Just when we thought the West’s reeling forests could not endure another scourge, say hello to the emerald ash borer. Most western residents are familiar with the mountain pine beetle which, according to numerous sources, has since 2013 infested the pine forests of all 19 western states and Canada. 88 million acres have been affected, and the beetle has an upwards of 90 percent kill rate.

“People talk about mountain pine beetle being bad, but this is much worse because the mountain pine beetle is moving through its natural environment. Eventually the forests will re-stabilize. This is very different,” says Denver City Forester Rob Davis.   

According to Davis, the emerald ash borer was found in Boulder, Colorado, in 2013. Most likely, though, it arrived in 2010 or 2009. By 2015, the entire city was infested. The incubation period is such that it takes a few seasons for the bug’s presence to be known. Once it’s apparent, though, the infestation is in full swing and the bugs’ population growth can be exponential.

The bug is not native, and that makes dealing with it much more challenging.

“They found emerald ash borer in 2003 in Detroit,” Davis says. “They find this bug, and it’s just wiping out ash trees all over. No one knows what it is; it’s never been seen before. They traced it back to Asia where it exists there naturally. It’s in check in nature there.”

Davis says ash on this continent are not evolved to cope with the pest. What foresters in the U.S. and Canada have on their hands is an introduced predator with a massive supply of unguarded food to sustain it.

Fortunately, Denver’s urban canopy is diverse—only about 15 to 17 percent of park and right-of-way trees are ash. It seems reasonable these days to have a diverse canopy, but monoculture used to be the name of the game.

“The field of urban forestry is about 25 years old,” says Sara Davis, Denver’s Urban Forestry Program Manager. “And the first big lesson in diversity was learned with Dutch elm disease as it rolled through the Midwest. You had huge monocultures—entire cities planted with just the American elm—and they were all of a sudden all dead of the same thing all at once.”

The city’s planting plan is more complicated than a rule-of-thumb system.

“We try to diversify our palette as much as we can which can be really challenging in Colorado because of our weather conditions and soils and that sort of thing,” says Rob Davis. “We try for 10/20/30: no more than 10 percent of one species, 20 percent of one genus and 30 percent of one family.”

What private homeowners do is another matter. Although you need a permit to plant in the right of way, many people are unaware and have planted to suit their desires.

Who’s responsible for maintaining, pruning and removing right-of-way trees can be a very contentious topic. These trees are the property of the city, no matter who plants them, but maintenance and removal is the responsibility of the landowner.

“Back in the early 1900s the code said everybody’s got the duty to plant trees, and everybody has the duty to maintain their city tree,” says Rob Davis. “It was the civic pride movement. Denver had no trees, and the strategy of the city was, ‘okay, we’re all going to do this together.’ Denver’s held that forever.”

To assess the potential impact of the emerald ash borer on the city’s park and street trees, surveying began in late 2014. Of the city’s 76,000 park trees, 6,000 are ash, as are 15 to 17 percent of the 200,000 street trees. That could mean Denver residents will have to deal with anywhere from 30,000 to 34,000 sick curbside ash. The private property numbers are more staggering: with millions of trees citywide, the U.S. Forest Service estimates there are roughly 330,000 ash in the city. 

“There’s a quarantine in place preventing the removal of firewood from Boulder, but there are no gates. And where does all the traffic from Boulder flow? Right down 36 to Denver. The idea of EAB being citywide in Boulder but not yet having taken root here seems impossible if you look at how it’s moved everywhere else.”

To prepare for the borer’s arrival, this May the city is launching a proactive and educational tree treatment and planting campaign. The exact launch date is to be determined. 

“The campaign will be called Be a Smart Ash,” says Sara Davis. “The idea was to have a campaign that is witty and fun and encourages people to learn more. [Starting with] the 2015 budget we were given $150,000 a year for five years.”

The city has contracted Ground Floor Media (groundfloormedia.com) of Denver to manage the campaign.

In addition to the media campaign, the city is planning an outward-facing website that will show the exact location of all right-of-way ash in the city. The presence of any private-property ash will be noted by a dot on the property’s dwelling. The website will also make available the benefits provided by the particular tree—benefits such as cooling savings, aesthetic value, air filtration, rainwater capture, etc.

As for what will happen to the trees themselves, the city is formulating a ten-year plan that will include chemical tree treatments, removal of dead or unhealthy trees (followed with replanting), and planting of new tree species in available space now. Tree planting ramps up this spring. 

After the initial treatments, the city will turn right-of-way ash back to homeowners who will be faced with a decision: either treat or remove their ash. Post city-managed treatment, any treatment or removal costs must be borne by the property owner. 

The overall aim is proactivity. In the end, says Sara Davis, the goal is “maintaining citywide canopy cover.”

Estimates on the cost of treatments, pruning and removal vary widely depending on the health and size of the tree and its location on the property, but bills can be quite large. According to homeadvisor.com, “The average national tree removal cost is $650, though homeowners can spend anywhere between $75 and $1,500 on the expenditure.” 

To help with the planting and outreach efforts, the city has partnered with The Park People (theparkpeople.org), an organization founded in 1969 with the expressed aim of raising private funds to support Denver’s parks.  “We will mostly be involved with the Emerald Ash Borer on the planting side of things,” says The Park People Executive Director Kim Yuan-Farrell. “Denver Forestry is hoping we can handle as many of the plantings as is possible for this and coming years so they can focus much of their efforts on the treatment and removal side of things.”

Yuan-Farrell says Denver Forestry has funding for replacement right-of-way trees. That funding will support the The Park People’s efforts. The Park People will channel people to their Denver Digs Trees program, a program that uses The Park People’s buying power to provide an array of free and affordable trees to interested landowners.

Denver Digs Trees has been an annual, ongoing program, but the importance of the program is now all the more acute. Yuan-Farrell says at present Denver’s canopy has “a lot of capacity for more trees, and as ash borer is discovered and trees are removed, there will be even more demand.” 

The finite details of the city’s media campaign as well as a schedule of treatments and plantings are yet to be fully cemented, but the city is culling weak ash trees in the parks and planting there is ongoing. The question remains: has Emerald Ash Borer arrived in Denver?

“There’s a quarantine in place preventing the removal of firewood from Boulder, but there are no gates,” says Rob Davis. “And where does all the traffic from Boulder flow? Right down 36 to Denver. The idea of EAB being citywide in Boulder but not yet having taken root here seems impossible if you look at how it’s moved everywhere else.”

Rob Bronk, owner of Mountain High Tree, Lawn & Landscape Co., sees things the same way. “Nobody wants to be quoted, but in conversations among peers there are folks working at key agencies—CSU, others—that think it’s already here due to the difficulty of spotting it early on,” he says. 

“And this time of year, without leaves, the symptoms are very hard to detect. Some people are assuming there’s a high likelihood that it’s moved out of the Boulder area. It’s been there three years, and it was assumed to be there three years prior to showing up.”

Bronk says his company is anticipating an increased need for its services, and Mountain High has purchased equipment they might not have purchased otherwise.

For more information on Denver Forestry, visit denvergov.org and search “Forestry.” For a concise, informative website on the emerald ash borer, visit emeraldashborer.info. And, if you wish to calculate your trees’ value, visit treebenefits.com/calculator.

Additionally, The Park People’s Community Forester program is now accepting applicants, and applications for trees through the Denver Digs Trees program will be accepted through March 7.