Long branches with notched bark littered the lawn of the Lincoln Park Zoo on Tuesday morning, a yawning sky visible where a thick canopy once stood.

For almost three hours, crews from Fernandez Tree Service hacked away at one of Chicago’s oldest trees, a centuries-old, sprawling bur oak that had reached the end of its life span. The nearly 70-foot giant was here long before the zoo was built in 1868, when the area was just a lakeshore covered with tall grass, and possibly even predating the incorporation of the city of Chicago.

Director of horticulture at Lincoln Park Zoo Katrina Quint said the tree is 250 to 300 years old. The caramel cross-sections of the trunk have diameters of 60 inches.

“It’s a huge hole. I feel that hole,” she told the Tribune, looking at the rubble after the chain saw buzzing stopped.

The massive bur oak has greeted zoo visitors for decades, its arching branches sheltering flamingo island and the primate house. Quint said the tree was part of the white oak family, and had the largest acorns of any oak. Fuzzy caps dropped each fall and coated the patio outside the zoo’s landmark cafe.

Quint said the beloved tree had “deeply-furrowed bark.” She said it was remarkable how long the tree lasted, considering its placement in such an urban setting with so much foot traffic.

Jeff Carter, 61, of Humboldt Park, was a tree-trimmer for about 30 years. He was born and raised in Chicago, and said his friends texted him about the fall of the Lincoln Park Zoo oak. He came to the zoo Tuesday to pay homage.

Staring at the sliced sections of the tree from behind caution tape, he said each cutting has a story.

”Weather, bugs, burns on the bark that heal over, the thickness of a tree ring,” he said. “There’s so much to say about each section of it.”

Quint said she saw the first sign of the tree’s decline in August 2021, when its leaves fell six to eight weeks earlier than normal.

In an effort to save it, she tried root invigoration, a process that involves pushing air into the ground and blowing out the soil near the root zone, using a tool that looks like a power washer. When people stand and walk on the ground, there’s no space left for oxygen and water, which is necessary for the plant to be able to pull up nutrients to feed itself.

The top of the tree was completely dead in August the following year. To Quint, the black branches meant the tree had become a hazard to zoogoers. It was time for the tree to go.

Quint said beyond reaching the end of its long life, extreme back and forth weather patterns may have also contributed to the large white oak’s decline. A bur oak in a natural setting with no climate variability can live up to 400 years.

“Those kinds of patterns do lend themselves to other fungal diseases,” she said. “The roots can rot.”

Passersby stopped and asked Quint if they could take home some wood.

The wood is being divvied up between several artisans to make pieces honoring the tree, Quint said. The zoo will use some of it for children’s playspaces, and potentially as perches for animals or as mulch in enclosures. A big blue truck picked up some pieces to bring to a kiln, so that artists could use it immediately instead of waiting years for it to dry.

One piece is going to the Illinois State Archaeological Survey to do dendrochronology and climate data for the Forest Preserves of Cook County. Another piece is going to Morton Arboretum to do an official aging of the tree.

Quint worked with Morton Arboretum over the winter, taking dormant cuttings of the tree to propagate and graft to woodstock. There are 36 genetic copies of the tree that can now be planted, said Quint.

Quercus macrocarpa, also referred to as mossy-cup oak, is native to Illinois. It has rounded leaves and a majestic shape, said Quint.

Lydia Scott, director of Chicago Region Trees Initiative, emphasized the important role that oak trees play for ecosystems in Illinois, but said they have been fragmented and decimated over the past two centuries.

The Chicago Region Trees Initiative is a collection of communities, individuals, governments and green industry partners who work to protect and improve forest spaces in Chicago.

Scott said that in northeastern Illinois, about 1 million acres of land used to be oak forests. There are only 17% of those oak ecosystems left, and 70% are in private ownership, meaning that they’re not in protected status, she said.

Scott said Illinois is in the Mississippi flyway for bird migration, and that oak trees are important stopping places for birds to rest and find insects to feed on, before continuing on their journey. Chicago Region Trees Initiative leads various teams that meet to talk about restoration projects.

Morton Arboretum’s Robert Fahey wrote about this native species loss in the 2015 Oak Ecosystems Recovery Plan, led by the Chicago Wilderness and the Oak Ecosystems Recovery Working Group. Fahey overlaid 1830s public land survey data with 1939 aerial photography and 2010 analysis to see where oak ecosystems used to exist and where they exist now.

“It’s really important that we educate people about the importance of native oak ecosystems so that those that have native populations on their properties will protect them, and those that don’t will plant native species to help reconnect our fragmented ecosystems,” said Scott.

There is a tree selector tool on the Morton Arboretum website, according to Scott. She said that everyone should try to plant oak trees if they have the space.

And if you don’t, it’s easy to find native companion species to the white oak. You can use the keyword “native,” and customize your search to the space you have available, she said.

At the zoo, people stopped to take photos of the branches in the grass throughout the day.

Susan Geoghegan, of Lincoln Park, said she watched the tree demolition from her high-rise apartment.

She said it makes you think about Chicago history, about where we were, and where we are now.

“It’s a sad day for Chicago,” she said.

Chicago grew up around the tree, Scott said. During its lifetime, the Chicago Fire happened, cafes were built around it and people picnicked underneath it.

“It’s incredible to think about what it’s been able to observe or be involved with as time has passed by,” Scott said. “It’s certainly a testament to the strength and virility of our native species.”

nsalzman@chicagotribune.com