Defending diversity

The journey home from Galway the other evening, a day of heavy rain, found the Maam Valley braided with floods from side to side. Killary Harbour, when we came to it, was stained a dark bronze the whole length of the fiord - this despite a high spring tide swirling in to meet the rivers. Aasleagh Falls, where we turn off into the mountains, was foaming froth like a mad Espresso machine, peat silt making coffee of the surging water.

A day like this reminds us how bare the mountains have become, how little vegetation there is to hold on to the rain and let it down gently, and cushion the peat from erosion. I wrote recently about the way overgrazing has changed the vegetation, so that heathery slopes have given way to wiry mat-grass that even the sheep won't eat.

I should have gone on to talk about some other, most valuable, plants we are losing - plants overlooked at the best of times because they don't have flowers, but reproduce by spores.

Heathers can catch the eye with brilliant colour. Mosses and liverworts flourish in their shadow, a carpet of rich textures and subtle shades now trampled to shreds by the sheep over wide areas of the hills. Among these "bryophytes", as botanists call them, are some of Europe's most rare and threatened plant species. Most Irish nature-lovers know some of the mosses of the mountain bogs - the sphagnums, anyway, whose wreaths and cushions hold so much water in their cells, and perhaps Campylopus, which makes the thick mats of greeny-black velvet. The liverworts are even less conspicuous and seem to seek out the shadiest, wettest niches, where their creeping leaves overlap each other like rows of little curvy-edged tiles.

Ireland did rather badly for diversity in the spread of Europe's plant-life after the last Ice Age - 815 plant species, compared with Britain's 1,172. But the island's climate did suit the bryophytes very well, and the hills of the west coast, from Donegal to Kerry, have many rare species and communities of worldwide importance.

The Twelve Bens in Connemara tend to do best in the literature, having attracted so many attentive botanists. Here is A.R. Perry, for example, from the National Museum of Wales, enthusing over leafy liverworts on the slopes of Muckanaght: "One of the most memorable sights of the mountains is the startling colour contrast provided by reddish-brown or rose-tinged hunks of Herberta adunea mixed up with the deep purple liverwort Pleurozia purpurea."

But I can't even offer you the colour of rarities such as Adelanthus lindenbergianus, which is found in Connemara, Donegal and south-west Scotland but nowhere else in Europe. As hunger presses sheep along the last accessible ledges, even rock-hugging liverworts come under threat.

A Scottish botanist, David Long of the Royal Botanic Gardens in Edinburgh, has been visiting Connemara for 15 years and has watched with horror the steady degradation of the region's dwarf-shrub heaths and bryophyte communities. "These are being very badly damaged," he told me in an email last week, "and my visit recently to the Twelve Bens showed that there is no let-up."

He was concerned that overgrazing should get its full weight in submissions to Minister Sile de Valera's National Biodiversity Plan, the main focus of which "will be on setting out strategies and actions to be undertaken to ensure the conservation and sustainable use of biological diversity". A newspaper advertisement proclaiming "Public Consultation" on the plan, and inviting submissions to the minister's Heritage Policy Division by September 12th, must have been almost as overlookable as a liverwort; certainly I missed it at the time.

The initiative follows on from Britain's Biodiversity Action Plan of 1995, prepared for John Gummer (a Tory goodie, where the environment was concerned) as a response to the original Biodiversity Convention signed by world leaders in Rio in 1992. The British report prepared - and costed - immediate action plans for more than 100 key species and 14 habitats, with a lot more to follow in another two to three years; we'll see what a Labour Government does with it.

As a model, it's immensely thorough and informative (and costs a wounding £56 from HMSO). And yes, since we're on the subject, it includes a dozen endangered mosses and liverworts among its 116 priority species. A few of these are shared with Ireland, as are species in other groups, such as the corncrake, natterjack toad, red squirrel, pipistrelle bat, pollan and freshwater pearl mussel, to name some that people will recognise.

The bryophytes are, indeed, a very good test of public understanding when it comes to talking about biodiversity. Mosses and liverworts are not casually "pretty" plants in the countryside (though anyone, looking close enough, must see their beauty). Aesthetics are not, of course, the point, or the Glutinous Snail, Medicinal Leech and Depressed River Mussel might not be among the UK's priorities for conservation.

Bryophytes are obviously useful in holding the peat of the overgrazed mountains together and one of them may, for all we know, yield a future cure for cancer, but the utility of species, while a useful argument in politics, is not really the point either.

Does it matter if we have, say, 41 kinds of moss and liverwort in Ireland, rather than 37? Yes, if that means that four have been lost (100 species of all sorts - dragonflies, butterflies, fish, mammals - have been lost in the UK this century). An ecosystem that loses species by human intervention has been damaged and degraded, sometimes in ways that take time to become clear.

It's instinct, as much as anything, that tells us that the more diversity of life the earth supports, the better its systems work for all of us - liverworts and leeches included.

Biodiversity: The UK Steering Group Report. Vol 1: Meeting the Rio Challenge, £26; Vol 2: Action Plans, £30.