NSF ON ROCKY MOUNTAIN BARK BEETLES AND WATER QUALITY

Photo:  Rocky Mountains. Credit:  Wikimedia, Williams Jim, U.S. Fish and Wildlife Service. 

FROM:  NATIONAL SCIENCE FOUNDATION 

Earth Week: Bark beetles change Rocky Mountain stream flows, affect water quality

What happens when millions of dead trees, killed by beetles, no longer need water?

On Earth Week--and in fact, every week now--trees in mountains across the western United States are dying, thanks to an infestation of bark beetles that reproduce in the trees' inner bark.

Some species of the beetles, such as the mountain pine beetle, attack and kill live trees. Others live in dead, weakened or dying hosts.

In Colorado alone, the mountain pine beetle has caused the deaths of more than 3.4 million acres of pine trees.

What effect do all these dead trees have on stream flow and water quality? Plenty, according to new research findings reported this week.

Dead trees don't drink water

"The unprecedented tree deaths caused by these beetles provided a new approach to estimating the interaction of trees with the water cycle in mountain headwaters like those of the Colorado and Platte Rivers," says hydrologist Reed Maxwell of the Colorado School of Mines.

Maxwell and colleagues have published results of their study of beetle effects on stream flows in this week's issue of the journal Nature Climate Change.

As the trees die, they stop taking up water from the soil, known as transpiration. Transpiration is the process of water movement through a plant and its evaporation from leaves, stems and flowers.

The "unused" water then becomes part of the local groundwater and leads to increased water flows in nearby streams.

The research is funded by the National Science Foundation's (NSF) Water, Sustainability and Climate (WSC) Program. WSC is part of NSF's Science, Engineering and Education for Sustainability initiative.

"Large-scale tree death due to pine beetles has many negative effects," says Tom Torgersen of NSF's Directorate for Geosciences and lead WSC program director.

"This loss of trees increases groundwater flow and water availability, seemingly a positive," Torgersen says.

"The total effect, however, of the extensive tree death and increased water flow has to be evaluated for how much of an increase, when does such an increase occur, and what's the water quality of the resulting flow?"

The answers aren't always good ones.

Green means go, red means stop, even for trees

Under normal circumstances, green trees use shallow groundwater in late summer for transpiration.

Red- and gray-phase trees--those affected by beetle infestations--stop transpiring, leading to higher water tables and greater water availability for groundwater flow to streams.

The new results show that the fraction of late-summer groundwater flows from affected watersheds is about 30 percent higher after beetles have infested an area, compared with watersheds with less severe beetle attacks.

"Water budget analysis confirms that transpiration loss resulting from beetle kill can account for the increase in groundwater contributions to streams," write Maxwell and scientists Lindsay Bearup and John McCray of the Colorado School of Mines, and David Clow of the U.S. Geological Survey, in their paper.

Dead trees create changes in water quality

"Using 'fingerprints' of different water sources, defined by the sources' water chemistry, we found that a higher fraction of late-summer streamflow in affected watersheds comes from groundwater rather than surface flows," says Bearup.

"Increases in stream flow and groundwater levels are very hard to detect because of fluctuations from changes in climate and in topography. Our approach using water chemistry allows us to 'dissect' the water in streams and better understand its source."

With millions of dead trees, adds Maxwell, "we asked: What's the potential effect if the trees stop using water? Our findings not only identify this change, but quantify how much water trees use."

An important implication of the research, Bearup says, is that the change can alter water quality.

The new results, she says, help explain earlier work by Colorado School of Mines scientists. "That research found an unexpected spike in carcinogenic disinfection by-products in late summer in water treatment plants."

Where were those water treatment plants located? In bark beetle-infested watersheds.

-- Cheryl Dybas, NSF
Investigators
Reed Maxwell
Eric Dickenson
Jonathan Sharp
Alexis Navarre-Sitchler
Related Institutions/Organizations
Colorado School of Mines

WATERSHEDS AFFECTED BY BARK BEETLES

 

Lodgepole Pines.  Credit:  Widimedia.

FROM: NATIONAL SCIENCE FOUNDATION
Ghosts of Forests Past: Bark Beetles Kill Lodgepole Pines, Affecting Entire Watersheds

In mountains across the Western United States, scientists are racing against time--against a tiny beetle--to save the last lodgepole pines.


Forests are bleeding out from the effects of the beetles, their conifers' needles turning crimson before the trees die.

Now, researchers are also hurrying to preserve the region's water quality, affected by the deaths of the pines.

"When these trees die," says hydrologist Reed Maxwell of the Colorado School of Mines, "the loss of the forest canopy affects hydrology and the cycling of essential nutrients."

Maxwell and other scientists recently published results of their study in the journal Biogeochemistry.

Co-authors, in addition to Maxwell, are Kristin Mikkelson, Lindsay Bearup, John McCray and Jonathan Sharp of the Colorado School of Mines, and John Stednick of Colorado State University. Mikkelson is the paper's first author.


Bark beetle numbers: heating up
"The mountain pine beetle outbreak in Western states has reached epidemic proportions," says Maxwell.

Bark beetles, as they're known, are native to the United States. They're so-named as the beetles reproduce in the inner bark of trees. Some species, such as the mountain pine beetle, attack and kill live trees. Others live in dead, weakened or dying hosts.

Massive outbreaks of mountain pine beetles in western North America since the mid-2000s have felled millions of acres of forests from New Mexico to British Columbia, threatening increases in mudslides and wildfires.

