EFFECTS OF LIVESTOCK EXCLUSION ON THE GROUND FLORA AND REGENERATION OF AN UPLAND ALNUS-GLUTINOSA WOODLAND

Vegetation composition and tree regeneration were compared between gra zing exclosures and unfenced areas of an hillside alder (Alnus glutino sa) woodland, at Coedydd Aber, North Wales. Sheep and ponies have had unrestricted access to the unfenced woodland throughout the 20 years s ince 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 w et pasture species. These changes appear to be a consequence of the re moval of both herbivory and physical disturbance caused by large herbi vores. Tree regeneration from seed was virtually absent from the unfen ced areas, and no alder regeneration was recorded in the woodland stud y plots. The exclosures contained high densities of young ash (Fraxinu s excelsior), and it is possible that, in the long term, ash will repl ace alder as the dominant tree in these stands.