Tracing our wild and wonderful flora

The first real gale of autumn pushed peaty waves right to the end of Killary Harbour, the long mountain fiord that separates Mayo from Galway. Even at the sheltered inner reaches, it jangled the fuchsia's scarlet bells, winnowed the spires of Japanese knotweed and threshed through the glossy ramparts of rhododendron. And for good measure, in this gusty assault upon aliens, it snatched at the huge green leaves of Gunnera tinctoria, now spreading in statuesque thickets along the shores of the fiord.

Gunnera is the "giant rhubarb" (though really no relation) which, like fuchsia, arrived from South America into the Big House gardens of the 19th Century and then took off into the wild. At this time of year it boasts great conical spikes of seeds that birds often carry far from the parent plant. From a familiar and long-established stronghold at Achill Island, Co Mayo, gunnera is spreading fast, notably where road-widening offers fresh banks of soil (as at Killary), but also on cuttings in blanket bog elsewhere on the wet, mild coast of the west.

Such alien invasions, and the reasons for their success, are part of the wider story of Ireland's greening unfolded in Flora Hibernica, just published by The Collins Press of Cork at £25 hardback. Its authors, Jonathan Pilcher and Valerie Hall, both academics at Queen's University Belfast, are enthusiastic botanists and also experts on landscape history.

Their book is a milestone in popular Irish botany, not only detailing the main wild flowers, plants and trees of Ireland, but explaining why they grow where they do. It appears at a time of great public pleasure in wild plants but little real knowledge, and is the first modern book to take an island-wide view, with lots of good pictures, aimed at the general, nature-loving reader.

Its title echoes others in these islands - Richard Mabey's very successful book, Flora Britannica, and Flora Celtica, the Scottish millennial project based at the Royal Botanical Gardens in Edinburgh. Both were very people-centred celebrations, combining the stories of native plants with collected lore about their uses in country life and culture.

Perhaps we need to wait for this kind of interest to mature in Ireland. Meanwhile, the emphasis in Flora Hibernica is on the variety of habitats and ecological conditions (most of them mild and moist) that have helped to shape our particular heritage of plants. The authors' insight into changes of the past goes back 15,000 years to the great melt of ice that opened Ireland to recolonisation by plant life.

I like the recollection of their search for ancient yews among the huge heaps of trees dragged out of Clonsast bog by Bord na M≤na. "We found that we could tell the difference between the species by hitting the tree trunks with a hammer! The yews rang like a bell . . ." And even today, a few of the first Arctic plants to grow on the Irish tundra - dwarf willow, crowberry, alpine club moss - still survive in places like the summit of Slieve Donard, the highest peak in the Mournes.

Most books on Ireland's wildflowers make an early beeline for the Burren, but while this one certainly explores the limestone flora, it has a welcome balance with less familiar habitats. The chapter on the seashore has a special fascination, studying the strategies that help plants to live in extreme conditions of salt or drought. Here, too, appear some rarities, like the seakale, once a peasant's vegetable and now a cultivated luxury, and the sea pea, which drifts ashore from America and grows to produce lovely amethyst flowers.

While very much an Ireland-wide book, the Belfast base of the authors brings a special insight into the northern flora - the damson and laburnum hedges, for example, of Co Armagh, the patches of limestone grassland in Fermanagh where almost a score of plant species may grow in an area no bigger than the palm of one's hand - or even the fairy foxgloves growing on the old jail wall in Downpatrick, Co Down.

The far-reaching perspective of both authors (Jonathan Pilcher is Professor of Palaeoecology and Valerie Hall a senior lecturer in Past Environmental Studies) gives valuable weight to their views on global warming and attitudes on conservation.

They already find signs of the drying of bog surfaces all over Ireland, with greater decay in the upper few centimetres of raised bogs than in peats of any time in the last 4,000 years. The drying of blanket bogs will make the impact of overgrazing and mechanical peat harvesting even worse.

The prospects for invading weeds and aliens invite comparisons with the end of the last glaciation, when competitive, invasive plants from further south ousted the native Arctic flora and became the new native plants of this island.

Already, warmer winters are favouring the spread of aliens such as gunnera at the expense of less competitive, but frost-hardy, native species.

As climate changes - yet again - just what are we to aim at in nature conservation? How appropriate is it to try to "pickle", as the authors put it, the habitats we have now, virtually all of which have been shaped by human influence? The only natural state in most of Ireland is dense, mixed forest, but how happy would future generations be if our woodland developed to a stable forest of sycamore and eucalyptus, with an understorey of rhododendron? Things will obviously change, affected not least by bigger population and demands for alternative energy sources (the land under wind-farms could yet be among the last nature reserves). In the meantime, urge the authors, it is the ordinary public, not EU directives, which will care for little clumps of trees in field corners, the overlooked, rough-grass embankments, or the plants in disused quarries. This expert, and stimulating book should help people see the point of it.

Flora Hibernica by Jonathan Pilcher and Valerie Hall is published by Collins Press, £25. For details, see www.collinspress.com