Bracken causing problems for farmers & conservationists. PACE teams brainstorm for solutions.
Bracken (scientific name Pteridium aquilinum) is a fern in the family Dennstaedtiaceae - 'the world's most successful weed' is threatening habitats and biodiversity across Africa and the rest of the world. Bracken is an extraordinarily cosmopolitan plant, it grows naturally and wild on all of the earth’s continents (except the Artic and Antartica) and in most land habitats except deserts.
It has many uses and has been used by humans for many thousands of years but is described as ‘An ubiquitous and aggressive species’, ‘Bracken is in no way threatened but is itself very often a threat'. Bracken is sometimes called a ‘species complex’ because a number of sub-species have been identified and there are different types in the northern and southern hemispheres, it is genetically variable, hybridizes and adapts to environmental changes. All in all bracken is quite a fascinating plant.
It was brought to the attention of Fred Banboye PACE Champion working with UNAFAS in Cameroon recently when he was carrying out (unrelated) research with cattle-rearing Mbororo communities in the Cameroon highlands. They complained that their grazing land is fast disappearing – it is being colonised by bracken and their cattle don’t eat bracken. They told Fred that when they spray it with weed killer the ‘next generation is four to five times thicker’ and they don’t know what to do because their grazing animals are losing their pasture.
Fred (above) shared the cattle-herder’s problem with his local network of PACE Ambassador’s and with other PACE Champions, asking if anyone had experience or ideas for organic ways that this can be solved. The experiences shared made it clear that bracken is a common problem, in many areas.
Ndzebam Godlove, a PACE educator told us - ‘One of the ways my mother taught me was removing it from its roots during rainy days. Then it gets rotten from the ground.’ ‘It works so well, we killed it on farm land in Wasi- Jakiri... ‘ But this doesn’t work the same in dry season as during the rains.’
Another recommendation was not to use weed killers - ‘Cut consecutively for three to four times. It will gradually diminish.’
The same day that this conversation was taking place the PACE coordinator observed and shared photos of bracken being controlled (in a forest park in London) by breaking and crushing the stems and fronds (pictured below).
Bracken is a well documented and universally observed pest to land managers, farmers and conservationists. Bracken itself stifles biodiversity and in the African upland habitats we are concerned with, as it infests farmland results in increased forest clearance as farmers slash and burn seeking fertile ground to cultivate or pasture their animals. Habitats and biodiversity are being lost.
The PACE groups continue to share ideas and have planned field work to collect local knowledge and experiment with control options.
If you have experience of successful ways to control bracken in Africa please do share with us, by e-mail PACE@tusk.org or on our Facebook page.
Some background on Bracken
Bracken likes plenty of light, and well drained ground. It grows between 1 - 4m tall, and has extensive underground rootstock (rhizomes) that send up large, triangular, divided leaves called fronds. Fronds can be 2m long (4m has been reported from South America) and shade out other species, and the thick, dry litter from dead fronds can also inhibit other species from growing. In addition, Bracken produces allelopathic chemicals – chemicals that inhibit growth of other species. The large and deep rhizome system that stores lots of carbohydrate can go as far as a metre into the ground. The rhizomes produce buds that enable rapid vegetative spread, and rapid regrowth after fire, dry or cold periods. Fire benefits colonisation by bracken (Roos et al, 2010). When hillsides are burned, bracken is often one of the first plants to emerge. The deep persistent rhizomes go far enough down into the soil not to be damaged by fire. Bracken also reproduces very effectively from spores, which grow rapidly on ground that has been cleared and sterilised by fire. The young establishing sporelings do well in high Ph, so they thrive on the potash minerals released from burning. As these leach away and the soil Ph reduces, the now mature bracken plant (which has switched its Ph preference) likes the low Ph, so continues to be more competitive than other species. Herbicides are reported to increase the vigour of bracken, this is because applying herbicide to the fronds may kill the active buds but it will have little effect on the dormant buds. A systemic herbicide is needed that reaches the rhizomes and kills them, as well as the fronds. Few weed killers are effective because they don’t reach down to the rhizomes. Add to this that bracken has great resistance to pathogenic microorganisms (bacteria and pests that cause disease) and it becomes clear why the plant is referred to as ‘The world’s most successful weed.’
