Ishmael Tirado watches as his fellow construction workers rebuild the Steeplechase Pier, a central feature of New York’s iconic Coney Island boardwalk. Planks of tropical ipê wood that were torn asunder by last year’s Hurricane Sandy lie in grey stacks behind him, ready to be scrapped or recycled, but fresh boards are tellingly absent. When the pier reopens this summer, visitors will encounter a shiny expanse of recycled plastic jutting out to sea on a platform of steel-reinforced concrete. “I think it’s a good idea,” Tirado says. “It’s more durable, and we are saving trees.”
Michael Bloomberg, New York’s mayor, would probably agree. He promised in 2008 to reduce the city’s dependence on tropical hardwoods such as ipê (pronounced ‘ee-pay’), and the city has since shifted towards concrete and plastic building materials. Many municipalities and consumers are making a similar choice as they build and maintain outdoor structures. But some researchers fear that a knee-jerk shift away from tropical timber could backfire on the environment.
“If it’s sustainable, the timber trade is generally a good thing,” says Duncan Brack, an environmental-policy analyst at Chatham House, a think tank in London. “There’s a real danger of pushing people towards things with higher environmental impacts.”
The scant data available suggest that ‘plastic wood’ — typically a composite of waste wood and plastic — exacts a higher climate-change cost than natural wood, which has the benefit of pulling carbon dioxide out of the atmosphere as it grows. One 2011 study, funded by the timber industry but independently peer-reviewed, found that the greenhouse-gas emissions from the manufacture of plastic wood are nearly three times higher than those from the production of chemically treated cedar.
Data from the Consortium for Research on Renewable Industrial Materials, a public–private partnership based at the University of Washington in Seattle, suggest that emissions from plastic-wood manufacture are 45–330% higher than those of redwood production, depending on whether the plastic is recycled and the extent to which it is supplemented with woody material. Yet plastic wood — which is often marketed as eco-friendly and low-maintenance — is growing in popularity. In the United States, it accounts for around 10% of the market for decking, according to the Freedonia Group, a business consultancy based in Cleveland, Ohio (see ‘Timber trade’).
The shift has also been driven by supply. In New York, the decision to use more concrete and plastic came after officials concluded that there was no natural timber comparable to ipê — which is prized for its strength and durability — available in sufficient quantity to meet the city’s needs. Although the upfront building costs are higher, the assumption is that plastics and concrete last decades with little or no maintenance.