Robert Andrus

Robert Andrus: Extreme heat, dry summers main cause of tree death in Colorado’s subalpine forests

Anonymous — Fri, 30 Jul 2021 18:55:43 +0000

Robert Andrus: Extreme heat, dry summers main cause of tree death in Colorado’s subalpine forests Anonymous (not verified) Fri, 07/30/2021 - 12:55

Kelsey Simpkins

Even in the absence of bark beetle outbreaks and wildfire, trees in Colorado subalpine forests are dying at increasing rates from warmer and drier summer conditions, found recent ��Ƶ Boulder research.

The study, published in February in the Journal of Ecology, also found that this trend is increasing. In fact, tree mortality in subalpine Colorado forests not affected by fire or bark beetle outbreaks in the last decade has more than tripled since the 1980s.

“We have bark beetle outbreaks and wildfires that cause very obvious mortality of trees in Colorado. But we’re showing that even in the areas that people go hiking in and where the forest looks healthy, mortality is increasing due to heat and dry conditions alone,” said Robert Andrus, lead author of the study and postdoctoral researcher at Washington State University. “It’s an early warning sign of climate change.”

These deaths are not only affecting larger trees, thus reducing forests’ carbon storage, but hotter and drier conditions are making it difficult for new trees to take root across the southern Rockies in Colorado, southern Wyoming and northern parts of New Mexico.

It’s well known that rising temperatures and increasing drought are causing tree deaths in forests around the globe. But here in Colorado, researchers found that heat and drought alone are responsible for over 70% of tree deaths in the 13 areas of subalpine forest they measured over the past 37 years. That’s compared with about 23% of tree deaths due to bark beetles and about 5% due to wind damage.

“It was really surprising to see how strong the relationship is between climate and tree mortality, to see that there was a very obvious effect of recent warmer and drier conditions on our subalpine forests,” said Andrus, who conducted this research while completing his graduate degree in physical geography at ��Ƶ Boulder. “The rate of increasing mortality is alarming.”

With temperatures in Colorado having risen by about 2 degrees Fahrenheit since the 1980s and increasing more quickly at higher elevations, estimates of another possible 2.5 or more degrees of warming in the next few decades due to climate change indicate that the rate of tree deaths will only increase.

Seeing the forest for the trees

Subalpine forests cover over 10,000 square miles in Colorado and are best known by those who ski or recreate in the mountains. Subalpine fir and Engelmann spruce dominate the area above the Peak to Peak Highway in the Front Range, and if you go over any mountain pass in Colorado, you're going into the subalpine zone, according to Andrus.

Previous research at ��Ƶ Boulder has shown how wildfire, beetle kill and the two combined can affect the mortality and health of Rocky Mountain subalpine forests. This new research isolated the effects of those two common stressors from those of heat and moisture to find out how much of an effect climate change is having on these tree populations.

“As trees die in increasing numbers due to fire, bark beetles and drought, the warmer and drier climate is making it much less likely that new tree seedlings can establish and replace the dead adult trees,” said Tom Veblen, co-author of the study and professor emeritus of geography.

Launched by Veblen when he arrived on campus in 1982, this is the longest running study of tree mortality in Colorado with measurements made frequently enough to identify the factors causing tree death. Every three years since, graduate students, postdoctoral researchers and undergraduate field assistants have diligently returned to the more than 5,000 marked trees on Niwot Ridge just west of Boulder. In these 13 subalpine forest plots, they recorded that more trees died during summers with higher maximum temperatures and greater moisture deficits.

They found that tree mortality increased from .26% per year during 1982 to 1993, to .82% per year during 2008 to 2019—more than tripling within 40 years.

“It is really challenging because it's not very visually obvious to the casual observer,” said Andrus. “But the thing to keep in mind is that while warmer, drier conditions are also causing more fire and bark beetle outbreaks, these slow and gradual changes are also important.”

Additional authors on this publication include Rachel Chai of the Veblen Lab at ��Ƶ Boulder; Brian Harvey, previously a postdoctoral researcher in geography at ��Ƶ Boulder and now an assistant professor at the University of Washington; and Kyle Rodman, previously a graduate student in the Veblen Lab at ��Ƶ Boulder and now a postdoctoral researcher at the University of Wisconsin Madison.

