Control of bracken and the restoration of heathland. I. Control of bracken.
Abstract
In trials in the Breckland region (Suffolk/Norfolk border), UK in 1978-88 on Calluna vulgaris heathland and grass (dominated by Festuca ovina) heathland sites, bracken (Pteridium aquilinum) was not treated, was cut once or twice/year from 1978-84, was treated with 4.4 kg asulam/ha in 1978 with or without cutting once/year in 1979-84 or was treated with 4.4 kg asulam in 1978 and 1979. Bracken control treatments were implemented with or without sowing 20 000 C. vulgaris seeds/m2 at the C. vulgaris site and with or without sowing a mixture of Holcus lanatus, Festuca spp. (mainly F. ovina), Lotus corniculatus and Rumex acetosella (at 5000, 10 000, 600 and 4400 seeds/m2, respectively). In 1985-88 bracken control measures<b> </b>were continued or stopped, thus allowing bracken recovery. No treatment eradicated bracken completely, although all had some control. Asulam was the most effective treatment in the 2 years after treatment, but bracken recovered rapidly thereafter. Yearly cutting reduced bracken fronds by 70%, and cutting twice yearly by >90%. After cutting was stopped, bracken recovered rapidly on plots cut yearly, but more slowly where it was cut twice-yearly. Reapplication of asulam produced a similar response to the initial application, with a rapid decrease followed by recovery. Heathland at the C. vulgaris site took 6 years to reach maximum biomass levels, and sowing did not affect biomass. On the grass heath, vegetation developed much faster on the sown plots where bracken was also controlled. At both sites, cutting appeared to accelerate vegetation establishment, probably because of litter disturbance. At the grass heath site, vegetation development suppressed bracken recovery 5-6 years after treatment started, when there was a maximum difference in grass biomass between unsown and sown plots. The relevance of these results to both conservation management and the assessment of bracken distribution and encroachment are discussed.