The Park Board’s strategy in its fight against emerald ash borer is changing the city’s tree canopy
The long winter means that Nick Hart and his fellow arborists have less time than usual as they race to get more than 8,000 trees planted this spring.
The tree-planting season, which was supposed to start on April 1 before blizzards pushed it several weeks out, is no joke. The work is slower for Hart and his crew, who are responsible for planting a couple dozen trees in the hustle and bustle of downtown Minneapolis in just one 10-hour day. With others working around the city, the Minneapolis Park and Recreation Board can plant about 250 a day between April and June.
“We’re hand-digging every hole. It can be tedious,” he said.
Forestry officials say the work is worth it. Some of the work is part of the Park Board’s routine replacement of dying trees throughout the city, but 5,000 of those trees are meant to replace ash trees infested by emerald ash borer. Following the infestation’s appearance in 2009, the city’s forestry officials put together an eight-year plan to remove 40,000 ash trees that are vulnerable to the invasive beetle and plant a more diverse mix of trees in their place.
Five years into the plan, officials say the infestation’s growth is slowing as a more diverse tree canopy takes root.
“We describe it as a once-in-a-generation pest problem that’s really altering the look of our public urban forest,” said Ralph Sievert, who directs the Park Board’s forestry department. “The whole idea is, holy cow, if you wait and the beetle population rises, you’re going to have so many trees dying that you’re going to be in trouble.”
Once infected, ash trees begin to crumble, dropping branches and becoming both a nuisance for the Park Board and a safety concern for homeowners. There isn’t a neighborhood that’s safe from the infestation. Of the city’s 87 neighborhoods, Sievert said most are already infected by emerald ash borer.
“But we look at it as if we’ll find it in all the other ones. We just haven’t found it yet,” he said.
The Park Board’s replacement plan has rapidly changed the city’s tree canopy. The population of ash trees, once one of the most common trees in Minneapolis, is dropping, representing just 5 percent of the public tree canopy, according to 2017 data from the Minneapolis Tree Advisory Commission. The Park Board’s forestry department manages hundreds of thousands of trees along roads, in parks and in wooded areas. It totals more trees than Minneapolis residents, Sievert said.
This year Minneapolis arborists will plant more than 8,200 trees, which is down from last year’s abnormally high planting effort of 10,300 trees. The work is funded by a special levy that brings in about $1.7 million annually solely to preserve the city’s tree canopy.
The Park Board staggers the work over the life of the plan, marking, removing and replacing only a portion of a block’s ash trees in a year. Rather than cutting them down and leaving a block bare, Sievert said they like neighborhood canopies to change gradually.
“By the time that you get to year eight, you have some trees that were planted in year one with some growth,” he said.
In place of the ash trees, arborists like Hart and his crew aren’t planting a single tree species, but a laundry list of rarer plants. A newly planted tree must be of a variety that comprises less than 10 percent of a neighborhood’s tree population, so ash and other removed trees get replaced by Kentucky coffee, river birch, London Planetree, Japanese tree lilac and Prairie Horizon alder, among others. Sievert said they plant a few disease-resistant elms, a “full circle” moment for the species that was once decimated by its own invasive tree species, Dutch elm disease.
“It’s a thoughtful way to make sure the next big pest or disease that comes into our area doesn’t totally decimate our forest,” said District 5 Commissioner Steffanie Musich, who serves on the Minneapolis Tree Advisory Commission.
The Park Board buys the trees from commercial nurseries around the country, with some coming from around the state and others coming as far away as Illinois or New York. While Sievert said they get demands for more fruit trees, the Park Board only plants a few hundred each year, as these trees typically don’t last long and cost more to maintain. Forestry officials would rather see larger trees that can hold up to the elements of an urban city.
“We’re constantly looking for cold hardiness, trees that will last through our winters, and we’re having good luck with those,” Sievert said.
Valerie McClannahan, a community forestry project lead with the Department of Natural Resources, works with cities around the state to manage invasive tree species and prepare plans to address them. She said larger cities like Minneapolis are ahead of the curve compared to smaller rural communities.
Ash trees make up roughly 30 percent of the state’s tree canopy, with some cities’ canopies as much as 70 percent ash. Replacing just one tree can cost $4,000 to remove, McClannahan said.
She hopes that cities put in work now to combat the infestation so that its spread across the state will take several decades, giving other communities time to prepare.
“If you imagine the sheer cost of what it’s going to look like, a lot of communities have been putting in efforts to manage the ash that they have, but there are so many communities out there that are still figuring out where to start,” she said.
Meanwhile, Minneapolis is just a few years out from completing its plan to replace its ash trees. Musich, who is serving her second term representing South Minneapolis, said she’s planted a couple hundred trees during her time as a commissioner. She said the work pays it forward to future generations who will have healthy trees to enjoy.
“At least some of those (trees) are going to be around for my kids and for my kids’ kids and their kids to potentially climb. That’s a beautiful thing,” she said.