Bracken fern (Pteridium aquilinum) is a widespread and resilient plant found across diverse global landscapes. Its common presence often leads to questions about its nature and potential hazards, including its environmental and health impacts.
Understanding Bracken
Bracken, scientifically known as Pteridium aquilinum, belongs to the fern family Dennstaedtiaceae. It is a vascular plant that reproduces through spores rather than seeds. This ancient lineage contributes to its robust and adaptable nature, allowing it to thrive in various environments. The plant exhibits a two-part life cycle, alternating between a dominant sporophyte phase (the large fern) and a smaller gametophyte phase. This versatility contributes to its widespread distribution.
Physical Characteristics and Global Presence
Bracken fern is recognized by its large, roughly triangular fronds that emerge from an extensive underground root system. These fronds can reach heights of 1 to 3 meters, and new fronds, known as fiddleheads, unfurl in the spring. The plant’s resilience stems from its thick, black, creeping rhizomes, which can extend horizontally for many meters underground and store nutrients. This rhizome system allows bracken to spread rapidly, often forming dense colonies, and to regenerate effectively even after disturbances like fire.
This fern is one of the most widely distributed vascular plants globally, found on all continents except Antarctica. It thrives in temperate and subtropical regions, inhabiting various environments from moorlands to woodlands and disturbed areas. Its lightweight spores are easily dispersed by wind and water, enabling it to colonize new territories efficiently. Its adaptability to diverse soil types and climates, ranging from acidic to neutral pH, contributes to its global prevalence.
Ecological Impact and Health Concerns
Bracken fern significantly impacts ecosystems due to its invasive nature. It forms dense stands that outcompete other plant species by shading them and releasing allelopathic chemicals, which suppress the growth of neighboring vegetation. This dominance can lead to monocultures, reducing biodiversity and altering habitats.
The fern contains several toxic compounds, including the carcinogen ptaquiloside and thiaminase. Ptaquiloside is concentrated in young fronds and rhizomes and can damage DNA, linked to cancerous lesions. Thiaminase, an enzyme, destroys thiamine (vitamin B1), leading to deficiency.
Livestock consuming bracken fern can experience severe health issues. Horses can develop “bracken staggers,” a neurological condition from thiamine deficiency, characterized by incoordination and weight loss. Cattle are susceptible to enzootic haematuria, a chronic poisoning causing intermittent bloody urine and leading to bladder tumors. These conditions typically require prolonged consumption, with symptoms appearing weeks or even years after initial exposure.
For humans, concerns exist about health risks from exposure or consumption. Studies in regions like Japan and Brazil, where young bracken shoots are traditionally consumed, show an association between bracken intake and certain cancers of the upper alimentary tract, including gastric and esophageal cancers. Ptaquiloside can also leach into water supplies, posing a risk. The International Agency for Research on Cancer classifies bracken fern as possibly carcinogenic to humans.
Managing Bracken
Managing bracken fern is challenging due to its extensive rhizome system and ability to regenerate. Control strategies often combine methods to deplete the plant’s energy reserves and prevent its spread. Mechanical removal includes cutting or crushing fronds repeatedly over several years. Regular cutting, multiple times during the growing season, weakens the plant by preventing photosynthesis and exhausting the rhizomes.
Chemical treatments, primarily using herbicides like glyphosate or asulam, are also employed. These herbicides are applied when fronds are fully developed to ensure maximum absorption and translocation to the rhizomes. While effective, chemical applications require careful consideration to minimize impact on non-target plants and the environment.
Biological control methods, though less common, involve using natural enemies to suppress bracken growth. This approach is complex and still under investigation. Regardless of the method, ongoing monitoring and follow-up treatments are necessary, as bracken can quickly recover if management efforts are not sustained.