The conservation of biodiversity and its sustainable management are internationally recognised as vital global concerns. Identification of the components of biodiversity and the threats they face are important steps in planning for conservation action. Tree species are ecologically, culturally and economically valuable components of biodiversity and their conservation is essential to the well-being of people in all countries of the world. With increasing general pressures on ecosystems and selective pressures on species, it has become apparent that many tree species are threatened with extinction. Information on the degree and extent of threat has, however, previously been scattered and scarce. The World List of Threatened Trees presents the results of the first survey of the conservation status of trees species worldwide. Assessment of the conservation status of the world's tree species is a major task given the overall number of trees believed to exist. The world's tree flora is estimated to total around 100,000 species.