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Subsequent years of beetle kill and wildfire slow regeneration of Colorado forests

Anonymous — Tue, 23 Feb 2021 00:07:13 +0000

Subsequent years of beetle kill and wildfire slow regeneration of Colorado forests Anonymous (not verified) Mon, 02/22/2021 - 17:07

Katie Rhodes , Boulder Weekly

Conifer trees — spruce, Douglas fir, and pine trees — make up many of Colorado’s subalpine forests, essential habitats for many of the state’s birds and small mammals. These historically dense forests are also essential for sequestering and storing carbon, and hold snowpack during the winter, making them necessary in preserving the state’s water resources. Frequent spruce beetle outbreaks, however, are now coinciding with large-scale wildfires to fundamentally change the way these forests naturally regenerate.

A recent study led by Robert Andrus, recent ��Ƶ Boulder Ph.D. graduate in physical geography, tracks the compounded disturbance interactions of more frequent spruce beetle outbreaks with increasingly devastating wildfires, and the effect this has on subalpine forest regrowth in the San Juan range of the Rocky Mountains. According to his research, an area that experiences a spruce beetle outbreak prior to a wildfire regenerates at a drastically lower rate than forests that have only experienced either beetle kill or wildfire. Climate change seems to be the main driving force: warming temperatures create drier conditions, which puts stress on the trees and prolongs the survival rate of bark beetles.

Historically, bark beetles — like the spruce beetle — and the trees they attack have co-evolved and cultivated a somewhat symbiotic relationship, with forests showing a relatively high rate of recovery after an outbreak as these beetles typically appear in low populations and kill only weak or dying trees. Now, however, the beetle populations are more abundant and are no longer just killing weakened trees, but mature conifers. Plus, the number and severity of outbreaks are increasing and coinciding (within a span of 2-8 years as documented in this study) with severe wildfires caused, at least in part, by drought and increased temperatures. According to previous research conducted by Andrus, a spruce beetle outbreak does not necessarily increase the severity of a wildfire in a region; there is no known link between these disturbances, but when combined they can convert Colorado’s dense forests into grassland and in turn shift entire ecosystems.

“As ecologists we don’t comment on this and say it’s good or bad,” Andrus says. “We’re just interested in how things are changing — and they are changing quickly.”

The latest major bark beetle outbreak in Colorado began in 2005, killing mostly large, dominant spruce trees, many of which were easily over 100 years old and produced the most seed (and conifers regenerate exclusively by seed). Andrus’ research shows that if the same forests that experience beetle kill also succumb to a wildfire in the years after, then there isn’t enough seed in the burned areas to regenerate the species, severely stunting forest re-growth.

“The combined effect of bark beetles knocking out the major seed sources and subsequent wildfires means there just won’t be enough seeds available to allow them to recover within the fire perimeter,” Andrus says.

It’s important to note that this research only covered fires in Rio Grande National Forest in the period between 2012 and 2020, and the state’s mature conifer forests can take over a century to replenish; however, short-term recovery is indicative of long-term recovery, and “with continued global warming, there will come a time when conditions caused by climate change exceed the forests’ ability to recover,” Andrus says.

2020’s East Troublesome Fire in Grand County — which burned more than 190,000 acres and is the second largest wildfire in state history — also occurred in an area previously affected by beetle kill. While Andrus says there is still no definitive data about how this will affect regrowth in the area, he says that spruce beetles, pine beetles and western balsam bark beetles are likely the pests that affected this area.

Regardless, the research team is hopeful that their work will be useful in “developing adaptive management strategies in the context of warming climate and shifting disturbance regimes,” they write in the report.

“Our goal with this research was just to show under what conditions forests will not recover. We’re just showing the trends,” Andrus explains. “It’s up to land management to look at it and decide, ‘Do we want to maintain some of these areas as grasslands? Or do we want to replant some areas?’ They have to take it from here.”

See the article in Boulder Weekly

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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 (��Ƶ Boulder 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 ��Ƶ Boulder 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 ��Ƶ Boulder. “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 ��Ƶ Boulder; 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 , ��Ƶ Boulder 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 ��Ƶ 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.

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 ��Ƶ and now a faculty member at the University of Wisconsin-Madison, contributed to this study.

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GEOG 4371 / 5371 Forest Geography

Anonymous — Thu, 08 Jun 2017 19:43:45 +0000

GEOG 4371 / 5371 Forest Geography Anonymous (not verified) Thu, 06/08/2017 - 13:43

Are you interested in forest ecology and in getting hands-on field experience for a future career in the environment? Have you ever wondered how trees grow so large and live so long? Are you curious about how disturbances such as bark beetles and fire impact our Colorado forests?