Bracken is unpalatable to grazing animals and if eaten can poison cattle, sheep, horses and other species. It contains a toxin Ptaquiloside and the young leaves when crushed or eaten release hydrogen cyanide. If there is other food available they tend not to eat the bracken.
A long-term solution to colonisation by bracken, that has been successful in American tropics and in temperate areas is to bring back enough trees to provide light canopy, but not too many to prevent grasses thriving. Bracken growth is retarded under a canopy (Douterlungne et al 2010, Page 1988, pers ob). It requires careful nursing of the tree seedlings, clearing the bracken until the saplings are established. Disturbing the soil is also successful, in areas where cattle are provided with hay, straw or other fodder where cattle hooves have crushed the fronds and trampled the ground generally remains bracken free. Free-range pigs have the same effect, because they turn the soil, damaging rhizomes and allowing water and frost to enter the soil.
How is bracken used?
Bracken has many uses, and it has been said that in the UK as traditional uses of bracken declined it’s spread as a weed increased.
Bracken fronds are a source of green and dark yellow dye and the rhizomes a source of black dye. It is used for making paper, for thatching buildings, for fibre work and weaving. In many parts of the world the young fronds and rhizomes are eaten, however it’s now known that the shikimic acid these contain is carcinogenic, it promotes stomach cancers, and mutagenic.
Bracken has been widely used as bedding for animals (and is later composted to give a nutrient-rich mulch). It is a source of potash (pot ash = plant ashes soaked in water in a pot giving a soluble form of potassium K+), used to make soap. It makes a rich compost and mulch that adds structure as well as nutrients to soil.
Bracken is useful as packaging, especially for delicate items. Because it has insecticidal properties bracken is a valuable packaging for perishable products like tomatoes, soft fruits, and fresh fish – it reduces decay caused by bacteria or insect attack during transportation and storage, especially valuable when they is no refrigeration. Bracken is also useful for protecting other goods from damage during transportation and storage.
On the negative side bracken litter is said to provide an ideal habitat for ticks and the spread of bracken has been linked to an increase in tick numbers. Ticks spread diseases that in addition to affecting birds, wild and domestic livestock, can also be transmitted to people (e.g. Lyme disease).
Bracken control group UK. http://www.brackencontrol.co.uk/research-information accessed July 2017.
Douterlungne D, Levy-Tacher SI, Golicher DJ, & Danobeytia FR. 2010. Applying Indigenous Knowledge to the Restoration of Degraded Tropical Rain Forest Clearings Dominated by Bracken Fern. Restoration Ecology Vol. 18, No. 3, pp. 322– 329 MAY 2010. https://www.researchgate.net/publication/230278814 open access [accessed Jul 30, 2017].
Jermy C & Camus J. 1991. The illustrated field guide to ferns and allied plants. Natural History Museum Publications. London.
Mabberley, D.J. 1990. The Plant-Book. Cambridge University Press.
Page, C. 1988. Ferns – A natural history of Britain’s Ferns. The New Naturalist. Collins. London.
Page, C. 1986. The strategies of bracken as a permanent ecological opportunist. Pages 173–181. in Smith, R. T. and J. A. Taylor. eds. Proceedings of the International Conference—Bracken '85/Bracken: Ecology, Land Use and Control Technology. Carnforth, England Parthenon Publishing.
Roos K, Rollenbeck R, Peters T, Bendix J, & Beck E. 2010. Growth of Tropical Bracken Pteridium arachnoideum): Response to Weather Variations and Burning. Invasive Plant Science and Management 3(4):402-411. https://doi.org/10.1614/IPSM-D-09-00031.1 open access [accessed Jul 30, 2017].