News and Events - The tree of heaven, or hell?

Monday 27 October 2014

The Ailanthus altissima has become a favourite in many UK parks, gardens, city streets and in landscaping schemes, dubbed the 'tree of heaven' due to its eagerness to reach upwards. In some parts of the world, the tree initially grows by as much as four metres a year - more than a centimetre a day - although between one and two metres is more usual. It can reach a height of 30m.

The tree, however, is now being called the 'tree of hell' by conservationist, as the Chinese import appears a threat to native plants. The Ailanthus altissima emits a poison to stop other species growing nearby, has a smell like 'rancid cashew nuts' and it sends out a mass of suckers that smother other plants. However, the called-for ban, which would add the tree to the Government's official list of banned invasive species, is likely to be fought against by the garden centre industry.

Conservation group Plantlife been compiling figures of tree species. The number of trees of heaven in the UK has gone up by 115% since 2000, making it the most rapidly spreading invasive species and ahead of piri piri burr - 96% - and American skunk cabbage - 88%.

Dr Trevor Dines, a botanist with conservation group Plantlife, said: "We're drawing experience from France and Spain where - trees of heaven - are a real problem. That's where this term 'tree of hell' has been coined.

"It has a very thick underground root system that puts up shoots every five to 10 centimetres. It creates very, very dense thickets. If you travel throughout Europe, particularly the south of France and Spain, you'll see whole areas, particularly urban areas, swallowed up by the tree of heaven. The tree's roots are so strong and spread so rapidly that they even cause havoc on archaeological sites. The thick root stock is very difficult to eradicate and it pushes up through buildings."

Plantlife plans to campaign to have tree of heaven added to the banned list along with a number of other plants. They are also seeking controls on some garden favourites such as cotoneasters.

Raoul Curtis-Machin, head of horticulture at the Horticultural Trades Association said while tree of heaven 'might become a weed in some areas' it was 'not even hardy' in parts of Scotland. Curtis-Machin said: "We're not in favour of going for outright bans," he said. "We would rather do it through firm guidance, explaining to gardeners they should not be planting weeds."

The Department for Environment, Food and Rural Affairs said it was reviewing which plant types should be banned. "Invasive species cost the UK economy over £1.8bn and threaten the survival of our own plants and animals," a spokesman said.