Cork Oak: a wonder tree on the edge

Ferdinand the Bull – resting in the shade of a cork oak tree, be-hung with clusters of ripening corks

I had a most fortuitous childhood. Amongst other things, I grew up surrounded by books, and I was encouraged to read and love them. Some of the books I read in my childhood survived the years, and I read them to my own children, who in turn read them to my grandchildren. One of these is the story of Ferdinand, a young bull growing up in Spain who, unlike the other young bulls, did not aspire to the bullfighting arena in Madrid, but preferred to smell the flowers and sit in the shade of a cork oak tree.

The book was beautifully illustrated, and I always loved the particular cork oak tree under which Ferdinand rested. It was a sturdy and shady little tree with a gnarled and pitted trunk … but was especially notable for the clusters of cork bottle stoppers hanging on its branches. It was an image that stayed with me for a long time.

Of course, knowing what I later came to know, corks do not occur in little inflorescences on the limbs of an oak tree to be gathered like bunches of grapes, but are manufactured from the tree’s bark. I have never been to cork oak country, but I know the tree and have studied the growing, harvesting and manufacture of cork products. It is a fascinating affair.

I will return to the cork forests and the cork industry in a moment, but first we must meet the tree.

And how better to introduce it than to quote the opening sentence from a fascinating (but, as we shall see, disturbing) book called Cork Oak Woodlands on the Edge edited by a trio of forest scientists [Endnote 1]:

… when uncorking a bottle of a good wine or using any of the dozens of prod­ucts made from natural cork, have you ever stopped to wonder where it comes from? If so, come with us now for a trip to the western Mediterranean, home of the cork oak (Quercus suber), one of the most extraordinary trees on Earth. Whether fully clothed, in its arm-thick, fissured, light grey bark, or with brick red trunks recently undressed by a once-a-decade harvest of its corky clothing, the tree has great beauty, mystery, and charm, as writers and travellers have long recounted. The landscapes where it occurs have the same charms or even more to those who know how to read them.

Native cork oak forest in Portugal, the trees recovering from bark harvest (Photo from A Tree a Day by Amy Jane Beer)

Alas, the beauty, mystery and charm of the cork oak tree, and the age-old industries of cork oak silviculture, and cork harvest and manufacture are now endangered in their homelands. How has this come about and what is to be done about it? Could it be that the cork oak will (as so many other trees have become) transferred from the status of commercially-valuable to merely ornamental?

Well, “merely” is not the right word at all. A good ornamental tree adds immeasurably to our well-being and to the quiet pleasures of garden and landscape; and the cork oak is one of the finest of ornamental trees, especially when growing in hot, dry climates. Consider the photograph (below) of a relatively young, but umbrageous corky in an urban park, combining beauty, habitat and cool shade on the hottest summer day. I have paused under this tree for relief from the sun on many a dog-walk, and always think of it as “a real corker” (a term my father always used to describe something outstanding):

A corker of a cork oak in a suburban park in Palmyra, Western Australia

Discovering the cork oak tree

As with so many of my dendrological experiences, it was in 1961 that I first became aware that there was such a thing in real life (as opposed to a children’s book) as a cork oak tree. This was the first year of my forestry studies in Canberra - an ideal place to study trees. Canberra was bounded by native forests in the Brindabella Ranges, and was a “planned metropolis”, designed as a city of parks and trees around a lake. Within a few minutes-walk or drive from the forestry school at Yarralumla you could find specimens of most of the famous trees of the world, planted as street trees, or as ornamentals in the city parks, arboreta or plantations.

We even studied a lovely little book called Trees in Canberra which gave details of every species and variety of tree planted in the city, and where to find them.

One of the trees I was introduced to through our botanical explorations around Canberra was the cork oak, which I now also came to know by its Latin name, Quercus suber.

Oaks (in general) are among the world’s best-known trees. If you live in England, Europe, Russia or north America you will have found them on all sides, in forests, parks, fields and woodlands. Everywhere they occur, they are part of a deep cultural experience. I still relish the memory of the time I visited the famous Forest of Dean on the England/Welsh border and patted the trunks of English oaks (Quercus robur) planted at the time of Nelson and the Napoleonic Wars, for timber for the “wooden walls” of the Royal Navy. This was living history.

There are many members of the oak “family” – cork oak is one of about 500 different species of oak, nearly all of which are found only in the northern Hemisphere. [In Australia, of course, we have sheoaks, but these are Casuarina not Quercus and the only similarity to the true oaks is the superficial appearance of the timber].

