Why are aspen dying?

July 1, 2013, Brigham Young University

(Phys.org) —If Utah's quaking aspen appear to be quaking more than usual this summer, the trees have reason to tremble, says a Brigham Young University biologist. In dappled forests across the West, aspen trees are battling deadly killers from heat stroke to bud-nipping predators to tree "heart attacks."

In a July special tree issue of Forest Ecology and Management, BYU biology professor Sam St. Clair and colleagues from across the west report that they are seeing troubling declines in aspen populations in Utah, Arizona, and Colorado. The die-offs are seen most dramatically at lower elevations where and hotter temperatures are killing older .

"Aspen trees, because of their sensitivity to drought, experience what I call 'plant heart attacks,'" says St. Clair, lead researcher on a multi-year study of aspen in Utah. "As you get hot dry conditions, taller aspen trees have to pull water up from the soil more strongly and it creates bubbles in the water and blocks the transport of water and nutrients up the tree. The tree will die from the top down."

The biology of aspen is complex because thousands of trees in one stand are all one organism, genetically identical clones tied to a mother root system. If the clone dies, thousands of trees can be lost.

In Fishlake National Forest, where aspen clones have been a part of the Utah landscape for thousands of years, St. Clair says the branches of many low-elevation aspen trees were bare last year even before the chill of fall. Researchers from Utah State University have made similar observations at nearby 107-acre "Pando," the largest documented genetic aspen clone.

Just as older aspen are dying from drought and hotter temperatures, younger trees are also dying, primarily from over-browsing by hungry deer, elk and livestock. Since aspen clones are all connected to a central root system, worry that if there are no young trees to photosynthesize and to sustain the organism, it will eventually die.

"If drought occurs for long enough and is severe enough, it would even kill the younger aspen trees. Extended drought over long periods of time would in time affect the mother root system that supports the whole clone," says St. Clair.

In the face of this trend, St. Clair and his BYU students are working with the Division of Wildlife Resources to study the effects of over-browsing, species facilitation, drought impact, recovery after fire, and other factors that may be killing trees. The research will be used to help establish land use guidelines throughout the western states.

"We're studying the sustainability of forests especially aspen forests at lower elevations where we are susceptible to losing them. I want to understand how these systems work," he says. "Aspen set the stage for all of the other organisms so aspen is at the foundation of everything that goes on here biologically."

The filtered light of the aspen canopy creates a micro-ecosystem that nurtures plant and animal species. In addition to providing forage and shelter for wildlife, St. Clair says aspen also help human populations by accumulating more snowpack that increases water availability for human use. Aspen stands also help regenerate forests after fire.

Within the aspen canopy, St. Clair has shown how aspen facilitates other species. In one instance, conifer trees grow at the base of aspen but they outgrow the aspen and eventually kill the host tree. Nature has a way of restoring balance to the system; fire wipes out the less desirable conifers but the aspen root clones survives.

"These systems are fire dependent. Fire will come into the system and the aspen will regenerate and start this cycle over," he says.

On Utah's Monroe Mountain, an area charred last year by a June forest fire, hundreds of aspen suckers quickly emerged from the mother . BYU and the DWR have fenced off small plots to see if protecting the seedlings from browsers will help them survive. Although they can't fence off every forest, St. Clair says solid research will help them to better understand what is killing aspen and how humans will be impacted if we lose these forests.

"It's a keystone species. All of the things we care about in our lives tie back to these systems functioning in a certain way. I want to understand the connection between the loss of aspen forests and what that means to society as a whole."

Explore further: Western aspen trees commonly carry extra set of chromosomes

More information: www.sciencedirect.com/science/journal/03781127/299

Related Stories

Western aspen trees commonly carry extra set of chromosomes

October 31, 2012

A large proportion of aspen in the western U.S. sport an extra set of chromosomes in their cells, a phenomenon termed triploidy, according to new research published Oct. 31 in the open access journal PLoS ONE by Karen Mock ...

Tree die-off triggered by hotter temperatures

February 11, 2013

A team of scientists, led by researchers at Carnegie's Department of Global Ecology, has determined that the recent widespread die-off of Colorado trembling aspen trees is a direct result of decreased precipitation exacerbated ...

Aspen's 'dandelion' habits challenge mountain evergreens

February 22, 2010

(PhysOrg.com) -- The face of high-elevation evergreen forests in Western Canada could be drastically altered as a combination of climate change, human and natural disturbances is making spruce and pine forests in the Rocky ...

The case of the dying aspens

December 12, 2011

Over the past 10 years, the death of forest trees due to drought and increased temperatures has been documented on all continents except Antarctica. This can in turn drive global warming by reducing the amount of carbon dioxide ...

Are wolves saving Yellowstone's aspen trees from elk?

September 1, 2010

Previous research has claimed that the reintroduction of wolves to Yellowstone National Park in 1995 is helping restore quaking aspen in risky areas where wolves prowl. But apparently elk hungry for winter food had a different ...

Recommended for you

Scale-eating fish adopt clever parasitic methods to survive

January 17, 2018

Think of them as extra-large parasites. A small group of fishes—possibly the world's cleverest carnivorous grazers—feeds on the scales of other fish in the tropics. The different species' approach differs: some ram their ...

How living systems compute solutions to problems

January 17, 2018

How do decisions get made in the natural world? One possibility is that the individuals or components in biological systems collectively compute solutions to challenges they face in their environments. Consider that fish ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.