Screw-top wines seal the end of Cork Oak forests

The first Director of this Botanic Garden, Ferdinand von Mueller, was rather fond of Cork Oak, Quercus suber. He planted it throughout the botanic gardens and surrounding Domain, and encouraged its use in regional parks and gardens around Victoria. I imagine he was besotted, as we all are, by its rough beauty and resilience.

I have mentioned Cork Oak in my blog before, but only in passing, through the Iberian Peninsula and regional botanic gardens in Victoria. It deserves it's own post, which it now has, and a rather lengthy one. Which may in part be due to my emerging interest in oaks generally...

The natural distribution of Cork Oak is most probably the Iberian Peninsula, in large parts of Spain and Portugal. Today it grows in seminatural settings (if I can use that term) around the Mediterranean, in north-west Africa and eastward on the northern side through into France and the islands of Corsica, Sardinia and Sicily. One the chief attractions of the species, apart from its beauty and hardiness, is of course the corky bark.

The leaves are tough and leathery, much like the Holm Oak (Quercus ilex) which grows with this species in Portugal and Spain. These leaves remain all year, so there is no autumnal display.

While the Cork Oak not native to the eastern Mediterranean, already by about  300 BCE, the Greek (natural) philosopher Theophrastus reports on it growing in Tyrrhenia (now part of Italy), and on hybrids between it and Turkey Oak (Quercus cerris) in Arcadia (Greece). He writes of the Cork Oak: “The wood is strong, the bark very thick and cracked, like that of the Aleppo pine, save that the cracks are larger … They strip off the bark, and they say that it should all be removed, otherwise the tree deteriorates: it is renewed again in about three years”. And why do they strip off that bark? Well, apart from the apparent benefit it bestows on the health of the tree, to produce cork.

I’ve read of cork being used through the known world (China, Egypt, Babylon and Persia) as a ‘float’ for fishing in 3000 BCE, but closer to the time of Theophrasus there are apparently records of it being used to seal a cask, for footwear and to coat roofs. As a seal for wine bottle or jar, there are records from the first century before the Common Era. By the following century, another natural philosopher, Pliny the Elder, is writing at length about the cork oak in Roman culture, noting that only priests may cut them down.

Today we use (or used to use) the outer bark layer of the Cork Oak in wine bottles, floor covering and sometimes (mostly for tourists) hats. Cork is usually (and most easily) stripped from the tree in late spring and summer, when the plant cells on the inner edge of the cork layer tear without being damaged.

As you will have gathered from Theophrastus, this doesn't kill the tree, making cork harvesting a potentially sustainable industry. Cork has a structure like honeycomb, with cells, as well as the spaces in between, filled with air (although with the carbon dioxide stripped out). So, cork cells work as small sound and heat insulators, absorbing pressure and shocks, as well blocking out gas exchange when compressed inside a bottle neck.

While cork has been harvested for millennia, commercial growing and production of cork from Cork Oak began in Portugal and Spain, where the species grows naturally, about three hundred years ago. It was harvested then, as it is now, with hand axes. Stripping cork is a highly skilled job and the those employed to wield the axe are (apparently) among the highest paid agricultural field workers in the world.

Kyneton Botanical Gardens, 2020

As described on the tourism website for cork-harvesting town of São Marcos da Serra, ‘a beautiful authentic and traditional village in the Central Algarve’ of Portugal:

"The cork strippers (tiradors) work in pairs, one man clambering up the tree while the other stays on the ground. In unison they chop delicately into the dead bark, gauging its thickness by the sound resonating from the steel axe, and carve out door-sized rectangular slabs. The spongy cork peels like an orange, with a crackling, tearing sound, baring the tree's bright yellow, living layer of bark. This paler colour will redden in a day or two; the inner bark will seal itself and take on an opaque, stuccoed look. As the years pass the bark will thicken and darken once again, to reddish mahogany, to chestnut, and back to silvery-charcoal grey."

You can see those colours as you travel around Portugal and Spain, or even the National Arboretum in Canberra, Australia. Although in Canberra, the bark is no longer harvested so the colours are now mostly shades of grey, and black. As this picture from 2014 shows.

When these trees were stripped it was, as in Portugal, repeated every 9-10 years. This younger trunk from a tree in the Mediterranean Garden at Kew Gardens, London, shows a little of the inner red bark.

