A big old tree speaks of history. Somehow, as cities rise, roads are paved and widened, buildings are torn down and replaced, as the very atmosphere of the earth is changing, a few majestic green giants survive.
Kris Bachtell loves big old trees and he knows many of them. As vice president for collections and horticulture at The Morton Arboretum in Lisle, he works among maples and elms that were planted a century ago when the 1,700-acre public garden was new and grand oaks that were already full-grown back then. He values old trees not only for the human history they have lived through but for the good that big trees do.
“Large, mature trees are the ones that provide the most benefits for people, such as shade, cooling, capturing rainwater, clearing air pollution, and improving mental health,” he said. “They produce more economic benefits, such as higher property values. And they support more wildlife.”
Bachtell keeps a lookout for surviving heritage trees: a grand old American elm squeezed into a narrow parkway in Naperville; a huge slippery elm, another native species, in a Lemont churchyard; a cottonwood that dates back before the construction of Comiskey Park; an Asian elm at the Arboretum that gave rise to the successful Accolade
elm cultivar that has been planted in cities around the world.
Others look too. The Chicago Region Trees Initiative, the Arboretum’s urban and community forestry program, invites everyone to contribute to tree history through the Witness Tree Project (mortonarb.org/witness-trees) to find and map surviving trees that were used as markers when Illinois was first surveyed in the 1830s and 1840s.
Many historic trees have been lost. They may be cut down to make way for buildings and roads, or lost to infestations such as emerald ash borer and Dutch elm disease. Trees along streets suffer from winter after winter of road salt and other de-icing chemicals. Droughts take a toll.
But some trees die because their time has come. “Trees have a lifetime,” Bachtell said. “They don’t live forever.”
One heartbreaker was a huge, widely beloved bur oak at the Lincoln Park Zoo that had to be cut down in 2023 because it was mostly dead. It was one of several oak trees that were already growing when the zoo was built in 1868. After the tree was felled, Arboretum researchers dated it to 1857 based on the annual growth rings in its wood.
Though the tree is gone, its genes are not, because the zoo’s horticulturists took cuttings from its remaining live branches. Expert growers at the Arboretum grafted the cuttings onto new oak rootstocks and potted them up to begin growing into saplings. The Arboretum has also grown seedlings from other historic trees, such as a 250-year-old oak that was cut down in 2016 in Naperville.
These trees are propagated for their history and their meaning for people. “An old tree is not necessarily genetically superior because it’s lived a long time,” Bachtell said. “It may just have been lucky.”
None of the young Lincoln Park bur oak trees are old enough yet to be planted in the ground, but more than 20 are being nurtured at the Arboretum and the zoo, according to Maureen Leahy, the zoo’s vice president of animal care and horticulture. Within the next few years a new young sapling — with the genetic and historical legacy of that grand old oak — will be taking root among the animals.
An old tree’s history can live on in another way: Scientists can learn from its growth rings. The rings not only tell the age of the tree, but can provide important data about the climate it has lived through during its many decades of life. A fat ring records a year with abundant rainfall that helped the tree grow fast; a skinny ring indicates a dry year. Such dendrological data is important to climate research.
Slabs from the Lincoln Park Zoo oak were given to the Illinois State Archeological Survey and added to the Arboretum’s Wood Archive, a collection of sections saved from trees that had to be felled from its tree collections and natural areas.
As useful as it is to save genes and data from heritage trees, Bachtell would prefer to save the trees. “If you have a big old tree, take care of it,” he said. Have it inspected periodically by a trained tree professional to check for problems, because “old trees accumulate troubles, and all living organisms have vulnerabilities.”
Allow it space, giving its roots room to spread out. Cover the roots with a layer of mulch. Protect the tree from construction damage. Water it during droughts.
“Show it respect and celebrate it,” he said. “That tree has lived through a lot of history.”
For tree and plant advice, contact the Plant Clinic at The Morton Arboretum (630-719-2424, mortonarb.org/plant-clinic, or plantclinic@mortonarb.org). Beth Botts is a staff writer at the Arboretum.