Uncontrollable forest fires, illegal logging and the expansion of human settlements are blamed for the demise, described after three years of study by conservation groups worldwide.
The project found that more than 8,750 of the world's 80,000 to 100,000 tree species are under threat. Almost 1,000 tree types are believed to be "critically endangered" and some species have been reduced to single figures. In Britain the most endangered species, of the Sorbus variety, is down to the teens and twenties in some areas, despite the growing success of a scheme backed by British retailers to use timber taken only from properly managed forests.
The report, carried out by the World Wide Fund for Nature (WWF), the World Conservation Monitoring Centre (WCMC) and the World Conservation Union (IUCN), will be launched at the Intergovernmental Forum on Forests in Geneva today, where delegates are tackling the growing crisis facing the world's forests.
Dr Steve Howard, head of the WWF's global forest and tree initiative, said yesterday: "With 77 species already extinct, this report has now confirmed our worst nightmare. The governments gathering this week must now realise the sense of urgency to increase forest protection, eliminate illegal logging and improve forest management."
Sarah Oldfield of the WCMC said: "We have found that threats to tree species are increasing and that unless conservation action is taken immediately, some species face certain extinction and many others will be joining the list of threatened trees."
Felling for timber and wood fuel, agriculture, expansion of human settlements and uncontrolled forest fires are among the factors threatening tree species, according to the report, which was funded by the Dutch government.
Environmentalists are urging people in Britain to ease the global crisis by buying only timber that the Forest Stewardship Council (FSC) has certified as coming from well- managed forests. The WWF has set up a business initiative with retailers in the UK who will sell wood only from approved sources.
"Retailers are getting together to do something about the problem. Members of the group source as much of their timber products as possible from FSC supplies,'' said Ed Matthew, a WWF spokesman.
He added: "The scheme is already proving to be a success. As demand for it has increased from retailers, more foresters from around the world are increasing the availability of FSC-approved timber.
"They are changing the way they manage these forests to ensure it complies with the standards. There are now 10 million hectares of FSC forest worldwide. It is really beginning to take off."
Researchers for the report - The World List of Threatened Trees - found that more than 75 per cent of threatened species are not subject to any conservation measures. Only 12 per cent are recorded in protected areas and only 8 per cent of species are known to be in cultivation.
The 11 species listed as threatened with extinction in the UK are all in the Sorbus group. The ones described as "critically endangered" include Ley's Whitebeam (Sorbus Leyana), with only 16 trees surviving in two sites in Breconshire, and the Sorbus Wilmottiana, which has been reduced to 20 trees in the Avon Gorge. Quarrying and log-felling are among the reasons blamed for their plight.