Arbutus Unedo

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Abstract
Study of A. unedo at Killarney shows that it is primarily a member of shrub- or scrub-communities on cliffs, broken rocky slopes, and rock-outcrops. In these habitats it is extremely successful and maintains itself by regeneration from seeds, flourishing equally on Carboniferous Limestone and Old Red Sandstone, the pH varying from 6.5-7 to 4-4.5. It is also a marginal plant of Quercus woodland, and sometimes forms part of the succession leading to climax Quercus woodland. It grows to tree-size in competition for light, but cannot compete suc-cessfully with Quercus and is always eventually shaded out. Data are given on seed-production and regeneration from seeds, and attention is drawn to the possible biological significance of the swollen stem-base found in young plants. Though primarily a plant of the Mediterranean region, A. unedo is distributed discontinuously in n.-w. Europe. Examination of the conditions in its northern stations suggests that its present distr. can be accounted for by a combination of climatic and habitat factors, and that the presence of the sp. in w. Ireland and Brittany is probably due to postglacial immigration from s. Europe.