Pine beetle damage expanded along Colorado's Front Range by an exponential amount between 2024 and 2025 amid a new outbreak, according to a newly released report from Colorado State Forest Service.
The 2025 Report on the Health of Colorado's Forests revealed that mountain pine beetles, which have plagued the Front Range for years, expanded nearly 150% between 2024 and last year. Notably, the report found that a new outbreak of these beetles, which are native, is currently spreading in ponderosa pine forests that are already at high risk of wildfires.
Thanks to a second consecutive year of above-average temperatures and below-average precipitation, those beetles, as well as other problematic insects like the emerald ash borer, have continued their spread in Colorado's forests.
The National Oceanic and Atmospheric Administration found that Colorado experienced its hottest average temperature on record for the first six months of the water year, which ran between October 2025 and March 2026. This past March was the second-driest on record, with only 0.45 inches of precipitation, only beaten by 0.39 inches of rain in March 1966.
Even with recent spring rain and snow, forests are stressed after the past winter. That means they are now even more vulnerable to mountain pine beetles and other health issues, as well as wildfire risk, the Colorado State Forest Service reported.
"The mountain pine beetle is the top forest health concern in Colorado," the report reads.
These beetles are native to Colorado and usually exist in low populations to help cull unhealthy and dying trees. However, outbreaks happen when beetles become more successful at reproducing, which typically happens "when susceptible host trees provide sufficient nutrition for the expanding populations and climate conditions reduce or weaken tree defenses, resulting in more available hosts," the report said. This can reach an extreme level, when the insects overwhelm large swaths of healthy trees.
The 150% jump in beetle expansion across the Front Range between 2024 and 2025 was recorded during the annual Aerial Detection Survey, which was conducted by the U.S. Forest Service and Colorado State Forest Service. During those flights, researchers found that mountain pine beetle has killed trees across about 5,544 acres of ponderosa pine forests in nine counties in 2025, including Larimer, Boulder, Gilpin, Jefferson, Clear Creek, Teller, Park, Douglas and El Paso counties.
That was up from 2,236 acres in that same geographic area in 2024.
Denver7 reported on a spike in pine beetles at the Elk Meadow Park in Jefferson County in May 2025. That report is here and below.
The report reads that mountain pine beetles are also expanding in forests in Gunnison, Chaffee and Park counties.
The aerial flights also found other insects spreading in the state, including:
- Western spruce budworm: These were the most widespread forest pest in 2024 and continue to cause defoliation in Douglas-fir and low-elevation mixed-conifer forests
- Western balsam bark beetle: These were the deadliest forest pest in 2024 and remain active in high-elevation spruce-fir forests
- Douglas-fir beetle: These continue to kill Douglas-fir trees in central and southern Colorado
- Roundheaded pine beetle/related bark beetles: These are expanding in ponderosa pine forests in southwestern Colorado
In 2025, researchers on this flight were only able to survey about 13.4 million acres, compared to nearly 30 million in 2024, due to "limitations in aircraft and pilot availability and funding," the report says.
Increase in wildfire risk
Areas of dead and dying trees are a major wildfire risk and with mountain pine beetles killing trees in the wildland-urban interface, where some residents live, the danger is even higher.
"Ponderosa pine forests historically endured a high-frequency, low-severity fire regime that has shifted to a low-frequency, high-severity fire regime because of changes in forest structure and fuel loading," the report reads. "Ample ignition sources, a preponderance of continuous fine dead or dry surface fuels, and alignment with strong winds on the Front Range produce high to very high burn probabilities year-round. This is amplified by persistent drought and ever-increasing temperatures – climate conditions that are also spurring the outbreak of mountain pine beetles."
This means that wildfire personnel will need to change fire management tactics.
"Current operational fire behavior models do a poor job of incorporating the complex effects and interactions of bark beetle-caused tree mortality on predictions of fire behavior. As such, fire managers are likely to experience surprises or unanticipated events during wildfires burning in bark beetle-affected forests," the Colorado State Forest Service reports.
Across the United States, the U.S. Forest Service saw a 35% reduction in treating, or removing, hazardous fuels in 2025 compared to 2024, per a new analysis by the Center for Western Priorities. In 2024, the USFS treated about 4.1 million acres. It treated about 2.6 million in 2025, the analysis found. However, Colorado was minimally impacted by this, with just a 1.4% reduction in burned fuels. The states most impacted were Montana, Oregon, Idaho and California.
The below map from the Center for Western Priorities shows USFS Forest Activity Tracking System data to illustrate the difference between fuel treatments in 2024 and 2025.
Emerald ash borer latest
The data collected in the Report on the Health of Colorado's Forests found that urban forests are undergoing their own struggles with insects, with new detections of emerald ash borer in 2025.
The emerald ash borer, or EAB, was discovered in Boulder in 2013 and has now spread to other parts of the Front Range, including Denver. It kills all ash trees native to North America. Denver alone is home to more than 30,000 of these trees, the Colorado State Forest Service said.
The beetles can live in an ash tree for years before it shows signs that it is infected.
In 2025, Denver, Aurora, Golden, Berthoud, Edgewater and Wheat Ridge all reported initial detections of EAB, the department said.
“It’s not really surprising to find it in these locations. We’ve all assumed it was in Denver for many years,” said Kathleen Alexander, Boulder city forester. “It’s very hard to detect EAB especially here in Colorado because we have so many other abiotic and biotic problems that can cause symptoms that look like EAB. … By the time you find EAB and detect it based on those symptoms, it’s already spread, so it’s to that point where it’s becoming a lot more obvious.”
However, there are no forests of ash trees that connect communities, so that makes it difficult for these insects to spread naturally. Instead, they have traveled across communities and the state in infested wood, the Colorado State Forest Service said.
To reduce their spread, Coloradans are asked to never transport raw ash wood or hardwood firewood.
Looking ahead
Staff with the Colorado State Forest Service work with partners at the local, state and federal level to help Coloradans learn more about beetles, the threats and how to join in projects to reduce their impacts.
They are also working to study the insects more.
"The CSFS also traps adult mountain pine beetles to better understand the timing for flights to new host trees and uses that data to inform management decisions," the Colorado State Forest Service said. "For example, knowing when adult beetles begin their flights to new trees impacts the timing of when pheromone packets should be placed on trees to deter beetles from attacking them. It also impacts when residents and land managers should prune or remove pine trees, since cut trees may give off a scent that attracts beetles."
In December, Gov. Jared Polis launched a task force to address the mountain pine beetle outbreak along the Front Range. The group will meet next on May 29 at 12:30 p.m. To learn more, or watch the meeting on Zoom, visit the task force website here.
The Colorado State Forest Service releases the Report on the Health of Colorado's Forests each year to update the Colorado General Assembly and public about the status of the state's forests. A full list of previous year's reports are here.
