Change and causes of change in the vascular plant flora of Ireland: 1970–1999

The analysis of decadal change in regional floras has received fresh impetus in recent years with studies often detecting anthropogenic effects and biotic homogenisation. Here we analyse the changing flora of the island of Ireland (i.e. both the Republic and Northern Ireland) using data derived from theNew Atlas of the British Flora(Prestonet al.2002b) to compare changing plant status from the previous national plant atlas of Perring and Walters (1962). We compare the number of 10km × 10km grid squares occupied by individual plant species and enter these into a regression analysis. The null hypothesis assumes that all the species will be located on the line of best fit hence the resulting residuals are used as an Index of Change. This Index was entered into correlation analysis with independent environmental indicators to interpret the potential causes of any change. Despite some potential sampling bias in the data the findings point to several factors being implicated in change with eutrophication being a major correlate of change of native species. Declines in archaeophytes was particularly pronounced for those species confined to single habitats. These and other findings are discussed in relation to land use change and agricultural intensification over the period of the survey.