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Rabbits

Tree Autecology and Biology

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East Usambaras

Pitcairn Islands

A perusal of the Irish literature shows that plant scientists survey vegetation with little considerations to historical factors (e.g. human impact, grazing) which have affected species composition and abundance. Grazing is often the main factor and wild rabbits have often been recognized as the main culprits. However, in Ireland plant scientists do not appear to have published any papers dealing with the impact of rabbits on vegetation (e.g. Irish Naturalists' Journal) giving the impression that rabbits had no impact on the Irish vegetation. Using historical evidence chiefly based on farming reports from the Coleraine Chronicle it is possible to show how variable and often dramatic the impact of rabbits has been since the early 19th century. As early as 1804 the rabbit's potential population growth and environmental impact were recorded. Numbers were kept under control until the early 20th century as many rabbits were killed for their meat or fur. By 1924 rabbits were considered a plague in many parts of the north of Ireland. Attempts to control them failed until the 1939-1945 war effort to increase food production nearly eliminated rabbit. However by the early 1950s rabbits had become a menace once again. Myxomatosis was first recorded in Northern Ireland in August 1954 and resulted in very low population numbers by late 1955. Subsequently their numbers have fluctuated greatly with a general trend towards higher populations. Rabbits, besides their often dramatic impact on farm crops, have greatly affected natural vegetation. As a result of fluctuating rabbit population sizes and differing plant susceptibility to rabbit grazing, the abundance and cover of many plant species has changed. Prior to myxomatosis Erica cinerea, unpalatable to rabbits, became dominant over Calluna vulgaris, but following the crash in rabbit numbers C. vulgaris gained dominance. The regeneration of most tree and shrub species was prevented by high numbers of rabbits, whereas the unpalatable Sambucus nigra regenerated freely around rabbit burrows. Following myxomatosis shrubs now dominant in semi-natural vegetation such as Ulex europaeus and Hippophae rhamnoides spread rapidly.