From the UC Davis Arboretum and Public Garden and UC Davis News

On May 30, 2024, under the shade of the UC Davis Arboretum’s 80-plus-year-old cork oak grove, a rarely seen exhibition of cork harvesting took place. This traditional practice, unfamiliar to most Americans, involves the careful stripping of a cork oak’s outer bark without harming the tree. Commonly performed by skilled craftspeople in Portugal and Spain, the demonstration was organized for students in the “Technology and Winery Systems” (VEN 135) class, regional wine industry stakeholders, and various campus affiliates.

Arranged by Cork Supply, the UC Davis Department of Viticulture and Enology, and the UC Davis Arboretum and Public Garden, the program provided a unique learning experience for attendees and educational outcomes extending beyond the event itself.

“Cork is a very important to our students,” said David Block, professor of viticulture and enology. “Having the opportunity to see the cork trees harvested right here, is really a unique experience. I am very happy that we were able to do this.”

For the UC Davis Arboretum and Public Garden, the event highlighted how managing the campus environment as a living museum supports multiple educational opportunities for students and the community. “Our strategic initiative, the UC Davis GATEways Project, connects our gardens and landscapes with the university's academic mission. This cork oak harvest is a perfect example of that commitment," said Kathleen Socolofsky, assistant vice chancellor and director of the UC Davis Arboretum and Public Garden.

Campus oak connection

The UC Davis campus boasts a rich history with oaks. Of the 25,000-plus trees in the Arboretum and Public Garden’s care, over 6,000 are oaks and 532 of those are cork oaks. Much of the campus’s incredible cork oak inventory was planted during World War II to address a national cork shortage. Today, cork oaks are one of the 109 kinds of oaks thriving at UC Davis. The diverse collection is now nationally accredited through the American Public Gardens Association Plant Collections Network. 

“We thought long and hard about the prospect of bark being removed from a heritage cork oak, but the decision became easier knowing we'd be working with the best people in the world, at the right time of year,” said Emily Griswold, director of GATEways horticulture and teaching gardens at the UC Davis Arboretum and Public Garden. “It's an important use of our collections to see them used for educational purposes in this way."

About the harvest

Two professional cork harvesters from Portugal demonstrated the process of stripping the tree’s bark for approximately 100 attendees. Throughout the exhibition, Greg Hirson, global director innovation for Cork Supply and UC Davis Viticulture and Enology alumni, answered questions and interpreted the activity of the experts in real time.

Similar to how a harvest happens in their home country, the team worked as a pair, relying solely on hand-axes to remove the tree’s outer layer of cork bark. Documented as one of the highest-paid agricultural jobs in the world for good reason, the delicate work of these experts is done without any automation between mid-May and the end of August – the active growing season for cork oaks, and the main reason why the harvest does not damage the tree’s health.

Upon removal of one of the sheets of cork, the audience was shown the layer of moisture coating the "belly" of the bark. This sign confirmed that the selected oak was in the right stage for harvesting.

Cork as a renewable resource

"Each cut must be made with care to ensure the tree remains healthy and can continue to produce cork,” said Frederico Mayer, purchasing director for Cork Supply. “A cork tree’s first harvest is not suitable for producing fine cork products like wine closures. It’s not until a cork oak’s third harvest, 18 years after the first, that you get bark that’s almost like vanilla ice cream.”

Cork oaks grow a thin layer of bark every year as a result of their unique genetic makeup. Post bark removal, the trees take about 9 years for their bark to become thick enough to harvest again. Over the course of a cork oak’s 150 to 200-year lifespan, a single tree can be harvested upwards of 15 times, exemplifying cork as a renewable resource. 

“There’s a misunderstanding that trees get cut down to make cork,” said Anna Brittain, executive director of Napa Green, a non-profit that performs sustainability and climate-action certifications for vineyards and wineries. “Cork is inarguably the most sustainable closure…and climate positive.”

Future plans

Could another harvest be planned in the future? “It is possible,” said Griswold. “In the meantime, we hope everyone visits this tree over the coming years to witness the transformation of the bark’s color and texture as it regenerates.”

Temporary signage is now on display by the harvested tree to explain its surprising appearance, with plans for permanent interpretive signage in development. UC Davis academics interested in obtaining pieces of the harvested cork for teaching or research purposes are encouraged to contact the Arboretum and Public Garden for more information.