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Almost 40 percent of trees in sub-Saharan African are threatened. At least 142 of the world’s tree species are already extinct in the wild. More than half of the world’s trees exist only within single countries.
These are a few of the surprising facts outlined in a recent report explaining the current condition of trees.
The State of the World’s Trees report, published earlier this month, covers the diversity of tree species across regions, main threats to their survival and key steps that can be made to protect threatened species. It serves as a five-year compilation of the Global Tree Assessment, which aims to assess the conservation status of every tree species in the world.
“This report is a wake-up call to everyone around the world that trees need help,” said Paul Smith, the secretary general of Botanic Gardens Conservation International (BGCI), in a press release. “Every tree species matters – to the millions of other species that depend on trees, and to people all over the world.”
The assessment is compiled by BGCI in coordination with the International Union for Conservation of Nature (IUCN) Species Survival Commission Global Tree Specialist Group, as well as a vast global network of universities, botanical gardens, research institutes and other partners.
Before the Global Tree Assessment was launched in 2015, the total number of tree species in the world was unknown. Since then, 58,497 species have been catalogued, and of these, at least 29.9 percent are threatened. Given the number of species with data insufficient for a conservation assessment, potentially 51.3 percent of species could be threatened with extinction.
Tropical regions of the world contain a huge share of the world’s tree diversity, with 40 percent within just Central and South America. But tropical regions across the Americas, Africa and Asia also have higher proportions of their species threatened with extinction; there are 3,644 such species within sub-Saharan Africa alone.
“We have seen massive declines in forest cover over the last 100 years, much of it now focused in biodiverse areas,” said Emily Beech, the Tree Red List Manager at BGCI, in an email. “The tropics are known to have a much larger number of species across all living organisms.
“Take Madagascar for an example. The island has over 3,000 tree species, of which 93 percent are endemic to the island – found only in Madagascar. Fifty-nine percent of those species are threatened, over 1,800 species. The reason there are so many species is the wealth of different climate niches that have allowed many different vegetation types to evolve.”
The report cites habitat loss as the greatest threat to tree diversity, particularly due to agriculture but also to livestock rearing, residential and commercial development, and energy production and mining. These combined affect 65 percent of all trees, according to the report.
Another major threat is timber exploitation. This is especially true for species harvested for their luxury wood, such as rosewood trees (of the genus Dalbergia). According to the UN Office on Drugs and Crime, most rosewood on the market is harvested from West Africa and exported to China where it is used to make expensive hongmu furniture. In 2020, Interpol reported that the illegal timber industry was worth almost USD 152 billion annually.
Climate change, however, is emerging to become another significant threat to trees. A warming planet is causing habitats to shift or change, while increasing the likelihood of destructive storms, flooding and sea level rises. The authors of the report also note that a changing climate can change forests’ fire regimes and give different pests and diseases opportunities to thrive in new areas.
Tree species extinctions would not only harm local ecosystems but could also deprive people of useful materials, as the report concludes that at least one in five tree species are used by people. Over 3,700 tree species are used for construction, but many others are also useful for medicine, ornamentation, food and various other purposes.
For example, the bark of the African Cherry Tree (Prunus africana), now listed as vulnerable on the IUCN Red List due to overharvesting, can be used to treat fever, malaria, kidney disease, urinary tract infections and prostate cancer.
Despite the dangers that trees face, efforts are being made to conserve threatened tree species. Other than protecting trees in their natural habitats, restoring degraded landscapes could be an opportunity to replenish forests by planting native and threatened tree species, according to Beech.
She says individuals can support threatened trees by supporting national and local botanic gardens and visiting and engaging with their education programs. Governments and international frameworks, meanwhile, must commit to protecting biodiversity, she says.
If a tree comes dangerously close to extinction, a final solution could be to grow it outside of its native habitat, such as in botanical gardens, or to conserve its seeds so they can be reintroduced in the future. These are both ex situ conservation tactics; 41 tree species currently exist in this way.
To protect threatened trees, the authors of the report provide several recommendations, including extending protected areas to cover more threatened tree species, ensuring that all threatened tree species are also conserved ex situ and increasing cross-sectoral funding for tree conservation.
A new tool to aid conservation action is the GlobalTree Portal, recently launched by BGCI, as an online database containing all known trees at a country or global level and their conservation status.
“The GlobalTree Portal is a first for tree conservation,” says Beech. “It highlights the gaps in tree conservation efforts to allow targeted conservation actions to save tree species from extinction.
“We hope this will inspire and catalyze action to protect threatened tree species around the world, as well as inform tree planting efforts to include native and threatened species.”