Environmentalists yesterday warned of the dangers of genetically modified super-trees which can cross pollinate with native trees over a distance of 400 miles and which are being grown in field trials without knowledge of the consequences.

Other GM modifications under trial raise the prospect of silent forests, devoid of insects, flowers and birds. The idea is to create super-trees that grow rapidly, resist rot, and defy insect attack. The trees would be sprayed from planes to kill all life around them.

In a report published yesterday, the World Wide Fund for Nature said 116 trials on GM trees had taken place since 1988 without proper controls or research into the effects on the wider environment. Seventy of the trials are being carried out in the United States and five are in Britain.

Francis Sullivan, director of programmes for WWF-UK, said there was the prospect of large blocks of land in Britain and North America being given over to one super species of tree, creating sterile environments. "The genie of genetically modified super-trees is already out of the bottle. We must make sure it does not get out of control otherwise such trees could run riot through the forests of the world without us knowing what are the consequences."

The report, which was written by Rachel Owusu for WWF, says that commercial planting of GM trees is likely to happen soon in Chile, China and Indonesia, despite the inadequate research into environmental impact. The report points out that pine pollen can travel up to 400 miles to reach another tree, making it impossible to monitor the effects of cross fertilisation on native stock. The organisation is calling for female only trees to be grown to avoid this risk.

Scientists are also trying to grow trees with salt tolerance and drought and frost resistance, which could thrive in more places. One of the experiments in Britain involves growing poplars with less lignin, the woody substance that makes trees strong. Removing some of this would make the trees softer and easier to pulp, which would in turn make paper cheaper to produce.

But environmental scientists believe that unintended side-effects pose risks, partly because trees live so long and are known to adapt to changing circumstances. For example, poplar trees bred in Germany not to flower - so as to avoid cross contamination - did so years earlier than they were programmed to do so, baffling the scientists.

GM trees that do cross fertilise with each other or with native species could create super "weed" tree species which would displace slower growing normal trees and at the same time destroy the habitat of many creatures. Trees provide food and shelter to many interdependent organisms including insects, birds and mammals. Their root systems are often vast and closely interact with soil organisms like bacteria and nematode worms.

Mr Sullivan said: "We are not against genetically modified trees in principle, but we want more research and above all openness about what is being planned. We need to know the pros and cons, about the dangers of cross fertilisation of native species, and of sterilising large areas of the landscape. Does this mean greater profits for a few timber companies, or more wood for all mankind? And are silent forests a price worth paying for these advantages?"

WWF is contacting its network of 100 companies, which are already committed to using timber from sustainable sources, to urge them to ban GM wood products. Sainsbury is among the companies which have already pledged a ban.

Among the 30 tree species that so far have been genetically modified are apple, banana, birch, chestnut, elm, peach, pear, pine, plum and walnut. In Britain, Shell has been carrying out two trials of eucalyptus in Kent to improve growth rates and examine herbicide tolerance. Derby university has modified the paradise apple to examine resistance to pests and diseases, and Astra Zeneca has had two trials in Bracknell, Berkshire, with low-lignin poplars - those trees were cut down by GM protesters in July.