What have we dune?

At the worst of the storms, when the barometer in the porch was tapping, as it were, on Empty, the sea rose up in some memorable earlymorning tides. Rolling on through the line of tumbling surf where the strand begins to shelve, the waves surged in around the dunes to drown the flat, grassy plain of the machair and subsume three separate swans' lagoons in one huge and shivering, grey-green lake.

From the window (doubleglazed now: the old one used to bend most horribly at anything past Force 8), we marked the water's progress fence by fence. Its final contours claimed more territory than any spring-tide flood we've seen. Judging from the old maps, this was how the shore looked long ago: sea inlets reaching in where sand is now. "And this," the wind seemed to howl, "is how it's going to look again very soon!"

Scientists have tried to put figures on the phenomenon of "storm-forcing" - the piling-up of water against exposed coasts, the actual change in the height of the sea as atmospheric pressure lifts its weighty hand. The largest surge levels expected "once every 50 years" are 0.75 metres off the west coast and one metre off the coast of Donegal. But the 50-year model may need some revision as global warming takes hold, and more and worse storms are matched to a general rise in sealevel.

The storm surge currents seem to split at Co Mayo, one lot swinging north, another south, so what actually sweeps ashore at Thallabawn is possibly less fierce than it could be. But it is enough to carve a few more chunks from the bottom of the lowest fields, a few more slices from the steep cliff of sand at the open sea-face of the dunes. On my next walk north to Roonagh, there will be even more gaps in the old green roads above the rocks.

Erosion of "soft" coastal areas is nothing new to Ireland: we live on a shrinking island. Of the 6,500 km of coast, some 750 km are lined with sand-dunes and many more with crumbling cliffs of glacial mud and gravel. The north of the island is still rising on the rebound from the weight of the last load of ice, but south of a line from Galway to Dublin it is tilting downwards, so that, on the Cork coast, sea-level has been rising by about one millimetre a year for the past 2,000 years.

Within a few decades this will double, and coastal changes will creep northwards along the coasts for the remainder of the century. The dynamics of erosion and deposition, of snatching sediment away at one place and piling it up in another, are complicated and hard to predict. For a while, a rising sea-level could actually "liberate" a lot of material that would build protective sand-bars offshore. But then it will go on to choke estuaries and, maybe, to break down the great dune barriers like those at Inch and Rossbehy in Co Kerry, which protect thousands of acres of estuary coast.

Ireland's dunes, often 5,000 years old or more, are generally well-anchored with vegetation - marram grass, most importantly, with its deep web of roots. They have survived some dramatic abuse from overgrazing, burning and cutting (which is also why we have so few dune systems with any trace of heather). They have also, historically, had catastrophic blow-outs - classically, the case of Rosapenna village in Co Donegal, overwhelmed with sand from dunes undermined by rabbit warrens about two centuries ago.

Could anything like this be triggered by a new regime of fiercer storms and higher waves? Plants like marram grass can't cope with much more than about half a metre of fresh sand a year. After that, a dune system can "go mobile", engulfing big areas of stable dune and farmland, even roads and houses. Places like Mayo's Mullet Peninsula, where the dunes face straight into Atlantic gales, seem especially at risk of tearing apart in the wind.

All this has an ironic resonance in the long-running row over sand dunes and golf courses. Ireland already has 40 per cent of the world's links courses and the international golf industry seems insatiable for more. The latest course will wind its way through more than 300 acres of dunes at Doonbeg, north of Kilkee in Co Clare.

This reduces the number of fixed dune systems remaining intact in Ireland to fewer than 10 out of 80. They are a fragile and diminishing natural habitat, with specialist plant and insect communities, and even a golf course designed to be "nature friendly" can extinguish species by trampling and mowing, by changing the pattern of nutrients and water levels, or by relegating the wild flora to isolated patches in the roughs.

The new EU Habitats Directive charges Ireland with saving the best that is left of our dunes - the most intact and pristine stretches of strong biological value. At Doonbeg, this amounts to some 50 acres out of the 300, and as the Australian course designer, Greg Norman, strode over the mossy dunes last November on a first reconnaissance, the top research botanist of the National Parks and Wildlife Service, Dr Tom Curtis, walked watchfully in his wake.

The ebullient Mr Norman, ecstatic over "land made by God", vowed to be "cognisant of the environment and sensitive to the duneland". Land movement would be minimal, and the top soil stored and put back where it came from. His two-loop course will "meander in and out". It is promising - but still a compromise.

Fifty acres of protected dunes is really not very much: a little island of biodiversity, a tiny reservoir of species whose natural ecosystem can never be recreated by human effort. Yet the actual stock of duneland worth saving is dwindling all the time, as overgrazing and other abuses take their toll.

Every site will need its own expert judgment. Some dunes we must defend at all costs from even the most seductively "eco-sensitive" propositions. In others, already degraded and compromised, even another golf course will be an ecological improvement - one unlikely, at the very least, to find itself blowing in the wind.