Control of bracken and restoration of heathland. VIII. The regeneration of the heathland community after 18 years of continued bracken control or 6 years of control followed by recovery.
Abstract
The effectiveness of a range of bracken (Pteridium aquilinum) control and heathland restoration treatments, in factorial combination, on heath development over an 18-year period, is described. Control treatments included cutting once and twice yearly between 1978 and 1996; spraying the herbicide asulam at the recommended rate (4.4 kg a.i. ha-1) in two treatments, 1978 and 1978 plus 1979, each followed by repeat doses in 1984 and 1990; and spraying asulam followed by cutting once yearly. Calluna seeds were added to half the plots to aid heathland establishment. After 6 years the experiment was split and bracken control was continued/re-applied on half the plots and stopped on the remainder. The effects of all treatments on the cover of colonizing species between 1986 and 1996 is described. Twenty-five species were recorded in the 10 years, but some were present only for a very short time. Initially Calluna establishment was good in some treatments, especially where Calluna seed was added and bracken was controlled; cutting bracken twice yearly was most effective. Other plots developed either a grass heath flora dominated by Agrostis capillaris, Deschampsia flexuosa, Dicranum scoparium, Festuca ovina and Rumex acetosella, or were dominated by either Calamagrostis epigejos or Carex arenaria. Some plots were invaded by Betula spp.; mortality was high but some survived to overtop the bracken by 1996. In 1990 and 1991 there was considerable mortality of Rumex acetosella and Calluna, respectively, almost certainly as a direct effect of the weather; these 2 years were the hottest and driest during the experimental period. The grass heath species showed distinct spatial effects during colonization, and tended to have a greater cover where bracken control was continued. Bracken litter was maintained at a low cover where treatment was continued, but increased to near untreated levels within 10 years, except where bracken was cut twice yearly. The cut twice yearly plots started from a lower level, but litter cover was still increasing at the end of the experimental period. A major influence on the vegetation development was the increasing numbers of rabbits which occurred during the course of the experiment. Rabbits had invaded all treatments by 1996 and increased the amount of bare ground in many treatments. Rabbit activity was greatest where the bracken control was increased. The original objectives of the restoration scheme 'to restore a Calluna heathland' have not been met, as the Calluna died. However, a reasonable Breck grass heath flora developed in many plots, which is a better community from a conservation viewpoint than dense bracken. The implications for the restoration of heathland on dense bracken communities is discussed and an integrated management approach is suggested.