Problems and Hazards Associated with Bracken Infestation
The problems and hazards presented by bracken currently far outweigh any benefits. The statement “On balance, allowing the continued spread of Bracken will damage more communities and affect more species than control aimed at halting the spread of bracken and removing it from the landscape” (Pakeman & Marrs, 1992) still holds true.
Little use is made of bracken for bedding these days although it can be of use as a base for compost where it can be safely harvested. It offers little benefit to other species apart from perhaps acting as a “nursery” for the egg and larval stages of species of butterfly, but the bracken monoculture that eventually results destroys the rich mosaic of flowering plants that the adults require for foraging and feeding. The few species of bird e.g. Whinchat, Willow Warbler and other wildlife that use bracken as a refuge are heavily outnumbered by the vast array of species whose habitats have been destroyed by this plant’s remorseless advance e.g. Hen Harrier, Merlin, Greenshank, Grouse, and Twite etc. and also most reptiles and mammals. Indeed, it is thought many of these could die out completely in many areas if bracken is not controlled.
Although vegetation mosaics that include bracken will enhance biodiversity initially, bracken that is left unchecked will eventually destroy most other plant life producing the dense monoculture typical of well-established infestations. Even species that appeared initially to be living in harmony with it (and even gaining a level of protection from it) such as violets, orchids, and bluebells are eventually eliminated by this plant’s competitive and allelopathic nature. The dense matt of litter that bracken produces at ground level has little ecological value (apart from possible soil structure improvement), indeed, this prevents the seeds of other species from germinating.
As well as destruction of grazing pasture, bracken can destroy heather (although vigorously growing young well-managed heather can compete against bracken). When this happens, it not only eliminates a source of food for grouse and other animals but will cause a significant loss of foraging area for many bee colonies whose hives are traditionally brought to the heather moors when the heather is in bloom.
There are a number of significant health issues associated with bracken infestation and these would include the following:-
Livestock Health
All parts of the bracken plant contain potent toxins and carcinogens and these cause a variety of illnesses within animals unfortunate enough to consume a sufficient quantity, these can be listed thus:-
- Serious vitamin B1 deficiency in horses
- Bright Blindness in sheep
- Haemorrhagic Syndrome in cattle and sheep
- Cancer of the stomach, spleen, and liver in cattle and sheep
- Fibrosarcomas of the jaw in sheep
Significant numbers of livestock die from one or other of these afflictions, (with the attendant commercial losses as well as animal suffering) as many an upland country vet will testify.
In addition to the above, dense bracken litter usually harbours a vast population of a species of tick (Ixodes ricinus) which often carries highly unpleasant diseases such as Lyme Disease and Looping Ill. This parasite will attach itself to any mammal (including man), bird and even some reptiles passing through the litter. It then bites into the host and draws blood to feed upon, and in so doing transmits the disease pathogens. Some birds including game birds are particularly prone to Louping Ill, whilst many cattle and sheep will suffer from the diseases carried to some level at some point (even pigs and wild boar are not immune), a significant loss of thriftiness is a frequent result.
Other animal health issues include the numerous cases where sheep that become ill or ‘struck’ with maggots (known in some areas as ‘fly strike’) will hide away in dense bracken thus putting themselves beyond veterinary help and dying most unpleasant deaths as a result. Further, infestation of bracken on erstwhile healthy and well drained mountainside pasture will often result in livestock being forced to spend more time grazing the damp pastureland on the valley floor upon which such diseases as liverfluke and foot rot often thrive (land that would otherwise be “kept up” for much of the spring and summer and used as hay meadow or for silage production); a significant rise in levels of these diseases is the usual result.
Human Health
A number of human health issues associated with bracken are suspected or known to occur, those that have come under “the spotlight” in recent times include:-
‘Lyme Disease’ – this has been known to occur when a person has been bitten by a tick carrying the disease. As stated above, these ticks are harboured by the bracken litter, and people working in such an area (or ramblers walking in the land under CROW Act rulings) are very much at risk of contracting this disease. Should misdiagnosis occur, and the illness be dismissed as a summer cold or flu (the initial symptoms are apparently similar) it can then lead to long-term fatigue, and create problems in the heart, joints and nervous system.
‘Cancer’ – this is probably the most read about (and possibly emotive) of the afflictions thought to be associated with bracken infestation. Although it is known that people who eat developing bracken shoots (i.e. croziers or “fiddleheads”) have quite a high chance of contracting cancer, such practice is relatively unknown in this country. However, it is a common practice in Japan, and it is known that Japan has the highest incidence of gastric and oesophageal cancer in the world (Evans,1967a; Marliere et al 2000); this is a significant indicator of the carcinogenicity in this plant’s make up.
Indeed, very many more times the normal levels of gastric cancer have been found in areas where there are large infestations of bracken such as Costa Rica and North Wales (Villalobos Salazar et al, 1989; Buckley, 1989), although the causal pathways have yet to be scientifically ascertained.
Transfer of bracken carcinogens to humans via drinking water (i.e. from water supplies arising off bracken covered mountains – a very common practice in North Wales) is suspected, but this has not yet been fully investigated, although Rasmussen (2003) has detected ptaquiloside (one of many bracken carcinogens) throughout plant-soil systems in Denmark; this chemical is water soluble and he considers this a potential risk to ground water supplies
Another likely causal pathway in transmitting bracken carcinogens to humans is via the clouds of dust-like spores emitted by bracken beds in July-September in certain years (the spores are known to contain carcinogens). People working on a regular basis in large expanses of bracken land could be at risk to this possibility. Many organisations now advise their workers to wear masks when working amongst mature bracken.
Hopefully, more detailed scientific work will be carried out in the not too distant future In order to fully quantify the health risks presented by bracken.