If you answered yes, then you should register for Forest Geography!

In Forest Geography, we combine a mixture of field trips, in-class labs, critical thinking, and lectures to give you a strong foundation in forest ecology. When possible, we try to hold class outside because it is easier to learn about trees when you can see and touch them!

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Department of Geography Excellence in Graduate Teaching Awards for Spring 2017

Anonymous — Wed, 10 May 2017 19:35:24 +0000

Department of Geography Excellence in Graduate Teaching Awards for Spring 2017 Anonymous (not verified) Wed, 05/10/2017 - 13:35 Joel Correia , Adam Mahood , Robert (Robbie) Andrus

The Department of Geography is pleased to announce the Excellence in Graduate Teaching Awards for Spring 2017. These awards recognize excellent teaching practices from our Department's graduate students while teaching or assisting with undergraduate classes or working with undergraduate students in a research setting. Joel Correia has been awarded the Excellence in Graduate Teaching-Graduate Part-Time Instructor (GPTI) award. Robert Andrus has been awarded the Excellence in Graduate Teaching-Teaching Assistant (TA) award. Adam Mahood has been awarded the Excellence in Graduate Teaching-Graduate Student Mentoring Award.

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Seven Geography Graduate Students Receive Beverly Sears Research Grants

Anonymous — Mon, 27 Mar 2017 18:14:55 +0000

Seven Geography Graduate Students Receive Beverly Sears Research Grants Anonymous (not verified) Mon, 03/27/2017 - 12:14 Robert (Robbie) Andrus , Joel Correia , Angela Cunningham , Zhaxi Duojie , Mehran Ghandehari , Eric Lovell , Kyle Rodman

Robert Andrus, Joel Correia, Angela Cunningham, Zhaxi Duojie, Mehran Ghandehari, Eric Lovell and Kyle Rodman have each received a Beverly Sears Research Grant. These grants provide funds to assist the student with their PhD research.

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Three Geography Graduate Students receive Spring 2017 Department Teaching Awards

Anonymous — Mon, 27 Mar 2017 18:02:15 +0000

Three Geography Graduate Students receive Spring 2017 Department Teaching Awards Anonymous (not verified) Mon, 03/27/2017 - 12:02 Joel Correia , Robert (Robbie) Andrus , Adam Mahood

The Department of Geography Annual Awards for Excellence in Graduate Teaching have been awarded to Joel Correia (GPTI award), Robert Andrus (TA award), and Adam Mahood (Mentoring Award).

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Robbie Andrus Awarded NSF DDRI

Anonymous — Wed, 17 Aug 2016 03:17:30 +0000

Robbie Andrus Awarded NSF DDRI Anonymous (not verified) Tue, 08/16/2016 - 21:17

Robbie was awarded a National Science Foundation Doctoral Dissertation Research Improvement (DDRI) grant. The award will support his dissertation research project titled "Assessing regeneration niche limitations to upslope migration of subalpine forests: Implications of a changing climate and shifting disturbance regimes".

For more information, see the NSF award page

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Graduate Student Awards - Spring 2016

Anonymous — Tue, 10 May 2016 02:59:27 +0000

Graduate Student Awards - Spring 2016 Anonymous (not verified) Mon, 05/09/2016 - 20:59

The Department of Geography, University of Colorado Boulder congratulates the winners the following Graduate Student Awards. These awards were recognized at our Spring Commencement Ceremony on May 6, 2016.

Gilbert F. White Doctoral Fellowship for 2016-2017 - Theodore Barnhart and Yang Yang

Adam Kolff Memorial Research Fellowship for MA Students - Gretchen Lang and Adam Mahood

Jennifer Dinaburg Memorial Research Fellowship for PhD Students - Robert Andrus, Angela Cunningham, Shae Frydenlund, Alice Hill, Rupak Shrestha, and Alana Wilson

James A. and Jeanne B. DeSana Graduate Research Scholarship - Theodore Barnhart, Shae Frydenlund, Julia Guarino, Aaron Malone, Rupak Shrestha, Kristy Weber, and Qinghuan Zhang

Department of Geography Excellence in Graduate Teaching Awards - Johannes Uhl (Teaching Assistant (TA) Award) and Shae Frydenlund (Graduate Student Mentoring Award).

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