The answer is yes. It is true, as you seem to suggest in your question, that the studies that are best known in recent centuries refer mainly to the extinction of animals, what is known as the sixth extinction. I would add that not in all animals completely, but that the studies are more focused on vertebrates, and of them in the large groups: mammals and birds. What is well known in these groups is the relationship between basal extinction, which would be the natural extinction that organisms have in their relationship with the environment, and the extinction rate that is calculated for the last two centuries and which is what which has led to talk of this sixth great extinction.
To give an example, basal extinction in mammals is thought to be one extinction event per million species per year, which is how it is measured. The result of that would be that one in every thousand species (0.001) would become extinct every century. And now, according to the lists of the International Union for Conservation of Nature (IUCN), stands at 1.8 species per year, which means that about 180 species would become extinct in a hundred years. But it is also thought that this figure is biased because it refers to the last five centuries. If we look only at the last 200 years, it is estimated that we are at 390 extinct species each century. These estimates are why we talk about the sixth extinction, because the basal rate has multiplied by forty.
Nothing close to this level of precision exists in plants because their extinctions are less well documented by the NICU. However, the extinction that exists in certain ecosystems and certain countries is better known thanks to conservation reports. The Royal Botanic Gardens at Kew (United Kingdom), commonly known as Kew Gardens, prepares the report every year State of the World's Plants and Fungi (Situation of plants and fungi in the world, in its Spanish translation). The last one has been the most devastating because it makes a correlation between the year of description of a plant species and its status on the IUCN lists. What has been seen is that this correlation does exist, the more recent the description of a species, the greater the threat situation. For example, 77% of the species that were described in 2020 (three out of every four species) are threatened and also at high levels of threat. Furthermore, it is estimated that a significant percentage of plant species preserved by a single specimen in our herbaria and even undescribed, correspond to already extinct species.
The total number of described species represents just over 10% of the total number of species estimated to exist. We know of 1.9 million species and it is estimated that there are around 8.7 million that actually exist. The degree of threat found in plants indicates that of that 90% that remains to be discovered, it is very likely that a minimum of 77% is already threatened.
That plants become extinct at that speed is very serious. Plants are the “bricks” of ecosystems, they are the primary producers, and, therefore, they are at the base of the trophic pyramid of an ecosystem. In the case of dominant plant species in an ecosystem, such as palm trees in tropical forests or grasses in grasslands, their disappearance would cause the collapse of these ecosystems. Africa is an example where deforestation and climate change are destroying ecosystems: it is estimated that 45% of its species will become extinct by 2085, and up to 97% will see their distribution range reduced. In it Royal Botanical Garden (CSIC) we work on a project on the Euphorbiaceae family, which includes the poinsettia and is especially rich in tropical forests around the world. Curiously, in Africa, although there are many genera of euphorbiaceae, many of them have very few species, one or two. By studying the evolution of these genera with DNA sequences, we have seen that they originated millions of years ago, when the continent had a more humid climate. What we think is that they were more diverse in the past and that climate change, agriculture and deforestation have decimated them. The complete extinction of these genera would mean the disappearance of unique evolutionary lines, with unique morphological, physiological and genetic traits that would be lost to science. And I think this is a confirmation of the bleak picture shown in the Kew Gardens report.
Isabel Sanmartin She is a scientific researcher and vice director of Research and Documentation at the Royal Botanical Garden (CSIC)
Question sent via email byPaula Garcia
Coordination and writing:Victoria Toro
We respond is a weekly scientific consultation, sponsored by the Dr. Antoni Esteve Foundation and the L'Oréal-Unesco 'For Women in Science' program, which answers readers' questions about science and technology. They are scientists and technologists, members of AMIT (Association of Women Researchers and Technologists), who answer these questions. Send your questions to [email protected] or on Twitter #nosotrasrespondemos.
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