the air, making them behave as authentic "pads," which contributes to the capability of cork to recover after compressed. Sources There are about 2,200,000 hectares of cork forest worldwide; 34% in Portugal and 27% in Spain. Annual production is about 300,000 tons; 49.6% from Portugal, 30.5% from Spain, 5.8% from Morocco, 4.9% from Algeria, 3.5% from Tunisia, 3.1% from Italy, and 2.6% from France. Once the trees are about 25 years old the cork is traditionally stripped from the trunks every nine years, with the first two harvests generally producing lower quality cork. The trees live for about 300 years. The cork industry is generally regarded as environmentally friendly. Cork production is generally considered sustainable because the cork tree is not cut down to obtain cork; only the bark is stripped to harvest the cork. The tree continues to live and grow. The sustainability of production and the easy recycling of cork products and by-products are two of its most distinctive aspects. Cork oak forests also prevent desertification and are a particular habitat in the Iberian Peninsula and the refuge of various endangered species. Carbon footprint studies conducted by Corticeira Amorim, Oeneo Bouchage of France and the Cork Supply Group of Portugal concluded that cork is the most environmentally friendly wine stopper in comparison to other alternatives. The Corticeira Amorim's study, in particular ("Analysis of the life cycle of Cork, Aluminum and Plastic Wine Closures"), was developed by PricewaterhouseCoopers, according to ISO 14040. Results concluded that, concerning the emission of greenhouse gases, each plastic stopper released 10 times more CO2, whilst an aluminium screw cap releases 26 times more CO2 than does a cork stopper. For example, to produce 1,000 cork stoppers 1.5 kg are emitted, but to produce the same amount of plastic stoppers 14 kg of are emitted and for the same amount of aluminium screw caps 37 kg are emitted. The cork oak is unrelated to the "cork trees" (Phellodendron), which have corky bark but are not used for cork production. Harvesting Cork is extracted only from early May to late August, when the cork can be separated from the tree without causing permanent damage. When the tree reaches 25–30 years of age and about 24 in (60 cm) in circumference, the cork can be removed for the first time. However, this first harvest almost always produces poor quality or "virgin" cork (Portuguese cortiça virgem; Spanish corcho