The Problems Caused by Bracken
- Rob Beeson
- Mar 28
- 8 min read
Bracken might appear to be a picturesque part of the landscape but it is a significant and growing problem for land managers, the environment, and even our health. This seemingly innocuous plant, scientifically known as Pteridium aquilinum, harbours a surprising number of negative impacts, and understanding them is crucial for the future of our landscapes.
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What Makes Bracken Such a Successful Spreader?
It's important to understand why bracken is so pervasive in the UK and across the globe (excluding Antarctica). This fern has a few clever tricks up its sleeves:
Shade Master: Bracken produces large fronds that form a dense canopy, effectively blocking sunlight and preventing other plant species from growing underneath.
Underground Powerhouse: It boasts a vast network of underground stems called rhizomes. These rhizomes act as storage units for food and nutrients, allowing bracken to bounce back after frost, fire, or even attempts at control. They also contain numerous buds that can sprout new fronds, ensuring its persistence.
Litter Layer Lockdown: When the fronds die back in autumn, they create a thick layer of litter. This layer further hinders the establishment of other plant species, reinforcing bracken's dominance.
Chemical Warfare: Bracken is packed with a variety of chemical compounds, some of which are nasty customers. These include substances that can deter herbivores and microbes, and even compounds with carcinogenic, cytotoxic, mutagenic, tumorigenic, and teratogenic properties.
The specific type of bracken found in the UK is usually Pteridium aquilinum subsp. aquilinum, while another variant, P. esculentum, is more common in the Southern Hemisphere.
The Great Bracken Census: Why We Don't Know the Full Extent
You might think it's easy to measure how much bracken there is in the UK – just look at a map, right? Unfortunately, it's not that simple. Accurately assessing bracken coverage is surprisingly challenging due to several factors:
Blending In: From above (like in satellite imagery), it can be difficult to distinguish bracken from grasslands, especially since 2007 when they were grouped together in UK land use maps.
Sparse vs. Dense: Bracken doesn't always grow in dense patches. Large areas can have sparse bracken cover (less than 25% frond cover), which is very hard to detect with current remote sensing technology.
Hidden Under Trees: Bracken loves to grow under tree canopies, making it invisible to aerial surveys. This hidden bracken can rapidly expand if the trees are removed, significantly impacting future estimates.
Linear Invaders: Bracken often thrives in linear features like hedges, fence lines, and road verges. While these might seem small, they act as pathways for bracken to invade new areas.
Cyclical Growth: Bracken populations can go through phases of increasing and decreasing frond density naturally. This means that a snapshot in time might not accurately reflect the long-term presence and potential of bracken.
Early estimates of bracken cover in Great Britain varied considerably. Later surveys, like the UK Countryside Survey, provided more detailed estimates but also highlighted significant uncertainties. Since 2007, the focus has been on "Bracken Broad Habitat" (95-100% cover), and these estimates have also fluctuated.
Worryingly, the total area of land infested with some bracken in 1990 was estimated to be a staggering 17,072 km², more than four times the area of dense bracken cover. This highlights a much wider potential problem of land with the capacity for further bracken expansion.
The lack of precise data on bracken extent makes it harder to understand the scale of the problems it causes and to track changes over time.
Bracken vs. Farming: A Costly Conflict
For land managers involved in livestock farming, bracken is a major headache. Its invasion leads to several significant issues:
Lost Pasture: Dense bracken directly reduces the amount of land available for grazing animals. Less grazing land means a lower capacity to support livestock.
Increased Costs: Farmers face higher costs for gathering their stock in bracken-infested areas, and they incur greater veterinary expenses due to bracken-related illnesses.
Animal Poisoning: Bracken is toxic to livestock. In mono-gastric animals (like horses and pigs), it can cause Vitamin B1 deficiency. In other grazing animals (like cattle and sheep), it's linked to gastric tract cancers and enzootic haematuria (a bloody urine disease). Historically, livestock deaths due to bracken ingestion were alarmingly high. Even low levels of grazing on bracken can have serious health consequences for animals.
Economic Burden: Back in 1988, bracken was estimated to cost the agricultural economy in the Least Favoured Areas of England and Wales a whopping £8.8 million. This figure likely understates the current economic impact.
Farmer Frustration: A significant proportion of farmers in affected areas recognize bracken as a problem, with a large majority (68% in one survey) favouring a national control scheme.
Conservation Concerns: Where Bracken Dominates, Diversity Suffers
While bracken can occasionally provide specific habitats for certain species, in the grand scheme of things, its spread often has negative consequences for biodiversity:
Reduced Species Richness: When bracken takes over, it outcompetes and displaces other native plant species, leading to a reduction in overall plant diversity. This, in turn, can negatively impact the animals that rely on those plants for food and shelter.
Threat to Woodlands: Bracken is considered one of the main native species contributing to reduced species diversity in British Broad-Leaved Woodlands. Its dense growth can suppress tree regeneration and limit the growth of woodland wildflowers.
Loss of Valuable Habitats: In most cases where bracken colonizes, the conservation value of the resulting bracken-dominated community is lower than that of the original habitat it replaced. For example, the conversion of heathland to bracken stands diminishes the unique flora and fauna associated with heathlands.
