Sarah Hart

Combined bark beetle outbreaks and wildfire spell uncertain future for forests

Anonymous — Tue, 09 Feb 2021 19:01:06 +0000

Combined bark beetle outbreaks and wildfire spell uncertain future for forests Anonymous (not verified) Tue, 02/09/2021 - 12:01

Kelsey Simpkins (CU ��«��Ƶ Today)

Banner image: A forest in the San Juan range of the Rocky Mountains, with dead Engelmann spruce trees alongside live aspen trees. (Credit: Robert Andrus)

Bark beetle outbreaks and wildfire alone are not a death sentence for Colorado’s beloved forests—but when combined, their toll may become more permanent, new CU ��«��Ƶ research shows.

It finds that when wildfire follows a severe spruce beetle outbreak in the Rocky Mountains, Engelmann spruce trees are unable to recover and grow back, while aspen tree roots survive underground. The study, published last month in Ecosphere, is one of the first to document the effects of bark beetle kill on high elevation forests’ recovery from wildfire.

“The fact that Aspen is regenerating prolifically after wildfire is not a surprise,” said Robert Andrus, who conducted this research while working on his PhD in physical geography at CU ��«��Ƶ. “The surprising piece here is that after beetle kill and then wildfire, there aren't really any spruce regenerating.”

Andrus’ previous research found that bark beetle outbreaks are not a death sentence to Colorado forests—even after overlapping outbreaks with different kinds of beetles—and that spruce bark beetle infestations do not affect fire severity.

This new research, conducted in the San Juan range of the Rocky Mountains, shows that subalpine forests that have not been attacked by bark beetles will likely recover after wildfire. But for forests that suffer from a severe bark beetle outbreak followed by wildfire within about five years, conifers cannot mount a comeback. While these subalpine forests can often take a century to recover from fire, this research on short-term recovery is a good predictor of longer-term trends.

“This combination, the spruce beetle outbreak and the fire, can alter the trajectory of the forest to dominance by aspen,” said Andrus, who is now a postdoctoral researcher at Washington State University.

For those worried about the future of Rocky Mountain forests farther north, more research is needed on areas burned in the 2020 East Troublesome Fire to understand how the mountain pine beetle outbreak prior to that fire will affect forest recovery, according to Andrus.

The next generation

Each bark beetle species specializes in attacking—and usually killing—a specific host tree species or closely related species. Several species of bark beetle are native to Colorado and usually exist at low abundances, killing only dying or weakened trees. But as the climate becomes hotter and drier, their populations can explode, causing outbreaks which kill large numbers of even the healthiest trees.

These large, healthy Engelmann spruce and subalpine fir trees are the ones that produce the most seeds. When bark beetles kill these trees and then fire sweeps in, the researchers found there simply aren’t enough seeds being produced in the burned areas to regenerate the forest.

Aspens, however, regrow from their root systems. While all three of these higher elevation trees have thin bark and die when exposed to fire, with their regenerative roots underground, aspens can bounce back where conifers cannot.

The researchers focused specifically on areas of forest affected by spruce bark beetle outbreaks, which attack Engelmann spruce, where fires such as Papoose, West Fork and Little Sands burned in 2012 and 2013 in Rio Grande National Forest. They found that for forests that suffer from a severe bark beetle outbreak followed by wildfire within about five years, Engelmann spruce and subalpine fir trees failed to recover in 74% of the 45 sites sampled.

This information will help inform land managers and policy makers about the implications for high elevation forest recovery following a combination of stressors and events.

And it’s more important information than ever. Not only do bark beetle outbreaks leave behind swaths of dead, dry trees—and fewer trees to produce seeds—but the climate is getting hotter and droughts are becoming more frequent, promoting larger fires.

“Bark beetle outbreaks have been killing lots and lots of trees throughout the western United States. And especially at higher elevation forests, what drives bark beetle outbreaks and what drives fire are similar conditions: generally warmer and drier conditions,” said Andrus.

But there is good news: The aspens that may come to dominate these southern Colorado forests can anchor their recovery, and keep forests from transitioning into grasslands.

“Where the aspen are regenerating, we expect to see a forest in those areas,” said Andrus.

Additional authors on this publication include Thomas Veblen at CU ��«��Ƶ; and Sarah Hart and Niko Tutland of Colorado State University.

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Forests bouncing back from beetles, but elk and deer slowing recovery

Anonymous — Thu, 13 Feb 2020 17:11:45 +0000

Forests bouncing back from beetles, but elk and deer slowing recovery Anonymous (not verified) Thu, 02/13/2020 - 10:11

Kelsey Simpkins , CU ��«��Ƶ Today

Trees killed by bark beetles remain standing in the southern Rocky Mountains. (Credit: Robert Andrus)

Two words, and a tiny little creature, strike fear in the hearts of many Colorado outdoor enthusiasts: bark beetle. But new research from CU ��«��Ƶ 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.

A stand of mature dead trees and younger, living trees, in the southern Rocky mountains. (Credit: Robert Andrus)

“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.

