Bracken Management: a Long-Term Balanced Plan

Bracken Management on Baildon Moor and surrounding woodlands: a Long-Term Balanced Plan

Baildon Parish Council, Bradford Metropolitan District Council; Friends of Baildon Moor 14/12/12

Bracken (Pteridium aquilinumis) is a characteristic moorland plant which over the last seventy years has increasingly out-competed characteristic ground-cover plants such as moor grasses, cowberry, bilberry and heathers and now covers a considerable part of Baildon Moor, with serious inroads into Shipley Glen and Baildon Bank.

Once valued and gathered for use as 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 linked to cancers in humans, through contact and water run-off. It can harbour high levels of sheep ticks, which can pass on Lyme Disease. Grazing from several farms with common rights has almost ceased since the foot and mouth outbreak over ten years ago but provided some control by stock trampling, though the consequent soil enrichment suits bracken but not many other moorland plants. Global climatic changes have also suited bracken well and contributed to its rapid increase in land coverage.

Bracken is a well-adapted pioneer plant which can colonise land quickly, with the potential to extend its area by as much as 3 % per year (6% globally is reported). This ability to expand rapidly is 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.

The main habitats on Baildon Moor are upland heathland, acid grassland and upland flushes. Other habitats include ponds, scrub and scattered young trees.

Upland moorlands form a valuable carbon store and play a role in regulating the effects of rainfall.

The biodiversity that depends on these uplands is very special and very rich. Many of the species only occur on upland moorland, tied to features unique to the habitat. The loss and degradation of such areas due to the dominance of bracken has caused many species to become rare and isolated. However, there are votes both for and against for bracken in the debate.

Birds:

Baildon Moor and other uplands of the South Pennines with both wet heath and heather moorland/acid grassland are of international importance for birds. The Moor and the surrounding woodlands are designated as Urban Common or open access land, with a right of access for quiet recreation and are a popular and important recreational space for potentially thousands of people, with recognised benefits to their health and wellbeing. This brings people and wildlife together, and it is increasingly evident from research that birds are vulnerable to disturbance, which is affecting their breeding success.

Where bracken is dominant it excludes most specialist heathland/moorland bird species of conservation concern, although there are a few species that may benefit from a certain proportion of bracken; e.g. nightjar and whinchat. Thinly covered areas are used, while the deeper stands provide a good food site for many resident or breeding birds, such as threatened ground-nesting species skylark, yellowhammer, curlew, plover and lapwing. Small stands of bracken are one of the habitats which provide nesting, feeding and roosting habitat for a variety of birds, for example willow warbler, ring ouzel, twite, whinchat and stonechat.

These stands also give cover, especially during the nesting season, from predators such as birds of prey and crows; and from free-ranging dogs and users straying off the paths which, usually unintentionally, disrupts nesting and can identify the nest site to predators. On heavily used spaces such as Baildon Moor, this may be an important protection. Clearing some areas within the deeper stands may provide safe havens.

Flora:

Bracken substitutes for woodland canopy, and shades plants such as common bluebell where the woodland does not exist. Some mosses and fungi also seem to benefit from the warm humid conditions found under bracken stands and in the frond litter. This may be less true within deeper litter.

Bracken populates some sites that would not be colonised by other species. Eradication in these areas without further consideration would lead to soil erosion and possible invasion by undesirable species such as Himalayan balsam (already established as a problem on the Moor). Seeding with suitable adapted species is an option.

On the other hand on many sites, bracken deploys many adaptive biological techniques to outcompete the characteristic moorland species. Its chemical diffusions, shady canopy and its 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 fern is removed, apparently because active plant toxins remain in the soil.

Trees, notably rowan, have also done well since grazing effectively ceased but young saplings struggle in high bracken. In decades to come, tree shade cover may increase, if permitted, and so may reduce bracken growth but this is both long-term and contentious in the change in character it would bring to the traditionally open space; both aesthetically and as a valuable upland habitat.

Rare ferns are found on the moor and can be co-located with bracken. It is important that these are not destroyed in the process of bracken control. Some of these include Adder’s Tongue (for which the moor is one of only 10 sites in Yorkshire), and possibly killanery and lemon-scented ferns.

