EVERETT — Dozens of trees towering 70 and 80 feet in the middle of Colby Avenue give the road a stately look in north Everett.

The trees growing between northbound and southbound traffic along nine blocks are deciduous, providing leafy shade in spring and summer.

But they also are a seasonal problem for nearby residents with allergies. The road and bike lanes get littered with leaves and twigs during fall and winter. Some of the trees are too crowded and take root too shallow, damaging the road and sidewalks.

There were 76 trees when the city had two studies done in 2019. Today, 68 still stand.

Everett’s parks department has a plan to replant a tree for each that comes down, whether by storms or because of their health. Its first dip into that one-for-one swap is a demonstration planting scheduled Wednesday and Thursday on the south half of the median at 17th Street.

“We’re not taking the trees down, we’re simply replacing them as they fail,” assistant parks director Kimberly Moore said.

Three are American sycamores. Most of the Colby trees are London planetrees, described as fast growing and capable of reaching 100 feet tall by the Arbor Day Foundation. They also require a lot of maintenance, according to the North Carolina State University extension.

That kind of single species density makes them vulnerable to disease and pests.

All of the trees are estimated between 75 and 85 years old, according to a report by American Forest Management.

The city can’t plant 80-year-old mature trees to replace the ones that fall or are felled. The Colby tree project instead focuses on replenishing the vegetation, possibly over decades.

“We could never replace the amount of canopy cover the trees along Colby are providing,” Moore said.

Urban forests are a way to address climate change through carbon storage and reducing stormwater runoff, in addition to shade from the canopies.

In an October 2021 story, Herald climate change writer Julie Titone reported that Everett’s tree canopy across private and public property was estimated at 25%. National conservation group American Forests recommends a 40% tree canopy.

Everett staff are planting a fagus sylvatica beech, northern pin oak and two American or Jefferson elm trees, all with trunks at least 5 inches wide, at the demonstration site. The intersection will be closed during the work. The cost for the trees was under $10,000, Moore said.

Holly James has lived in the Northwest Neighborhood for 22 years. She said she enjoys the trees and understands the need to remove them as their health and risks dictate.

“We’re torn that we love them, but some of them are sick,” James said. “We have to face the fact that some of them are diseased and sick and dying.”

But she was disappointed the neighborhood association that she heads wasn’t involved more in the plan. James also disagreed with some of the tree species selected for the demonstration and potential plantings.

“I don’t think the replacement plan is biodiverse enough and ecologically aware,” James said. “Will they actually produce shade?”

The North Carolina State University extension describes each of the three species at the demonstration site as good shade trees that can grow around 80 feet tall. The city chose the species based on growing conditions on Colby, having root systems that reach deep instead of disrupting the road and sidewalks, fall color and sight lines for drivers, Moore said. “Supply chain issues” related to the initial size of the plantings also were part of the decision, she said.

People can comment on the trees after they are planted.

“We can still change course if these four trees do not present well,” Moore said.

A count of trees on city property is under way, funded in part by a $40,000 state Department of Natural Resources grant. The tally is starting in south Everett and could cover up to 3,500 trees, Moore said.

The city also is getting software to create a tree inventory that people can review what trees are in city parks and their stormwater benefit, among other data.

Ben Watanabe: 425-339-3037; bwatanabe@heraldnet.com; Twitter: @benwatanabe.