Ecology of the Pembrokeshire Islands: III. The Effect of Grazing on the Vegetation

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Abstract
Heavy rabbit grazing and wind action have similar effects in limiting the size of plants and delaying flowering. Armerietum is the most resistant community and exists where either wind or grazing is severe or where both are moderate. Plants are classified as "rabbit-avoided", "resistant or "non-resistant". A wind-resistant flora is automatically rabbit-resistant and reacts differently from an inland flora to rabbit attack. Intense grazing causes an increase, not a decrease, in spp. no. by suppressing aggressive dominants and maintaining a community open enough for ephemerals. Flowering is increased, not decreased, owing to the production of laterals after grazing of apex. Maritime dicotyledons, not grasses, are more resistant to rabbit attack and lichens are commoner in grazed swards than are bryophytes as they are more salt resistant. In exposed areas curtailment of grazing leads to replacement of Armerietum by Festucetum rubrae; in sheltered areas of Callunetum by Agrostidetum tenuis or Pteridietum. Curtailment of exposure in grazed areas leads to replacement of Armerietum by Holcus or Agrostis grassland. With abatement of both grazing and exposure the postulated succession is Armeria - pasture grasses - meadow grasses -Calluna - shrubs.

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