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vert bar Floras of the Irish Isles

Matthew Jebb (National Botanic Gardens).
Last updated: 8th February 2009

A composite map of Ireland's main offshore islands Project Description

A literature survey of Irish island floras (Achill, Aran, Aranmore, Clare, Inishbofin, Inishturk, Mullet and Rathlin) revealed a correlation between the log of the islandís area to the log of species richness (below).

Aran, Clare, Inishbofin and Lambay have been surveyed on a number of occasions, and each separate survey was included in the calculation. These island floras conformed to a regression line, which indicated that with every doubling in area, an Irish islandís floral diversity increases by ca. 3.4 %.

Both these findings are in accordance with work on island biogeography elsewhere. Macarthur and Wilson (1967) found that islands in similar geographic settings demonstrated a correlation between area and species number. Furthermore they found that islands denuded of species would return to a similar level of diversity, but that the composition would be unpredictable and often very different on each occasion.

Over time the eighty two taxa that are absent from Lambay today (see Vascular flora of Lambay), as well as the seventy-eight that have not previously been recorded, but are present today, may arrive, flourish and once again disappear from the Island's flora. Islands thus provide an insight into floristic dynamics that is not discernible in a mainland setting. A logarithmic plot of species number to area of Irish islands

MacArthur, R. H. and E. O. Wilson. 1967. The Theory of Island Biogeography. Princeton University Press, Princeton, New Jersey.