The world’s seed-bearing plants have been disappearing at a rate of nearly 3 species a year since 1900 ― which is up to 500 times higher than would be expected as a result of natural forces alone, according to the largest survey yet of plant extinctions.

The project looked at more than 330,000 species and found that plants on islands and in the tropics were the most likely to be declared extinct. Trees, shrubs and other woody perennials had the highest probability of disappearing regardless of where they were located. The results were published on 10 June in Nature Ecology & Evolution.

Even though the researchers carefully curated the plant extinction database, the study’s numbers are almost certainly an underestimate of the problem, says Jurriaan de Vos, a phylogeneticist at the University of Basel in Switzerland. Some plant species are “functionally extinct”, he notes, and are present only in botanical gardens or in such small numbers in the wild that researchers don’t expect the population to survive.

World’s largest plant survey reveals alarming extinction rate