Denver Volunteers Wage War on Invasive 'Tree of Heaven'

A Fast-Growing Threat in Denver’s Urban Canopy

A volunteer effort is underway across Denver neighborhoods to identify and remove one of the city’s most problematic invasive plants: the tree of heaven. According to a report from 9News, a local group has been working to kill off populations of the tree, which has been spreading through yards, alleys, fence lines and vacant lots across the metro area.

The tree, scientifically known as Ailanthus altissima, is not native to Colorado or North America. It originated in China and was introduced to the United States in the late 1700s, prized initially as a fast-growing ornamental shade tree. That same rapid growth, however, has turned it into a persistent and costly problem for cities nationwide — and Denver is no exception.

Why This Tree Is a Problem

Tree of heaven earns its menacing reputation for several reasons. It grows extraordinarily fast, often reaching maturity and producing seeds within just a few years. A single female tree can produce hundreds of thousands of seeds annually, allowing it to colonize new ground quickly. Its root system is aggressive enough to crack sidewalks, invade sewer lines and damage building foundations, making it a headache for property owners and city infrastructure crews alike.

The species also releases chemical compounds into the surrounding soil — a process known as allelopathy — that suppress the growth of nearby native plants, giving it an unfair competitive advantage over Colorado’s indigenous vegetation. Once established, tree of heaven is notoriously difficult to eradicate. Simply cutting it down often backfires, triggering the plant to send up dozens of new suckers from its roots, effectively multiplying rather than eliminating the problem.

Perhaps the most alarming concern tied to the tree, as highlighted in the 9News report, is its role as the preferred host plant for the spotted lanternfly, an invasive insect that has devastated vineyards, orchards and hardwood forests in parts of the eastern United States since it was first detected in Pennsylvania in 2014. The spotted lanternfly feeds on more than 70 plant species and has caused significant agricultural damage in states like New York, New Jersey and Ohio. While the pest has not yet established a foothold in Colorado, experts and volunteers worry that letting tree of heaven populations flourish here could create an inviting habitat should the lanternfly ever make its way west. Removing the host plant proactively is seen as a key strategy in preventing that scenario.

The Volunteer Response

In response to these growing concerns, a local group has taken on the task of locating and removing tree of heaven specimens from Denver neighborhoods before the problem becomes more entrenched, according to 9News. The effort reflects a broader pattern seen in cities around the country, where community-driven removal campaigns have become one of the primary tools for managing invasive species, particularly when government resources for urban forestry and invasive plant management are limited.

Volunteer-led invasive species removal has a track record in Colorado, with similar grassroots efforts historically targeting other problem plants like tamarisk along waterways and Russian olive trees on open space. The tree of heaven campaign appears to follow that same community-science model: residents are being asked to learn to identify the tree, report sightings, and in some cases assist directly with removal efforts on public or shared land.

How to Identify Tree of Heaven

For Denver residents wondering whether the tree is growing on their own property, there are a few identifying characteristics to watch for. Tree of heaven has compound leaves made up of many narrow, pointed leaflets arranged along a central stem, giving it a resemblance to native sumac or black walnut trees — a similarity that often causes confusion. One of the most reliable ways to distinguish it is by smell: when a leaf or stem is crushed, tree of heaven emits a strong, unpleasant odor that’s frequently compared to rotting peanuts or burnt rubber.

The tree also tends to sprout aggressively in disturbed soil, along fence lines, in alleys, cracks in pavement, and other neglected urban spaces — areas where native species struggle to establish themselves. Its bark is smooth and gray when young, and it produces large clusters of seeds with a papery, winged casing that allows them to spread widely on the wind.

What Residents Can Do

Experts generally caution against simply cutting the tree down, since that approach tends to stimulate more aggressive regrowth from the root system. Effective removal typically requires either persistent, repeated cutting over multiple growing seasons to exhaust the root system, or targeted herbicide application directly to the stump or bark — methods that are more effective when done with guidance from those experienced in invasive species control.

Residents who suspect they have tree of heaven on their property, or who want to get involved in the local removal effort reported by 9News, are encouraged to learn more about identification before attempting removal on their own, given how easily the species can be confused with native look-alikes. Community involvement, organizers suggest, is central to controlling the spread, since the tree can take root on both public and private land throughout the city.

A Small Effort With Broader Stakes

While a cluster of volunteers pulling saplings out of alleyways might seem like a modest story against the backdrop of Denver’s bigger headlines, the stakes tied to invasive species management are not insignificant. Left unchecked, aggressive invasive plants can reshape urban ecosystems, strain city infrastructure, and — in the case of tree of heaven — potentially pave the way for destructive pests like the spotted lanternfly to gain a foothold should they ever reach Colorado.

For now, Denver has not reported any confirmed spotted lanternfly sightings, and the insect remains primarily an East Coast and Midwest problem. But the volunteer campaign against tree of heaven reflects a precautionary, boots-on-the-ground approach: addressing a known invasive species today in hopes of heading off a potentially larger ecological and economic problem tomorrow.

As the effort continues, organizers are likely to lean on public awareness as much as physical removal, encouraging Denver residents to learn the signs of this unwelcome backyard guest and to think twice before dismissing it as just another shade tree.