FABIO COLOMBINIBrazil Nut tree in the Amazon Jungle: human influence may explain disseminationFABIO COLOMBINI
The distribution of Brazil Nut trees in the Amazon region has been a topic of dispute for many decades. Because the fruit that contains the seeds is hard and not easily dispersed, specialists were unable to explain the existence of forests of Brazil Nut trees – areas densely covered by trees of the Bertholletia excelsa species – all over the Amazon Region. One of the traditional explanations stated that rodents such as the agouti, and birds, such as the macaw, were responsible for spreading the seeds. Two recent papers reinforce another hypothesis: that most of the Brazil Nut trees were grown and cultivated by indigenous people before the Europeans’ arrival in South America. The first study was based on human activity in the forest; the second, on genetic and linguistic analyses of indigenous languages.
Ricardo Scoles, from the Federal University of West Pará, and Rogério Gribel, from the National Institute of Amazonian Research, were the authors of one of the papers. Their work was based on the supposition that the intense activity conducted by the region’s ancient inhabitants in the areas where the Brazil Nut trees exist left a “signature” on the tree population, and that this mark can be identified. They compared Brazil Nut trees from the region around the Trombetas River with trees from the region around the Madeira River. The former was densely populated by indigenous people prior to the discovery of Brazil. However, this population dropped drastically in the sixteenth century. The population living in the second region remained there even after the Portuguese colonized Brazil.
The researchers found significant differences in both. The more ancient Brazil Nut forests had older trees and fewer seeds available for new germinations; in contrast, the trees in regions that were constantly populated were generally younger and more productive.
“The data supports the idea that the Brazil Nut forests, even those that are not considered primary and native forests, resulted from anthropogenic influences,” the researchers wrote in the article published in the journal Human Ecology. “In our opinion, the concentration of Brazil Nut forests in the Amazon Region is explained by the traditional stewardship of the Amazonian landscape, especially in the pre-colonial period,” says Scoles. “For example, the estimates of the trees’ average age, calculated according to the tree rings on many of the trees in the region of the Trombetas River, show that their age coincides with the time when the indigenous population was dwindling in the Amazon Region.”
Many Brazil Nut trees are 400 years old and there are reports of trees over one thousand years old. The first hypothesis that the Brazil Nut trees might have been grown and cultivated by ancient indigenous people of the Amazon came from Italian-Brazilian botanist and ethnologist Adolpho Ducke (1876-1959), in 1946. Many experts have agreed with this hypothesis, while other experts have challenged it in the last few decades.
The fruit of the Brazil Nut tree, which contain the desired seeds, are difficult to open and therefore it seems that they do not have a simple scattering mechanism. When left on their own, it is difficult for the fruit to scatter over a small area, let alone over an entire forest. The first person to describe this phenomenon was Switzerland’s Jacques Huber, in 1910. Another expert on this matter is Carlos Peres, from the University of East Anglia in the United Kingdom. Peres, a native of the State of Pará, is a renowned environmental biologist. In 1997, he reinforced this hypothesis when he stated that the agouti, a common sharp-toothed rodent native to the Amazon Jungle, might have been responsible for giving the Brazil Nut trees the push they needed to multiply.
Peres observed the behavior of the agoutis and noticed that they were able to open the fruit and pick out the seeds. The agoutis would eat one out of every four seeds at the site, and would bury the other seeds to eat them later. One can assume that not all the buried seeds were gathered later on, and were therefore able to germinate and to produce a new tree.
However, another mystery persisted: how was the tree able to spread over so many regions in the jungle in such a striking manner? In the opinion of some researchers, only the actions of human populations, and not natural mechanisms, could have achieved this. The theory was further supported by Glenn Shepard Jr., from the Museu Paraense Emilio Goeldi museum(MPEG), and by Henri Ramirez, from the Federal University of Rondônia (Ufro), who conducted a multidisciplinary survey with the help of Rogério Gribel, from Inpa. They collected evidence, including biological evidence in the form of generic analyses of the Brazil Nut tree population, and linguistic evidence, by correlating several indigenous languages, to decipher the historical importance of the Brazil Nut for the region’s populations.
One of the most important revelations has come from the DNA analysis conducted by Rogério Gribel and Maristerra Lemes, from Inpa, and their collaborators. When comparing the tree populations in parts of the Amazon Region, the researchers noticed that these populations were all homogeneous; in other words, there were very few genetic differences from one region to the next. This indicates that the geographical dissemination of the Brazil Nut happened very fast and in relatively recent times. This makes it even more complicated to imagine a natural way of spreading them.
