A successful fern, or a case for control

A successful fern, or a case for control

Credit: Chris Maguire 

This month's blog on bracken and the need for control by Jonathan Stone, Reserves Officer

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A successful coloniser

One of Radnorshire’s most characteristic plants and one which the RWT’s conservation volunteers spend much of the summer months controlling is bracken, whose scientific name, Pteridium aquilinum, means ‘eagle-like fern’.  In evolutionary terms it is one of the most successful ferns – fossil evidence suggests that it has been around for at least 55 million years.

Bracken spreads rapidly by means of strong underground rhizomes.  A single plant can reach 400 feet in diameter and be hundreds of years old.  It does particularly well on deep acidic soils but is intolerant of waterlogged soils and shade, and is damaged by frost.

Bracken releases chemicals into the soil which inhibit the growth of other plants, and after it is removed, herbs may be inhibited for a full growing season.  It also uses fire to its advantage.  It produces a highly flammable layer of dried fronds, and after a fire its deeply buried rhizomes sprout vigorously before most competing vegetation can get established.


Uses for bracken

In the Middle Ages bracken was considered so valuable that it was used to pay rents.   It was used as roofing thatch and as fuel when a quick hot fire was desired.  The ash was a source of potash for the glass industry and for making soap and bleach.  The rhizomes were used in tanning leathers and to dye wool yellow.  In parts of Wales bracken is still used for livestock bedding since it is more absorbent, warmer and easier to handle than straw.  It is also used as a green mulch and compost.

In some parts of the world, particularly Japan and Korea, bracken is even eaten by humans, despite having been shown to be carcinogenic in rats and mice.  All parts of the plant, including rootstocks, fresh or dry leaves, fiddleheads and spores, contain toxic compounds.

Bracken is a potential source of insecticides and also has potential as a biofuel.  Moreover it increases soil fertility by bringing larger amounts of phosphate, nitrogen, and potassium into circulation.


Bracken as habitat

Despite its invasive habits, bracken can be an important habitat in its own right.  It supports over 40 species of invertebrate, forming an important part of the diet for 27 of these while 11 are found only on bracken. It is an important breeding habitat for moorland birds, in particular whinchat.  Ring ouzel, hen harrier and merlin use it for breeding cover, and warblers, tree-pipits and nightjars along with reptiles and mammals benefit from its shelter. 

In some areas bluebells and other woodland plants grow underneath bracken.  Violets are the food plant of fritillary butterfly caterpillars, and the adults often lay their eggs on violets growing under bracken.  At Gilfach, we are careful about how we manage the bracken because we have several fritillary species, including the small pearl-bordered and the dark green.


Why control bracken?

The key reasons why we control bracken at Gilfach are to safeguard other more valuable habitats which may be shaded out and swamped by bracken litter, to ease shepherding and gathering, and in certain areas to encourage woodland regeneration.  Control is appropriate where bracken is already invading heather or unimproved grassland of conservation interest, where there is a dense patch of bracken that threatens to colonise adjacent areas of heather or unimproved grassland, and in woodland or on land next to woodland where regeneration is to be encouraged.  We concentrate our efforts on areas which still have some ground vegetation that will help the site to recover.

However bracken control is not always appropriate and we avoid sites where there is little benefit from control and where bracken forms a substitute woodland community, supporting interesting plants and insects.  We also leave untouched steep slopes with deep bracken litter and little opportunity for vegetation to recover following treatment, as control on sites like this can lead to severe erosion.

Control of bracken should not be done without considering what vegetation might replace it.  As bracken cover closes and litter accumulates, fewer plant species are able to survive.


Control methods

Other land managers often spray bracken with the herbicide asulam, but we don’t use this because of the possible impact on other ferns and lichens and certain flowering plants.  Instead we use physical methods of control, which means cutting or crushing the growing fronds so that the surviving rhizomes are gradually starved.  These methods need a long-term approach to succeed.

We start cutting in June and cut the re-growth about six weeks later.  It takes three successive years of cutting to significantly reduce the vigour of the bracken.  Accessible areas are cut by machine, but where the gradient is too steep or the ground too rocky the conservation volunteers cut by hand using scythes and dashel (thistle) bashers.  Crushing with a roller is useful on difficult terrain, though less effective than cutting,  The most effective method of all is laborious hand pulling, which can only be used on small areas.  Where there are ground-nesting birds, cutting and crushing are timed to avoid the nesting and fledging period.

Establishing tree-cover can, in the long term, suppress bracken growth by shading, though it can be difficult to get trees established in competition with bracken.  This is the long term aim for the bracken slope next to the Gammallt woodland at Gilfach.

Given a chance, bracken will stage a rapid come-back, and effective control demands monitoring and repeated follow-ups.  Trampling by stock can help to suppress surviving fronds, and young fronds growing just below the surface in spring are particularly sensitive to treading.  In some areas vigorous heather regeneration may keep bracken in check, but not if stocking levels are too high.


The benefits

In several areas at Gilfach bracken has been controlled for ten or more years in succession, and its vigour and density have been very substantially reduced.  The flora is returning to the meadows by the Marteg, with harebell, heath bedstraw, mountain pansy, tormentil, bird’s-foot trefoil, betony and mouse-ear hawkweed blooming  where before there was dense bracken litter, while parts of the higher rocky slopes are purple with heather again.