Deer graze in Rocky Mountain National Park. (Credit: Unsplash)

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.

Bark beetle outbreaks are natural disturbances, and the beetles and the trees they depend on have co-evolved together over tens of thousands of years. But these days, outbreaks are increasing—primarily driven by warmer and drier conditions caused by climate change.

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.

A male elk stands in a forest clearing. (Credit: Meredith Fontana)

Impacts of ungulates

The study is unique, as it 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. Which tree species they find tastiest will also affect the species composition of the new forest canopy.

Avid Colorado skiers and mountaineers looking forward to typical, green forests, however, will have to be patient. Although these forests are likely to bounce back from multiple bark beetle outbreaks, “we don't expect full forest recovery for decades,” said Andrus.

Sarah Hart, also a PhD graduate of CU and now a faculty member at the University of Wisconsin-Madison, contributed to this study.

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Sarah Hart Accepts Tenure Track Position at UW

Anonymous — Fri, 20 Jul 2018 15:48:56 +0000

Sarah Hart Accepts Tenure Track Position at UW Anonymous (not verified) Fri, 07/20/2018 - 09:48

Sarah Hart (Ph.D., CU Geography 2014) has accepted a new position as a tenure track assistant professor in the Department of Forest and Wildlife Ecology at University of Wisconsin at Madison.

University of Wisconsin at Madison

While at CU ��«��Ƶ, Sarah's research interests were broadly based on the impacts of past and future climate variability on environmental systems. She researched relationships between climate and bark beetle disturbance in subalpine forests and focused on biogeography and dendrochronology. Her advisor was Tom Veblen. Prior to her new position, she was an assistant professor at Washington State University where she focused on disturbance ecology and forest biogeography.

Sarah Hart

Last summer, she worked on an outreach video about the climate-sensitivity of subalpine forests wtih CU Ph.D. student Robbie Andrus. In August, 2017 Sarah presented her reseach on spatial patterns of spruce beetle outbreak at the Ecological Society of America’s 2017 Annual Meeting in Portland, Oregon. Her most recent paper, "Summer and winter drought drive the initiation and spread of spruce beetle outbreak", can be viewed here. Tom Veblen, Dominik Schneider, and Noah Molotch were co-authors.

Congratulations Sarah!

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Study: Western forests decimated by pine beetles not more likely to burn

Anonymous — Thu, 26 Mar 2015 01:11:16 +0000

Study: Western forests decimated by pine beetles not more likely to burn Anonymous (not verified) Wed, 03/25/2015 - 19:11

Western U.S. forests killed by the mountain pine beetle epidemic are no more at risk to burn than healthy Western forests, according to new findings by the ��«��Ƶ that fly in the face of both public perception and policy.

The CU-��«��Ƶ study authors looked at the three peak years of Western wildfires since 2002, using maps produced by federal land management agencies. The researchers superimposed maps of areas burned in the West in 2006, 2007 and 2012 on maps of areas identified as infested by mountain pine beetles.

Read CU ��«��Ƶ Today article

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Massive spruce beetle outbreak in Colorado tied to drought, according to new CU study

Anonymous — Sat, 12 Oct 2013 03:18:45 +0000

Massive spruce beetle outbreak in Colorado tied to drought, according to new CU study Anonymous (not verified) Fri, 10/11/2013 - 21:18

A new ��«��Ƶ study indicates drought high in the northern Colorado mountains is the primary trigger of a massive spruce beetle outbreak that is tied to long-term changes in sea-surface temperatures from the Northern Atlantic Ocean, a trend that is expected to continue for decades. The new study is important because it shows that drought is a better predictor of spruce beetle outbreaks in northern Colorado than temperature alone, said lead study author Sarah Hart, a CU-��«��Ƶ doctoral student in geography. Drought conditions appear to decrease host tree defenses against spruce beetles, which attack the inner layers of bark, feeding and breeding in the phloem, a soft inner bark tissue, which impedes tree growth and eventually kills vast swaths of forest.

See more at CU ��«��Ƶ Today (link no longer available)

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Sarah Hart Receives National Geographic Young Explorers Grant

Anonymous — Fri, 08 Apr 2011 17:39:03 +0000

Sarah Hart Receives National Geographic Young Explorers Grant Anonymous (not verified) Fri, 04/08/2011 - 11:39

Sarah is the recipient of a National Geographic Young Explorers Grant. National Geographic provides these grants to help cover "field project costs for hard-working, passionate, creative individuals with great ideas".

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Sarah Hart Receives John Marr Ecology Fund Award

Anonymous — Mon, 04 Apr 2011 17:18:45 +0000

Sarah Hart Receives John Marr Ecology Fund Award Anonymous (not verified) Mon, 04/04/2011 - 11:18

Sarah received this award through the Graduate School's John Marr Ecology Fund. Its purpose is to provide grants of $300 to $1000 for Ph.D. candidates doing field research in plant ecology in the Rocky Mountains or the Arctic.

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