From Trees in Canberra (written in 1960) I learned:

Cork oak is readily distinguished [from other oaks) by the thick, corky, deeply-fissured bark. It is native to the Mediterranean regions both in southern Europe and North Africa, and also Asia Minor. A particularly important tree because it provides most of the world’s cork supply, which is obtained by stripping the outer bark in early summer. This sustains a large industry in Portugal, Spain. southern France, Morrocco and Algeria. Cork oak, when well-grown, is a splendid tree with a wide spreading crown. It is evergreen and when not stripped has an attractive grey, furrowed bark …

Leaves and acorns of Cork Oak (picture taken from my friend Matt Ritter’s wonderful little book “A Californian’s Guide to the Trees Among Us”)

In addition to the leafy, shady cork oaks scattered through the suburbs of Canberra, the city also had an actual cork oak plantation, established in 1917 for experimental purposes. The aim was to see if cork could be commercially produced in Australia.  A cork industry never eventuated, but cork was harvested from the Canberra plantation and was found to meet international standards. There is an interesting story about the source of the acorns for this plantation. Initially a few came from cork oaks planted as ornamentals elsewhere in Australia, but the city horticulturalists needed them in quantity, so a shipment of acorns from Portugal was arranged. The shipment was lost at sea when the ship on which they were being carried was torpedoed by a U-boat. A second shipment arrived intact.

The cork oak plantation in Canberra at age 100, photographed not long after the experimental harvest. The plantation is now incorporated into the National Arboretum

Apart from its distinctive bark, the other interesting thing about cork oak is that it is not deciduous, as are nearly all oaks. It looks “a bit crook” (as that great Australianism has it) in mid-winter, the foliage becoming yellow and sparse, but the tree never actually becomes leafless.

Living under a cork oak

Appointed a junior forestry officer in WA after graduating from forestry school I soon became close-up and personal with “my own” cork oak tree. Down in Pemberton I lived in the Single Officer’s Quarters – a one-room weatherboard and iron-roofed hut, crouched under a cork oak tree. The hut had a wood stove and was cosy in the winter, but it was also cool in the summer, always in the deep, dark shade of the cork oak standing outside the front door.  I developed a personal friendship with this tree – I would give the trunk a pat and wish it good morning as I walked past on my way up to the office every morning.

The cork oak at the front of the Single Officer’s hut at Pemberton, photographed in 2025 (by David Meehan). The tree is in its winter phase with typical thin, yellow foliage.

The photograph reminds me of one of the other nice things about this cork oak. Because it was partly deciduous and stood on the north side of the hut, it let in the winter sun, which was at such a premium in that cold, damp spot.

I often wondered who the visionary was who planted this tree. It was probably either that great pioneering forester Don Stewart or his protégé Johnny Meachem, both of whom planted many lovely ornamental trees around departmental settlements. On the other hand, I can confirm that it was my colleague Jack Bradshaw who (in 1989) planted the superb grove of cork oaks which are now a showpiece at the famous Foresters Wood [Endnote 2].

Cork

All trees have bark, the role of which is to protect the inner workings of the tree’s stem from extremes of temperature, dehydration, fire and attack from insect pests, disease and animals. There are a multitude of different types of bark, from paperbark to ironbark. The bark of the cork oak is probably the most remarkable.

The massive, corky bark in the crown of a venerable cork oak in the Government House gardens in Perth

The thick outer layer of bark on the cork oak is impregnated with a waxy substance called suberin. This imbues the woody bark with many extraordinary properties, including flexibility, insulation against heat and noise, and impermeability to water and gases. Cork is tasteless and flavourless, does not conduct electricity and is highly elastic, being able to spring back after being compressed. It is non-biodegradable, being immune to rot, and will last hundreds of years [Endnote 3].

Even more remarkable, cork is self-regenerating. The outer bark can be completely removed from the tree, and if this is done correctly, the tree survives, the bark regrows and in time the process can be repeated over and again.

From the earliest times cork bark was used for its most well-known application: the manufacture of bottle stoppers for sealing wine bottles. Then over the centuries a whole range of new uses evolved, including life jackets, fishing nets, floats, footwear, hats and industrial insulation. Roman legionnaires wore cork-soled sandals, which were spongy and protected their feet when marching on hot, stony roads. The pith helmets worn by Englishmen in India were usually made of cork, because it was light and provided excellent insultation when they went out (with mad dogs) in the mid-day sun.