Invertebrates:

Bracken is known to support 40 species of invertebrate (including nine moths): for 27 of these bracken forms an important part of the diet and 11 of these species are found only on bracken. However, study of the area cleared by BEES since 2000 on the NNW portion of the Moor reported a significant increase in the number of insect and plant species.

Archaeology:

Baildon Moor has many archaeological remains dating from the Neolithic and Bronze Ages through to the Industrial Revolution. The root systems of established bracken stands degrade archaeological sites by disrupting the strata and other physical evidence. These rhizomes may travel a metre or more underground between fronds and form 90% of the plant; only the remainder being visible. Under the Natural England Higher Level Stewardship (HLS) plan and at English Heritage’s request, some chemical control has been undertaken around several ancient sites (such as the fine piece of rock art above Glovershaw Quarry); mechanical means being proscribed as potentially damaging.

Bracken Management:

On balance, removing bracken encourages primary habitats to re-establish, which are overall of greater importance for wildlife. Restoring areas to moorland will make it more sustainable and can provide more space for birds and other wildlife. This will ease the safe access for people, and address the requirement to restore moorland which the stakeholders are consistently pressed on to do by people who use the moor.

However, many species of bird, mammal, plant and invertebrates use bracken for feeding, shelter and nesting, either opportunistically or as their adapted habitat; therefore its control needs to be undertaken in in a balanced and informed manner with up to date localised data on its use by all species.

Bracken management is a complex question with complex answers, which need to part of a unified approach. It is difficult and can be expensive. Any plan for Baildon Moor needs to be about cost-effective and practical limitation and control, rather than an expectation for eradication. The Natural England HLS (Higher Level Stewardship) plan gives a target, in the areas to treated, for a reduction to 0-5% coverage within seven years. This seems neither possible; especially with Asulam being now unavailable for use; nor desirable from several perspectives. Given the decades taken to arrive at the current high level of bracken coverage, slowing or reversing the process will be also be of necessity be long-term, with commitment, consistency and persistence from all parties being absolutely key for success.

The HLS plan calls for a range of control methods for the various types of site. This remains relevant in many respects, notably the identification and classification of the stands but would benefit from input of expert wildlife advice and detail on re-colonisation for each micro-site. There are three main approaches to management:

  • repeatedly cutting or rolling the fronds
  • applying herbicide
  • encouraging other vegetation to grow in place of bracken

All methods need full and regular follow up over a long period. Any bracken control programme must be completed, otherwise bracken will re-establish.

The largest single target area (and block of grant aid) delineated by NE called for helicopter aerial spraying of Asulam on the north side of the moor. This is a widely used and generally both effective and selective and would have been by far the most cost-effective means of control; though follow up would have been essential. Test results suggest that although Asulam has a dramatic effect when first applied, bracken control depends on depleting the rhizomes, so annual cutting delivers a better result in the longer term. All techniques are more effective when they are combined with follow-up applications of another herbicide several years after the initial Asulam treatment – preferably by spot-spraying at ground level. Asulam is no longer registered for use after 2012 so this was a unique opportunity for a visible gain, with a low-cost large-scale scope. (NB: this herbicide is not a “banned substance” (an emotive term); toxicity is deemed low; but rather is now restricted by the EU until specific uses can be defined). It is very possible that Asulam may be permitted for specific use after 2012, so could be one part of the overall management plan again.

While likely to be useful in its effect, there were a number of concerns with aerial spraying, not least its application in a heavily used public space. In discussion, FoBM and BMDC agreed with the BPC position that helicopter aerial spraying of parts of the moor would not take place. However, the grant allocation of approximately £11,500 for this cannot be now claimed so this does leave a short fall in the budget. Alternative, ground control methods for this area are estimated at least £22,000; weed-wiping may be more.

This is a complex question with complex answers, which need to part of a wider approach. All methods need follow up over time. The HLS plan remains relevant in many respects, notably the identification and classification of the stands. This needs to be supplemented by expert wildlife advice and detail on re-colonisation.