Climate change could be to blame. The beetles' numbers were once kept in check by cold winter temperatures and trees that had plenty of water to use as a defense.

But winters have become warmer, and droughts have left trees water-stressed and less able to withstand an onslaught of winged invaders.

"A small change in temperature leads to a large change in the number of beetles--and now to a large change in water quality," says Tom Torgersen, director of the National Science Foundation's (NSF) Water, Sustainability and Climate (WSC) Program, which funded the research.

WSC is part of NSF's Science, Engineering and Education portfolio of investments.

"Bark beetles have killed 95 percent of mature lodgepole pines," says Maxwell.

Death of a lodgepole pine

But the trees don't die immediately.

When beetles invade, a blue fungus spreads inside a tree's trunk, choking off transpiration and killing the tree in about two years.

The trees turn blood-red, then the ashen gray of death, dropping their needles to the forest floor.

"Some of the most important effects of bark beetles may be changes in the hydrologic cycle," says Maxwell, "via snow accumulation under trees and water transpiration from trees and other plants."

Biogeochemical changes may be even more important, he says, with carbon and nitrogen cycles interrupted.

"We're studying these hydrologic and geochemical processes through a combination of field work, lab research and computer modeling," says Maxwell.


Whither the beetles, so the trees, forests...and waters
Changes in tree canopies affect snowpack development and snowmelt.

For example, a lack of needles on branches lets more snow fall through the canopy--snow that would otherwise be caught on branches. A tree without needles also has less shade beneath it.

The result is a shallower snowpack, earlier snowmelt and less water in spring.

"The real question," Maxwell says, "is how these processes translate from individual trees to hillslopes to large watersheds."

Dead trees don't transpire water. Once a forest has died, this important flow of moisture from the ground to the atmosphere ceases.

That can mean a loss of as much as 60 percent of the water budget, although increases in ground evaporation or transpiration from understory shrubs and bushes may compensate for some of the lack.

"Combined with what's happening to snowpack depth," says Maxwell, "it becomes a complicated relationship that can change the timing and magnitude of spring runoff from snowmelt--and an entire year's water resources."

Tree mortality also appears to affect forest carbon and nitrogen cycles through increases in dissolved organic carbon.

"We've seen changes in drinking water quality in beetle-affected watersheds that are almost certainly related to high dissolved organic carbon levels," says Maxwell.

As Maxwell, Mikkelson, Bearup and colleagues discovered, there's a lag time between beetle infestation and water quality declines, "so tree and forest water transport processes are very likely involved," says Maxwell.


All watersheds great and small
The observations prompted the researchers to study processes at the individual tree and hillslope scale to better understand what's happening in watersheds large and small.

"Watersheds are complex, interrelated systems," says Maxwell, "which makes understanding them more challenging.

"We're developing complex, numerical models of bark beetle-infested watersheds that include our best understanding of how and where water flows. The models are allowing us to isolate individual processes by turning them on and off in 'what-if' scenarios."

Along with on-the-ground observations, he says, "they're showing us more of the complex story of pine beetle effects on Western watersheds.

"We now know that healthy watersheds ultimately depend on healthy forests."

Western streams and rivers soon may be part of dead and dying forests, surrounded only by the ghosts of lodgepole pines past.

BARK BEETLES IN PINE TREES CONTRIBUTE TO AIR POLLUTION IN TOURIST AREAS

Photo Credit:  U.S. Park Service
FROM:  NATIONAL SCIENCE  FOUNDATION
Beetle-infested Pine Trees Contribute to Air Pollution and Haze in Forests
Popular summer tourist destinations may 'see' the effects
May 23, 2012
The hordes of bark beetles that have bored their way through more than six billion trees in the western United States and British Columbia since the 1990s do more than kill stately pine, spruce and other trees.

Results of a new study show that these pests can make trees release up to 20 times more of the organic substances that foster haze and air pollution in forested areas.
A paper reporting the findings appears today in the journalEnvironmental Science & Technology, published by the American Chemical Society.

Scientists Kara Huff Hartz of Southern Illinois University Carbondale, Gannet Hallar of the Desert Research Institute's Storm Peak Laboratory in Steamboat Springs, Colo., and colleagues say that western North America is experiencing a population explosion of mountain pine beetles, a type of bark beetle that damages and kills pines and other trees.

The beetles bore into the bark of pine trees to lay eggs.
Gases called volatile organic compounds (VOCs) are released from the bore holes, which act as defense mechanisms against the beetles.

VOCs, however, also contribute to the smog and haze that obscures views of natural landscapes in U.S. national parks and other natural areas where tourists flock in summer.

"These results highlight one of the many potential feedbacks due to aerosols, which continue to be the greatest challenge to improving predictive models for air quality, visibility and climate," says Alex Pszenny, program director in the National Science Foundation's Division of Atmospheric and Geospace Sciences, which funded the research.

To determine how beetle attacks affect the atmosphere, the researchers measured VOC levels in the air near healthy and infected pine trees.

They found that beetle-infested trees release up to 20 times more VOCs than healthy trees near the ground surface.

The predominant type of VOC released by trees was called ß-phellandrene.
The data suggest that the bark beetle epidemic in the western United States could have led to higher concentrations of organic compounds in the air, which may contribute to haze.
The haze, say the scientists, may in turn harm human health, reduce visibility and affect climate.

Other authors of the paper are Hardik Amin and Aaron Brown of Southern Illinois University Carbondale; P. Tyson Atkins of the Desert Research Institute; Rachel Russo of the University of New Hampshire; and Barkley Sive of Appalachian State University in Boone, N.C.