There are 60,065 tree species in the world, according to the first ever count of global tree species – published in the Journal of Sustainable Forestry by Botanic Gardens Conservation International (BGCI), a global network of botanic gardens based in Kew Gardens.
In accordance with the IUCN’s Global Tree Specialist Group, a tree is defined as:
‘a woody plant with usually a single stem growing to a height of at least two metres, or if multi-stemmed, then at least one vertical stem five centimetres in diameter at breast height’
Brazil is the country with both the most tree species, at 8,715 (followed by Colombia, 5,776, and Indonesia, 5,142) as well as the most endemic tree species with 4,333 (followed by Madagascar’s 2,991 and Australia’s 2,584). For comparison, the UK has a mere 84 different tree species. Overall, 58 per cent of worldwide tree species turn out to be endemic to individual countries, higher than researchers anticipated.
Furthermore, the ‘GlobalTreeSearch’ results reveal that, of the 20,000 trees species which have been assessed for their conservation status, as many as 9,600 ‘are known to be threatened with extinction’. While the researchers note that there is ‘a bias for threatened assessments on the IUCN Red List’ and therefore this proportion cannot be scaled up to the full 60,065 species, utilising data from BGCI’s ThreatSearch reveals that ‘at least one in five trees are threatened with extinction’. Ongoing research under the Global Tree Assessment project banner over the next few years aims to discern which of the remaining un-assessed tree species are in need of conservation action, a goal they hope to achieve by 2020.
The study was conducted amalgamating 375,500 lines of data from over 500 published sources, and combining records from existing databases such as the World Checklist of Selected Plant Families, the Flora of China, and the African Plant Database.
‘Although it seems extraordinary that it has taken us until 2017 to publish the first global, authoritative list of tree species,’ explains Dr Paul Smith, BGCI’s Secretary General, ‘it is worth remembering that GlobalTreeSearch represents a huge scientific effort encompassing the discovery, collection and describing of tens of thousands of plant species. This is “big science” involving the work of thousands of botanists over a period of centuries.’