Lincoln Park Zoo is set to remove a massive bur oak

For the next few months, Katrina Quint has one request for Lincoln Park Zoo visitors: look up.

Across from the white-cheeked gibbon enclosure sits a large, sprawling oak tree, about 45 feet tall. As it dies naturally, the tree is going to be removed this spring. There is no disease, but this year the tree produced only a few leaves and its upper branches were “completely dead,” said Quint, the zoo’s director of horticulture.

The tree has potentially been on the site since about 1800, according to Quint’s estimates, based on the diameter of the tree’s trunk, before the incorporation of the city of Chicago. It is the oldest of several large oak trees around which the zoo was built in 1868, Quint said.

The tree can be easily missed, it is similar in height to the tree around it. But upon closer inspection, you can see the huge size of its trunk. “Two people can barely touch with their arms wrapped around the base of a tree,” Quint said.

While many people may not notice the tree regularly, its absence will change the fabric of the landscape, Quint said.

Mary Ann Stott, 74, said she has been visiting the Lincoln Park Zoo since she was 9 months old and is “heartbroken” to see the tree die.

“This tree has just witnessed so much history and so much change,” Stott said.

About 10 years ago, the Lincoln Park Zoo went from simply maintaining its landscape to working toward arboretum status and becoming a community garden, Quint said. In 2019, the zoo received Arboretum status, an accreditation that recognizes the site as a place for monitoring and preserving woody plants.

Part of that transition meant prioritizing the zoo’s existing assets — such as the oaks that account for much of the tree canopy.

In August 2020, the oldest tree shed all its leaves, much too early and a signal to zoo staff that something was wrong. In an effort to save it, they tried to encourage the roots, a process that involves drawing air into the ground and blowing away the soil near the root zone with a tool similar to a power washer. The process aims to loosen soil compaction, which occurs when the soil is compacted to the point where water and nutrients cannot reach the roots. This year the tree produced few leaves.

“This is the natural end of this tree,” said Quint. “It’s so old that unfortunately it won’t last forever. I wish it didn’t happen.”

In addition to age, Quint also said she believes the unpredictable swings in weather over the past five years — overwatering due to spring rains followed by periods of heavy storms and drought during the summer — are factors in the tree’s deterioration.

Quint, who started working at the zoo three years ago, said she rescues acorns dropped from the zoo’s trees. These acorns will be grown to strengthen the tree canopy, part of the zoo’s long-term plan to protect the landscape in the future as the effects of climate change worsen. Thanks to the squirrels’ natural work, the zoo already has about 15 young oaks ranging in age from infancy to 15 years old, she said. There are 40 oak trees growing on the territory of the zoo, including six of the oldest trees

Quint said the zoo rescued six acorns produced by the oak tree, but many more may have fallen from the tree, but that is difficult to confirm. The zoo also hopes to save a few cuttings to grow as well.

Parts of the tree had already been cut due to the storm and for the safety of passing visitors, leaving branches ending in clean cuts hanging over the sidewalk between the white-cheeked gibbon habitat and the zoo’s lawn. The decision to remove the tree entirely was a difficult one, Quint said.

“Once the tree is completely gone, people will notice, and I feel like they haven’t taken the risk to really see how majestic this tree is, or take the time to appreciate it,” Quint said.

There’s no doubt that the oak tree at Lincoln Park Zoo is old, but how old it is is up for debate.

Quintus estimated its age at 250 to 300 years. The number was obtained by measuring the diameter of the tree trunk and comparing it to a chart from the Morton Arboretum.

However, Christy Rawlinson, forest ecologist at the Morton Arboretum, said the use of this chart is no longer recommended and that tree size, especially for older, larger trees, is not an effective predictor of age.

The “quintessential Midwestern oak,” known for its large leaves and mossy acorns, has a possible age of 250 to 300 years, Rawlinson said. “But we’re starting to see the oldest trees of this kind ever found.”

Rawlinson said the only way to tell a tree’s age is to count its rings from a cross-section cut in half, or from a tree core, a pencil-sized piece of wood removed from the tree. Quint said the zoo may take a core sample, but has not yet done so.

The oldest tree that Rawlinson said she found at the Morton Arboretum was planted in 1772. These old historic trees are rare but scattered throughout the city, she said.

“The Lincoln Park Zoo is really in an area that was historically wooded,” she said.

For the past 10 years, Stott’s phone screensaver has been an image of an oak tree in the middle of a cornfield, taken on Randall Road in Batavia.

“To me, the oak tree symbolizes strength, courage and resilience,” she said.

Viridiana Aranga and Jimen Segura, who came from Texas, sat down on a bench under an oak tree to rest on Monday. They said they didn’t notice the tree during their visit, but after reading a small gold plaque placed in front of the tree, they each took a photo of the tree.

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“You have no idea how old the tree is, but it’s really interesting,” said 25-year-old Aranga. “It’s part of history.”

As a gardener and arborist, Kelly Cullison of Round Lake said she can’t help but notice the trees she comes across. She plans to visit the Lincoln Park Zoo in early December to see the tree.

“It’s personally heartbreaking to say goodbye, seeing a long-term decline,” she said.

Callison said she hopes the zoo will honor the tree’s history by preserving its cross-section and displaying it, pointing to tree rings that correspond to important historical events, such as women’s liberation or the year the iPhone was released.

Stott hopes to visit the oak again before spring to “thank it for being such a wonderful tree.”

“I’m going to miss this tree,” Stott said. “And I think if we respected everything, like the trees, like the plants, like all the wildlife that lives here, it would be a whole different world. Sometimes we’re just so busy running that we don’t notice the beauty that’s right in front of us.”

mellis@chicagotribune.com