Cork oaks were useful in other ways, including the timber (which makes good charcoal), and the acorns which are nutritious. In the traditional diets of the Mediterranean and North Africa, dried cork oak acorns were ground into flour and used as a thickening in soups or stews or were mixed with cereals for making bread. Pigs love acorns and for centuries have been taken into the oak woodlands to fatten on acorns at the right time of the year. In modern times a product of pigs fed on cork oak acorns is known as “Black Ham” and has become prized as a delicacy all over Europe.

The foliage of the cork oak is also palatable to stock. This has its pros and cons. Grazing will control and eliminate cork oak seedlings in woodlands where they are not needed, which is useful and costs nothing. However, where seedling recruitment is needed to regenerate and refresh a woodland of old trees, care must be taken to exclude stock until the foliage of the young corkies is out of reach; unless this is done reforestation will fail.

Finally, the cork oak woodlands have two other minor but (in places) important products – edible mushrooms (for example truffles) and selling hunting licenses (for deer and wild boar) to “sportsmen” from the cities.

An aside: the “corky” cricket ball

When I was a kid, we played backyard cricket nearly every day, every summer. However, a “real” cricket ball, the lustrous leather-clad four-piece six-stitcher, was rarely available because of its expense. The six-stitcher was also easily damaged because our rough-and-tumble games were played on concrete pitches or out on the road. The substitute for the six-stitcher was the “corky” – a cricket ball made of a compound of cork and rubber, and painted red. It could be spun but not swung, and they degraded rapidly with use, losing their paint after an over or two and then becoming progressively smaller over time. Every now and again a corky would crack from side-to-side, the result of a full-blooded pull into a neighbouring brick fence. But they were cheap and easily replaced, and a much better fit for cricket than the only other alternative of the day, a worn old tennis ball.

A brand new six stitcher cricket ball – a thing of great beauty with a wonderful “feel” in the hand, especially if you were a fast bowler.

That same compound of cork and rubber still makes up the core of the modern Kookaburra six-stitcher used today in cricket matches all over the world, yet another wonderful product of the cork oak tree.

Back to bark

The thick bark of the cork oak also renders the tree highly fire resistant, enabling the woodlands to withstand even quite hot fires. Not only this, but the foliage of the cork oak is pretty much non-flammable. If you are looking for a tree to plant near the homestead in a bushfire-prone climate, the corky is ideal – it will dampen and survive a fire, as well as being shady and beautiful.

The management of cork oaks to optimize cork production has a long history. Over hundreds of years, the wild forests of dense cork oaks were thinned down to open woodlands with scattered trees, below which pasture was established and sheep and cattle grazed, an approach known today as “agroforestry”.  Genetic improvement is sometimes regarded as a modern concept but over the centuries in cork oak country, new plantings used acorns from the best producing mother trees, and inferior trees were progressively culled.

A superb managed woodland of cork oaks standing over a legume crop

In Spain and Portugal, these cork oak woodlands were mostly privately owned by small landowners who made their (subsistence) living from their herds and flocks, and from cork harvest. The skills and traditions of cork oak silviculture were handed down from father to son, from generation to generation. Old trees were venerated and new young trees planted as required so as to sustain the crop; fire and grazing were carefully managed.

Cork can be harvested from a tree on about a 9-10-year cycle, and harvesting commences once a tree is about 25 years old. Cork harvest is a marvelously skilled operation, using techniques passed down through families for generations. It must be precisely timed just for the short period in the year when the bark can be freed from the trunk with relative ease. It is all done by hand, no machine ever having been invented that can do the job without damaging the precious inner bark. Using a special wide-mouthed, short-handled axe and a pry-bar, the strippers work the corky outer bark off the tree in great cylindrical sheets, later to be pressed flat and dried. Modern strippers also use mini-chainsaws and snippers to make the initial cuts, but the job is still done by human hand, requiring know-how, agility, keen axemanship and strength.

Cork bark stripper at work.

Stack of stripped bark (both photos from Aronson et al)

The bark is usually removed only from the lower trunk, leaving the trees looking strangely undressed, the red inner bark exposed like petticoats (but it later becomes dark, almost black). The months immediately after stripping are a critical time in the management of the cork oak woodlands – fire must be completely excluded until new layers of outer bark regrow. Fortunately, bark regrowth happens quite rapidly, and ten years later the whole operation can be repeated. In many places in Spain, Portugal and north Africa, trees have been stripped every decade for centuries. [Endnote 4]. Once the bark is thick enough, low intensity fires can be run through the woodlands to regenerate pastures and reduce the fire hazard, without damaging the oak trees in the slightest. [Endnote 5].

