5 June 2018

Quercus suber: An example of sustainability

The 'cork tree' Quercus suber boasts a rich history of uses from bottle stoppers to bike brakes. Intern Jake Newitt investigates.

By Jake Newitt

The cork oak at Kew

A journey of plant uses 

As an intern on the PAFTOL project, I've been learning about the different uses of plants, as well as the roles they play in their ecosystems. 
I've been investigating plants that are truly remarkable. So far I've explored the cancer-killing properties of Madagascar periwinkle, as well as the antimicrobial properties of the 'fern tree' Jacaranda mimosifolia. 
Both plants that I've looked at so far are found in Kew's spectacular glasshouses, but the latest plant to capture my interest is found in the Mediterranean garden. That plant is Quercus suber, otherwise known as the cork oak.

From wine to boats 

Cork bark is well used because of its remarkable properties. It is highly impermeable to liquid, and is an excellent insulator of heat, sound and vibration. 
Cork is the outer layer than can be found on almost all trees and forms a natural armour. Quercus suber is unusual because it forms an exceptionally thick layer that can be sustainably harvested without damaging the tree. 
It is thought that the cork tree evolved this layer to protect itself from wildfire, which is a frequent occurrence in its native range of Portugal. 
The cells in cork tree bark are organised in such a way that makes it highly elastic. It is this property which makes it so good for its eponymous use as the humble bottle stopper. 
Cork’s ability to be easily compressed means that it forms a tight seal in a bottle. Importantly, the impermeable nature of the material means that the wine does not leak. Oxygen that can cause the wine to spoil, is also kept out. 
The oldest container of wine that has been found corked is around 2000 years old. The uses of cork don’t stop there. 
In addition to its water-resistant properties, cork’s low density and porous structure mean that it can be used as a fishing float. The earliest example of this dates back 5000 years. 
This porous structure also lends cork its thermal and acoustic insulation properties; floor and ceiling tiles are often made with a cork component for this purpose. 
The applications for cork composite material are even more widespread. 
Notable examples include usage in the construction of spacecraft as well as concrete with enhanced thermal insulation.

Ecological sustainability 

Quercus suber is often grown in 'agroforestry systems'. 
This means that relatively low tree densities are planted among forage species, which are grazed by cattle during the summer. 
Land is more profitable in this way than when it is for a single purpose. 
A cork oak is ready for first harvest twenty-five years after planting. Workers are highly trained to remove the cork without damaging the tree. 
Mature cork oaks can be stripped of their bark every twelve years or so, and a tree can be harvested twelve times in its lifetime. 
In addition to these commercially valuable attributes, Quercus suber forests are known to harbour endangered species such as the Barbary macaque (North Africa), and the Iberian lynx (Portugal and Spain). 
The Portuguese Cork Association reports that the longevity and structural persistence of cork oak trees helps to support high floral and faunal biodiversity. 
We live in an age where natural resources like plants are well utilised for food, medicine, and material properties. 
The way that the Quercus suber is farmed gives us a solid example to follow in using plants in a sustainable and eco-friendly manner.