Individual study: The response of bracken Pteridium aquilinum rhizomes to 18 years of cutting and herbicide control or 6 years of control followed by recovery, Cavenham Heath, Suffolk, England
Marrs R.H., Johnson S.W. & Le Duc M.G. (1998) Control of bracken and restoration of heathland. VII. The response of bracken rhizomes to 18 years of continued bracken control or 6 years of control followed by recovery. Journal of Applied Ecology, 35, 748-757
Bracken Pteridium aquilinum in some habitats, such as heathland, can be highly invasive. In spite many efforts to find a long-term solution to its control, no practical method has yet been found. The main reason for this is the resilience of the large underground rhizome system. The effects of six bracken control treatments (various cutting and herbicide treatments) applied in combination with a heather Calluna vulgaris seeding treatment on the rhizome system of bracken at Cavenham Heath in Breckland, eastern England was assessed after 18 years.
Study site: The bracken control experiment was established in 1978 at Cavenham Heath (a Calluna-dominated lowland heath), Suffolk, eastern England (National Grid reference TL 755725; 52º19'N, 0º34'E).
Bracken control treatments: Six bracken control treatments (in factorial combination with Calluna seeding treatments) were applied commencing 1978:
i) untreated control
ii) cutting once yearly (1978-1996) in late July
iii) cutting twice yearly (1978-1996), mid-June and late July
iv) spraying with asulam at the recommended rate (4.4 kg a.i./ha) in 1978
v) spraying with asulam in 1978 and 1979
vi) spraying with asulam in 1978, yearly cutting in June thereafter
Spraying was followed by repeat doses in 1984 and 1990.
Calluna seeding treatments: Two treatments were appled:
i) an unseeded control (natural colonisation)
ii) seeded with local seed at a rate of 20,000 seed/m²
After 6 years the experiment was split and bracken control was continued/reapplied on half the plots and stopped on the remainder. The effects of treatment on the numbers of active and dormant bracken buds and the length and biomass on both frond-bearing and storage rhizomes were measured.
Effectiveness of treatments: When applied over the 18 years, all bracken treatments reduced all rhizome measures, but treatments that included cutting were more effective than herbicide alone. The best treatment after 10–12 years was cutting twice yearly, but after 18 years this treatment had apparently reached equilibrium and the cutting-once-yearly treatment was superior. No treatment eradicated the bracken in 18 years of continuous treatment.
Response after treatment cessation: When bracken control treatments were stopped after 6 years, rhizome recovery started within 4 years and there was significant recovery thereafter. After 12 years the least effective treatment, cut once yearly, although still showing a significant reduction in rhizome biomass, had recovered to 88% of the untreated plots. The most effective treatment was cutting twice yearly for 6 years, where most measures of rhizome performance remained at approximately 50% of untreated plots 12 years after cutting stopped.
Conclusions: The results from this field study suggest that if bracken is to be suppressed on a long-term basis continuous control is needed as complete eradication is unlikely. The long time scale found for total bracken recovery after (only) 6 years of treatment indicates that large areas of bracken treated in the past will take some time to recover to pretreatment levels.
Note: If using or referring to this published study, please read and quote the original paper. The original paper can be viewed at:http://www.blackwell-synergy.com/doi/abs/10.1046/j.1365-2664.1998.355346.x