There are more than 73,000 species of trees currently on earth, but the number of trees with multi-layered harvestable bark is much smaller. One tree with harvestable bark is the cork oak tree, which is from the beech family and under the oak genus, meaning it produces acorns, and its leaves are arranged in a spiral shape. Oak trees are known for their hardiness and come in more than 600 subspecies, which can be evergreen or deciduous. Cork oak trees are live oaks or evergreen trees that don't shed their leaves each autumn.
Green acorns developing on a branch of a cork oak tree.
Cork oak trees can live for more than 200 years and reach a height between 40 and 70 feet with a width of more than 40 feet. They are excellent shade trees and help prevent soil loss with their expansive root network.
A few properties make the cork oak tree (Quercus Suber) stand out from the hundreds of other types of oak trees. These properties also make it an intriguing tree for environmental protection and suitability.
The cork oak tree is a subspecies of an oak tree well known for its unique multi-layered bark. Like other multi-layered bark trees, the bark of the cork tree can be carefully harvested without harming the tree. Cork bark has three layers, and the top two layers can be harvested, leaving the innermost layer to protect the tree and regrow the two outer layers. The outer two layers are carefully harvested by hand by agricultural craftsmen who have handed down their knowledge through generations.
One of the most remarkable things about the cork oak tree is its ability to withstand high heat and even wildfires. For the same reason that cork makes an excellent choice for flooring or wall tiles, cork oak trees are ideal in fire-prone ecosystems - excellent thermal insulation. The outer two layers of cork bark act as a heat shield for the inner tree, protecting it from extreme temperatures and direct flames. The outer cork bark may smolder under some fires, but it is unlikely to catch fire, helping to act as a fire break and preventing the fire from spreading. The wide, tall branches of the cork oak tree also help slow wind speeds, a significant concern in fire-prone regions.
Cork oak trees are also drought-resistant once they are established. They have an extensive root system that helps to ground the soil, preventing soil erosion and topsoil loss. The multi-layered bark of established cork trees also helps prevent moisture loss, even under hot and arid conditions, allowing the tree to thrive in lower precipitation environments.
A well established cork oak tree in California.
Cork trees grow best in sandy, well-drained soils with a high PH level and low nitrogen and phosphorus. Traditional cork forests have hot and dry summers, often plagued by droughts and relatively mild winters. They do best in areas where the minimum temperature does not drop below 10 degrees Fahrenheit (-10C); however, they can still grow well in slightly colder climates. In the US, cork trees are rated for full sun and hardiness zones 8-11 or globally in climate zones 5-24, meaning they can be grown in various climates. Unlike many trees, cork trees also thrive at higher elevations. Cork forests in the Mediterranean are often found beyond 300m (950ft) above sea level.
Ideal Cork Growing Conditions
Hardiness Zones 8-11
Climate Zones 5-24
Well Drained Soil
High PH Soil
Low Nitrogen and Phosphorus
Full Sun to Partial Sun
Many of these climatological factors can be found outside of the Mediterranean. They may offer new locations where cork trees can grow and thrive, expanding the benefits these trees provide to the global ecosystem and encouraging the use of their sustainable harvest.