By Athayde Tonhasca
Brazil nuts are high up in the list of superfoods, a gimmicky but highly profitable market. For some internet gurus, the nuts protect you against inflammation, heart disease, diabetes and cancer; and, inescapably as superfoods go, they are loaded with ‘antioxidants that fight free radicals’ – a scientifically baseless but commercially catchy label. Hype aside, Brazil nuts are highly nutritious: they are loaded with proteins, carbohydrates, unsaturated lipids, vitamins and essential minerals such as calcium, magnesium, phosphorus and potassium. But their main claim to fame is to be one of the best sources of selenium, an essential element for a range of metabolic processes in our bodies. These nuts have their detractors because of the unlikely risk of selenium poisoning for those who over-indulge in them, and the danger posed by aflatoxins (carcinogens produced by certain fungi) when the nuts are not stored properly. The healthy aspects of Brazil nuts are clearly winning over the popular perception because the European and American markets keep growing steadily. Which is good news for the main nut producers Bolivia (the world’s major exporter), Brazil and Peru.
The nuts are in fact seeds extracted from the hard, coconut-like fruits produced by the Brazil nut tree (Bertholletia excelsa). Named excelsa (high, exalted, lofty) by naturalists and explorers Alexander von Humboldt and Aimé Bonpland, this is one of the tallest trees in the Amazon region. Some individuals reach heights of 30 to 50 m, with trunks of 1 to 2 m in diameter – up to 5 m in older specimens. And they can live long lives: radiocarbon dating has identified some 800- and 1000-year-old trees (Camargo et al., 1994).
Brazil nuts are gathered from fruits fallen to the forest floor during the rainy season. The work, carried out by native people and small farmers, has one serious risk: the thick-walled fruit of the Brazil nut tree is 10-15 cm in diameter and weighs on average 750 g. A fruit of this size falling from about 7 m generates sufficient kinetic energy to fracture a skull and cause severe to fatal injuries (Ideta et al., 2021).
Brazil nuts are harvested almost entirely from wild trees because tree cultivation has been largely unsuccessful. One of the reasons for the failure to turn the tree into a farm commodity is its pollination requirements.
The Brazil nut tree reproduces by cross-fertilisation, but its flower is not the run-of-the-mill, pollinator-friendly structure found in most plants. It has a curled extension – called a ligule – that forms a hood over the petals, which are pressed together like an inverted cup. Ligule and petals create a chamber that conceals stamens, stigma, and the nectaries. To access the nectar, an insect has to squeeze itself between the ligule and the tightly packed petals. If successful, the visitor may come out dusted with pollen and transfer it to another flower.
The flowers of the Brazil nut tree receive many visitors, including hummingbirds, moths, butterflies, beetles, and several bees. But getting into a flower for its nectar is not for the nimble or weak; only the largest and strongest bees can lift the ligule to reach the reproductive organs. This select heavy-weight club includes bumble bees (Bombus spp.), Centris spp., Epicharis spp., orchid bees (Eulaema spp.), and carpenter bees (Xylocopa spp.).
In the central Amazon rainforest, the orchid bee E. mocsaryi and carpenter bee X. frontalis are especially important Brazil nut tree pollinators because of their abundance and frequency of flower visitations (Cavalcante et al., 2012). Watch X. frontalis hard at work.
The large bees that pollinate the Brazil nut tree can fly long distances, which is important for maintaining its genetic diversity: trees typically grow in groups of individuals that are isolated from each other in the forest. These bees are solitary or semi-social, and none of them have been domesticated; so their survival depends on the natural habitats that supply nesting sites, food – one type of tree alone will not provide for the whole season – and other resources such as orchid fragrances, which are collected by male orchid bees.
Other characters play an important part in the life of a Brazil nut tree: rodents. The fruit capsule is too hard for most animals that could be interested in the nutritious seeds – but not to agoutis (Dasyprocta spp.). Thanks to their powerful teeth, they can gnaw their way to the seeds. Sometimes an agouti can’t eat all the seeds at once, so the prudent animal takes them some distance away (up to 20 m) and buries them as a food reserve for leaner times. But it so happens that the agouti’s memory is not the sharpest; it often forgets the way back to the food cache. Or the agouti itself may become a meal for a large cat before returning to its seeds. Either way, the buried seeds germinate. This unintentional planting by agoutis, pacas (Cuniculus spp.) and the southern Amazon red squirrel (Sciurus spadiceus) is the only route to seed dispersal for the Brazil nut tree, thus is vital for its survival. Follow the exploits of a forgetful agouti in the forest.
As one can imagine, these required interactions with bees and rodents don’t bode well for the future of the Brazilian nut tree. Amazonian ecosystems have been eroded away by the relentless march of deforestation and land conversion to agriculture and pastures. To make things worse for the tree, its wood is highly valuable (its felling is illegal, but that doesn’t stop illegal loggers). One of the consequences of the devastation is the increasing scarcity of Brazil nuts in Brazil, which helps explain why Bolivia took the lead as the main exporter.
We may take the hard-nosed view that we can’t do anything about the plight of the Brazil nut tree, but that’s not quite right. One could be inquisitive and demanding about the origin of a nice piece of hardwood furniture for sale, or the juicy steak in a restaurant or supermarket freezer (much of exported South American beef comes from deforested areas). Or we could accept a life without Brazil nuts: after all, to us they are just comfort food. But the tree’s demise could be a portent. In the 1980s, doomsday prophet Paul Ehrlich and his wife Anne Ehrlich famously compared species’ roles in an ecosystem to rivets in an aeroplane’s wing. Aircraft manufacturers use more rivets than necessary to affix the wings, so removing a few of them would make little difference. But if they continue to be taken away, at some point a critical rivet is lost, and the aeroplane will crash. Similarly, how many species can you lose before an ecosystem fails? We don’t have an answer for that, or even know whether the Ehrlichs’ model is realistic. The eventual loss of the Brazil nut tree could be just one redundant rivet popped out of the body of biodiversity; or it could be a warning of bad things to come to bees, agoutis, the forest and its peoples, and, at the end of the queue, to us, sophisticated Brazil nut munchers.