All methods need full and regular follow up over a long period. Any bracken control programme must be completed, otherwise bracken will re-establish.

We must continue to build a detailed longer-term plan between the stakeholders: BMDC (as landowner and responsible party), BPC, FoBM and other groups such as the Bradford Ornithological Group (BOG). A three-way working group is in place and needs to agree and help implement a bracken control plan for the medium-longer term. This is essential if a real impact is to be made.

We are considering all options for reducing the bracken cover on the moor:

Key points

  • A large-scale unified approach is more cost-effective than a piecemeal approach and will give better results
  • Identify and target specific areas for control, with accurate mapping. The CSS (and Natural England) are using satellite mapping and monitoring for this. Groundwork would need a similar level of recording.
  • Ensure that each bracken stand has no high conservation value of its own before commencing control
  • Management to maintain scattered stands of bracken on appropriate sites can provide good habitat for a variety of wildlife. These would need to be extensive enough to provide cover and to be a barrier to other users, while thinner growth at the edges will be useful for other wildlife.
  • Tackle advancing areas first. Such encroachments around the top of Hope Hill have been treated this year as a small scale trial, as have one or two paths.
  • The timing of control work needs to consider other wildlife activity, especially nesting birds and their unfledged young, and deer fawns.
  • Development of a plan for re-colonisation by plants suited to each site before clearance work is undertaken is essential. Distinctions need to be drawn between areas with underlying cover which should regenerate, and those under deep bracken cover for example, where this understory does not exist. Sloped areas where soil would erode without any cover (typically gradient more than 15° max) might not be tackled for that reason.
  • Whatever management techniques are adopted, they all have consequences, both foreseen and unintended. Full risk assessments must be undertaken to explicitly and clearly cover long-term effectiveness, benefits and impacts on landscape, people, soil, flora, fauna and water.

Methods of bracken control

Though cutting and rolling both reduce bracken vigour and encourage recovery of vegetation, they do not provide full control. Alternative methods are needed to achieve this, as is consideration for what replaces the bracken.

Cutting regimes:

Cutting is most effective when bracken is at, or near, full frond. This is even more efficient if bracken is cut twice in the same growing season. In many upland areas slow growth may mean two cuts are not possible. In this case a single cut, close to the ground, in mid late July can increase the potential for early frost damage to regenerating bracken and surface rhizomes.

Annual cutting will need to be repeated until the bracken disappears, which can take in excess of 10 years (up to 26 has been reported) in well-established stands.

Cutting once will produce an even stand with more active buds, which may increase the effectiveness of chemical treatment in the following year.

Where ground-nesting birds are present, RSPB et al advice is for cutting to be avoided during May to July. These areas can be left until last or avoided until after any nests have become inactive. The period to wait is likely to be only a matter of days or a couple of weeks. If in doubt seek specialist advice.

Large-scale or indiscriminate cutting will not be selective in avoiding trees, desirable plants and wildlife, nor is it suitable to areas with surface archaeological features or rocky areas.

FoBM volunteers manually strim a number of paths to keep these clear, times and weather permitting. User traffic helps reduce regrowth but at least two cuts a year are needed. This is heavily manually intensive, with training required and is currently paid for from FoBM funds only.

Execution options:

  • Hand & autoscythe cutting; piled composting (such as done by BEES): highly manually intensive but reasonably selective in avoiding trees and other desirable features. Cutting three times a year. Started in 2000. Increased biodiversity reported.
  • Manually strimming, manually intensive, with training required. Suitable for paths and some inclines. Cutting 2-3 times a year
  • Close cutting with ATV or tractor drawn specialist farming implement; Cutting 2 times a year
  • Cutting and baling with tractor drawn farming implement; rotational; collect for use in ericaceous compost as alternative to peat.

Rolling:

If cutting is not possible, consider rolling the bracken. The timing is the same as for cutting. There are a number of small machines on the market designed specifically for this type of work, which can be towed behind tractors or 4×4 vehicles.

Rolling does not cut off the stems but leaves them attached to the root to bleed the sap; this reduces food energy for bud development in the following year.