A new tree will take at least 25 years to be ready for its first harvest and even then, the first stripping produces cork of an irregular structure and too firm to be easily handled. The early harvests are used for flooring and insulation. It takes until the third harvest to produce a cork with an even structure good enough to be used for wine bottles. By the time the tree is 80 years old, 40-60 kilograms of cork can be stripped in a single harvest. With some care, those trees will be productive for 200 or more years, providing at least 20 harvests and perhaps a tonne of raw cork (the equivalent, I gather, of about 65,000 wine bungs).

So, while screw-tops may be better at stopping wine from spoiling (although that, or at least the quality of wine sealed with plastic-coated metal, will be disputed by some), cork production is considered generally good for the environment. In Portugal, the carefully manicured landscape with oak trees and livestock is called a montado, as photographed here in 2017 near Redondo.

The montado is managed to allow local oaks to flourish, while their acorns and shade support grazing animals, and small-scale crops. The leaf fall is retained as humus, good for crops and good for water retention by the soils in the scorching summers. As the demand for cork diminishes worldwide, these finely tuned montados are at risk of collapse, leading (according to WWF) to “increased poverty, more forest fires, loss of biodiversity, and faster desertification”.

There are threats in addition to the growing popularity of screw-capped wines, one (according to the Food and Agriculture Organisation of the United Nations) being the perverse outcome of a Portuguese law passed in the 1970s. The law was introduced to stem the replacement of cork trees by eucalypts. At the time some 200,000 hectares had been transformed into a bastardised version (my terminology, based on visits there) of Australian bushland.

As the FAO put it: “The law states that without permission from the government, it’s illegal to cut down any cork oak in Portugal, dead or alive. A landowner caught clearing a montado pays a steep fine and is barred from using the land for 25 years. The law has helped preserve montados in lean times, but land managers call it too restrictive; they can’t cull sick trees quickly to prevent infections [by Phytophora cinnamomi, following drought and insect stress] from spreading. And although the Portuguese love their cork oaks, most people believe the law would not survive if cork revenues dried up.”

For Australians, the concept of manipulating native species in this way may feel a bit odd, but then Aboriginal farming practices and fire management over tens of thousands of years have produced the  vegetation we try to preserve and conserve today. Fire is also part of the dynamic in the oak forests of Portugal. That country used to produce around 50% of the cork in the world, and Spain just over 30%, but a large fire in Portugal in 2003 destroyed much of their forest leaving Spain as the highest producer today.

Mount Beckworth Scenic Park, 2009

Let me finish by returning to that plantation in the National Arboretum in Canberra. It was the designer of the city of Canberra, Walter Burley Griffin, who saw the potential of cork oak in a climate not unlike that found in Portugal. A shortage of cork during the First World War led to Burley Griffin to source acorns from Melbourne Gardens, from those early plantings of Mueller (but note, not the earliest in Australia*), and in 1916 the first oaks were grown and trialled at Yarralumla Nursery in Canberra. A year later more acorns, this time rom Kyneton, were sent to Canberra, again with the assistance of Burley Griffin.

These too were most likely a result of Mueller’s enthusiasm for the species – his cork oaks can be seen in many regional botanic gardens in Victoria. To establish a commercial crop, many more thousands of trees would be needed so late in the war, a ship left Spain with some 30,000 acorns. That particular ship didn’t make it to Australia but eventually, in 1920, nearly 10,000 cork oaks were planted in eight hectares at Green Hills. In the 1940s, more acorns were sourced from Portugal, Morocco and Madrid.

* Fellow Cork Oak enthusiast, Stuart Read, reminds me (in a comment below, added 17 September 2020) that Mueller wasn't the first to grow Cork Oaks in Australia. William Macarthur brought in Cork Oaks aboard the 'Lord Eldon', in 1817, planting them in Sydney and Parramatta. And Hambledon Cottage near Paramatta has a Cork Oak probably from the 1840s. William Macarthur at Camden Park was also growing Cork Oaks but they didn't take off.
Images: No pictures of flowers or fruit (acorns) today. All my photographs seem to be of the bark - not surprisingly. There were no fruits on the trees in winter when I ventured out in the Melbourne Gardens to photograph a few leaves on the oddly shaped specimen at the top of the stairs down from Hopetoun Lawn to Long Island, and the well-formed tree in The Ian Potter Foundation Children's Garden.