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

Abstract

Summary This paper examines the effectiveness of a range of bracken control and heathland restoration treatments on bracken performance over an 18‐year period on a Calluna health in Breckland, UK. Initial treatments were a combination of cutting and spraying with asulam, with and without sowing Calluna seeds. After 6 years a further treatment was added, with the bracken treatments being either continued/reapplied or discontinued. Seeding with Calluna had no long‐term effect on bracken levels recorded under any bracken control treatment. No treatment eradicated bracken completely, although all achieved some control. Asulam was the most effective treatment in the 2 years after application, but bracken recovered rapidly thereafter. Bracken frond biomass was reduced to c. 6% of untreated levels after 18 years by cutting once yearly, irrespective of whether combined with an initial asulam application or not, but to 3% by cutting twice yearly. Re‐applications of asulam produced similar responses to the initial application, with a rapid decrease followed by recovery. Where bracken control was stopped after 6 years there was an increase in bracken in all treatments compared to where control was continued/reapplied. However, even after 12 years of remission, frond biomass was lower than that of untreated bracken in most treatments. Where cutting was applied twice yearly for 6 years and then allowed to recover for 12 years, the frond biomass was still less than 40% of untreated values. The response of bracken to asulam was compared to predictions from published models and a reasonable fit was obtained, although the sensitivity of one such model to the efficacy of the initial bracken reduction was noted. The implications of these results for both long‐term bracken control and the monitoring of bracken stocks are discussed.