Staff and volunteers from the Morton Arboretum came in groups of four after sunset, fanning out in search of Chicago’s trees. By the time the night was over, nearly 500 had been tagged along downtown city streets.

Members of the Arboretum, 4100 Route 53, in collaboration with the city, placed “value tags” on trees on April 28 in celebration of Arbor Day. Located in Millennium Park, around City Hall and along downtown State Street, among others, the green “tags”—displaying the economic service each individual tree provides throughout a 15-year period—are meant to remind residents of the tree’s environmental benefits to the city.

“This says they also have real measurable value by making contributions to our well-being every day,” said Edith Makra, community trees advocate for the Arboretum, as she pointed to a recently tagged Callery pear tree along Dearborn Street valued at $1,206.

Along with the Arboretum’s tree census, which offers a regional view of trees’ environmental benefits, as previously reported in The Chronicle on Sept. 7, 2010, the Arboretum’s first-ever tree taggings are meant to offer a different perspective of Chicago’s urban forest—one tree at a time.

“The idea is that every tree counts,” Makra explained. “So every tree has value.”

Kirsten Bronoski, Web designer for the Arboretum; Mary Samerdyke, tour guide; Sai Rabichandran, statistical analyst and Makra; arrived in reflective yellow over-vests to locate and tag their designated trees.

The trees’ monetary value was based on trunk diameter, age and location, according to Bronoski. Each tree species was assigned a value based on ways it gives to the environment through pollution removal and other factors. For example, Makra explained that elm trees, which are commonly found in the city, have a rough surface leaf and are better at trapping air pollution than smooth-surfaced tree leaves.

Of the several tree species tagged during the course of the night, including Hybrid elms, Kentucky coffee and Basswood trees, only the Callery pears are flowering.

Hybrid elms were the result of one of the country’s first experiences with invasive species. When the once commonly planted American elm trees succumbed in large numbers to Dutch elm disease, the trees were bred with Chinese elms. This eventually resulted in a strain resistant to the disease known as Hybrid elms, which are located throughout the city, including Dearborn Street.

“I would hope [the tags] make people stop and think about what a tree means literally and what its value is in terms of economics,” Samerdyke said. “But also, what does it mean to us as people?”

As passersby noted the tags on their way through the South Loop, many stopped to read the signs, which will stay posted downtown until mid-May.

“I think it’s wonderful,” said Charlie J. Brown, business consultant visiting from Norfolk, Va. “[The tags] draw your attention to the trees, and you’re [going to] want to find out what it’s all about. So I think it’ll raise awareness. I think it’s a great idea.”