I won’t go into the manufacture of cork products here, but there are many videos on the internet showing how the strips of bark are processed into various products, such as wine bottle stoppers. [Endnote 6]

The cork industry is facing hard times.

As any of us who enjoy a nice bottle of wine know, the bottles mostly no longer come with corks (well, that is the case with the wine I can afford). All over the world, cork bottle stoppers have been replaced by metal or plastic screw caps. I have a lovely old corkscrew that I purchased in Bordeaux in France about 40 years ago (appropriately, the wooden handle is made from the trunk of a grape vine), but it has pulled no corks now for a long time.

There is also an insidious product on the market these days called Synthetic Cork. This is made from petrochemical-based plastics, hardly something to appeal to “green” shoppers (most of whom, in my experience, drink wine by the vat), but wine producers are happy because the cost of the synthetic cork is a fraction of the cost of tree-grown cork.

There is one bit of good news, however. Champaign makers still use traditional cork stoppers, and the world does not seem to be running out of champaign drinkers. The responsible champaign drinker can even recycle the corks – many wine and liquor stores these days collect used corks and send them off for conversion into other cork products.

Apart from bottle stoppers, other uses are still being found for cork in the modern world, exploiting its wonderful properties. Corkboard flooring is used increasingly around the world, as it provides a soft “feel” under foot, plus excellent heat and noise insulation. Cork is also used as insultation in spacecraft, where its non-flammability is of special value. The good news is that while these are small markets, they are big enough to keep the cork industry’s head above water.

The bad news is that the cork woodlands are in trouble.

As we have seen, cork substitutes have resulted in a decline in the demand for cork from cork oaks. Regrettably, at the same time significant social changes are occurring in cork oak country. Young people these days, perhaps fourth or fifth generation landowners of the small holdings where cork oaks are grown, are tiring of the life of  hard scrabble self-sufficiency and are moving away from rural areas to the cities. This has led to a decline in the care and nurturing of the trees. Moreover, bushfires and droughts are taking their toll and poorly managed grazing is preventing recruitment of young oaks in ancient woodlands. Fires and drought occurred in the past, of course, but then there were people living in the woodlands whose livelihood was tied to the trees, and who knew how to ameliorate or mitigate their impact. The growing demand for ‘black ham’ (made from pigs fed on cork oak acorns) is another factor leading to grazing pressure on the woodlands.

Nobody has much optimism for the survival of the North African cork oak woodlands, where drought is overlaid by massive overgrazing, lack of bushfire control and the cutting of trees for firewood for domestic fuel. It is also possible even that a cork industry based on the traditional natural, but carefully managed woodlands in Portugal and Spain will not survive. At best it faces an uncertain future. This will be a result not only of the falling demand for cork bottle stoppers but because in many places the cork oak woodlands themselves are being converted to cereal cropping or to citrus orchards or timber plantations of pine or eucalypts. This is especially occurring where small family land holdings have been purchased and then amalgamated under corporate ownership.  Timber plantations, in particular, are popular, because they provide assured income for little input and can be harvested mechanically.

To all this can be added the steady migration of retirees and tree huggers from urban England into the cork oak country of rural Portugal. The attraction is obvious: a small rural property in a beautiful, sunny landscape, a 17^th century stone farmhouse, the cost of living a fraction of that back in the UK, freedom from the gloom and danger of modern city life … and room for a pony. Many former smallholdings in the hills of rural Portugal, in the same family for generations, are now a holiday home for Londoners who cannot afford a thatched cottage in the Cotswolds, or a change of life for ex-urban immigrants, very few of whom have any interest in growing cork, or the slightest idea on how to sustainably manage a cork oak woodland [Endnote 7].

But not all is lost.

Fortunately, the tree itself is not endangered. Indeed, the reverse might be the case. In those parts of the world with a Mediterranean climate the cork oak has come to be seen as one of the finest of all ornamental trees. It is easy to grow, tough, fire-resistant, and provides a deep, cool shade nearly all-year around, and is just the shot for those who look for relief on a hot midsummer’s day, or who are concerned about global warming and urban heat islands.

Another promising factor is that, increasingly, cork oak woodlands are being seen as environmentally important, worth conserving in their own right. They protect the soil from erosion in arid countries and help (some people think) to counter global warming by storing carbon.  They represent a unique socio-economic system and are a heritage landscape. This recognition could result in governments or environmental NGOs investing in cork oak woodland conservation and management, replacing traditional family landowners.

