REDUCING BRACKEN COVERAGE ON JERSEY’S COASTAL LANDS
- To reduce extent of bracken coverage on coastal areas
- To restore native coastal grassland and heathland vegetation
- To restore coastland bird and other animal populations
Bracken Pteridium aquilinum is a highly successful and widespread species of fern found throughout temperate regions of the world. This perennial, it dies back in winter, grows up to 2m in height and often covers extensive areas where it suppresses other vegetation with natural chemicals. Changes in land management practices have tended to favour the spread of bracken, namely:
- The decline in grazing, particularly cattle and thus less trampling of bracken;
- Sub-optimal management of heather and/or grassland;
- Decline of cutting bracken for bedding.
A number of other problems can be associated with bracken:
- A reduction in the potential grazing area available to cattle and horses;
- It can replace other important habitats such as heathland;
- It can harbour sheep ticks which may cause disease in livestock and humans;
- It is toxic and carcinogenic to stock and may have a negative impact on human health.
What are we doing?
There are a number of techniques for controlling bracken, appropriate for different situations. It is important that with any of the methods used that follow-up treatment and aftercare must be well planned and implemented as bracken will recover if control is neglected.
In 2011, the Department of Environment’s Natural Environment Team managed 167 vergees (30.2ha) of bracken over seven sites including Les Landes, Les Blanche Banques, La Landes do Ouest, Ouaisné, Portelet-Noirmont and on the north coast. Contractors put in 330.5 man/days work (including tractor time) on bracken control while in simultaneous projects the Jersey Probation Services spent 220 man/days on bracken cutting and Jersey Conservation Volunteers a further 8.75 days.
During the next five years the National Trust for Jersey plans to reduce the coverage of bracken in the Le Don Paton area by about 28 vergees (5ha) increasing the grazeable area from 102 vergees (18.3ha) to 130 vergees (23.4ha).
Fronds are cut during early summer, before and up to the point of maximum frond expansion. The aim is to ensure a maximum withdrawal of carbohydrates and nutrients from the rhizome reserves. Fronds should be cut in late July/early August but cutting may be carried out one, two or three times annually. This will not eliminate bracken but will reduce its vigour and prevent further encroachment.
Bracken-bruising machines may also reduce bracken densities. Bruising can be more effective than cutting because the plant continues to send nutrients into the bruised/damaged part of the plant rather than sending up new shoots as happens following cutting. Bruising should be carried out in June/July when fronds are emerging and when the plant is withdrawing energy from the rhizome. Follow-up treatment in July and August will provide maximum control. Bruising should take place in successive seasons to exhaust the plants.
Herbicide action is unlikely to have a significant effect on the amount of rhizome carbohydrate reserves, so herbicides which attack frond buds on the rhizome are most successful. Commercial herbicides using Asulam [methyl 4-aminobenzenesulphonyl carbamate], which is specific to fern species such as bracken and is less likely to affect other vegetation or wildlife, are the most widely used herbicides for bracken control. The spray is translocated into the rhizome and accumulates in both active and dormant buds where it effects a lethal action. Asulam frequently produces a very good reduction in fronds in the year after spraying, but there is often rapid frond recovery unless other treatments are applied in following years. Multiple applications of Asulam are more effective than single applications, slowing the speed of recovery. Follow up spraying, once cover has been reduced, may be spot sprayed with a knapsack and lance. Alternatively, weed wiping may be appropriate. This may be particularly useful near to the Mourier Valley stream where water quality is important and buffer zones must be maintained. It may also be useful if boom-spraying is limited by the coastal climatic conditions and number of suitable ‘spraying days’. Weed wiping may be less effective at high frond density and plant height. Where bracken is growing amongst heather, spraying is most appropriate as cutting or rolling will damage the heather, particularly if the heather is woody and mature. Spraying may also be more appropriate where there are ground nesting birds or reptile populations present which could be damaged by mechanical control methods. Note: there will be changes to the sprays available for bracken clearance in 2013 as the active ingredient Asulam was removed from sale in December 2011 and existing stocks of Asulox will have 12 months after this date for storage and use.
Livestock will consume small amounts of bracken but not in sufficient quantity to reduce cover significantly. Importantly, bracken is toxic to livestock when consumed in quantity, and so livestock grazing should not be used as a method for bracken control due to welfare concerns. However, livestock can be a useful management tool through trampling. Cattle and ponies are particularly useful for this due to their larger size (compared to sheep). However, sheep may offer some control of bracken once initial control has been undertaken. Where there is still a grass sward beneath the bracken, management to remove the tall bracken may allow sheep to graze the sward, exerting trampling pressure on the regenerating bracken and help to maintain the grass.
Read more about the grazing project here
Dense stands of bracken such as those on the National Trust side of the Mourier Valley may have a thick layer of litter. This layer will smother regenerating vegetation, whilst containing rhizomes and protecting them from frost and drought. Ideally, this layer should be removed to speed up restoration of the ground vegetation. In small areas this can be achieved by raking by hand as is already practiced by the NT. A forage harvester has been used to pick up and remove the litter, although it is only effective on flat sites. Alternatively, implements such as discs or rotovators can be set at a depth to break up the litter but leave the mineral soil profile undisturbed. Following removal/disturbance of the litter some rhizomes close to the surface may be killed by frost and drought (this could be very effective on the NT side which suffers from drought in late summer).
It is planned to reduce the area of bracken in Jersey at selected sites over the next five years. The methods of clearance chosen are likely to be dependent on local conditions and resources available. The site at Mourier Valley will be extensively cleared in order to bring this back to more natural coastal grassland and heathland habitat.
In 2012 an area of 10 vergees of bracken will be treated using an Asulam based herbicide. This will be undertaken on the steeper valley slopes using spray equipment that is more commonly used to chemically spray potato cotils.
This operation will greatly reduce the coverage of bracken, however, follow-up work will be required to remove the underlying litter layer. This will involve machinery works estimated at £3,000
Following the exposure of the mineral soil, it will beneficial if heather and coastal grassland seed can be spread over this area.
Total Cost £5,500
Follow-up spraying and treatment
Estimated at £1,000 per year
Total Cost for a 5 year project = £9,500