New trees offset impacts of the emerald ash borer

Boulder County Parks and Open Space recently completed several planting projects to offset canopy loss on open space property caused by the emerald ash borer. County staff and volunteers planted 52 new trees at four trailheads throughout the county, including at the Niwot Loop and Lefthand Valley Grange Trailheads.

Funding for the project was provided, in part, by a $1,500 grant that Boulder County received from the Colorado Tree Coalition (CTC), a nonprofit that works with commercial and municipal arborists to preserve, renew, and enhance community forests. Since 1991, the CTC has awarded 528 grants resulting in more than 75,000 trees being planted throughout Colorado.

Mary Tiernan, Urban Forestry Resource Specialist with Boulder County Parks and Open Space, said that the CTC has done a lot of work in recent years in terms of emerald ash borer response, specifically helping people plan and respond after the beetle has come through an area.

The emerald ash borer, a non-native species, was first identified in Boulder County in September 2013. The larvae of this shiny, green beetle kill ash trees of the Fraxinus genus by boring into the tree and feeding on its inner bark, disrupting the tree's ability to transport nutrients and water.

Colorado's native ash trees are popular ornamental trees, with the Colorado Department of Agriculture estimating there are around 1.45 million ash trees in the Denver Metro area alone.

According to Tiernan, Boulder County has taken out approximately 200 ash trees in the last five to 10 years as well as running an extensive informational campaign to help educate homeowners on how to treat their ash trees to stave off the emerald ash borer.

The county also facilitated an ash adoption program that resulted in 66 permits to treat over 200 ash trees in the Boulder County Right of Way. The program, which was taken over by the BOCO Transportation Department in 2019, ensures that these ash trees will continue to be treated to protect them against the emerald ash borer for the life of the tree.

And while all these efforts helped mitigate the spread of the emerald ash borer, Tiernan said the county is now working to offset the aftermath of the lost ash trees.

"The goal [of the planting project] was to get some of that canopy back on open space," she said.

Tiernan said this round of the planting project was mainly focused on planting trees at trailhead areas to provide shade for users and as a habitat for wildlife.

The 52 trees that were planted range in size from larger balled-and-burlapped trees (where the bottom of the tree has been cut out of the ground and wrapped in wire caging and burlap) to smaller trees with a root ball the size of a basketball. Tiernan said the average cost per tree is between $100-500 depending on the size of the plant.

"We focus more on replacing the canopy at the trailheads. For trees that died in more open space areas, if there is not a safety concern, we let that tree die. That's very intentional as it creates amazing habitat," said Tiernan, who pointed out that a large dead tree is often utilized by birds and other wildlife.

"We're trying to find a balance between a nice, manicured landscape versus a totally natural landscape," she said.

And for the choice of what new trees to plant, Tiernan said the other focus was on diversity. Instead of planting a single type of tree, they opted to plant at least six different species, in the hope of preventing another mass die-off as historically witnessed by the widespread death of the American elm or chestnut and, now, the ash tree.

"All over the Front Range, people's goal is to plant a whole array of different types of trees so we don't have another issue like this happen again," said Tiernan.

The Niwot Loop Trailhead received three new Douglas hawthorn trees. The trailhead area around Left Hand Grange Park is now home to a newly planted mix of crusader hawthorn, autumn brilliance serviceberry, shadblow serviceberry, eastern red cedar and American plum.

The newly planted trees will get a good headstart on life with ongoing maintenance from Boulder County Parks and Open Space staff, including watering, pruning and mulching. For trees planted in places where there is no readily accessible irrigation, a seasonal worker will continue to water the small trees for five to 10 years or until the county's senior arborist says they are established enough to survive on their own.

"We're very intentional about all our planting and planning to make sure that the tree will be cared for after we put it in the ground," said Tiernan.

And while the CTC grant and the recently completed planting project will certainly help with lost ash tree replacement, Tiernan said that this is all part of a continuous management plan to put the right tree in the right place and make sure that the trees are growing naturally where they are best suited to thrive.

"It's really an ongoing effort to try to cultivate the healthiest canopy we can for users, wildlife, and long-term sustainability," she said.