There may even be a resurgence in the use of cork bottle stoppers for wine bottles, as problems associated with disposal of plastic stoppers become more worrying.

I am optimistic. The cork oak is one of nature’s wonders and the cork oak woodlands are yet to be fully appreciated internationally.  But their day is coming.

A concluding story: “The Governor’s Oak”

From time to time I have come across some wonderful old cork oaks in botanic gardens around Australia, including the glorious specimen in the Royal Tasmanian Botanic Garden, planted in 1857, and the beauties in the Government House Gardens in Perth. One of the latter was the source of my own cork oak tree. Bear with me while I retell this story for the umpteenth time.

It was about 2010, I think, and I was in the city for an appointment. Having parked under the Concert Hall, I set off  along Adelaide Terrace, dawdling. I had half an hour to kill, and no desire to spend it in a coffee shop. 

Just then, my eye caught a sign on the gate to Government House: the gardens were open, and visitors were welcome. I could not resist, and was soon inside and enjoying myself, doing what I like best, communing with trees. The gardens of Government House are just the place for this, having a splendid variety of trees, many of which date back to the earliest days of the Swan River colony in the 1830s and 40s.

A magnificent Cork Oak in the Government House gardens, Perth.

 I immediately spotted a shapely and elegant cork oak, a real corker, and gazed at it admiringly for several minutes. As I did so, a mischievous idea came to my mind. Checking to see that nobody was watching, I surreptitiously pocketed a handful of the acorns that were lying about under the tree. A year later I germinated one, raised the seedling in a pot and then, with appropriate ceremony, planted it near our cottage at Gwambygine.

Fifteen years later, “The Governor’s Oak” as we call it, is a sturdy little tree, three metres in height and very healthy. The trunk is already clothed in corky bark. It is slow growing …  not by oak standards but compared to the fast-growing native eucalypts that mostly I have planted, and it has had to put up with several very dry years. But cork oaks are long-lived, and hopefully this one will be throwing welcome summer shade a century or more ahead, and (even better) producing acorns for other people to germinate and plant, ensuring the Governor’s Oak lives on.

The Governor’s Oak at Gwambygine – the crown looks thin because although cork oaks are ever-green, they turn yellowish and lose some of their leaves during the winter.

However, I did feel a little guilty about having pinched the acorn, so one day I wrote to the Governor (at that time Kim Beazley) and came clean. He could not have been nicer about it, writing me a lovely letter, and explaining that the parent tree is getting on for 150 years of age, having been planted in 1875. He was happy to hear that one of its progeny had been propagated and that the new tree was in good hands. My guilt was more than assuaged, and I am now able to contemplate my corky with pride and optimism for its future.

Epitaph

A final memory: Ferdinand the Bull, resting in the shade of his favourite cork oak tree, as well I might do when my bullfighting days are over.

 End Notes

1.      Cork Oak Woodland on the Edge (2009) edited by James Aronson, Joao Pereira and Juli Pausas is published by the Society for Ecological Restoration International.

2.      Here is a photograph (by Jack Bradshaw) of the lovely grove of cork oaks at WA’s famous Foresters Wood.

                              Details are available by downloading the Forester’s Wood app.

3.      Although they are basically sterile, occasionally a cork will contain a fungus which reacts with chlorinated compounds that have contaminated the cork-making process or the wine bottling. This causes a reaction that spoils the aroma and taste of the wine,  contaminated bottles being described as “corked”.

4.      There is a wonderful video on cork bark harvesting on the internet:

https://www.youtube.com/watch?v=ztr-RP0XYd8].

5.      The inner bark of the cork oak is also sometimes harvested, as it has a high tannin content, tannin being the key ingredient in leather-making. However, as with the brown mallet tree in Western Australia, stripping the inner bark always kills the tree.  

6.      This is also a very good little film on cork processing, with an optimistic view of the future: 

https://www.youtube.com/watch?v=k_zBkqBTFtE#:~:text=The%20Portuguese%20company%20Corticeira%20Amorim%20is%20the,visited%20Amorim's%20headquarters%20to%20see%20how%20the

7.      I met an American woman once who had been an academic for many years in Oxford and London. She acquired a cottage in rural Portugal and this became their home away from home. ‘We would leave damp, dark, cold, grey England and arrive in Portugal to be greeted by warmth, sunshine, shady oak trees and the smell of orange blossoms” she told me.

Say no more.