Effects of livestock exclusion on the ground flora and regeneration of an upland Alnus glutinosa woodland

Abstract

Vegetation composition and tree regeneration were compared between grazing exclosures and unfenced areas of an hillside alder (Alnus glutinosa) woodland, at Coedydd Aber, North Wales. Sheep and ponies have had unrestricted access to the unfenced woodland throughout the 20 years since the exclosures were erected. The exclosures had a well developed field layer with significantly higher cover of plant litter, dead wood, bryophytes and woodland species; the unfenced woodland had a sparse field layer and significantly higher cover of bare soil, grasses and wet pasture species. These changes appear to be a consequence of the removal of both herbivory and physical disturbance caused by large herbivores. Tree regeneration from seed was virtually absent from the unfenced areas, and no alder regeneration was recorded in the woodland study plots. The exclosures contained high densities of young ash (Fraxinus excelsior), and it is possible that, in the long term, ash will replace alder as the dominant tree in these stands.