Milwaukee arborists caring for canopy to stay ahead of climate change

Winter is prime pruning season, and although we’re about to bump into spring, you might still see crews on city streets and boulevards pruning trees. It’s one of the ways the city is working to keep Milwaukee’s urban canopy healthy.

WUWM environmental reporter Susan Bence visited a crew doing some pruning on the Milwaukee’s Northwest Side to learn how they’re adapting to climate change. She spoke with the City of Milwaukee’s Urban Forestry Manager, Randy Krause. He’s been pruning trees for 30 years, and he took over the city’s urban forestry services management in 2019.

He watches a city crew scale trees — some with ropes, others with ladders. They’re lopping off branches from the canopy. Down the street, a truck hoists an arborist up in a bucket to reach a taller, more mature tree.

Krause says the idea is to help the trees sustain the rigors of more severe storms.

“It’s really important — even with the younger trees that we set that structure up properly — so when they grow to mature size, they can withstand higher winds and stronger storms,” he says.

Crews prune trees with the aim of establishing a central leader tree “with smaller lateral leaves that radiate out from that central leader is kind of like the perfect tree,” Krause says.

Today, a crew of 38 apprentices and 44 skilled arborists tend approximately 190,000 trees along Milwaukee streets and boulevards.

“Ways we’ve evolved over the years is we continue to diversify our street tree population, which is really important from the standpoint of maintaining a sustainable urban forest — especially in the face of not only climate change, but also pests, diseases and insects,” Krause says.

Part of the diversification process involves bringing in buckeye, tulip poplar and black gum trees to supplement the North Side’s urban canopy.

“Some of those trees that normally are indigenous a little bit farther south of us, we’re starting to bring in,” Krause says. “We’re experimenting with those trees to see if they’ll grow for us [up here].”

But along the street Krause’s crew is working on, it’s mainly ash trees.

“These are all ash trees along here. We have approximately a little under 26,000 ash trees out on the street, which is about 13% of our overall population,” Krause says.

A nonnative beetle called the emerald ash borer has eaten the life out of ash trees in many areas of the United States. In Wisconsin, the first EAB infestation was detected in 2008.

A year later, Milwaukee started injecting its healthiest and most established ash trees to protect them from the beetle.

Although the treatments were initially going to be a temporary measure, Krause says the city has continued to treat its ash population ever since.

“[Ash trees’] larger canopy provides really important benefits — storm water retention, moderating heat stress through the shade, cleaning the air, cleaning our water,” he says. “So, they contribute a lot to our communities and our environment.”