Daniel das Neves“The agoutis might be the explanation for the concentrated spatial distribution of the individual trees in the forest,” says Scoles. “However, it is impossible to understand how these rodents, with no human help, could be the explanation for the spreading of the Bertholletia excelsa over the entire Amazon Region. Scattering by the agouti is highly inefficient and covers only a short distance. In addition, how could these rodents have crossed the enormous rivers while holding seeds in their mouths?”
Other animals that also eat Brazil Nuts, such as the macaws, might have helped to scatter the seeds at medium distances, a hypothesis that Scoles does not believe in. “Macaws usually spoil fruit production because they eat the fruit before it is ripe,” he says. The phenomenon has been sufficiently documented; in addition, it seems to be more complicated than merely imagining that the ancient indigenous people were interested in planting and consuming Brazil Nuts. “It is easier for us to explain the large-scale distribution by saying that the seeds were scattered long ago, voluntarily or involuntarily, by human beings,” Scoles concludes.
A comparison made by Shepard and Ramirez between the geographic distribution of the Brazil Nut trees and the sapucaias (cream nut tree) showed that the area where the sapucaia is found contains various geographically distinct species, indicating a deeper evolutionary history and a lengthier dissemination process. “The Brazil Nut tree, on the other hand, is a single species in the entire Amazon Region, indicating a more recent history,” says Shepard. The cream nut tree resembles the Brazil nut tree; however, the fruit of the cream nut tree make it easier for the seeds to spread.
In addition, populations of cream nut trees showed very slight genetic variations over hundreds of kilometers, while the Brazil Nut trees had no genetic variations over thousands of kilometers throughout the Amazon Region. This has led researchers to believe that different mechanisms formed the two tree populations.
Linguistics
One of the most interesting aspects of the study conducted by Shepard and Ramirez is the use of linguistic comparisons to identify certain elements of ancient peoples’ culture. The two authors are very cautious in their analysis of this information, but they present interesting data. When comparing the terms used by the three biggest Amazon language families (Arawak, Carib and Tupi) in regions where Brazil Nut trees are found, the researchers noticed that in general it is possible to identify a common origin for the word that describes the Brazil Nut in the first two languages, but not in the third language. The natives who speak the Tupi family language commonly refer to the seed by using a “borrowed” word from another language.
The correlation of this linguistic data has led Shepard and Ramirez to believe that the Brazil Nut became an important element in indigenous culture, especially during the first millennium A.D., coinciding with the natives’ adoption of more intense agriculture and a more sedentary life style.
Concerning the origin of the Bertholletia, linguistic analysis seems to corroborate the genetic studies that suggest that the tree appeared in the north or central region of the Amazon, and then scattered (or was cultivated) in the west and in the south. This would help explain why there is no specific word for this tree in the roots of the Tupi language, as this branch of the native language seems to have appeared in the southern part, in what is nowadays the State of Rondônia. This might also explain why there are no vestiges of the consumption of Brazil Nuts in four thousand-year old archeological sites in Rondonia, even though there are many Brazil Nut forests in the state.
In spite of these indications, none of the researchers who believe in the anthropogenic hypothesis in relation to Brazil Nut forests have said that this discussion is over. “The definitive confirmation would be archeological and archeo-botanical evidence, showing, for example, vestiges of Brazil Nuts in archeological sites from a specific date onwards,” Shepard points out.
“Eurico Miller, an archaeologist from Rondonia, told me it is strange that no signs of Brazil Nuts have been found in ancient archeological sites in Rondônia, even though many Brazil Nut trees grow in that state,” says Shepard. “Miller’s personal comment would have to be confirmed by real evidence and we would have to establish when Brazil Nuts became part of the archeobotany-related vestiges in Rondônia and in other regions.”
According to Ricardo Scoles, two lines of research might also clarify the enigma. The first would entail the effort of correlating the Brazil Nut tree’s geographical distribution data, including the archeological sites, with the so-called “Amazonian dark earth” – an indication that these ancient natives engaged in farming. The idea is to demonstrate that Brazil Nut forests were formed in regions populated by the ancient indigenous people.
Another confirmation might come from the genetic studies on the varieties of this species to determine more accurately how and when the Bertholletia was dispersed throughout the Amazon Region. According to Scoles, both lines of research are already being pursued by researchers from Inpa. “I believe that they will provide some conclusive data in relation to the anthropogenic nature of the Brazil Nut forests.” But the issue is still open.
Scientific articles
SCOLES, R. and GRIBEL, R. Population structure of Brazil Nut (Bertholletia excels, Lecythidaceae) stands in two areas with different occupation histories in the Brazilian Amazon. Human Ecology. v. 39, p. 455-64. 2011.
SHEPARD JR., G.H. and RAMIREZ, H. “Made in Brazil”: human dispersal of the Brazil Nut (Bertholletia excels, Lecythidaceae) in Ancient Amazonia. Economic Botany. v. 65 (1), p. 44-65. 2011.