Each rolling operation can reduce shoots by about one third, reducing a dense stand of bracken into more scattered fronds.

Rolling for three consecutive years has been shown to be more effective than carrying out a one-off operation. Even so, bracken control will need to continue for more than three years to avoid re-colonisation.

Some residual effect is apparent south of Acrehow Hill where rolling was commissioned several years ago.

Against this, rolling would damage most plant life including trees and harm or disrupt birds and animals. Expert monitoring of the site and thus choosing the timing carefully may reduce this impact.

This is not suitable to areas with surface archaeological features or rocky areas.

Execution options:

  • Horse drawn log (as used several years ago)
  • Tractor drawn specialist farming implement
  • Mass trampling by a line of people

Grazing regimes:

Temporary close grazing or mob stocking on small areas away from nests, particularly using cattle, horses, pigs or ponies in May and June, may crush emerging bracken fronds resulting in reduced bracken cover. Sufficient fodder will be required to prevent livestock eating the bracken. During winter, livestock can trample the developing plants and allow frost to penetrate the rhizomes.

Trampling also increases the rate of breakdown of dense bracken litter, encouraging other species.

Mob stocking can damage other vegetation beneath the bracken canopy. It can also lead to nutrient enrichment and damage bird nests. Where the management objective is to restore heather moorland, and other semi-natural vegetation communities, mob stocking is often inappropriate. However, this may work well on steep areas such as Shipley Glen where human access is difficult and general herbicide undesirable.

Execution options:

  • Identify suitable livestock farmer to provide stock and manage the herd

Herbicide treatment:

Fronds are normally mature from mid-July to the end of August. By this time most birds can be expected to have completed breeding and are not likely to be affected by herbicide application.

Where stands are more open, and there is an issue of affecting non-target species of flora, consider the possibility of weedwiping or application with a hand lance.

Glyphosate is currently recommended to spray dense areas of bracken with no understorey and breaks down on contact with soil. Herbicide treatment is highly effective if a full programme of primary treatment and aftercare is undertaken, but there are other views on the side effects that need to be part of the discussion.

Encouraging other vegetation to grow in place of bracken

Seeding with suitable adapted species is possible but given bracken’s ability to supress co-existing plants, treatment or preparation may be needed first in order to give these a foothold.

Gorse is used by smaller birds and provides a barrier to users but requires well drained soil. Heather may struggle on higher pH areas, such in acid grassland.

In the longer term, tree cover will reduce bracken cover, but some plants will be present in shade.

Summary:

  • Taking no action is not an option; on the balance of biodiversity and in the interest of users
  • Full eradication is neither possible nor desirable; some selected areas will remain
  • Plan needs to be wide scale but any selected control approach must be variegated and localised to suit micro-conditions
  • The process of reduction will of necessity be a long-term commitment , with consistency and persistence from all parties being key
  • Long-term plan should start in Q1 2013
  • HLS grant for aerial spraying can no longer be claimed, funds ((est. £22k) must be sought for replacement control approaches

Actions to proceed:

  • Costings required for long-term adoption of various control techniques: CSS with FoBM. The HLS provides for some grants; it does not cover the woodlands; FoBM/Woodlands Manager
  • Identify suitable plants for re-colonisation; as co-existing species or as seeds/young plants
  • Identification of the specific sites for ground-nesting birds; FoBM; with BOG
  • Identification of the specific sites for rare ferns & other species of concern: FoBM & CSS; with experts
  • Identify suitable close grazing/mob stocking livestock farmer to provide stock and manage the herd; CSS; FoBM; BPC
  • Build risk-benefit matrix for each target site

David Sturge
Chair, Friends of Baildon Moor
www.baildonmoor.org
References:
http://www.rspb.org.uk/ourwork/conservation/advice/heap.aspx
http://www.rspb.org.uk/ourwork/farming/advice/details.aspx?id=204253
http://www.ilkleymoor.org/discovering-ilkley-moor/flora-and-fauna
http://www.naturalengland.org.uk/images/2005_tcm6-23271.pdf
http://www.bees-ymca.org.uk/places_baildonmoor
http://www.dalefootcomposts.co.uk/