Science: Alien Life On British Soil

Foreign plant species may be damaging our floral heritage. Malcolm Smith reports

The Traditional English cottage garden is changing fast. You only need examine the seed packets in your local garden centre to see that. Old-time stalwarts of the well-tended border, like hollyhocks or pansies, are passe. Wild flowers such as cowslips and primroses are de rigueur. More than 50 suppliers of wild flower seed and plants can furnish your requirements countrywide.

Wild plants are also being returned to the countryside. Having spent the last half century ploughing them up, building over them and spraying them with herbicides, swathes of road and motorway verge now glow with a palette of vibrant colours unseen for a generation. Where once a monotony of ryegrass would have sufficed, today's verges are being speckled with the burnt purple of betony, with vibrant yellow-wort and the blue of speedwells.

You would think that this reawakening to nature's beauty would be welcomed by botanists and conservationists everywhere, but it isn't. One problem is that much of the newly sown seed doesn't have its origins in Britain. Although from the same flower family, species can vary considerably from place to place. For instance, yellow bird's-foot trefoil from the southern Alps or Kidney Vetch from central and eastern Europe may, or may not, be similar to the British version.

The other problem is that species alien to these shores are being planted, arriving unannounced in seed mixtures, or simply "escaping" from gardens. This is how Californian lobelia and American winter cress have been added to our flora. Botanists visiting the Isle of Wight recently noticed that nearly all of its bluebells had a Spanish look - a result of hybridisation between the Iberian invader which had escaped from parks and gardens and the local populace.

But isn't all this botanical xenophobia over the top? Isn't a bit of plant immigration good for us, adding more colour and diversity of species and variety to a countryside bleached of most of it by decades of over- intensive agriculture? Not according to Flora Locale, a new botanical initiative set up to argue the case for keeping wild plants where they belong.

"We want to see caution applied until we know what's going on," says Sue Everett, the initiative's co-ordinator. "We simply don't know which imported varieties, or different species, will oust what plants from our native flora. And if introductions are taking place everywhere," she adds, "how will we possibly be able to tell whether a species popping up somewhere new is a result of something like climate change or somebody deciding to plant it in a seed mixture?"

But people have been introducing new plants to Britain long before the Victorians ever took up the obsession. Blue cornflowers, now a much lamented rarity sprayed out of cereal fields, were introduced by Stone Age settlers. The Romans brought sweet chestnuts. And the Victorians went on expeditions to find increasingly exotic wonders to decorate their gardens and estates.

True, there are problems as a result. But only from a handful of what botanists call "invasive aliens" that have gone bush. Rhododendron is a good example. Introduced as gamebird cover, it has spread like a glossy green triffid through many oak woods in the west of Britain, choking out young trees and killing off natural ground cover. Indian Balsam, a 6ft- high Himalayan native with a predilection for damp ground, first escaped from gardens in 1855. Today it is spreading along riverbanks and ecologists fear it is invading wet woodlands where its robust growth could elbow out many of the flowering natives.

The decline in our native plants, due mainly to habitat destruction and not because of aliens muscling in, has been astonishing. Between the Fifties and the late Eighties, according to Dr Tim Rich and Rosemary Woodruff, two plant experts formerly at the Institute of Terrestrial Ecology, 195 of England's native plants and 50 of Scotland's have declined substantially.

Ironically, others have increased - no fewer than 174 in England and 86 in Scotland. But the lion's share of these are species that wouldn't naturally be here; garden escapes such as buddleia and stonecrops, or shrubs introduced in landscaping schemes such as berberis and escallonia.

"If we had a healthy native flora," argues Tim Rich, "we would be much less worried about introduced plants, except where they spread at the expense of native ones." He cites a recent example that is causing concern, Pigmy Weed, a robust Australian which is swamping ponds across southern England, and ousting native flowers like the Hampshire purslane.

But why is Flora Locale worked up if a species native to Britain is being spread wider, albeit using seed from another country? Is this not a form of botanical ethnic cleansing by another name? The organisation's concern is that plants such as the more robust Germanic variety of bird's foot trefoil from the Alps might elbow out our more delicate, and almost identical- looking, British versions. Sainfoin, a pink grassland flower, is already succumbing to the spread of a hardier continental variety of the same species. But these are the exceptions, not the rule. Some introduced varieties of British species simply don't do as well as the natives anyway. In a study of hedgerow hawthorn in mid-Wales, for instance, Dr Andrew Jones found that continental European versions fared less well than local stock. Considering that local varieties and species have had aeons to adapt to local conditions, this result is not altogether surprising.

Losing species by more subtle means is another Flora Locale concern. Hybridisation between species, such as the Spanish and British bluebell on the Isle of Wight, is an example. Given time and enough Anglo-Spanish liaisons, the bluebell as we know and love it may change its appearance. Botanical purists might well lament the loss, though whether most people on woodland walks would feel likewise is debatable.

But is this obsession with racial purity necessary? Some conservationists and geneticists think not. "The question is," according to Steve Jones, professor of Biology at University College, London, "do we worry about the species or the genes? In hybrids, we may lose the species as we recognise it, but its genes are still there. We have become obsessed with cataloguing and pigeon-holing species. It's even more pernickety to catalogue and differentiate between varieties of a species," he argues.

Donald Thomas, head of Forestry Commission's Forest Practice Division, has some sympathy with this view. "But we also need a robust genetic base in species if conditions are going to change suddenly, because of climate-warming, for instance. So the more genetic variety species has, the better. Taking an analogy, it's the difference between a disease striking a totally isolated Brazilian rainforest tribe and the huge variety of North American society. You know which survives the better," he adds.

Contrary to the caution expressed by Flora Locale, increasing genetic diversity has been an objective of the reintroduction of one of our rarest birds of prey, the Red Kite, in England and Scotland. The remaining Welsh population, itself increasing, is known to be genetically rather restricted. Birds from Sweden released in Scotland, and from Spain into England will, when the populations eventually interbreed, create a heady mix of Welsh, Swedish and Spanish genes. The idea is that such a mixed population, albeit of one species as we recognise it, will be more able to cope with a new disease or some sudden environmental change.

In any case, we know next to nothing for most species about the breadth of their genetic variety. Collecting acorns locally to increase the area of oak woods in Snowdonia is fine as long as one accepts that the genes in those acorns reflect a chequered history of bringing in oaks from England, Germany and, maybe, further afield.

But, if so many of Britain's very own plants weren't in retreat, Flora Locale's call for caution would fall on deaf ears. In reality, with preserving local diversity an aim of the Biodiversity Convention signed in Rio, and with genetically engineered, fast-growing grasses being developed which could swamp any wild flowers sown with them, and with no slacking in the pace of plant and seed imports, its caution is difficult to fault.

Flora Locale can be contacted at 36 Kingfisher Court, Hambridge Road, Newbury, Berks RG14 5SJ.