to 600 metres. It is a large fern with stems or fronds usually reaching between 1 and 2 metres in length. It is a natural component of many habitat types and supports a number of other species. Where bracken is widespread, it is often regarded as a threat to wildlife habitats, agriculture and cultural sites.
Bracken spreads through a vigorous rhizome system, which can be extensive in older bracken colonies. Bracken patches can appear in new places as a result of rhizomes being spread by animal movement or as a result of spores. As the fronds die off in winter, they collapse on the ground, forming a natural mulch.
Historically, farmers would harvest bracken and use it for livestock winter bedding and fertiliser. This is now rare. Deforestation and clear felling of forests have also enabled bracken to increase in density. Bracken now covers large areas of Scotland’s moors and uplands and can present problems for farmers, crofters, land managers and visitors to these areas, as well as suppress biodiversity.
Bracken impacts
Biodiversity
Where it is part of a mosaic of habitats, bracken can benefit wildlife, including scarce species. It can support some woodland flowering plants under its canopy, including bluebells, chickweed wintergreen and common dog violet. The pearl-bordered fritillary and other fritillaries (butterflies) thrive in bracken and dog violet habitats on sunny, south-facing hillsides. Caterpillars of a few moth species, a short-winged bug and the common froghopper feed on the fronds.
Where bracken is dominant, it can have negative impacts on many heathland and moorland bird species. However, smaller stands of bracken provide cover, nesting, feeding and roosting habitat for a variety of birds.
Mammals such as red deer and sheep rarely eat bracken, since its fronds contain toxic compounds. Wild boar (Sus scrofa) will dig up and eat the rhizomes, controlling its spread.
As it becomes denser, bracken will outcompete other vegetation, reducing biodiversity.
Agriculture
Widespread bracken reduces the grazing area available for livestock. It is toxic to cattle, sheep, pigs and horses, who will avoid eating it unless nothing else is available. It is of particular concern to farmers and crofters on hill grazings and marginal land.
Human health
Bracken is inhabited by sheep or deer ticks, transferring onto hosts such as sheep and humans who brush against the bracken. Bracken litter provides an ideal habitat for ticks and has been linked to a perceived increase in tick numbers.
Controlling bracken
There are a number of methods used to control bracken.
Bracken is resistant to many herbicides. Glyphosate will control bracken but also affect other vegetation. Asulam, sold as Asulox, is a herbicide that is particularly effective on ferns, since it is absorbed into the rhizomes. It can be applied from the air by helicopter, which is particularly helpful for rugged terrain. Asulam was banned by the EU in 2011 because of concerns about its effect on crops. Annual temporary arrangements have been put in place to allow the chemical to be used for bracken control in Scotland. Emergency authorisation requires a strong case for the importance of controlling bracken, the absence of alternatives, a plan for the limited and controlled use of the chemical, and protective measures for people and the environment.
Asulam is known to permeate soil and leach into watercourses, where it affects organisms – aquatic plants in particular. This will have knock-on effects on other animals in the ecosystem. There is insufficient research on its long-term effects on birds and wild mammals. After spraying, sites where bracken has been controlled will require follow-up treatment and long-term management. Managing land where bracken has been controlled for grassland or heathland is common, but may not be the most sustainable outcome – in terms of biodiversity as well as the need for ongoing
Bracken can be cut, topped, crushed, bashed or ploughed to reduce its vigour. Some of these techniques will have negative impacts for other species, particularly crushing with a roller or ploughing. These methods are often more labour-intensive than applying Asulam, particularly on hard-to-reach sites.
However, the most sustainable, low-cost and fair way for Scotland to cope with its bracken problem is to understand why it is a particular problem for us – and how to fix the root cause of the problem.
Living with bracken
The use of the herbicidal spray Asulam is not a sustainable option for a Scotland that is coming to terms with the twin climate and biodiversity crises. The most effective long-term control strategy for bracken is to establish alternative habitats and land uses that will resist recolonisation of bracken.
In Scotland – which has less woodland cover than almost any other country in Europe – the return of trees would alleviate our need to control bracken. Bracken is a woodland plant. Under permanent woodland cover, bracken growth is limited to individual fronds. In a rewilded Scotland, woodland cover would be far more extensive than it is today.
The Scottish Government’s vision is to increase woodland cover in Scotland to 21% by 2023. However, we are falling far short of our annual targets. Prioritising the natural regeneration of forest cover, incentivising agroforestry and encouraging woodland crofts would all help accelerate woodland growth.
Bracken has a number of uses. It can be used to produce peat-free compost, biofuel, animal bedding, mulch and fertiliser. Traditional control of bracken through cutting and harvesting would require more people actively working the land – fairly rewarded through a redesigned government subsidy schemes that recognises the public benefits of their work.
Bracken tolerates a wide range of soils, but favours non-wetlands. Increasing the number and size of wetland habitats in Scotland, creating a mosaic of different habitats, is key to repairing our ecosystem and suppressing problem species like bracken.
Grazing animals walking through and disturbing bracken can cause areas of bracken to die off. While bracken fronds are toxic to sheep, some breeds – like the Soay sheep – have been used at sites to control bracken as they chew the base of the stalk. This can be combined with methods like annual cutting to keep bracken density down.
Wild boar became extinct in the UK around the 13th century due to over-hunting and habitat loss. Largely due to escapes from farms, wild boar are now found in a few areas in Scotland. Wild boar are important ecosystem engineers who may suppress bracken growth. The Guisachan Wild Boar Project, a experimental project where wild boar were introduced to an area on the edge of Glen Affric, showed that boar rooting up bracken roots increased the number of pine saplings in an area where bracken had previously shaded out young trees.
Lyme disease is a growing concern in Scotland. Like bracken, it is a symptom of a broken ecosystem. Fragmented habitats, missing species and invasive species all contribute to the imbalances in our natural world. Changes in human behaviour, climate change and human impacts on the landscape have all contributed to increased bracken coverage. Addressing these drivers, rather than merely treating the symptoms, is the key to managing bracken sustainably.
Our vision is of a rewilded Scotland, where people work with nature, not against it.
Recommendations
- Accelerate woodland regeneration, augmented by planting where necessary, in areas where bracken is a known problem
- Develop a national plan for the non-chemical control of bracken that takes ecosystem restoration as its starting point, including a strategy for extensive grazing of a mix of herbivores, including wild boar, to restore natural processes
- Incentivise the non-chemical control of bracken through a whole-ecosystem approach, including mechanical treatment methods as well as habitat restoration
- Produce research into the range, population size, rate of spread and effects on other species of feral boar populations
- Provide skills training for land managers on practical, affordable management techniques for controlling bracken
- Develop a strategy for ticks in Scotland that takes a whole-ecosystem approach to control of numbers
References
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