Davenport arborist Chris Johnson's eyes widened, and he had to take a step back as he tried to explain the effect of the emerald ash borer to members of the Davenport City Council.

The tiny, green invasive species originating from Asia was discovered in Rock Island County in 2013, but it was suspected to have been in the area for six to seven years prior. Two years later, it surfaced in Davenport.

Now, the ash borer is damaging trees at an alarming rate with removal of hazardous and unhealthy ash trees more than tripling since its discovery in Davenport.

"Once the infestations kind of bloom and explode, you find it all the time," Johnson said. "That's the case that's going on now with all of our ash removal. We're essentially finding it in every ash tree we remove."

The city's forestry program is funded mostly through its capital improvement plan, and the city conducted a tree inventory from 2011 to 2013 in recognition of a potential problem.

It wasn't until 2015 that the city began removing trees. But in that year, 152 out of more than 3,600 ash trees were replaced.

This year, the city has planned to remove 500 ash trees from right of ways, parks and golf courses from its inventory of a little more than 3,000 ash trees.

The idea, however, is to spread out removal so areas don't become too sparse.

"The goal is to not hit any spot or specific ward too heavily any given year," Johnson said. "We don't want to deforest any whole ward or area."

One of the biggest looming issues lies on private property.

For unhealthy trees on private property, Johnson said the city has a nuisance abatement program, but because of the ash borer's effects, it will be unenforceable.

"If the tree is hazardous, we try to force the citizen, homeowner or property owner to remove that hazardous tree," Johnson said. "The problem with this is it's going to be such an impact that it's almost like a bomb going off."

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Although the city hasn't been purchasing ash trees, private property owners have been buying them at nurseries since disease began plaguing the American elm.

Johnson said that in many cases two ash trees were planted for every elm.

"I think the private property ash population percentage-wise is far higher than we ever had," Johnson said.

For the number of private trees, Johnson said, removal would cost in the hundreds of millions of dollars.

Johnson said chemical treatment is a viable option for private property owners, but not for the city because of the size of its trees.

Regardless of which way the city and private property owners go, it will be an ongoing problem.

"The problem with the treatment is you are treating for the life of the tree," Johnson said. "You can't stop treating because that chemical will eventually get out of the tree. As long as there is ash borer population, the bug is going to reinfest the tree."