Tallying the zoo’s trees chronicles historic and current landscape and shapes plantings for the future.
Massive branches that arch overhead, bright flowers in spring, cooling green shade on a summer day: So much of the pleasure of a stroll through Lincoln Park Zoo comes from the majesty and grace of its trees.
Along a path, you may pass new saplings and grand old giants. Near the Helen Brach Primate House is one huge bur oak estimated to be 220 years old; the trunk is so wide that “it would take three people to hug it,” says Joe Rothleutner, director of horticulture. The tree was already broad and shady when the zoo was founded 150 years ago.
When this and other nearby oaks were young, they sprouted from acorns in dunes along the wild shoreline of Lake Michigan. By the time upstart Chicago decided it needed a park and a zoo, these trees were large enough to be valued features of the landscape. Around them, dunes became lawns, new animal noises filled the air, buildings rose, paths were paved, and hundreds more trees were planted.
The zoo now has about 1,500 trees of 300 types, according to a new tree inventory conducted by the horticulture staff. They include nine kinds of oaks, seven of them Chicago-area native species.
“We wanted to understand all the different kinds of trees we have and what we need to do for them,” says Rothleutner. Reliable plant records only go back to 2009, so every tree from Nature Boardwalk to Walter Family Arctic Tundra had to be visited, identified, and measured.
Now there’s a database where the lives and health of the trees can be monitored, in much the same way that the zoo tracks its animals. “Some of these trees will still be living in 100 or 150 years,” Rothleutner says. “And preventative care is important.”
He and Abby Lorenz, manager of plant records and horticulture programs, are using the data to guide a greater investment in science-based care for existing trees and planting for the future. Preserving the zoo’s historic trees requires extra measures such as pruning to remove dead or damaged limbs and fungicide treatments to hold off disease. “Medical bills tend to go up for all of us as we get older,” he says.
The inventory also helps them plan what trees to plant. No tree lives forever, and young trees must be added to continuously renew the tree canopy. But they need to be carefully chosen.
It’s critical not to plant too many of one kind, like the American elms that once lined parks and streets, easy prey for the Dutch elm disease that nearly annihilated them. To avoid that, the zoo plants many different species in the hope that no matter what challenges its trees face in the future, some will survive.
The historic oaks on the South Lawn have already seen the world’s climate change. Trees planted today will live to see even more changes—hotter summers, more drought, bigger storms, invasive insects, diseases, and new hazards. “It’s hard to anticipate what’s going to happen,” Rothleutner says. “Our only real safeguard is to plant a wide variety of trees.”
A northern catalpa tree stands just east of the zoo parking lot.
New plantings include not only native species but hardy trees from around the world, such as katsura, zelkova, and ginkgo trees from Asia. More flowering trees are being added to enrich the spring display.
Where possible, Rothleutner and his staff choose trees that suggest the stories of nearby animals. No African tree could survive a Chicago winter, but near Regenstein African Journey there’s a tropical feeling in the huge leaves of an umbrella magnolia, a tree from the Appalachian Mountains.
Trees live long, and in a century the umbrella magnolia may still stand while the zoo continues to grow and evolve. One thing is sure: With foresight and care for its trees, the zoo will still be green.
posted from Lincoln Park Zoo news