One-third of the world鈥檚 tree species are threatened with extinction 鈥� here are five of聽them
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One in three of the world鈥檚 tree species are , according to a recent report by 鈥� the first attempt to estimate the conservation status of all of Earth鈥檚 trees.
Well-known species, including magnolias, oaks and maples are among those at risk. More than 400 species have fewer than 50 individuals remaining in the wild, and 142 tree species are already extinct. Human activity is the overwhelming culprit, especially forest clearance for farming, logging for timber and the spread of invasive pests and diseases.
When myself and colleagues first came up with of a worldwide assessment of tree species in 2015, it seemed like an impossible task. Back then, nobody even knew how many there were, let alone how they were all faring. The first task was to make a list of all tree species that have been described in scientific literature. It turns out there are nearly 60,000, most of which live in tropical forests, and scientists continue to describe new species each year.
We then had to determine which of these are under threat of extinction. Given the huge number of species, this was a much bigger task than any conservation assessment undertaken previously. We created a global network of more than 500 experts, each assessing the species they were most familiar with, and the report is the result of that enormous collaborative effort which took five years to complete.
There are twice as many threatened tree species globally than threatened mammals, birds, amphibians and reptiles combined. But trees are also food and habitat for of the Earth鈥檚 known land-based plants and animals. Losing tree species can cause cascades of extinction among the many species that depend on them.
Trees are very valuable to people too. are used as a source of food, fuel, timber or medicine. Others have important . Worryingly, some of the most useful and significant species are among those facing extinction. Here are five of them.
Dipterocarps
Dipterocarps belong to a large family of timber trees, comprising , most of which are found in the tropical forests of south Asia. Related to hibiscus plants, most dipterocarps are tall with evergreen leaves and winged seeds. They are often the most abundant trees in the canopy of forests where they occur.
These trees possess high-quality timber, worth (拢123). Over worth of dipterocarp timber is exported each year from the island of Borneo alone, where 182 species are threatened with extinction, including the tallest known tropical tree, Shorea faguetiana.
Agarwood
Agarwood is fragrant and produces a highly valuable resin called aloes, used in perfumes and incense. It is one of the most valuable raw materials in the world, worth up to US$100,000 a kg and with a global trade valued at .
The production of this resinous wood is stimulated when these trees are attacked by a fungus. Overharvesting of the resin has led to more than 20 species being threatened, including the main source of agarwood, Aquilaria malaccensis.
African Cherry
Prunus africana has bark containing a range of compounds which can reduce inflammation, making it useful for treating a range of diseases, including malaria, kidney disease and prostate disorders. The international trade in the bark is , but overharvesting has meant this species is threatened throughout its range in central and southern Africa.
Mahogany
Swietenia macrophylla is one of the most valuable tropical hardwoods, valued for making furniture and musical instruments such as guitars. Mahogany wood is durable and has a beautiful colour. A single tree can be worth many thousands of dollars.
Native to the tropical forests of the Americas, mahogany was one of the first trees to be listed as an endangered species, owing to widespread illegal logging.
Pacific yew
Taxus brevifolia is the source of the anti-cancer drug Paclitaxel, which has a global trade worth . Native to the Pacific Northwest of North America, this evergreen conifer is now categorised as Near Threatened by the International Union for the Conservation of Nature (IUCN), primarily because of logging. Other yew species, which are also a source of this drug, are even more threatened, such as in the Himalayas.
While individual trees are important for both humans and wildlife, the collective value of forest ecosystems is far higher. Forests cover approximately of the world鈥檚 land surface and their total economic value has been estimated at around . Forests contain and help provide . These benefits could be lost if tree species go extinct.
As well as supporting wildlife and people, tree diversity can help forests cope with disturbance. For example, having a diverse range of tree species in a forest reduces the damage that can do, and makes the ecosystem .
As tree species die out, forest ecosystems are placed at . Conserving both forests and the tree species they contain can combat climate change and preserve biodiversity. The world must urgently protect threatened trees, restore degraded forests and ensure that the harvesting of useful tree species is sustainable.
, Professor in Conservation Ecology,
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