Introducing The Colorado Footprint, a monthly column that follows stories about Colorado’s environment and the solutions-based projects, people, and ideas bettering the Centennial State. OutThere Colorado is driven by our deep respect for our environment, and our passionate commitment to sustainable tourism and conservation. We believe in the right for everyone – from all backgrounds and cultures – to enjoy our natural world, and we believe that we must all do so responsibly. This column aims to highlight those engaged in the vital work of protecting and preserving Colorado’s environment.
Sometime in the late 2000s, a fleet of metallic-green, penny-sized beetles hitchhiked hundreds of miles across the Great Plains. Experts guess they caught a ride in a bundle of firewood, hiding in small enclaves under the bark of once-alive ash trees — maybe in a happy-go-lucky Midwest camper’s trunk as they drove west for a visit to Boulder, Colorado.
“We’ve never been able to prove it,” says Laura Pottorff, from the Colorado Department of Agriculture. “But that’s our best guess — that’s how we know the bug moves.”
The bug she’s talking about is the Emerald Ash Borer (EAB) — the hitchhiking culprit that, as of May 2018, has cost municipalities in 33 different U.S. states (nearly all east of Colorado) millions of dollars in health and environmental damage ensuing from the death of ash trees. In Boulder, where 25 percent of the urban canopy is comprised of ash coverage, the fact that EAB survived its hitchhike and began reproducing in its new home was not a good sign.
EAB is a covert, non-native beetle that feeds on and will kill every species of North American ash. Originally found in Michigan in 2002, EAB bores holes under ash bark to eat its inner layers, cutting off a tree’s flow of nutrients and water. As the tree branches, then trunk, slowly starve, you can reach up to a twig during its last months and snap it off like a pretzel twist, watching the dust rise.
Nearly all cases of EAB infestation are fatal, and within two to four years of the bug’s first tunnel, ash trees will die. The first trace of EABs in Boulder was discovered in September 2013, and every year since then, they’ve spread a little bit further, from ash tree to ash tree.
But, because the bug can only travel about a half-mile each year on its own, Boulder County remains the only infected region in Colorado so far, says Pottorff, who runs Colorado’s EAB quarantine program. “We knew it was somewhat inevitable, that we would get it.”
While an EAB border patrol around the county or state isn’t feasible, the state’s Department of Agriculture has deployed education programs intending to inform travelers and visitors of EAB’s damage and the importance of not bringing potential EAB vehicles (like firewood or wood chips) into the state. Cities like Denver have yet to identify any EAB signs, but as they watch the beetle wreak havoc across the nation and consider their own one-in-six ash tree ratio, they are preparing for its arrival with tree location data and insecticides nonetheless.
Boulder, now entering its fifth season of handling EAB, is in full combat mode. “At any given time, any tree could be infected,” says Kathleen Alexander, Boulder’s city forester. “We have found symptomatic ash trees in every part of the city.”
Right now there are two methods of attack: inject a pesticide at the base of the tree or simply remove and replace the tree. The City of Boulder has chosen to preserve 25 percent of its public trees with pesticides, and is currently replacing the rest as time and funds allow. But for trees on private property, the city has little influence in how landowners approach their ash trees.
To say it would be devastating if EAB killed all of Boulder’s ash trees would be no overstatement, according to Alexander. While only one in eight trees digging into Boulder’s public soil are ash, their mature spread and large leaf sprawl account for an entire fourth of the city’s urban canopy.
“Trees provide huge environmental, social and economic benefits to the community,” Alexander says: “from carbon sequestration to the removal of other air pollutants, to energy savings through the shade, reducing storm damage, improving water quality, erosion control, and so on.”
A 2018 study by the USDA Forest Service concurs. “Urbanization and urban forests are likely to be one the most important forest influences and influential forests of the 21st Century,” David Nowak, a senior scientist on the USDA’s Forest Inventory and Analysis team, writes in the report.
Further, the report shows the U.S.’s 5.5 billion urban trees provide roughly $18 billion in annual benefits, thanks to the very aforementioned reasons by Alexander. Plus, as Nowak states, “A healthy and well-managed urban forest can help reduce some of the environmental issues associated with urbanization such as increased air temperatures and energy use, reduced air and water quality, and increased human stress, and ultimately help people living within and around urban areas.”
To lose a fourth of Boulder’s urban canopy would be to expose hundreds of city acres to direct sun and increased weather damage, in addition to decreasing property values and slashing a quarter of the power of the most powerful air filter the city can employ.
Unfortunately EAB’s presence is really only noticed once the tree is already died. “It’s impossible for us to detect early,” says Pottorff. EAB bore their holes up high in the tree and work their way down, she explains. “The symptoms we would see if tree was beginning initial stages of decline [due to EAB] can easily be confused with symptoms of normal [natural] decline.”
That’s in part because ash trees are not native to Colorado. “You look at pictures of Denver 100 years ago, there were no trees. Zilch,” says Pottorff. “[Ash trees] wouldn’t be here if we didn’t put them here, if we didn’t irrigate them.”
Years ago, “we over-relied on them,” she explains. “Ash trees can handle harsher weather environments than other trees can, so we planted too many of them when we should have been diversifying.”
It’s a fact not worth lamenting, says Pottorff. Rather, it’s a human mistake we can learn from. The best thing to do as a resident along the Front Range, according to both Pottorff and Alexander, is to be proactive about replacing ash trees.
As the City of Boulder continues to inspect and address trees in public parks and along streets to find which are worth saving and which best be replaced, Alexander says, “What’s important for people to know … is that even if they don’t have an ash tree that needs to be replaced, if they have space, they should still consider planting a tree and helping our urban canopy.”
What We Believe
We are driven by our deep respect for our environment, and our passionate commitment to sustainable tourism and conservation. We believe in the right for everyone - from all backgrounds and cultures - to enjoy our natural world, and we believe that we must all do so responsibly. Learn More