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Colorado’s warm and dry winters have tipped the balance in a long-running ecological tug-of-war.

The mountain pine beetles, native insects to the Centennial State, have recently exploded in numbers in the Front Range after a decade of relatively low populations. The mild winter temperatures have allowed more beetle larvae to survive, while the lack of water has weakened pine trees’ natural defenses against the bugs.��

Already, thousands of pine trees along the U.S. 285 and I-70 corridors are turning brown. The devastation prompted Gov. Jared Polis to�� an executive order in December to slow the spread of the beetles.��

“A very high level of tree mortality, especially among ponderosa pines, is likely to continue for the next decade,” the order��.��

But the insects are not the antagonists of the story, said��Samuel Ramsey, assistant professor in the Department of Ecology and Evolutionary Biology and the BioFrontiers Institute.��

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Samuel Ramsey looking at a beehive in his lab. (Credit: Patrick Campbell/���Ҵ�ý�ƽ������)

“They are doing exactly what evolution has primed them to do, and they are just able to do it to the maximum because of the ways that climactic contexts have shifted.�� That is our fault,” he said.

The impact extends beyond tree loss. For the Front Range, a densely populated region already under persistent wildfire threat, dead trees can exacerbate risk.��

To unpack what’s behind the outbreak and what may come next, ���Ҵ�ý�ƽ������ Today sat down with Ramsey to chat about its causes, the outlook for Colorado’s forests and steps people can take to limit the damage.

The Mountain pine beetles are native to Colorado. Why are they causing problems now?

As the climate has shifted, it has knocked the beetles out of their normal balance with the trees.�� Because the weather has been warm for longer stretches of time, these beetles are able to produce an additional generation of babies, in addition to the dozens of offspring they usually produce.

How do the pine beetles attack trees?

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An adult mountain pine beetle. (Credit: Colorado State Forest Service)

The mountain pine beetles are smaller than a grain of rice. When a single pine beetle attacks a tree, it actually can’t do much damage.�� So, when a pine beetle locates a tree, it will release a smell that tells all the pine beetles in the area to come and attack it. When 1,000 pine beetles all attack the same tree, some get through and lay eggs in the tree. Once inside, the beetles will gum up the tree’s vascular system, cutting off its water and nutrient supply.��

Do trees have a defense mechanism for keeping beetles out?

They did in the original climactic circumstances, such as secreting sap to push out the beetles. But when there isn't enough water, they can only produce a small amount of sap, and that is not enough to fend off thousands of beetles that just keep coming at them.

With the warm weather, pine beetles are also maturing faster. That means the trees are starting their battle against the beetles earlier than they had planned. The trees are also fighting later into the season because of the additional generation of beetles.����

How bad will this round of the outbreak be?

I'm not a prognosticator, so I cannot tell you that this is going to be a terrible year. But the data is pointing in the direction. In the past, when we have had the same set of circumstances, we have had a banner year for mountain pine beetles. It is that out of more than 4 million acres of pine forests across the state, more than 80% were damaged by the beetles between 1996 and 2013.

This winter has been really warm. That means that more pine beetles are going to survive the winter. So starting this year, their population will be large enough to likely overcome the defense of a lot of these trees. We could have dead stands of pine trees just sitting there ready to welcome the next wildfire.����

Are mountain pine beetle outbreaks unique to Colorado?

The mountain pine beetles are distributed in many parts of North America, but Colorado kind of has a perfect storm of circumstances. We have these issues with a warmer winter. Really high winds can help these pine beetles move farther distances when they're flying. In addition, the wind can drive wildfires. Together, those factors make the risks here especially high.��

Are there any actions individuals can take to reduce the damage?

There are ways that we can lean into our agency here.

If you have a pine tree in your yard, you need to make sure that it has adequate water by watering it and reducing competition for water from other plants around it.����

If you are getting firewood, get it and burn it locally. It’s a really, really bad idea to move firewood, because you could inadvertently help spread the beetles.����

If you're seeing mountain pine beetles in your area, and you haven't seen that before, contact your local forest service office.��

The pheromone packets people used in the past might not be the best solution, because they won't stop an infestation, and sometimes they can make the problem worse by drawing more beetles to an area than would've arrived otherwise.

As the climate continues to warm, these sorts of ecological issues are going to happen more often. So we need to make sure that instead of only treating the symptoms of climate change, we are reducing the amount of carbon that is going into the atmosphere.��