One in five of the world’s plant species — the basis of life on Earth — are at risk of extinction, according to a landmark study.
At first glance, the 20 percent figure looks far better than a previous official estimate of almost three-quarters, but the findings are being greeted with deep concern.
The report published yesterday was the first comprehensive assessment of plants, from giant tropical rainforests to the rarest of delicate orchids. It concludes that the real figure is at least 22 percent and could well be higher as hundreds of species being discovered by scientists each year are likely to be in the “at risk” category.
“We think this is a conservative estimate,” said Eimear Nic Lughadha, one of the scientists at Kew Gardens in west London responsible for the project.
The previous estimate, that 70 percent of plants were either endangered or critically endangered, was based on what scientists acknowledge were studies heavily biased toward species already thought to be under threat.
The new study is crucial to understanding the level of threat to all the natural world’s biodiversity, said Craig Hilton-Taylor, of the International Union for the Conservation of Nature (IUCN), which runs the world’s official “red lists” of threatened species.
“Plants are the basis of life, and ... it has many implications,” he said.
The results will be presented to world leaders meeting at Nagoya, Japan, next month to discuss the world’s biodiversity crisis, along with new red lists for vertebrates and several groups of the planet’s millions of invertebrate species.
“This is a base point,” Lughadha said. “What we do from now is going to lead to the future of plants. We need to challenge the idea that plants are there to be exploited by us.”
Politicians and conservation experts at Nagoya will also be told that by far the biggest threat to plants is human, especially intensive agriculture, livestock grazing, logging and infrastructure development.
Scientists studied 4,000 species from the estimated 380,000 to 400,000 so far known to science and assessed the level or risk based on a combination of the absolute number of plants estimated in the wild, the known decline and the total area in which they are thought to live. Of the 4,000, 63 percent were found to be of “least concern,” 10 percent not threatened, 11 percent vulnerable, 7 percent endangered and 4 percent critically endangered. Another 5 percent were rated “data-deficient.”
The proportion of species deemed at risk in this “sampled” red list for plants result is similar to the IUCN’s red list for mammals, worse than that for birds (less than 10 percent at risk) and better than the number for amphibians (more than a quarter under threat). Nearly two out of three of all threatened plant species are found in tropical rainforests. This is partly because of the widespread risks of logging and clearance for other agriculture, analysts said.
The assessment was done using experts and collections at Kew Gardens, the Natural History Museum in London, and Missouri Botanical Garden in the US, plus specialist experts from the IUCN.