The ecology and conservation of Arctostaphylos uva-ursi Bearberry heath habitats in the Burren, Western Ireland
Hanrahan, Sarah Ann
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This thesis focuses on Arctostaphylos uva-ursi and co-occurring species within vulnerable habitats in the Burren region of western Ireland. The objectives of this research were: to describe the plant communities; to monitor their response to cutting as a management tool to restore overgrown heaths to good conservation-status by promoting the growth of Arctostaphylos and other key prostrate dwarf shrubs Empetrum nigrum and Dryas octopetala; and to explore the reproductive biology of Arctostaphylos. The Burren Arctostaphylos-rich heaths were compared to EU protected habitats, such as Alpine and Boreal heaths and European dry heaths. Threats to these rare habitats were identified, mainly the encroachment of more vigorous species, such as Calluna vulgaris, at least partly due to under-grazing. Thus tall over-mature Calluna was cut and removed in experimental trials and the effects on the vegetation cover and species composition were monitored in the short-term study. As climate change is an added potential threat, baseline data were obtained for the reproduction of Arctostaphylos, its pollination mechanisms, rates of fruit and seed set in the Burren upland and lowland populations as well as its phenology; pollinator-exclusion experiments and observations were undertaken. Four distinct communities were identified: the Arctostaphylos – Sesleria heathy grasslands, found throughout the Burren; the Dryas – Empetrum heaths and the Calluna – Arctostaphylos heaths, both restricted to the uplands, the latter subject to the cutting trials; and the rarest and most vulnerable Arctostaphylos – Juniperus communis heath in the eastern Burren lowlands. Cutting trials reduced Calluna cover, increased species richness and diversity; Molinia was reduced by the spring cut and bracken appeared to decrease following cutting in autumn. In terms of reproductive biology, Arctostaphylos flowers were visited mainly by bumblebees, fruit and seed production took place more in open-pollinated than in pollinator-excluded flowers, but curiously seedlings were not observed in the field.