In a report issued on the sidelines of a major UN conference on biodiversity, an alliance of four expert groups urged governments to select low-risk species of crops for biofuels and impose new controls to manage invasive plants.

"The dangers that invasive species pose to the world couldn't be more serious," said Sarah Simons, executive director of the Global Invasive Species Programme (GISP).

"They are one of the top causes of global species loss, they can threaten livelihoods and human health and they cost us billions in control and mitigation efforts. We simply cannot afford to stand by and do nothing."

The report, "Biofuel Crops and Non-Native Species: Mitigating the Risk of Invasion," points the finger in particular at the giant reed (Arundo donax), a native of West Asia that has become invasive in parts of North and Central America.

Proposed as a biofuel crop, the reed is naturally flammable and thus increases the likelihood of wildfires.

It is also very thirsty, sucking up 2,000 litres (500 gallons) of water for one metre (3.25 feet) of standing growth, which adds to stress in dry regions.

Another problem plant is the African oil palm (Elaeis guineensis Jacquin), which is grown for biodiesel. In parts of Brazil, it has turned areas of forest with mixed biodiversity in a homogenous layer of palm trees, the GISP said.

The GISP is a partnership gathering the International Union for Conservation of Nature (IUCN); CABI, formerly known as the Commonwealth Agricultural Bureaux; the South African National Biodiversity Institute (SANBI) and the Nature Conservancy.

According to figures cited by a GISP press release, invasive species cost the world 1.4 trillion dollars annually, or five percent of the global economy.

The United States alone spends 120 billion dollars annually to tackle more than 800 kinds of invasive pests.

The report was issued on the second day of an 11-day meeting of the UN Convention on Biodiversity (CBD), established at the Earth Summit in Rio de Janeiro in 1992.

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