Science paper: overharvesting of Brazil nuts leading to fewer trees

December 18, 2003

GAINESVILLE, Fla. — Brazil nuts, those time-honored holiday stocking stuffers, will continue to help save the rainforest — as long at least a few of the brown morsels are left behind to grow into trees.

A group of researchers has discovered that overharvesting of Brazil nuts, the only commercially available nut collected exclusively from wild trees, has significantly reduced the number of seedling and young trees in the trees’ native Amazon. An article about the research, co-authored by a University of Florida scientist, is scheduled to appear Friday in the journal Science.

Because Brazil nut trees can live 500 years or longer, their decline won’t affect harvests anytime soon. On the contrary, the scientists say consumers should buy more of the nuts, because they support an environmentally friendly industry that depends on rainforest preservation rather than destruction.

The study reveals that even the seemingly innocuous activity of harvesting wild-grown nuts can have a long-term impact, and that managers may need to take steps to ensure that more Brazil nuts grow into young trees, the scientists say.

“It’s a very simple message: If you collect too many seeds, you’re not going to have seedlings,” said Karen Kainer, who has a joint appointment as an assistant professor with UF’s Center for Latin American Studies’ tropical conservation and development program and the School of Forest Resources and Conservation.

Avecita Chicchon, director of the Latin America and Caribbean Program for the Wildlife Conservation Society, said the findings point up the need to begin Brazil nut conservation programs.

“For the past two decades, Brazil nut extraction has been promoted as an economic alternative to logging and other destructive economic activities without words of caution,” she said. “These findings tell us that Brazil nut economic systems are still much better than other extraction systems in the Amazon, but it is crucial to establish annual harvesting quota today, even in lightly used areas.”

The Brazil nut tree, known scientifically as Bertholletia excelsa, flourishes throughout the Amazon’s lowland forests. Large and long-lived, mature Brazil nut trees produce hundreds of extremely hard, softball-sized fruits containing 10 to 25 seeds or “nuts.” Local harvesters collect the fruit on the ground, where they fall from heights of 150 feet or more, and open them with machetes.

In the sparsely populated Amazon, where barter is common and opportunities to earn cash are few, Brazil nuts are a vital industry. In the Brazilian Amazon alone, harvesters annually collect about 45,000 tons valued at about $43 million worldwide, according to the Science paper. In parts of the Amazon forest where traditional peoples still live in the forest, the nuts are their primary source of income, Kainer said.

Wild trees are the exclusive source of Brazil nuts because plantations have not been successful, Kainer said, a situation for which she said there are several possible explanations. In the wild, large bees called euglossines are important pollinators of Brazil nut trees, but these bees depend on orchids that grow almost exclusively in the rainforest and may not thrive in plantations. The nutritive content of the soil in plantations also may be a problem, she said.

Some scientists have argued that collection of the nuts doesn’t affect the wild trees, which makes some intuitive sense. Even the best harvesters can’t get 100 percent of the nuts. Rabbit-sized rodents called agoutis also target the nuts, burying them like squirrels for later consumption. These agoutis don’t retrieve all of their stashes, and their buried nuts are an important source of new trees. As Kainer put it, “there are just leaks in the system, and you don’t need that many to rejuvenate.”

The scientists examined the issue comprehensively, comparing surveys of young and adult Brazil nut trees in nearly two dozen Amazonian forest stands with current and historical data about nut harvests in each. The research was conducted in parts of the Brazilian, Peruvian and Bolivian Amazon.

For the surveys, the scientists recorded every tree with a trunk diameter of at least 10 centimeters, or about 4 inches. To learn how each stand was harvested, they examined records, interviewed nut gatherers and, in some cases, counted the number of opened or harvested Brazil fruits on the ground. The stands ranged in size from about 22 acres to about 3,336 acres, and some of the historical harvest data dated back to 1900.

The result of the research was unambiguous, the authors wrote.

New trees “were most common in unharvested and lightly harvested stands, uncommon to rare in moderately harvested stands and virtually absent where seeds had been persistently collected in the 20th century,” the paper says. “The clear message from this study is that current Brazil nut harvesting practices at many Amazonian forest sites are not sustainable in the long term.”

Kainer said Brazil nuts have long been considered a model “nontimber forest product” because they enable local populations to earn cash without engaging in more destructive practices, such as timbering or clearing the land for farming. In fact, because Brazil nut trees flourish only in the wild, they provide an economic incentive to preserve the rainforest. While the research does not indicate any short-term threat to this ecologically sustainable industry, it does suggest managers should plan for the future now, she said. Options include limiting harvests, restricting harvest seasons, or nurturing and planting more Brazil nut trees, she said.