The answer is yes. It is true, as you seem to suggest in your question, that the most well-known studies of the last few centuries relate mainly to animal extinctions, the so-called sixth extinction. I would like to add that this is not entirely the case for all animals, but that studies tend to focus on vertebrates, namely the major groups: mammals and birds. What is well known in these groups is the relationship between basal extinction, that is, the natural extinction that organisms have in their relationship with the environment, and the extinction rate calculated for the last two centuries and which has led to the talk of this sixth great extinction.
To give an example, basal extinction in mammals is assumed to be one extinction event per million species per year, and that is how it is measured. The result would be that one in a thousand species (0.001) would become extinct every century. And now, according to the International Union for Conservation of Nature (IUCN) lists, it is at 1.8 species per year, meaning that in a hundred years about 180 species would go extinct. However, this figure is also believed to be distorted as it refers to the last five centuries. If we look only at the last 200 years, an estimated 390 species become extinct every century. These estimates are why we talk about the sixth extinction, because the basal rate has multiplied forty-fold.
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There is not nearly this level of precision with plants, as their extinction from the NICU is less well documented. However, extinctions in certain ecosystems and certain countries are better known thanks to conservation reports. The Royal Botanic Gardens in Kew (UK), commonly known as Kew Gardens, produces the State of the World's Plants and Fungi report every year. The latter was the most devastating because it establishes a link between the year a plant species was described and its status on the IUCN lists. It has been shown that this connection exists: the more recent the description of a species, the greater the threat. For example, 77% of species described in 2020 (three out of four species) are threatened and also have a high threat level. In addition, it is estimated that a significant percentage of plant species preserved in 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 estimated total number of species. We know of 1.9 million species and it is estimated that there are actually around 8.7 million species. The level of threat identified in plants shows that of the 90% that remain to be discovered, it is very likely that at least 77% are already threatened.
The fact that plants are dying out so quickly is very serious. Plants are the “building blocks” of ecosystems, they are the primary producers and therefore 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 lead to the collapse of these ecosystems. Africa is an example of how deforestation and climate change are destroying ecosystems: it is estimated that by 2085, 45% of species will be extinct and up to 97% will have their range restricted. At the Royal Botanical Garden (CSIC) we are working on a project on the Euphorbiaceae family, which includes the poinsettia and is particularly rich in tropical forests around the world. Curiously, although there are many genera of Euphorbiaceae in Africa, many of them have very few species, one or two. By studying the evolution of these genera using DNA sequences, we have seen that they emerged millions of years ago when the continent had a wetter climate. We believe they were more diverse in the past and have been decimated by climate change, agriculture and deforestation. The complete extinction of these genera would mean the disappearance of unique evolutionary lineages with unique morphological, physiological and genetic characteristics that would be lost to science. And I think that this is a confirmation of the bleak picture presented in the Kew Gardens report.
Isabel Sanmartin She is a scientific researcher and deputy director of research and documentation at the Royal Botanical Garden (CSIC).
Question emailed from Paula García
Coordination and writing:Victoria Toro
We Respond is a weekly scientific consultation hosted by Dr. Antoni Esteve Foundation and the L'Oréal-Unesco “For Women in Science” program and 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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