More than 9,000 tree species around the world have yet to be properly discovered and described by scientists. Of these, 40% exist only in South America, mainly in the Amazon and in the regions between the forest and the Andes, says a new study, which also estimated the totality of tree species on the planet.
According to the new account, there would be 73,000, a number that already includes the trees still unknown to science.
A significant fraction of this total, both among the species already described and among those that still need to be found and studied, corresponds to trees that are probably rare, with a small population or restricted to very specific areas of the globe.
Hence the importance of estimating and searching for these species: the role they play in their environments is also poorly understood, and they are particularly vulnerable to deforestation and other changes brought about by human action.
The data have just been published in an article in the American scientific journal PNAS. Coordinated by Peter Reich, from the University of Minnesota, USA, the work had the collaboration of researchers from dozens of countries around the world, including scientists from several Brazilian institutions.
You don’t need to use a crystal ball to estimate how many tree species are still unknown. The central point of the method involves the crossing of data already recorded on tree biodiversity with the so-called sampling effort, that is, how much an area has already been studied by scientists.
“Imagine that you have a graph with the number of individual trees on the X axis and the number of their species on the Y axis”, explains Pedro Brancalion, professor at the Department of Forest Sciences at USP in Piracicaba and co-author of the new study.
“The curve of this graph, at the beginning, rises quickly, and then this rhythm decreases, because you have already found most of the species. In regions like the interior of São Paulo, for example, even if I increased the sampling effort a lot, the curve wouldn’t change that much, because the area is already well known. But there are regions where this curve doesn’t show any sign of going down anytime soon, which is an indication that many species can still be discovered.”
Even in the Amazon, he recalls, the sampling effort varies significantly from place to place. With the exception of expeditions to more distant and isolated locations, which demand great investment and logistical effort, the tendency is for sampling to be concentrated along major rivers and roads.
This means that many areas of the forest still harbor a significant diversity of trees not yet described.
The proportion of undiscovered species that are likely to be South American roughly mirrors that of known species from South America, which account for 43% of the world total – second, far behind, is occupied by Eurasia, with 22% of Earth’s tree species, according to the survey.
It is estimated that one third of the global total of species is composed of rare trees. Half of the South American species are also considered endemic, that is, they do not occur on any other continent.
The reasons for South America’s exuberance in terms of tree species are still not entirely clear.
Among the possible factors may be the presence of the largest continuous areas of tropical forests (since it is in this type of forest that biodiversity is usually greater) and the lower presence of environmental disturbances (with less human impact, since the region was colonized by the our species later than other continents, and also a more stable tropical climate over tens of millions of years).
Source: Folha
