High-elevation forests in the southern Rocky Mountains bouncing back from beetles, but elk and deer slowing recovery

From Science Daily.

Summary: New research reveals that even simultaneous bark beetle outbreaks are not a death sentence to the state’s beloved forests. The study found that high-elevation forests in the southern Rocky Mountains actually have a good chance of recovery, even after overlapping outbreaks with different kinds of beetles. One thing that is slowing their recovery down: Foraging elk and deer.

Two words, and a tiny little creature, strike fear in the hearts of many Colorado outdoor enthusiasts: bark beetle. But new research from University of Colorado Boulder reveals that even simultaneous bark beetle outbreaks are not a death sentence to the state’s beloved forests.

The study, published this month in the journal Ecology, found that high-elevation forests in the southern Rocky Mountains actually have a good chance of recovery, even after overlapping outbreaks with different kinds of beetles. One thing that is slowing their recovery down: Foraging elk and deer.

“This is actually a bright point, at least for the next several decades,” said Robert Andrus, lead author of the study and recent PhD graduate in physical geography. “Even though we had multiple bark beetle outbreaks, we found that 86 percent of the stands of trees that we surveyed are currently on a trajectory for recovery.”

Between 2005 and 2017, a severe outbreak of spruce bark beetles swept through more than 741,000 acres of high-elevation forest in the southern Rocky Mountains near Wolf Creek Pass — killing more than 90 percent of Engelmann spruce trees in many stands. At the same time, the western balsam bark beetle infested subalpine fir trees across almost 124,000 acres within the same area.

If you go skiing in Colorado, you’re usually in a high-elevation, Engelmann spruce and subalpine fir forest, said Andrus.

The researchers wanted to know if these overlapping events, caused by two different types of bark beetles, would limit the ability of the forest to recover. So they measured more than 14,000 trees in 105 stands in the eastern San Juan Mountains, tallying the surviving species and the number of deaths. They had expected that the combined effects of two bark beetle outbreaks would prevent forest recovery, but they found that the forests were quite resilient.

That’s an important contrast from what happens following a severe fire, which can cause forests to convert to grasslands, according to previous research by Thomas Veblen, coauthor of the study and Distinguished Professor of Geography.

“It’s important that we perform these sorts of studies, because we need different management responses depending on the forest type and the kind of disturbance,” said Veblen.

They also found that greater tree species diversity prior to the bark beetle outbreaks was a key component of resilient forests.

Tens of millions of acres across the Western United States and North America have been affected in the past two decades, and Colorado has not been spared. A severe mountain pine beetle outbreak began in 1996, easily visible along I-70 and in Rocky Mountain National Park. Since 2000, more than 1.8 million acres of Engelmann spruce statewide have been affected by spruce beetles in high-elevation forests.

With continued warming there will come a time where conditions caused by climate change exceed the forests’ ability to recover, said Veblen.

Impacts of Ungulates

The study is the first to consider the effects of two different types of beetles that affect two different dominant tree species, as well as the effects of browsing elk and deer in the same area.

Bark beetles prefer bigger, mature trees with thicker bark, which offer more nutrients and better protection in the wintertime. They typically leave the younger, juvenile trees alone — allowing the next generation to recover and repopulate the forest.

But while in the field, researchers noticed many smaller trees were being munched on by elk and deer. Known as “ungulates,” these animals like to nibble the top of young trees, which can stunt the trees’ vertical growth. They found more than half of the tops of all smaller trees had been browsed.

That doesn’t mean that those trees are going to die — ungulates are just more likely to slow the rate of forest recovery.

Avid Colorado skiers and mountaineers looking forward to typical, green forests, however, will have to be patient.

“We don’t expect full forest recovery for decades,” said Andrus.

Story Source: Materials provided by University of Colorado at Boulder. Original written by Kelsey Simpkins. Note: Content may be edited for style and length.

Journal Reference: Robert A. Andrus, Sarah J. Hart, Thomas T. Veblen. Forest recovery following synchronous outbreaks of spruce and western balsam bark beetle is slowed by ungulate browsing. Ecology, 2020; DOI: 10.1002/ecy.2998

8 thoughts on “High-elevation forests in the southern Rocky Mountains bouncing back from beetles, but elk and deer slowing recovery”

  1. Eventually wolves will help move those deer and elk around in Colorado, which has the potential to keep the ungulates moving more, and munching less.

