A mountain pine beetle outbreak is spreading rapidly through Colorado’s ponderosa pine forests and is expected to intensify over the summer under what foresters have called prime conditions for the insect. That is according to the Colorado State Forest Service, whose 2025 forest health report, released this month, recorded a 148 per cent increase in beetle-impacted acreage between 2024 and 2025, with aerial surveys over parts of nine counties showing 5,544 acres of dead or dying trees, up from 2,236 acres a year earlier.
Beyond the sheer volume, it is the distribution of the infestation that has unsettled foresters, with affected trees recorded at almost every Colorado latitude, from the northern border down to Pueblo on the Front Range, and from Grand Junction to the southern boundary on the Western Slope. The report described the activity as well distributed across the region, “raising concerns for widespread mortality as these pockets expand,” it said.
With the state’s snowpack sitting at just 15 per cent of the median as of 29 May, forests are being deprived of the moisture they need to resist both wildfire and the beetle’s advance, and the outbreak now ranks as Colorado’s foremost insect forest health concern. Dead and dying stands left in the beetle’s wake add fuel to a fire outlook the forest service already regards as severe, with much of the state’s forestland classed as having a high burn probability heading into summer.
Even with beetles present, weather remains the primary driver of wildfire, though beetle-killed trees still carrying red needles can move flames more readily through the forest canopy. CSFS fire mitigation specialist Chad Julian wrote that lower fuel moisture in those red needles lowers the threshold for ignition and spread, “the change to crown fire risk is clear—it increases,” he said.
Complicating efforts to gauge the outbreak’s true scale, the aerial surveys behind the data — flown with the US Forest Service — covered just 13.4 million acres last year, down from nearly 30 million acres in 2024 as aircraft, staff and funding tightened. That reduction, amounting to roughly half the state’s forested land, leaves the 2025 figures as a lower-resolution snapshot, the Forest Service has cautioned, likely understating the full extent of the damage.
Like wildfire, mountain pine beetles thrive in the hot, dry conditions that dehydrate a tree and weaken the resin defences it relies on to fend them off, whilst the insects compound the harm by spreading a fungus that starves the tree of nutrients and usually kills it within a year. Colorado’s warmest winter on record has tilted the odds further in the beetle’s favour, leaving lower-elevation ponderosa forests short of early-season moisture and, on the Front Range, densely stocked with trees already vulnerable to attack.
Signs that the warmth has accelerated the lifecycle are already showing, with beetles observed in late larval stages in May, raising the prospect of flight in mid-June — two to four weeks ahead of the usual mid-July to mid-September window — alongside a larger surviving population poised to attack.
The current infestation revives memories of the epidemic that tore through 3.4 million acres of Colorado forest between the late 1990s and 2013, an area roughly the size of Connecticut and equal to about 14 per cent of the state’s forested land, before heavy precipitation and flooding in the early 2010s brought it to a halt. Whereas that outbreak moved mainly through higher-elevation lodgepole pines and helped kill the trees at the heart of the 2020 East Troublesome and Cameron Peak fires, the state’s two largest on record, the present wave is working through lower-elevation ponderosa stands.
There remains some cause for optimism despite the drought and the beetles, with the Colorado Climate Center now putting the chance of an El Niño forming this year at 82 per cent alongside model signals pointing to a strong monsoon. Colorado Climate Center engagement climatologist Allie Mazurek said El Niño typically delivers “wetter than normal conditions,” particularly across southern Colorado, though a single wet season is unlikely to be enough.
Even so, breaking a beetle outbreak usually takes more than one good year, with the forest service noting that trees need several seasons of adequate precipitation and cooler temperatures to rebuild the defences that let them ward off bark beetles and other pests.
