Humanity has caused an average of more than two plant species a year to be wiped off the Earth since the middle of the eighteenth century, according to the first comprehensive attempt to chart worldwide plant extinctions.
The botany world’s best guess was that fewer than 150 species had gone extinct, but that was based on the Red List of Threatened Species, which is known to cover only a small proportion of all plants.
The true number appears to be around four times higher, at 571 plant species being driven to extinction between 1753 and 2018. A Swedish and British team came to the figure after analysing a previously unpublished database kept by Kew Gardens.
Casualties of human activity
Species destroyed include the Chile sandalwood (Santalum fernandezianum) which was only found on one group of Pacific islands, and the St Helena olive tree (Nesiota elliptica), which only lived on the island it is named after.
The rate of loss is happening as much as 500 times faster than the background rate of extinction for plants, the speed at which they have naturally been lost before humanity’s impact. But even the grim toll of 571 is likely to be lower than the reality, says Aelys Humphreys of Kew Gardens. “We are quite sure this is an underestimate.” That’s because some biodiverse parts of the world are poorly studied, and some plants have been reduced to such low numbers they are considered ‘functionally extinct’.
The number of plant extinctions is much greater than the number for birds, mammals, and amphibians. That’s what researchers would expect, given there are more plant species overall. The geography of the extinctions in plants and animals is strikingly similar though. Island species are inherently vulnerable and have been particularly badly hit, as have species living in regions with a tropical or Mediterranean climate, as they simply have a rich variety of life. Hawaii has seen more losses than anywhere else in the world with 79 extinctions alone, but other hotspots include Brazil, Australia and Madagascar.
Only a handful of the 571 lost plants are ever likely to be rediscovered, because the database includes previous rediscoveries and most of the lost species have been extinct a long time, says Humphreys.
Journal reference: Nature Ecology and Evolution, DOI: 10.1038/s41559-019-0906-2
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