    DNA tests confirm 4 wolves are living in northwestern Colorado

    https://www.denverpost.com/2020/02/13/colorado-wolves-dna-tests/

    Colorado Parks and Wildlife unveiled the results of genetic tests Thursday that confirm the presence of wolves — three females and one male related to each other — in the northwestern part of the state.

    State biologists received a notice confirming that four scat samples collected last month near a scavenged elk carcass in Moffat County came from wolves. CPW officials said the evidence suggests the wolves, the first group documented in Colorado since the 1940s, likely are siblings. DNA testing did not determine ages.

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  2. Its always elk and deer and livestock impacts either direct browsing or indirect by displacing elk and deer from their preferred habitats, or consuming the grasses they both rely upon for a majority of their diets. Every time we look at this situation for aspen, it always comes back to cows and sheep are consuming 85% of the available vegetation that elk and deer would use. Here at our wildlife preserve, which has not been grazed by livestock for 25 years, when a deer or elk digs thru the snow in winter they find tall bunch grasses. On public lands next door they will not find anything as these are grazed to the ground every year.

    This article has no credibility as it does not describe the context in which it is occurring.

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  3. These conclusions seem fairly obvious to me.

    “They also found that greater tree species diversity prior to the bark beetle outbreaks was a key component of resilient forests.”
    That makes sense, because not every species of tree is susceptible to the same species of beetles. People have been observing this in western forests for a long time.

    Deer and elk eat seedlings. That’s one of the reasons that people used to put vexar tubes or netting around seedling tops when they were planted.

    I don’t find any of these conclusions very surprising. In fact, I would think that those things have been known for a very long time. I guess the information is new because scientists hadn’t measured it before?

    Matthew, I don’t know much about wolf behavior. Will deer and elk stay out of areas with seedlings because of wolves, or will there just be fewer deer and elk to eat seedlings?

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    • I also agree that the conclusions of the study seem fairly obvious. I also do believe that other scientists have found basically the same thing in previous studies. The forest protect movement has been saying basically the same thing about bark beetles and forests for decades now. The timber industry? Well, not so much at all. They’d rather use bark beetles as an excuse to do more logging of public lands, including clearcutting. Wolves and other native predators keep prey (in this case, deer and elk) on the move. In some cases, that has been observed to reduce the impact of deer and elk browsing in specific locations.

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  4. Wolves move elk very little, and have little effect on where elk graze. It’s much more beneficial to eat good food than to worry about wolves as shown by the now famous study by Middleton and repeated in Yellowstone etc.

    A lot of the early “studies” on wolves were more advocacy than science as people sought reasons for wolves. People like to have a reason for things.
    https://www.uwyo.edu/uw/news/2013/06/uw-study-wolf-harrassment-has-little-impact-on-elk.html
    https://phys.org/news/2018-06-yellowstone-landscape-scary.html

    In 90% of cases, there was no difference between real and simulated elk movements, indicating that our sample of real elk mostly ignored the risk of wolf predation.”
    https://www.sciencedaily.com/releases/2019/03/190326132726.htm

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    • Thanks for the links, Som! I thought this from the last one was interesting.

      “Why don’t elk budge for wolves? “A main reason is that elk tend to be philopatric, which means they have an inherent tendency to habitually return to the same wintering and summering areas year after year,” says MacNulty. “Familiarity with an area helps them find the high quality forage they need, and this outweighs the small chance they encounter and fall prey to wolves.”

      MacNulty and Cusack estimated that elk in their study encountered wolves once every 7 to 11 days, and previous research found that elk frequently survive their encounters with wolves. Low risk of predation was also reflected in relatively high rates of annual survival, particularly among younger adults. “Elk in their prime do not have a massive incentive to avoid wolves, especially in winter when forage is scarce,” explains MacNulty.

      He says that elk intransigence towards wolves is a reminder that altered movement behavior is not the only way prey species avoid predation.

      “Antipredator behaviors during encounters — including fighting back, grouping, and running — are effective ways for large-bodied, philopatric prey like elk to avoid predation without abandoning or reconfiguring their home ranges,” he says.

      “This has implications for understanding how wolves and other predators, including humans, affect the distribution of philopatric prey like elk. Predators removing different numbers of elk in different areas is the main way they affect elk distribution. Elk movement away from risky areas, if it happens, is secondary.”

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