Trees in the Atlantic forest already have ‘extinction debt’ – 01/13/2024 – Reinaldo José Lopes

“Extinction debt”: I imagine that most readers of this column have not yet had the displeasure of encountering such an example of terminological cruelty. Well, it was this expression that kept running around in my head after reading an important scientific article published this week by Brazilian researchers.

The theme of the work, coordinated by Renato Ferreira de Lima, from USP in Piracicaba, is the conservation status of trees in the Atlantic forest. The main conclusions of the study have already been brilliantly explained in a report by colleague André Julião, from Agência Fapesp. In short, 82% of the more than 2,000 tree species considered endemic to the biome (that is, they only exist in the Atlantic Forest, and nowhere else in the world) are at least at some risk of disappearing forever.

The Atlantic Forest is a set of ecosystems that are both so important to the history of Brazil, and so mistreated by generations and generations of Brazilians, that it is worth going into more detail about some of the concepts behind the research. And this takes us back to the “extinction debt”.

As Lima and his colleagues explain in the article published in Science magazine, classifying species at different levels of extinction risk is done following the criteria established by the so-called IUCN Red List (International Union for the Conservation of Nature).

These criteria include things like a species’ population decline, the fact that it is restricted to a very small territory, or that its population is very small even though it has not declined much. Using small territory and population criteria, the researchers explain, would distort conservation assessments of Atlantic forest trees.

This is because many of them still occur in wide areas, with the vast majority of individuals exceeding 10,000, considered an important threshold of extinction risk. But it would be a big mistake to consider that these species are in a relatively peaceful situation, because many of them have experienced a brutal population decline (sometimes by 90%) relatively recently.

“Most of the area losses in the Atlantic forest occurred between the last 70 years and 50 years, which, for many tree species, corresponds to two or three generations”, write the study authors. “Thus, despite less deforestation today, the effects of habitat loss, fragmentation and selective logging on these long-lived species may not have had sufficient time to express themselves.”

This is why there is no contradiction, for example, between the apparent abundance of araucaria —one of the biome’s most emblematic species— in the South region and their risk of extinction. Forest fragmentation, that is, the shredding of the original forests into countless little pieces in a sea of ​​agricultural and urban areas, means that clusters of araucaria and other species are nothing more than genetic islands. Without the ability to connect with other populations and exchange genes with them, in the long term they tend to lose diversity, wither and disappear.

This is the extinction debt that hangs over the Atlantic forest. But the big mistake is to act as if it were impossible to cover this “overdraft” whose hole was created by our improvidence. The work published in Science accurately maps the problem. Strategies to reconnect forest fragments can undo a considerable part of the damage, and sometimes, to do this, it is enough to let the forest reconstitute itself. Renegotiating this debt would bring Brazilians riches that are increasingly scarce in today’s world: fertile soil, clean water and the inheritance of millions of years of evolution, which no amount of money can buy.

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