About 30 percent of tree species worldwide are threatened with extinction. This is stated in the report published on Wednesday by the international botanical gardens organization BGCI. The main causes of the decline are agriculture and forest clearing. Urbanization, climate change, forest fires and invasive exotics also play a role.
There are 58,497 tree species worldwide, according to the report – although new species are still being discovered with some regularity, especially in tropical areas. Like animals, there is a Red List for trees. A rare species that is at risk of extinction is then given the status ‘endangered’. According to the report, 17,510 species fall into that category. A decline in the tree stock is bad news for the entire earth, because trees are not only essential for other species, but also for, for example, combating erosion and regulating the climate.
Brazil is the world leader in tree diversity, but also in endangered tree species: of the 8,847 different species, 1,788 are threatened with extinction. The situation is also worrying on tropical islands such as Madagascar. More than half of the 3,129 tree species there are endangered. “That’s because there are many endemic species growing on the island: trees that are specific to one place,” says biologist Xander van der Burgt, who works at London’s Kew Gardens as an expert on African trees. Elsewhere in Africa there are fewer endemic trees, but species are threatened by intensification of agriculture, urbanization and mining, among other things. “And of some species there are very few specimens. In 2018, Wageningen biologist Frans Breteler discovered a new tree species in the Gambia – and it is the only one of its kind. If it is cut down, you will lose it.”
The main causes of the decline are agriculture and forest clearing
From Kew Gardens, Tropical Important Plant Areas are designated to protect trees, in consultation with local authorities. “In Guinea, for example, we are working on setting up a number of national parks. That will benefit the trees.”
Situation in the Netherlands not urgent
The situation in the Netherlands is not dire, according to the report: of the 44 species included, none are endangered. However, this does not mean that nothing is wrong, emphasizes ecologist Bas Lerink of Wageningen University & Research. “We do have rare varieties, such as the wild apple.”
In addition, invasive exotics have recently caused a decline in certain species. The typesetter, a species of beetle, has severely affected Norway spruce in recent years. “That is not an endangered tree species, but the numbers have decreased considerably. The ash tree also has to endure a lot, because of the false ash membrane calyx, an Asian type of fungus.”
Climate change will make it easier for some invasive species to settle in the Netherlands in the future. Warming itself can also affect future tree populations, for example because certain species are less able to withstand drought. That is why Dutch scientists are experimenting with ‘climate forests’, in which heat- and drought-tolerant species are planted.
A version of this article also appeared in NRC on the morning of September 2, 2021