However, it's worth noting that in some specific situations, bracken can act as a temporary surrogate for woodland canopy, providing shade and shelter for the food plants of certain butterfly species. It can also offer habitat for some bird species like the Whinchat. Despite these isolated benefits, the overwhelming evidence points to a net loss of biodiversity due to bracken expansion.
The Human Element: Health Concerns Linked to Bracken
The problems associated with bracken aren't limited to agriculture and ecology; there are also potential risks to human health:
Carcinogenic Compounds: Bracken contains several secondary plant compounds, some of which are known to be carcinogenic (cancer-causing) and mutagenic (can cause genetic mutations). While direct causation in humans is unproven, correlative data suggests a possible link to certain cancers.
Water Contamination: One of the carcinogenic compounds produced by bracken, ptaquiloside, has been detected in potable water supplies. This is a significant concern as it raises questions about the potential for exposure through drinking water, particularly from private wells where monitoring might be less frequent.
Tick-Borne Diseases: Bracken-dominated vegetation provides an ideal habitat for ticks. Ticks are vectors for various diseases affecting both humans (like Lyme disease and Tick-borne encephalitis) and animals (like Louping Ill). Increased bracken cover can lead to higher tick populations and, consequently, a greater risk of these diseases.
These potential health risks underscore the importance of managing bracken and understanding its distribution.
The Economic Fallout: Beyond the Farm Gate
The economic impacts of bracken extend beyond the direct costs to agriculture. Its presence can affect:
Recreation and Tourism: Dense bracken can hinder access to the countryside for recreational activities like hiking and birdwatching. This can negatively impact tourism-dependent economies.
Game Management: Bracken can reduce the quality of habitat for certain game species.
Land Value: Extensive bracken infestation can potentially reduce the value of agricultural and amenity land.
While quantifying these broader economic impacts is complex, they contribute to the overall burden associated with uncontrolled bracken growth.
The Control Challenge: Life After Asulam
For many years, the herbicide asulam was the most effective and safest option for controlling large areas of bracken, especially in difficult terrain using helicopter application. However, due to EU regulations and subsequent commercial decisions by the manufacturers, asulam is no longer available for use in Great Britain.
The withdrawal of asulam has created a significant gap in bracken control options. While other methods exist, they often have limitations:
Mechanical Control (cutting, bruising, ploughing): These methods can be effective over the long term but are labour-intensive, require repeated treatments over many years (often 8-25 years of multiple cuts per year!), and are not always feasible on steep or rocky terrain. Bruising, in particular, has shown inconsistent results compared to cutting and asulam.
Herbicidal Control (glyphosate): Glyphosate is now the main chemical option, but it is non-selective, meaning it can harm other desirable plants. It's also not licensed for aerial application, limiting its use in many affected areas. Weed wiping with glyphosate can offer some selectivity but has the same terrain limitations as cutting.
Biocontrol: While research into biological control methods (using insects or fungi) has been ongoing, these approaches are still in the development phase and not yet available for large-scale use. Grazing animals (cattle, horses, hardy sheep, or pigs) can help control bracken through trampling over long periods, but there are significant animal welfare concerns due to bracken's toxicity. Tree planting as a potential long-term control method by shading out bracken is being explored but requires further research.
The loss of asulam has highlighted the urgent need for renewed leadership, research into alternative control methods, and the development of a strategic framework for managing bracken across the UK.
The Looming Shadow of Climate Change
Adding to the challenges, climate change is predicted to further exacerbate the bracken problem. Models suggest that warmer temperatures and longer frost-free periods are likely to increase bracken productivity and its potential to spread into new areas. This makes finding effective and sustainable control solutions even more critical. Reduced grazing pressure due to changes in agricultural practices or rewilding initiatives could also contribute to increased bracken expansion.
Time for Action: Addressing the Bracken Barrage
Bracken is clearly more than just a common fern. Its aggressive growth and the multitude of problems it causes – from economic losses in agriculture to threats to biodiversity and potential human health risks – demand serious attention. The withdrawal of asulam has created a pressing need for a coordinated and strategic approach to bracken management in the UK.
Key actions needed include:
Better Data: Investing in improved methods for accurately mapping the full extent of bracken infestation, including sparse cover, woodland bracken, and linear features, using technologies like AI, remote sensing, and drones. Reinstating comprehensive surveys like the Countryside Survey with detailed bracken assessments is crucial.
Innovative Control: Supporting research and development of improved mechanical control machinery for challenging terrains, more selective herbicides with safe application methods (including drone technology), and the potential of biocontrol agents. Rigorous testing of existing methods like bruising is also necessary to understand their effectiveness.
Integrated Management: Developing and promoting integrated bracken management strategies that combine different control techniques and consider site-specific conditions. This should include exploring follow-up treatments like grazing, with careful consideration of animal welfare.
Policy and Funding: Ensuring that agricultural and environmental schemes (like ELMS) are adapted to support effective long-term bracken control and vegetation restoration. Increased research funding informed by expert groups like the Bracken Control Group is essential.
Monitoring and Adaptation: Implementing long-term monitoring programs to assess the effectiveness of control measures and adapt strategies as needed. Continued monitoring for asulam derivatives in water bodies is also important to identify potential alternative sources if they persist.
The challenges posed by bracken are significant, but with a focused effort on research, innovation, and collaborative action, we can work towards mitigating its negative impacts and ensuring healthier and more diverse landscapes for the future.
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