Welsh Journals

THE RABBIT EFFECT ON THE GROWTH OF CERTAIN PLANTS ON SKOMER WITH PARTICULAR REFERENCE TO RED CAMPION (Silene dioica (L.) Clairo) AND GROUND IVY (Glechoma hederacea LJ. G. H. KNIGHT AIM OF STUDY For over 10 years I have recorded intermittently the effect of the Rabbit on the survival and success of woodland plants in Warwickshire. Despite its reduced population following myxomatosis its influence in woods is still profound and significant although often overlooked, but on the mainland there is always a nagging doubt that a particular effect might be due to some other herbivore such as deer, hares or squirrels, for example, whereas on Skomer, aside from a few goats, these doubts do not seriously arise. Moreover the dense Rabbit population demonstrated the effects decisively, beyond all reasonable doubt. Allowances had to be made, of course, for the special habitat factors which operate on Skomer, such as extreme exposure to wind, salt spray and sun with increased risk of dessication, and the heavy accumulation of animal "fertiliser" chiefly from the Lesser Black-backed Gull colonies. The Rabbit affects plants in 4 ways, in the following order of im- portance: 1. grazing 2. burrowing 3. raking (scraping) 4. urinating; and from the point of view of grazing, which is by far the most important of these biotic factors, plants can be divided into 3 categories: 1. the "untouchables" 2. plants with limited palatability 3. the favourites The following observations and conclusions arise, therefore, from a long term study which culminated in a visit to Skomer from 27 May to 2 June, 1973, and consequently attention has been focussed principally on those species on the island which also commonly occur in midland woods. They will be considered in order of their palatability to rabbits. 1. The Untouchables. Abundant were Bracken (Pteridium aquilinum), Nettles (Urtica dioica), Ground Ivy (Glechoma hederacea), Wood Sage (Teucrium scorodonia) and Ragwort (Senecio jacobea). Occasional were Spear Thistle (Cirsium vulgare), Yarrow (Achillea millefolium), Water Mint (Mentha aquatica) and Burdock (Arctium minus). Rare was Ivy (Hedera helix) at North Haven. So far as I could judge these species were never damaged by Rabbits, and it will be noted that three of them are members of the Labiatae, two of which, Wood Sage and Ground Ivy, were amongst the most widespread and abundant species on the island.