A leading naturalist has accused his fellow conservationists of being "ecological fascists" for trying to eradicate alien plants and animals that threaten native species.
Richard Mabey, author of the plant encyclopedia Flora Britannica, claims that attempts to kill off Spanish bluebells and the ruddy duck are unnecessary, and are little different from Nazi attempts to "purify" Germany in the 1930s.
Mr Mabey also says that the language often used by conservationists in this debate, such as "alien" and "invasive", was a reminder of Nazi eugenics programmes.
"Nature hasn't the slightest respect for species and racial barriers," he said. "Evolution has always been a matter of change, of moving on ... of miscegenation, symbiosis and partnerships of all kinds."
Mr Mabey told The Independent on Sunday he believed there were cases where, if there were local problems or local demand, killing off non-native species was justified. That could include cases where rhododendron bushes were smothering local plants or where American mink were decimating local water voles.
But he said claims about some invasive species, particularly giant hogweed and Japanese knotweed, were overstated and scientifically unjustified. Many species now seen as native, such as the pheasant, were actually naturalised foreigners. He said the only eradication campaign he supported was with foreign aquatic weeds that were choking British rivers.
His remarks, first made in his column for BBC Wildlife Magazine and now circulating widely among environmentalists, have infuriated leading conservationists but have been applauded by animal rights activists.
Conservationists insist that their government-funded campaigns to stop damaging alien species from spreading across the UK were very well justified on scientific and ecological grounds.
They claim that defending weaker or more delicate natives from stronger or more aggressive exotic plants and animals increases diversity and protects individual species. This was effectively anti-Nazi, as it ensured that different populations could survive and prosper.
The conservation world has been split by rows over attempts to cull or wipe out alien species. Scottish Natural Heritage (SNH) has faced international criticism for deciding to kill dozens of hedgehogs that were imported into the Hebrides in 1974. They are eating rare, protected wading bird eggs.
Government ministers and the Royal Society for the Protection of Birds have been pilloried for culling 5,000 ruddy ducks, a bird originally from North America, as a favour to Spain because they are interbreeding with rare Spanish white-headed ducks.
George Anderson, an SNH spokesman, insisted that in many cases exotic species which did no harm were simply left alone.
"All over the world, unique native wildlife is being wiped out by species which have been brought in by people. I can see nothing wrong with people trying to rectify those mistakes. Anyone who compares that activity with fascism is lacking in perspective, and ... is doing something of a disservice to the memory of fascism's victims," he said.
Martin Harper, director of the charity Plantlife, one of Britain's most respected native flora conservation charities, said Mr Mabey's arguments were confused - humans deliberately importing plants was not evolution, just interference. "If we're going to be ambivalent or relaxed about changes initiated by humans, we're going to upset the natural balance of things," he said.
Giant hogweed, Heracleum mantegazzianum
Case against: Introduced to Victorian Britain as a garden plant, it has now colonised most of the country. It is an offence to plant hogweed in the wild. It grows faster and bigger than native plants, which are then crowded out. Its sap can burn and blister skin.
Case for: Richard Mabey claims it is "extremely desirable". It can enrich the landscape and can provide cover for rare plants such as the marsh orchid. People know it is toxic, so they avoid it.
Ruddy duck, Oxyura Jamaicensis
Case against: Arriving from North America in the 1940s, this dominant bird bred with native ducks. In some areas, there are no pure native species left. The Spanish are losing their rare white-headed duck to the UK-based ruddy. Britain is spending £10m to cull the 5,000 birds here.
Case for: Mr Mabey says the bird is showy and much loved. A stronger, brighter, fitter bird has evolved. Spain's white-headed ducks are dying out because Spanish hunters shoot them.
Spanish bluebell, Hyacinthoides hispanica
Case against: Experts fear the Spanish plant, sold by garden centres, is breeding with more delicate native bluebells. Hybrids are squeezing out English varieties. The charity Plantlife has championed the rarer native, because the UK is home to 50 per cent of the worldwide stock.
Case for: Cross-breeding and competition are facts of nature, and will increase diversity and the plants' ability to survive. The Spanish plants grow better and give many people pleasure.
Japanese knotweed, Fallopia japonica
Case against: Introduced in the early 1800s; spread countrywide by the 1960s. Chokes off all other plants and is very hard to remove. It is illegal to plant it in the wild, and the Government has spent millions trying to eradicate it.
Case for: Mr Mabey is "relaxed" about the "attractive" plant. Nottingham University research found it was far less threatening than claimed. In cities it supports many native insects.
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