Control of bracken and restoration of heathland. VI. The response of bracken fronds to 18 years of continued bracken control or 6 years of control followed by recovery.
A range of bracken (Pteridium aquilinum) control and heathland restoration treatments were applied over an 18 year period on a Calluna vulgaris heath in Breckland, UK. A combination of cutting and spraying with asulam, with and without sowing C. vulgaris seeds were tested. After 6 years, treatment was either continued/re-applied, or discontinued. Seeding with 20 000 C. vulgaris seeds per m2 had no long-term effect on bracken levels. No treatment eradicated bracken completely, although all achieved some control. Asulam was initially the most effective treatment, but biomass rapidly recovered after 2 years. Frond biomass was reduced to ∼6% of untreated levels after 18 years by cutting once yearly, with or without asulam application and to 3% by cutting twice yearly. Where bracken control was stopped after 6 years there was an increase in bracken in all treatments. However, frond biomass was lower in most treatments than in controls after 12 years of recovery. The most effective treatment was cutting twice yearly for 6 years. Even after a 12 year recovery, frond biomass was <40% of untreated values. The implications for both long-term bracken control and monitoring bracken stocks are discussed.