There's been a lot of talk lately about the eco-friendliness of various types of wine closures. When word got out a few years ago that 70 percent of the world's cork is used in wine production, many environmentalists began to worry that demand for cork products was putting a huge strain on the world's few remaining cork forests. For a while, plastic and glass alternatives were heralded as a greener choice — but as wineries made the switch, cork forests in Portugal, Spain and other Mediterranean countries actually began to suffer.

In the Coruche district of Portugal, cork oaks are vital to an entire ecosystem and actually help stave off devastating effects of global warming. Their roots hold the soil together, preventing it from being washed away during the deluges that often come after weeks of no rain in this hot, extreme climate. Cork forests contain a diverse array of life, including animals, birds and insects that aren't found anywhere else in the world. Some wildlife depends on the cork forests for survival, including the Iberian lynx, the Barbary deer and the Egyptian mongoose.

If people stopped buying cork, these forests would disappear: Demand for cork products is what keeps them protected from conversion to other uses, abandonment and degradation. People care for the forests because they're vital to the local economy. According to a 2006 World Wildlife Fund report (PDF), loss of commercial demand for cork puts Mediterranean cork oak landscapes at risk of intensified forest fires, loss of irreplaceable biodiversity, accelerated desertification and economic crisis.

So if there are so few cork oak forests left in the world, how is demand not causing problems with overharvesting? Cork is a highly sustainable resource when properly managed. A single tree can live hundreds of years, and after each harvest — every nine years or so — the cork, which lies just under the bark, grows back several centimeters thick. Not a single tree is cut down during the harvest — a delicate process that requires highly skilled workers to painstakingly cut the bark with sharpened axes.

A recent independent study by PricewaterhouseCoopers found that the preservation of cork forests isn't the only reason natural cork wine stoppers are more eco-friendly than plastic and aluminum screw-cap alternatives. Researchers found that plastic stoppers result in nearly 10 times more greenhouse gas emissions than natural cork during a 100-year period. Aluminum screw caps are responsible for 24 times more emissions during the same time frame. Natural cork is also biodegradable and recyclable.

"Cork taint" is often used as a rationale for replacing natural cork with synthetic alternatives, but tainted wine is also found in bottles with noncork stoppers or in plastic packages. Taint, caused by the presence of 2,4,6-trichloroanisole, leads to undesirable smells and tastes but is harmless. Screw caps and synthetic corks can also be prone to another aroma taint called sulphidisation, which is caused when the reduced oxygen supply concentrates sulphurous smells that come from preservatives in the stopper or cap.

Ultimately, winemakers will heed consumer preferences when it comes to choosing wine bottle closures, so it's up to all of us to request natural cork stoppers. Antonio Ferreira, who has been a landowner and cork farmer in Coruche for many years, emphasized the importance of the cork retaining economic value in an interview with the BBC last year.

"It's not just a tree we are trying to protect here. It is a whole environment," Ferreira said. "The forest you see around you now has been like this for hundreds of years. It is meant to be this way."

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