Forests make an enormous contribution to life on earth. Cork oak forests are a part of it. They protect the environment because they regulate the water balance and protect the soil from desertification. Their use is active environmental and climate protection.
The cork oak is an evergreen deciduous tree, it turns about 250 - 350 years old. During its lifetime, the tree absorbs a considerable amount of carbon dioxide, CO2, from the air through photosynthesis and slowly builds up its cork skin. The bark is harvested about every ten years from an age of about 30 years. With less than 1.5 hectares of cork oak forest, the annual CO2 emissions of a middle-class car can be offset. Today, cork oaks are barked on about 1 million hectares in Portugal and Spain. Together they supply 300,000 tons of cork per year, which accounts for about 75% of world production.
The special properties make cork so versatile. Cork is strong and elastic. It contains suberin and waxes that make the material water-repellent. The cork bark protects the tree from heat, dehydration, infections, pests and forest fires.
This natural protection makes it the ideal building material. Cork is heat, cold and sound insulating. It is light, floatable, flame retardant, resistant to ageing, easy to maintain, decorative and a renewable raw material.
The Chinese cork oak (Quercus variabilis) occurs in southeast China. It can be crossed with the cork oak (Quercus suber), the resulting offspring are frost harder than both parents (heterosis) and can grow up to a maximum height of 45 meters.
NABU from Hamburg has compared Roman sandals and a space shuttle in a publication. "Cork is found in both, one as footfall insulation, the other as heat protection. The extraordinary properties of the natural substance cork have been used by humans since antiquity," they write on their website.
In fact, the use of cork has been known for thousands of years. Everyone knows cork closures, which became known as bottle corks with the development of the glass industry in the 17th century.
A maximum of one third of the cork bark is peeled off during harvesting and the tree is stimulated to grow again quickly. The harvest is sorted by quality, dried and soaked for processing. The harvest is "a guarantee for the preservation of the cork oak forests," writes NABU.
Cork has good thermal conductivity. With 0.042 - 0.060 W/mK the value can compete with glass and mineral fibre products. It is a renewable and therefore CO2-neutral raw material and perfect for ecological house building. Cork regulates air humidity more strongly than mineral fibres or polystyrene and thus creates a better indoor climate. Cork loses little of its insulating effect when it absorbs water. The poor flammability is another advantage of cork. In contrast to mineral fibres, there is also no health risk (e.g. for allergy sufferers) when processing and using the material.
In the 1960s, the use of the natural building material cork declined sharply. The cork industry could not supply the market sufficiently, cheaper plastics came onto the market as competition. Styrofoam, mineral fibres and other plastics conquered the market.
The technical standard of the cork industry at that time had nothing to oppose this. One attempt to stay in the market was to increase the cork harvest. The result was an overuse of the cork oaks, which led to damage to the trees. Urgently needed afforestation did not pay off. The cork oak stands lost their importance, had to give way to building areas or were displaced by eucalyptus forests and agricultural land.
In recent years, new technologies and the value of sensible natural products have given cork back its positive image as a raw material and led to its renaissance. Today, cork residues can also be processed as high-quality granulate. The ecological and economic increase in value leads to a broad customer acceptance and makes reforestation on a large scale possible and economical.
Health and environmental awareness are playing an increasingly important role. The development of safe binders, alternatives to chlorine bleach and much more has led to an increase in demand. Nevertheless, it remains a raw material that needs a habitat in order to develop healthily. That is why prudent use is important.