RIVER FALLS — The Emerald Ash Borer (EAB) has been responsible for the death and decline of tens of millions of ash trees in North America, according to the USDA, and Pierce County is no stranger to the problem.

EAB is an invasive species of wood-boring beetle that consumes tissues under ash tree bark, killing the tree, the Wisconsin DNR website states. The species was first discovered in Detroit in 2002 and has now spread to 30 states. The species was confirmed to be in River Falls in 2019, which played a part in the city’s creation of the Emerald Ash Borer Community Preparedness Plan in 2019.

The plan states River Falls opted to plant ash trees to replace American Elm due to Dutch Elm Disease, and some boulevards were planted with almost entirely ash trees. Starting in 2004, the city no longer planted ash trees in boulevard tree plantings and have attempted to diversify the city’s tree population. As EAB can only fly ½ mile from the tree they emerge, the high concentration of ash trees in River Falls increased the threat in River Falls.

As of 2019, River Falls had about 2,000 ash trees, which was around 25% of the boulevard tree population. A city-wide removal and replacement of all of the ash trees was estimated at $1,050,000.

“Experience has shown us that after 30 plus years of removal of diseased elms the City still has a few elms on our right of ways and the cost of removal was spread out over many years. The most likely scenario will probably see the City having a spike of activity within the next 2-5 years followed by a lower but steady number of infected trees in subsequent years,” the 2019 plan states.

In July 2023, the city unveiled an Ash Tree Inventory, Condition Assessment, & Management Plan. With 1,451 ash trees being assessed, 730 were trees recommended for removal and 721 recommended for treatment.

“Once a tree is infected with EAB it will begin to decline over a period of 2-3 years. The burden of removing many trees in a short period of time can put a heavy strain on the City’s budget, personnel, and resources. The City can lessen this impact now by preemptively removing a portion of non-infested trees each year. The ash inventory will prioritize the removal of non-infected ash,” the plan states.

Since 2019, the city has done some treatment and removal of ash trees, interim City Forester Troy Connolly of River Falls Public Works said, and they are continuing to evaluate the trees each year and make decisions on whether to treat or remove them.

The removal prioritization from the 2023 plan is as follows:

1. Hazardous trees: Any tree dead or alive that has the potential to entirely or partially fail and impact a target can be considered a hazard.
2. Dead or dying ash trees.
3. Trees with poor structure
4. Trees causing infrastructure damage.
5. Trees planted or growing in undesirable locations.
6. All other trees.

Due to how quickly EAB can wreak havoc on the ash tree population, the city faces a lot of challenges to address the situation before dying trees cause property damage or safety issues.

Associate Professor of Conservation and Environmental Science at UWRF Kevyn Juneau believes there are safety concerns and potential for damage to property as the trees deteriorate, and storms like the city has seen recently can only increase that risk.

“The trees kind of dry, and they become pretty brittle,” Juneau said. “What we’ve been finding is that they will fail unexpectedly. And there’s been some cases where branches have fallen out of trees when the weather’s pretty stable.”

EAB can also enter other areas through firewood, so Juneau said the city has a responsibility to help avoid this any way they can.

The city is aware of these issues, and Connolly said the city has 500 trees budgeted for removal next year. Connolly said there was treatment done this year to all of the downtown ash trees and some other trees outside of that area. While there were plans to treat more trees on the west side of River Falls, deterioration found through the evaluation process pushed them beyond the threshold where treatment may have made a difference in saving the tree.

The treatment option for EAB involves pesticides with a two-year cycle. While pesticides can be successful in saving a tree from EAB, it also comes with some drawbacks. The treatment option can be costly, brings the need for reevaluation after the two-year cycle and Juneau said the species can build resistance to it over time.

“It doesn’t mean we shouldn’t try,” Juneau said. “It just means that we need to recognize that in the face of this invasive species that we need to think of multiple solutions.”

Juneau said if there are trees that have a special value to someone to keep alive, this may work, but city-wide, it may not be a viable option forever. Juneau said there are microscopic, stingless wasps that have been released as a natural predator to EAB, but with the unstable weather in the state, just one of the four species released have settled in.

“We want to keep those trees as best we can, but at some point it’s just not financially possible,” Connolly said.

Connolly said the biggest challenge is the number of hours in a day for staff to remove or treat the trees. As River Falls has no dedicated urban forestry department, it is the responsibility of the Public Works Department to handle the situation.

“All of us streets and parks guys are the ones who go out and deal with trees that we can manage,” Connolly said. “And then, of course, we have a contractor for trees that we can’t take down ourselves if they’re too big or in too bad of a spot.

“It’s a very fine balance between trees and other projects,” Connolly said.

The city grinds all its own stumps and plants its own trees.

River Falls has now faced a pair of tree species disasters in recent memory between the elm and ash trees. Both Juneau and Connolly acknowledged a major contributor to this issue is a lack of tree diversity, but Connolly said the city now has an improved approach to tree planting. The city now has a lengthy list of tree species to select from when planting.

“Had the trees been a good mix, then we wouldn’t be in the situation that we are right now,” Juneau said.

For Juneau, who has a background in invasive species, there does not appear to be too much hope in River Falls or the rest of the continent for the ash tree population.

“When it comes to ash trees, I truly believe that we are witnessing the functional extinction of ash species across the country,” Juneau said. “It’s estimated that about 98% of the trees that become infected with Emerald Ash Borer actually die within six years.”

Juneau said the trees will not entirely go extinct, but the ecosystems will not function like they used to.

Despite this, Juneau said that does not mean the city should stop trying. He said they still have a responsibility to slow the spread and keep trees alive where they can.

With how fast the spread of EAB was, Juneau said it may not have been possible for River Falls to prevent the current situation, but Juneau said he hopes EAB helps the region become more aware of other invasive species before they arrive.

“It takes the whole region to be able to be proactive,” Juneau said. “All it takes is one log to bring it into the area.”