Cork oaks are making homes warmer, cars lighter and clothes biodegradable — while still feeding the birds and absorbing carbon.
“We are seeing a growing interest in cork as a sustainable material,” says Rui Novais, a materials expert at the University of Aveiro in Portugal. “Compared with materials like polyurethane foam [used for thermal insulation], products made with cork require less energy and produce less CO2 emissions.” The cork oak’s thick bark adapted to defend the tree from fire, making it a powerful insulating material that’s been used to shield fuel tanks on NASA spacecraft and electric car batteries. It’s also resistant to water and oil, and can withstand compression while retaining springiness. “It’s an extraordinary, renewable and biodegradable material,” says Novais. “It’s also very durable. It has been demonstrated that cork products remain virtually unchanged for more than 50 years.” Part of the carbon absorbed by cork oak trees is transferred to cork products, which can be used for long periods, repurposed and recycled. Several studies found that cork is carbon negative, meaning it can store more carbon than what is required to produce it. When cork planks are trimmed and punched to form natural cork stoppers, the leftovers are ground into granules and pressed together to form cork sheets or blocks. “Even cork dust is used to produce energy,” says João Rui Ferreira, secretary general of the Portuguese Cork Association. “It feeds the industry’s boilers and powers some of the production.”
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Most of the cork produced in Portugal grows in the gently undulating hills and plains in the south of the country, in an ancient agroforestry system known as montado. This savannah-like ecosystem combines cork, holm oaks and olive trees with pastures, grazing livestock, crops and fallows. “The soil in southern Portugal is very poor, there is very little rain and temperatures are very high in the summer,” says Teresa Pinto-Correia, a professor at the University of Évora in Portugal specializing in rural landscapes and agricultural systems. “But this kind of system is productive even when resources are scarce and conditions are difficult.” For centuries, locals have preserved the montado because cork provided landowners with a source of income. This mosaic of habitats supports hundreds of species, including the Iberian lynx, the world’s most endangered wildcat, and the threatened Imperial eagle. One of the world’s oldest known cork oak trees, planted in 1783 in Águas de Moura, is known as “the whistler” because so many birds visit its large sprawling branches. Iberian pigs feed on acorns and goats graze the interwoven pastures. Interspersing cork oak trees with animals and crops can boost production and biodiversity, but also build soil, control erosion, retain water, combat desertification and sequester carbon, says Pinto-Correia.
