Vive la diversity

FOLLOW the butterflies, and you are brought very soon to the warmest spot on the acre, a few square metres of hedgebank and pebbly garden path at the western corner of the house. Here, as May was waning, the first branches of hawthorn relaxed at last into blossom and clumps of ox eye daisies began to unclench their buds.

All over Ireland this spring, in such pockets of warmth and shelter, the plants and insects have done their best to stay on schedule. Another week of showers and familiar Atlantic winds should see the old, moist meadows of the west fulfilling their usual June festival of flowers: buttercups and daisies, orchids and clovers, yellow rattle, ragged robin.

An ancient meadow in full bloom looks right, smells right, and spreads a lot of happiness. Even a cow, given the choice, will head for the field with the greatest variety of herbs. Yet, all over the temperate world, we have been grubbing them out, ploughing them up and carpeting the land with one or two kinds of readily mowable, bright green grass.

Nothing could be further from natural biodiversity than these oblongs of perennial ryegrass, supposedly so much more efficient and productive than old, mossy herb age, thronged with bumblebees. Yet new field experiments are showing that mixed species grassland is not only more stable and can resist droughts better, but actually captures more nitrogen and stops it leaching out of the soil.

The idea that biodiversity begets more robust and productive ecosystems is an old one. Charles Darwin, in Origin of the Species, wrote: "If a plot of ground be sown with one species of grass, and a similar plot be sown with several distinct genera of grasses, a greater number of plants and dry herb age can be raised in the latter than in the former case.

Darwin's successors in ecology have generally held to his belief that "the greatest amount of life can be supported by great diversification of life - a principle he felt was shown over and over again in nature. But some of today's ecosceptics, wearied by alarms about depletion of species, have produced theoretical models, to suggest that a few thousand kinds of flowers or insects more or less might have no importance. The rare ones that we worry about, they tell us, might even be redundant and ecosystems might rely only on a few, key species. This has been mainly computer work, carried out very often by the kind of scientist who can't wait to take over a final management of nature.

It's a relief, therefore, to be encouraged in the feelings we have when we admire an "unimproved" meadow, crowded with all kinds of grasses and flowers. In February this year, the science journal Nature published the latest work from a research team headed by David Tilman of the University of Minnesota, in the heart of the American prairies.

His earlier, 11 year study of native grassland ecosystems included, by chance, the worst drought in Minnesota for 50 years. He found that ecosystemsrich in variety of species recovered far more quickly than those with only a few. Now, using 147 grassland plots and controlling the number of species that grow in them, he has produced more evidence that biodiversity does, in fact, "work" better.

Not only does plant productivity increase in ratio with the diversity of species in the test plots, but soil nitrogen is used more completely. The same pattern in confirm in Minnesota's native, undisturbed grassland, the equivalent of Ireland's most ancient meadows. Total plant cover increases significantly with greater richness of species, and the land shows an even more sustained fertility.

This work is hugely significant for the value of biodiversity as an abstract, ecological principle. It has big implications for the long term health of our grasslands. It also gives special point to conservation of the species rich, semi natural grasslands that survive as old meadows and in overlooked corners of Irish farms.

The Irish Wildlife Trust (just named from the Irish Wildlife Federation) has recently decided to relaunch a grasslands habitats campaign, and has appointed a full time conservation officer, Dr Rosaleen Dwyer, to run it. An early objective might be to persuade Teagasc and the farming community of the value of a richer grassland.

THE campaign flows from the meadow project begun five years ago with the help of Timotei, the herbal shampoo company. This conserved two important meadows, at Bullock Island in the Shannon Callows and next to the Gearagh nature "reserve near Macroom in Co Cork.

Timotei also joined the National Parks and Wildlife Service in funding PhD research by Clare Byrne in Trinity College, Dublin. She is carrying out part of it in the Phoenix Park, where she studies the effects of various mowing and fertiliser regimes. But it has also taken her out into the Leinster countryside, searching for vestiges of "unimproved", species rich grassland.

She has found many pockets of it in corners of farms, often remote from the house and on slopes too steep for machines, or on land with drainage problems. Farmers tend to ignore these areas and let them revert to scrub. The Irish Wildlife Trust want landowners to appreciate them and actively manage them to maintain and increase their species. It will also target REPS advisers to raise their awareness of ancient grasslands and the value of maintaining them.

The trust will step up conservation of endangered grassland habitats such as those of the west coast machair land and the inland esker ridges and enlist schools in creating local meadows and protecting, conservation sites. .