Berries not plentiful - but tasty

A beaujolais year for blackberries, says a friend who appreciates both. It is not, perhaps, the bumper crop that some recent summers have brought, but one with great distinction of flavour, each drupe of the berry a dark, purple raindrop, well worth savouring.

It does rather depend, of course, on which blackberry you sample, just as a wine may depend on the grape. The bramble is Rubus fruticosus, simple enough, but all kinds of genetic variations take shelter under its prickly umbrella. So far, more than 80 "species" of bramble have been recorded for Ireland, and new endemics are being added all the time as botanists find clear local differences in form and habit.

Different zones of the island have different collections of brambles, sometimes but not always echoing those of similar regions and habitats in Britain. There are northern brambles and westerly ones, upland and valley kinds, and brambles that lurk in remnants of ancient woodland. It is a pity, given their capacity for difference, that brambles cannot tell us more about the age and history of their hedgerows.

It's about 25 years since the British ecologist Max Hooper offered a formula for dating hedges which set off excited explorations all over England. He had been counting the tree and shrub species in hundreds of hedges of documented age and found a striking correlation: the age of a hedge in centuries generally equals the average number of woody species in a 30-metre stretch (Oliver Rackham has an assessment of this, and a list of the species, in his History Of The Countryside, published by Dent).

Armed with Hooper's rule of thumb, professionals and amateurs went off into the ancient countrysides of Britain, where some hedges are actually "ghosts" of wild woodland surviving on the boundaries of the earliest field systems. The oldest hedges of all were found in a parish in Suffolk, where many have seven or more species and three have no fewer than 13. But most local groups were pleased enough with counts that took their hedges back to the Middle Ages.

In Ireland, so far, this "archaeology" of hedgerows has been less dramatic and definite. The Neolithic stone walls preserved beneath the bog at Ceide in north Mayo show that some of our field systems began as early as any in these islands. Around Cruachain, the Celtic royal site in Co Roscommon, the "ghosts" of rectangular field banks, early medieval and perhaps older, underly the modern pattern. Somewhere in such palimpsests, fragments of ancient vegetation could, conceivably, have been incorporated from one landscape change to the next, surviving and evolving towards the modern hedgerow.

But while diversity of species is usually a guide to age, Irish ecological conditions may speed up the rate at which new woody plants and trees take root in an earth bank: blackthorn and elder, ash and ivy, sycamore and wild rose piling in beside the original planted hawthorn or whin (brambles too, of course, though not everyone believes they should count).

A 1985 study of 31 hedges around Knock, Co Mayo, found that, using Hooper's Rule, some could seem to date to the 17th century or earlier. But there was very little enclosure in the west before the 18th century. And there were hedges of four and even five species among those known to be planted later than the Ordnance Survey of 1837. So Hooper's Rule does not always fit in Ireland.

Our oldest hedgerows, as Professor Fred Aalen describes in the new Atlas Of The Irish Rural Landscape (Cork University Press, £35), are in Leinster, where "their tall, vigorous growth and diverse species composition reflect their age". Hedges of hawthorn, ash and elder are typical, and often grew up on the mearings of old, open-field strips when the fields of the Pale were enclosed in late medieval times.

Elsewhere in Leinster, little of the medieval field systems survived the wholesale reshaping and hawthorn-hedging of the land by estate landlords. Their work survives most clearly today in the stud farms on former demesnes in Meath, Dublin and Kildare. The mix of species changes with local soil conditions, and an intriguing map in the Atlas shows how hedges vary around the island, from the fat-land bull-stoppers with a core of thorns to hedges dominated by whins or willow.

The destruction of hedgerows by farmers has been one of Europe's more insidious ecological tragedies. In Britain, the process has scarcely eased since the 1960s - 75,000 miles of hedgerow disappeared between 1984-90 alone. In Ireland, the cattle-based tradition has slowed things down, and when David Hickie surveyed the intensive tillage area of north Co Dublin in the mid-1980s, he was relieved to find that "only" 16.7 per cent on the hedgerows had vanished since 1937, a figure not much above the national average.

It is in just that area now, however, that the Ballyboughal Hedgerow Society has been founded, to research and protect the oldest and most varied of its leafy boundaries.* But the pressures of intensive winter cereal-growing often take first effect on unconsidered internal hedges, no less beautiful for their modest interminglings of willow, hazel and wild rose.

Across the country, in Leitrim, says a picture caption in the rural Atlas, "shaggy hedges of willow, birch and hawthorn sprout undisciplined by human hand, lending a forlorn air to the landscape". They could certainly do with some attention. But what's even sadder is that, in a county with the highest uptake of REPS, some farmers have been ripping out hedgerows with machinery this summer as a preliminary to making "nature-friendly" plans to earn the payments.

It is to try to reinstate the hedgerow, as working stock-proof barrier, shelter and wildlife resource, that the Leitrim branch of Crann is undertaking a project supported by the Heritage Council of Ireland. There'll be a survey of the hedges, mostly by schoolchildren, and then demonstrations around the county of hedgelaying, tree-pruning and the right way to use trimming machinery.

The project will be launched with a "hedgerow awareness" walk next Sunday, September 21st, with well-known tree-people, naturalists and REPS planners leading the way. It starts at the Crann Leitrim Office in Hyde Street, Mohill, at 2 p.m. (* Contact Ann Lynch at 018433745.)