FAQs: Bracken Management in Great Britain

Photo by Zeynel Cebeci

These frequently asked questions are taken from a report published by the Future Landscapes Forum on the issues caused by bracken in the UK.

• What is bracken and why is it such a successful plant in the UK?

• How much bracken is there in Great Britain and is it increasing?

• What problems does bracken cause for land managers and the environment?

• Why is the withdrawal of the herbicide asulam a significant concern for bracken control?

• What are the alternative methods for controlling bracken now that asulam is unavailable?

• How effective are the alternative bracken control methods compared to asulam?

• What are the key knowledge gaps and actions needed to improve bracken management in the UK?

• What is the long-term outlook for bracken management in Great Britain given the current situation?

What is bracken and why is it such a successful plant in the UK?

Bracken is a fern characterized by its large fronds that form a dense summer canopy, effectively shading out other vegetation. It possesses an extensive underground rhizome system which stores nutrients and allows for regeneration after frost, fire, or physical disturbance. This rhizome also contains numerous dormant buds that can sprout new fronds. In autumn, the dead fronds create a litter layer that inhibits the establishment of other plant species. Furthermore, bracken produces a variety of secondary chemical compounds, some of which are toxic, acting as defenses against herbivores and microbes, and potentially exhibiting allelopathic effects that suppress neighboring plants. The dominant bracken variant in the UK is Pteridium aquilinum subsp. aquilinum.

How much bracken is there in Great Britain and is it increasing?

Accurately measuring the total extent of bracken in Great Britain is challenging. While remote sensing can detect dense bracken in open areas, it often misses sparse patches (less than 25% cover), bracken growing under trees or in linear features like hedges, and is complicated by bracken's cyclical growth patterns. Consequently, bracken has been included within "acid grassland" in UK land cover maps since 2007 for consistency. Early estimates of dense bracken cover varied considerably between survey methods, ranging from approximately 2,600 km² to 4,390 km². However, a 1990 survey that included all levels of bracken infestation (dense, sparse, under woodland, and in linear features) estimated a total of 17,072 km² of land with some bracken present, suggesting the problem is far more widespread than dense cover estimates indicate. Assessing change over time is also difficult, but experts believe bracken extent and density are likely increasing due to climate change (longer frost-free periods) and reduced grazing pressure in some areas.

What problems does bracken cause for land managers and the environment?

While bracken can occasionally provide habitat for certain species, its expansion generally reduces biodiversity by outcompeting native plant communities. It poses significant problems for livestock agriculture by reducing grazing land, increasing stock gathering costs, and causing poisoning (due to thiaminase and carcinogenic compounds), potentially leading to diseases and even death. There are also concerns about correlative links between bracken and certain human cancers, and a known carcinogenic compound (ptaquiloside) has been detected in drinking water sources. Bracken thickets can harbor high densities of ticks, increasing the risk of Lyme disease and other tick-borne illnesses for both humans and animals. Additionally, bracken can negatively impact water quality and soil carbon stocks by altering soil chemistry and carbon turnover.

Why is the withdrawal of the herbicide asulam a significant concern for bracken control?

Asulam was considered the safest and most effective herbicide for controlling bracken, particularly because it was licensed for aerial application via helicopter. This was crucial for treating large, inaccessible areas like steep slopes and rocky terrain. Asulam was also relatively selective, primarily targeting bracken and other ferns with limited impact on other vegetation. Its removal leaves a major gap in bracken control options, as the remaining licensed herbicide, glyphosate, is non-selective and not approved for aerial spraying, making it less suitable for many situations where underlying or adjacent plant species need protection.

What are the alternative methods for controlling bracken now that asulam is unavailable?

Without asulam, bracken control relies on mechanical techniques (cutting, pulling, bruising, ploughing/discing/rotavating), the herbicide glyphosate, and potential future biocontrol methods. Mechanical control requires repeated treatments over many years to be effective, and its practicality is limited by terrain. Glyphosate can be applied using ground sprayers or weed wipers, but its non-selective nature can harm other vegetation. Weed wiping offers some selectivity by targeting taller bracken. Biocontrol options like insects or fungi are still in the research and development stages. Planting trees to shade out bracken and using grazing animals (cattle, horses, or specific sheep breeds) to trample it are also possibilities, but these require careful management and consideration of animal welfare due to bracken's toxicity.

How effective are the alternative bracken control methods compared to asulam?

Studies during the "asulam era" showed that effective bracken control, regardless of the method, requires sustained effort and often multiple treatments over several years. Asulam provided good short- to medium-term control (up to 10 years) and excellent results when followed by annual spot treatments. While long-term data for other herbicides is lacking, the principle of needing repeat applications or spot treatments likely holds. Mechanical cutting requires a minimum of 8 years of intensive cutting (two to three times per year) and potentially much longer to achieve good control, with the risk of rapid recovery if treatments cease. Bruising has shown inconsistent results. Therefore, no single current alternative offers the same combination of effectiveness, ease of application across diverse terrains, and relative selectivity as asulam.

What are the key knowledge gaps and actions needed to improve bracken management in the UK?

Significant knowledge gaps exist regarding the precise current extent of bracken infestation across all cover densities and habitats in the UK. Better estimation methods are needed, potentially utilizing AI with remote sensing data (spectral, LiDAR, digital elevation models) and a repeat of the comprehensive 1990 Countryside Survey with enhanced techniques like drone surveys. Furthermore, research is crucial to improve existing control methods (e.g., developing better cutting and bruising machinery, optimizing grazing strategies with animal welfare considerations), explore alternative herbicides and application techniques (including drones), and further investigate biocontrol options. A UK Bracken Strategic Framework is welcomed, but it must involve all stakeholders in its development and allow for ongoing improvement of bracken management guidance.

What is the long-term outlook for bracken management in Great Britain given the current situation?

The long-term outlook requires a concerted and sustained effort. Without asulam, managing bracken will likely be more challenging, requiring integrated approaches combining different control methods tailored to specific sites and long-term commitment. An adaptive management strategy with continuous monitoring and repeat treatments will be essential to prevent bracken from regaining dominance. Adjustments to agri-environment scheme agreements may be necessary to support effective bracken control. Increased research funding and collaboration among scientists, practitioners, and policymakers, as advocated by the Bracken Control Group, are crucial to develop and implement effective and sustainable bracken management strategies for the future.

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