EDUARDO CESARBrazil-nut tree in a pasture in Acre: risk of demographic collapseEDUARDO CESAR
For decades, agriculture, cattle raising and hydroelectric power stations have been encroaching on the space of the brazil-nut trees, which have a thin trunk and a vast rounded crown and can reach a height of 50 meters. Even when they survive, in isolation, amid plantations or pastures, they can no longer manage to reproduce themselves and end up dying. Now, another danger is taking shape: overexploitation, even of the younger trees, which is threatening the survival of the species and the exploitation of brazil-nuts.
“The removal of almost all the seeds of the brazil-nut trees reduces the probability of adult plants arising, which in itself is already very small”, says biologist Cláudia Baider, one of the authors of an article published in December in Science, with these conclusions. “The situation is very serious”, reiterates the coordinator of the study, Carlos Peres, who left the Biosciences Institute of the University of São Paulo (USP) eight years ago, to install himself in the University of East Anglia, in the United Kingdom. “But there is still time to revert the threats, because of the reproductive longevity of the brazil-nut tree, which can live for over 500 years.”
Done following surveys of three brazil-nut tree groves that Cláudia accompanied for her doctorate, carried out under the supervision of Peres, this work brought together teams from Bolivia, from Holland, from the United States and from Peru – and from Brazil, there were specialists taking part from two units of Embrapa, in the states of Acre and in Pará, and from the National Institute for Amazon Research (Inpa), from the state of Amazonas. After comparing 23 populations of brazil-nut trees (Bertholletia excelsa) from the Brazilian, Bolivian and Peruvian Amazon, the researchers concluded that natural harvesting – usually seen as an economic activity with little or no environmental impact – has altered the age structure of the trees: gathering of brazil-nuts has been so intense in the last century that the replacement of the older trees by young ones no longer occurs at the desired pace, hampering the succession of generations of brazil-nut trees.
One of the risks pointed out in this study is the phenomenon known as demographic collapse, when the majority of the individuals in a population (of plants or of animals) is old and does not generate any more descendants. If the number of young ones diminishes constantly, the species tends to disappear little by little, at least in the region it occupies. The majority of the trees exploited today, Cláudia recalls, has been the same for many decades. “The major part of the brazil-nut trees is on its way towards a collapse”, says she. “If we do nothing and carry on with the annual removal of almost all the brazil-nuts, there will still be something to gather in the next 50 or hundred years, but the volume will get smaller and smaller, which will reduce the economic interest of this activity”, she warns. Nowadays, 45,000 tons of brazil-nuts are collected a year in the Brazilian Amazon alone, bringing an income of close to US$ 30 million.
The nurseries and the agouti
According to Peres, there are alternatives for reverting the situation, like planting saplings cultivated in nurseries in the brazil-nut tree groves themselves, defining quotas for seeds to be gathered by area, interrupting the gathering in a grove temporarily, or rotation amongst the areas under production. Is something being done now? “Hardly anything”, says he. “The majority of native brazil-nut tree groves is not being managed, and there are no forest certification criteria for establishing what a population exploited in a sustainable manner is.”
To ensure the continuity of production and of the species itself, one also has to look with more attention at the agouti (Dasyprocta spp.), which nibbles the hard shell of the fruit of the brazil-nut tree. After a good half hour’s effort, the agouti opens up the fruit, eats a few seeds and buries some others, guaranteeing food in the future. “Some seeds are forgotten, germinate, and grow”, notes Cláudia, who since August 2003 has been working in the national herbarium of Mauritius, an island in the middle of the Indian Ocean. “But, as the pressure for gathering the seeds is high, there’s not much left for the agoutis to bury.”
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