When it comes to how wildlife adjust to living in forests ravaged by the beetle outbreak in Colorado, there are winners and losers, according to new research.
The mountain pine and spruce beetle epidemic has wiped out about 21% of Colorado’s 24.4 million acres of forested land since 1996, perhaps the starkest change on the landscape in recorded history.
“It’s such a huge impact,” said Jake Ivan, a senior research scientist with Colorado Parks and Wildlife. “This level of outbreak, that we know of, is bigger than anything, at least in recorded history. And maybe beyond.”
Because the outbreak is relatively new to the landscape, not much study has been done on how species are affected by living in beetle-kill forests.
Recently, however, CPW and the U.S. Forest Service partnered to take the first step to understand how wildlife have responded, among the first pieces of work to quantify the consequences of the beetle outbreak to animals.
“It’s still a relatively new phenomenon,” Ivan said. “We just don’t know much about it.”
First studyBark and spruce beetles are native to Colorado. But dense forests and rising global temperatures set the stage to allow them to overrun Colorado’s mountains, an event that researchers in the report called “unmatched in recorded history.”
Over the summers of 2013 and 2014, about 300 game cameras were placed throughout the state at elevations between 8,500 and 12,000 feet, specifically in lodgepole pine and Engelmann spruce forests affected by beetle kill.
The cameras were able to capture more than 336,600 images of 26 mammal species, of which researchers noted habits of 13 species.
Ivan said there were no definitive conclusions in the study. Instead, it’s the first piece of the puzzle to figure out which animals thrive and which animals struggle in beetle-kill habitats.
WinnersThe winners: ungulates such as elk, deer and moose.
All the ungulates seemed to respond positively to the “dietary boon” of the diverse and abundant vegetation on the forest floor, the report said, as well as the cover and safety the thick understory vegetation allows after large trees die.
But there were differences among them. Elk and moose, for instance, preferred areas of high-severity beetle kill, while deer seemed unaffected. Instead, deer preferred to be in areas of beetle kill a couple of years after the outbreak started.
Marmots, too, seemed to thrive in beetle-kill areas, the report said. Red foxes also tended to populate beetle-kill zones a couple of years after outbreaks.
LosersThe losers: red squirrels, chipmunks and coyotes.
Red squirrels exhibited the strongest negative response of all animals included in the study, likely because of the disappearance of their main food source, cone crops, and an aversion to dense vegetation on the ground.
And the red squirrel’s decline can affect the whole food chain, the study showed, including birds that rely on the rodent for prey and vegetation that is influenced by its habits.
Ground squirrels, chipmunks and coyotes – which have wider diets – also showed negative responses to beetle-kill areas, but not to the degree of red squirrels.
Most surprising to researchers was that bears, snowshoe hares and porcupines – all expected to flourish in beetle-kill areas – showed no discernible impact.
Southwest ColoradoAbout 75 of the 300 cameras were placed in the San Juan Mountains, but the study didn’t go so far as to break down whether wildlife in Southwest Colorado have reacted differently than other parts of the state, Ivan said.
The beetle outbreak started on Wolf Creek Pass in the late 1990s and has since gone on to tear through more than 120,000 acres of the Weminuche Wilderness, Colorado’s largest wilderness area at almost 500,000 acres.
Aaron Kimple, forest health program director for Mountain Studies Institute, said the forest looked pretty bleak all those years. But more recently, he said there’s more life than meets the eye.
“There’s green there, there’s regeneration happening,” he said.
Standing and fallen dead trees, Kimple said, provide protective areas for vegetation and certain animals to thrive.
“There’s always pressure to get the dead stands out,” he said. “But dead stands support habitat.”
Lawrence Lujan, a spokesman for the Forest Service, wrote in an email the agency is “actively working to treat beetle-killed forests through thinning, prescribed fire and other fuel-reduction methods to reduce the risk of catastrophic wildland fires, which have additional impacts on wildlife habitat.”
Ivan said more study needs to be done on how beetle-kill forests affect wildlife – a lot of the hypotheses drawn are just that, guesswork.
“There’s a lot of things up there we value, and we need to get a handle on this,” he said. “And it’s not an isolated impact. It’s a huge impact across the whole state.