Suburbs' trees of the future: Morton Arboretum to start regional planting spree in its 100th year

A little-known linden tree so obscure it could stump the average botanist is playing a big role in the Morton Arboretum's 100th anniversary celebration.

The arboretum has selected Zamoyski's linden, named for a Polish nobleman, as its official centennial tree. And it's not just a ceremonial title. The arboretum is bringing the specially cultivated linden into the horticultural mainstream as part of a tree-planting spree across the Chicago region.

The arboretum kicked off the long-haul project in honor of Earth Day and its 100th year by hosting a planting ceremony that added a centennial linden to the grounds of the outdoor museum in Lisle.

The arboretum will plant 3,000 trees - triple its original goal, thanks to a recent donation - throughout Cook, DuPage, Kane, Kendall, Lake, McHenry and Will counties to improve an urban forest threatened by climate change and invasive species.

"We know that the Chicago region needs more trees compared to other metropolitan areas," said Gerard Donnelly, arboretum president and CEO.

The planting campaign focuses on the same seven-county region where the arboretum conducted a 2020 tree census, repeating a survey from a decade earlier. Invasive European buckthorn accounted for 36% of stems in the latest census count. The woody shrub creates dense thickets that block sunlight to a forest's floor, preventing the regeneration of oaks and other native species.

"The forest has changed dramatically in just 10 years' time," Donnelly said. "We know where trees are and which communities of people need the benefits of trees the most."

The census also showed that 23% of the region is covered by tree and shrub canopies, an increase of two percentage points from the last assessment, despite the loss of millions of ash trees felled by the emerald ash borer.

Tree canopy coverage in the city of Chicago, however, fell from 19% to 16%. Underresourced neighborhoods lost more and had fewer trees replaced, said Lydia Scott, director of The Chicago Region Trees Initiative, an arboretum-founded partnership that's managing the planting efforts.

"The goal is to try to get municipalities to about 40% canopy cover, because that's where we start to see some of the climate benefits really come into play," Scott said.

To help put the region closer to that lofty goal, the arboretum will plant nearly 20 different species of trees over three seasons. Scott said 520 will be going into the ground this spring in 16 communities.

Some of the first trees will be planted in Carpentersville, La Grange and Prospect Heights. The rest will be planted in the fall and spring of 2023.

Naperville, Woodridge, Darien and Downers Grove Township are receiving more than 300 trees to replace those destroyed in a tornado that struck neighborhoods almost a year ago in June 2021. The new trees are about an inch and a half in diameter, Scott said.

"We like to get them about that size because they're easy for people to be able to manage on their own," she said.

The Zamoyski's linden tree earned the centennial designation for some distinctive features: a tall, graceful shape and relative resistance to Japanese beetles.

On a search for rare trees in the late 1930s, John van Gemert, the arboretum's propagator, sent back scions, or small twigs, of Zamoyski's linden from his trip to the Kórnik Arboretum in Poland. Arboretum visitors can admire one of the resulting trees, a towering specimen in front of the research and administration building. In the spring, it produces cream-colored flowering buds.

"It's not really known to horticulture here in the United States," Donnelly said.

But a number of centennial lindens will be planted for the milestone year. The trees were produced from the arboretum's mature Zamoyski's linden.

The arboretum is funding the "Centennial Tree Planting Initiative" entirely with philanthropic dollars. A major gift from Susan and Stephen Baird, president and CEO of Baird & Warner, allowed the arboretum to increase the total number of trees planted from to 3,000 instead of 1,000.