For three years, the biologist Alessandra Nasser Caiafa crossed Brazil several times to map the diversity of the Mata Atlantica rainforest trees. This dense, lush vegetation that used to cover most of the Brazilian coast is still home to many species of plants and animals found nowhere else, some of which are under the threat of extinction. In her journey, she neither resorted to boots nor to a knife: she analyzed 225 scientific documents (books, theses and articles) kept in the 28 research institutions that she visited from 2004 to 2007. In this time, if she were to walk through the forest, Alessandra would only cover a small portion of the vast area already covered by other researchers.
In these readings, the biologist from Minas Gerais state, who currently teaches at the Federal University of Recôncavo da Bahia (UFRB), confirmed why the Mata Atlantica forest is considered one of the world’s richest ecosystems when it comes to the diversity of species. In the stretch that extends from the state of Espírito Santo to the state of Rio Grande do Sul, there are 846 tree species, ranging from the frail Plinia rivularis, whose height does not exceed four meters and which produces reddish fruit similar to the jaboticaba fruit, to the prodigious Cariniana estrellensis, whose name in the native Tupi-Guarani language means forest giant and which can grow 60 meters tall.
However, the greatest surprise arose when Alessandra analyzed how these species are distributed in this strip, which extends along almost 2,900 kilometers from North to South and that advances some 100 kilometers inland. Despite the variety of species, most (59%) are rare trees, found in limited areas or in a specific forest environment. A considerable proportion, 11% of the species, or almost 1 out of every 10, are extremely rare: there are only very few samples of them, concentrated at some point along the coast, the very reason for the risk that they will disappear.
“Such information encourages similar research efforts, given that in the Northeast, for example, there is a huge lack of data on the diversity of the Mata Atlantica forest trees,” states Alessandra. “The study applied an evaluation system that is internationally acknowledged,” explains the botanist Fernando Roberto Martins, from the State University of Campinas (Unicamp), Alessandra’s PhD advisor and co-author of the article published this year in Biodiversity and Conservation. “We quantified and qualified how rare the Mata Altlantica trees were. We now have a more reliable picture of how these species are distributed,” he adds.
Rare and very rare
In their study, Alessandra and Martins used a classification scale that determines how rare a species is, based on three criteria: affinity with a given environment, local abundance and distribution across the studied area.
These three factors combined lead to a scale with eight levels; one for common species and seven for increasingly rare species. The first level of rarity comprises those trees found at different altitudes, varied moisture levels, and with widespread geographical distribution, but that are not very abundant locally along certain stretches (4.5% of the 846 species). As for the seventh level of rarity, that of exceedingly rare species, it encompassed 11% of the trees: all with extremely low capacity to adapt to other environments and with small populations distributed over fairly limited areas.
The researchers found rare species along the entire area studied. According to Martins, historical, geographic and biological factors explain this pattern. In the dry climate typical of the glacial periods, the most recent of which occurred between 18 thousand and 14 thousand years ago, the only large trees that could survive were in more humid areas, such as the valleys and slopes near the sea, in keeping with the theory of refugia that Jürgen Haffer, a German scientist, proposed in the 1960’s. Adapted to Brazilian reality by the geographer Aziz Ab’Saber, this theory has recently been contested.
“Several successive events causing restriction and spreading drove the pattern of distribution of the Mata Atlantica species along the South and Southeast coasts,” explains Martins, who adds that at present, this pattern is directly influenced by human activity and destruction of the forest.
Thus, it is not by chance that many of the extremely rare trees are on the list of endangered species, prepared by the Biodiversitas Foundation in 2005. What concerns the researchers is that the disappearance of the rarest species might give rise to a domino effect, affecting the availability of food for several groups of animals. “The extinction of a single species breaks the node of a network of interaction, leading to the disappearance of several others,” Martins explains. Other possible consequences are the depletion of the soil and the increase of carbon dioxide in the air.
Alessandra considers the progress of the agricultural frontiers as a problem, along with the growth of towns in the Mata Atlantica area, highlighting that “it is necessary to awaken public authorities and landowners to the importance of these rare species.” One possible means of protection, she suggests, would be to create smaller conservation units in areas with the largest number of extremely rare species.
CAIAFA, A. N.; MARTINS, F. R. Forms of rarity of tree species in the southern Brazilian Atlantic rainforest. Biodiversity and Conservation. v. 19, p. 2.597-618. 19 May 2010.