March’s Tree of the Month: Cork Oak

Our stately cork oak stands in Section K of our historic East Campus, with major branches stretching out over the Andrew B. Hammond family monument.
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Perhaps no singular tree in the entire Cypress Lawn Arboretum collection is so grand as this – unassuming, still, in the lee of the ever-so-stately Hammond family monument, its gargantuan branches reach for the sun in all directions. Its evergreen leaves catch the afternoon light and flicker delicately on the eastward Pacific breeze. Its mighty trunk stands resolutely, a comforting presence that is simply always there.

The cork oak, or Quercus suber in the scientific Latin, is beyond a doubt, a tree of wonders. Hailing from the ancient Mediterranean basin of southwestern Europe and northwestern Africa, the cork oak has — since time immemorial — been a species of cultural significance and use all across the globe. Even the ancient Romans utilized parts of this tree to fashion their sandals and to buoy their fishing nets in the Mediterranean Sea. From the culture of antiquity, and on to the present day, the cork oak has been with us, tethered to human progress.

This cork oak specimen is well over a century in age, and was likely one of the first trees planted by our founder, Hamden Noble, in the formative days of Cypress Lawn Memorial Park.
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The biology and evolutionary history of Quercus suber, in of itself, makes this tree a species worth celebrating. Having lived in the Mediterranean region since the Tertiary Period several million years ago, the cork oak is an absolute survivor, tolerant of a changing climate and resilient in the face of environmental catastrophe. This species is what is known as a pyrophyte, meaning that it is adapted to withstand major fires. Its bark, thick and spongy (which has other benefits we shall see), can tolerate intense burn events. Even when most of the foliage has been scorched from the canopy, Quercus suber is known to resprout in the aftermath of fire and once again live and thrive. In this way, it is among the most fire-tolerant tree species on Earth.

The evergreen leaves of Quercus suber can survive as photosynthetic machines - literally the solar panels of nature! - for around two years. The cork oak is regularly shedding some of its older leaves throughout the seasons.
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Another adaptation the cork oak uses during difficult environmental conditions is a trait that it shares with all kinds of oak trees, of which there are 600 extant (still living, the opposite of extinct) species globally. This evolution is the tap root, which is a single major root that penetrates deep into the soil in order to reach the subterranean water table, where moisture is much more available than it is above this level. When an acorn first germinates, it uses most of the energy stored in the seed to drive a solitary root down into the earth, searching for the water table. Once the oak finds this water, it is able to hydrate mostly from this source for the majority of its lifetime. This adaptation allows for oak trees, and especially Quercus suber, to thrive in drought conditions. This mechanism for survival has given the cork oak the ability to withstand a drying climate in the Mediterranean basin over the recent geologic past.

Much like our native Californian coast live oak (Quercus agrifolia), the leaves of the cork oak are not shed annually in the fall, which is a life history trait of many other oaks, which go dormant in the winter — or are deciduous. Instead, the evergreen Quercus suber will always be shedding just a few leaves on a continuous basis, as they age and lose productivity for capturing energy from the sun. The lifespan of any one leaf is typically about two years, and the ground underneath a mature cork oak will most assuredly always have a scattering of fallen leaves around it. These dead leaves even help the cork oak to survive in the long term, as tannins and other secondary chemicals in the decomposing foliage act to suppress the germination and growth of other plants. Thus, the cork oak has evolved multifaceted strategies to live and thrive in diverse and challenging climatic conditions.

The fire-resilient bark of the cork oak is the primary feature of this tree that has linked it to human culture and progress since prehistoric times. Both an evolutionary marvel and a highly versatile and renewable product, the cork of Quercus suber is a true gift wrought by nature.
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The cultural relationship of cork oaks with human civilization is deeply rooted, much like the trees themselves. In the montados of Portugal and Spain, these trees are grown today in open pastoral groves, which operate as multifaceted agricultural landscapes that generate a variety of crops and support a wide biodiversity of native understory species. The first and foremost crop of the famed montados is what gives Quercus suber its common name – cork!  The bark of the cork oak is the traditional source material used to stopper wine bottles and also has utility in corkboards, in the interior of cricket balls, in handbags, and several other cork-based products. Fortunately, the bark of these magnificent trees can be harvested once every nine years, will regrow without threatening the living being, and is considered to be a renewable resource.  Throughout the Portuguese montados of the Douro River Valley, specialized harvesters carefully separate the bark from cork oaks in large slabs with a small axe, a traditional agroforestry practice that has supported rural communities in Portugal for generations.  Throughout the country, there are strict laws for regulating harvest practice, including the height to which bark may be removed, the recurring interval of harvest, and other policies that protect both the healthy trees and the cork as a sustainable cultural resource.

While standing at the base of the girthy trunk of our ancient cork oak, a look up into the canopy will surely give you a feeling of wonder, an awe-inspiring sense of connection and kinship with this majestic living being. Don’t be afraid to touch - it’s bark is tougher than it’s bite!
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In parts of both the Portuguese Douro River Valley and the Napa Valley (a bit closer to home here at Cypress Lawn), grape orchards are often planted in tandem with cork oak groves. These two-product agricultural landscapes allow farmers to source both their wine and the corks that stopper each bottle from the very same field!  Grapes of the port wine industry are often grown in the partial shade of cork oaks and are then transported by barge down the Douro River for eventual barrel-aging in the wine-houses of Porto, where the river mouth opens to the Atlantic. Some of these barrels are even made from cork oak wood. Of course, at bottling time, the story comes full circle as a small piece of a tree from the original grape orchard is used to seal the port wine until it is ready for drinking! Thus, the cork oak is indelibly linked to the global wine industry.

The ponderous branches of the cork oak frame the elegant Niebaum family monument, a reminder of the living legacy, of people entwined with plants, that is so deeply rooted in our history here at Cypress Lawn Arboretum.
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On our grounds here at Cypress Lawn, there is a meaningful link between Quercus suber and the realm of viticulture.  Several vintners, including Raymond Signorello, Gustave Niebaum, and Alfred Tubbs, rest in peace mere steps from our singular cork oak specimen.  Signorello’s monument includes a marble cameo of Bacchus, the Roman god of wine and agriculture, a subtle reminder of the ancient connection between human spirituality, wine, and the mighty cork oak.  While the original planting plan of our founder Hamden Noble was lost to history in the great San Francisco earthquake fire of 1906, one can only imagine that it was a part of Noble’s original vision to afford California’s resident winemakers the opportunity to be laid to rest in the shade of a stalwart cork oak, connecting them to their life’s work even from beyond the veil.

Just opposite the main drive through Cypress Lawn, with perhaps the best perpetual view of our cork oak, lies the family of Gustave Ferdinand Niebaum (1842-1908). This Finnish-born sea captain spent the latter years of his life devoted to wine-making in the Napa Valley, where his 1000-acre estate today still thrives as the modern Inglenook Vineyards.
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At the Arboretum, we hope to embrace and celebrate this underlying significance of the relationship between one of our specimen trees and the lives of our decedents.

In honor of this connection, future wine tasting ceremonies will be held at the conclusion of “Tree Tour” community events in the shade of our very own cork oak. Please feel free to join us and commemorate this special kinship between people and plants by uncorking a bottle and raising a glass!