The effect of rabbit (Oryctolagus cuniculus) grazing damage on the growth, botanical composition and yield of a ryegrass re-seed

A perennial ryegrass sward was established in the autumn of 1989 in an enclosed 0.3 ha site and was exposed to captive wild rabbit (Oryctolagus cuniculus) grazing. Rabbit numbers were varied from 16 rabbits ha^-1 in winter to 55 rabbits ha^-1 corresponding to natural fluctuations in the field. The original sward was grown for three seasons (1989/1990 to 1990/1991) and a range of grazing regimes imposed. In 1989/1990 four grazing regimes were arranged in a replicated split block design in the experimental area. These were ungrazed, winter grazed, spring grazed and totally grazed. In the second year of the experiment all plots were exposed to grazing with the exception of the originally protected plots. This was to examine the effects of longer-term grazing damage on a ryegrass sward. In the final year half of all treatments were protected to study recovery of a sward which had been damaged previously. The remainder of the plots were exposed to grazing. Three cuts were harvested in each year and the productivity assessed in terms of yield and botanical composition. There was a significant reduction in ryegrass proportion in grazed swards following the first winter of grazing, while clover, other grasses and weeds were enhanced. The promotion of clover content in grazed swards was a feature throughout the 3 yr of the study. In the second year, protection of grazed swards led to a restoration of yields, although the botanical composition remained altered. The exposure of previously ungrazed plots in the final year of the experiment showed that these swards were particularly attractive to rabbits and they suffered the greatest yield losses relative to the protected plots at the first cut in 1991. In this year dry weather conditions were experienced following the first cut and demonstrated that yield losses are exacerbated when rabbit grazing is compounded with adverse growing conditions. The results overall indicate that protection of ryegrass swards at the establishment phase is important, but that a degree of recovery is possible by providing protection at a later stage, although the ryegrass component is still impaired in swards which suffer early damage.