Foreign plants are vilified for upsetting natives and vandalising landscapes. But few deserve such bad press, says Steve Farrar

War has been declared on alien invaders. Egged on by newspaper headlines on "fast-growing 'killer' plants" that "infect", "contaminate" and "vandalise" the British countryside, and by scientists such as Harvard biologist Edward O. Wilson, who sees them as "stealth destroyers", conservationists are fighting to rid our islands of unwanted interlopers.

Developers now spend millions of pounds to dispose of Japanese knotweed and giant hogweed - two species deemed so dangerous that they require special attention. Expeditions to remove rhododendrons from Snowdonia and the Lake District are organised. There are even calls to chop down centuries-old beech trees in Scottish glens.

Few would dispute the need to protect particular sites from being overrun by invasive species. But some feel things have gone too far, that the legislation is ill-conceived and that language loaded with racist overtones reflects cultural not scientific concerns. A few suggest that we might try loving the aliens instead of fearing them.

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While James Hitchmough, professor of ecology at Sheffield University, notes that the invasives - a subset of alien plant species - cause great ecological damage, he is concerned that the hysteria targets them all. "The issue has become polarised into a blanket 'alien bad, native good' position in the UK, while some alien species that naturalised within historical times are now cherished and protected," he says.

Some 100,000 species of plant have been introduced into the UK in recent centuries, many via the nation's gardens. Only a handful have escaped into the wild, thrived and pushed out native species. The most demonised, Japanese knotweed, arrived in the early 1800s as an expensive garden curiosity. By the 1960s, though, it was establishing itself in town and country, proving to be tough, fast growing, simple to propagate and damaging to manmade structures.

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Max Wade, consultant ecologist at environmental consultancy RPS, says that it was an obvious target - easily recognised, ugly and the "foreign" name did not help. But it is too late to get rid of it and the cost would be far too high. So Wade argues that while it should be prevented from spreading further across the country, in those areas that it has already reached it should be managed only when it presents a specific problem.

Furthermore, the same treatment should be meted out to invasive native plants, such as birch trees spreading across heathland or bracken smothering hillsides. Even then, according to Phil Grime, professor of plant ecology at Sheffield, there are more significant threats to the countryside: "Alien invaders constitute only a minor part of the profound changes taking place in the British flora as a consequence of changing patterns of land use and climate change." His research has indicated that it is just such factors that open the way to invasive species.

Charles Warren, senior lecturer in geography at St Andrews University, would prefer the focus to be on species that are invasive and cause damage.

"The alien/native distinction comes apart in your hands," he says. Such definitions are subject to many subjective criteria. There are no scientific answers to questions such as what happens when devolution shifts geopolitical boundaries or how long before an alien plant is redefined as native?

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"There are now conservationists who advocate taking a chainsaw to old avenues of beech trees in Scotland simply because they were only native to southern England," Warren says. "The degree of purism exhibited by some strikes me as ridiculous."

Ian Rotherham, a reader in the Tourism Leisure and Environmental Change Research Unit at Sheffield Hallam University and organiser of a recent conference that considered the issue, notes: "There are invasive species that everyone thinks are the bad guys, but our judgment is often very subjective."

The anti-alien approach, with its overarching regulations and sporadic pogroms, fails to acknowledge that many alien plants are well loved by local people and even invasives can, on occasion, benefit the environment.

Two facets of the dilemma can be seen in Sheffield. A fig tree wood on the banks of the Don, nurtured by the once artificially heated waters, has gained protected status. Nearby, otters have returned to the city, finding the shelter they need beneath the Japanese knotweed that grows from the river's once-barren banks.

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