Posts tagged Clark University
CU study: Spruce beetle infestation in N. Colo. tied to drought
Oct 10th
A new University of Colorado Boulder 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-Boulder 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.
This spruce forest hit with a double whammy– Spruce bark beetles killed the trees then a forest fire burned it.
Spruce beetles, like their close relatives, mountain pine beetles, are attacking large areas of coniferous forests across the West. While the mountain pine beetle outbreak in the Southern Rocky Mountains is the best known and appears to be the worst in the historical record, the lesser known spruce beetle infestation has the potential to be equally or even more devastating in Colorado, said Hart, lead author on the new study.
“It was interesting that drought was a better predictor for spruce beetle outbreaks than temperature,” said Hart of the geography department. “The study suggests that spruce beetle outbreaks occur when warm and dry conditions cause stress in the host trees.”
A paper on the subject was published online in the journal Ecology. Co-authors include CU-Boulder geography Professor Thomas Veblen; former CU-Boulder graduate student Karen Eisenhart, now at Edinboro University of Pennsylvania; and former CU-Boulder students Daniel Jarvis and Dominik Kulakowski, now at Clark University in Worcester, Mass. The National Science Foundation and the National Geographic Society funded the study.
The new study also puts to rest false claims that fire suppression in the West is the trigger for spruce beetle outbreaks, said Veblen.
Spruce beetles range from Alaska to Arizona and live in forests of Engelmann spruce and subalpine fir trees in Colorado. The CU-Boulder study area included sites in the White River, Routt, Arapaho, Roosevelt and Grand Mesa national forests as well as in Rocky Mountain National Park.
The CU-Boulder team assembled a long-term record of spruce beetle outbreaks from the northern Front Range to the Grand Mesa in western Colorado using a combination of historical documents and tree ring data from 1650 to 2011. Broad-scale outbreaks were charted by the team from 1843-1860, 1882-1889, 1931-1957 and 2004 to 2010.
The researchers used a variety of statistical methods to tease out causes for variations in the dataset at 18 sites in Colorado. “The extent to which we could distinguish between the warming signals and the drought signals was surprising,” said Veblen. “These are two things that easily can get mixed together in most tree ring analyses.”
European Spruce bark beetle
There are several lines of evidence that drought is the main driver of the spruce beetle outbreak. The new study showed when northwest Colorado was in a warm, wet climate period from 1976 to 1998, for example, both spruce beetle reproduction and tree defenses like “pitching” beetles out of tree interiors with resin were likely high. But during that period of warming, outbreak was minimal.
The strongest climate correlation to spruce beetle outbreaks was above average annual values for the Atlantic Multi-decadal Oscillation, or AMO, a long-term phenomenon that changes sea-surface temperatures in the North Atlantic. Believed to shift from cool to warm phases roughly every 60 years, positive AMO conditions are linked to warmer and drier conditions over much of North America, including the West.
Veblen said the AMO shifted from its cool to warm phase in the 1990s, meaning the climate phenomenon could be contributing to drought conditions in the West into the middle of this century. A 2006 tree-ring study involving Veblen, his former student, Thomas Kitzberger and researchers from several other institutions concluded that the warm phase of AMO also was correlated to increased wildfires in the West.
In addition to AMO, the researchers looked at two other ocean-atmosphere oscillations — the El Nino Southern Oscillation and the Pacific Decadal Oscillation — as well as past temperatures, precipitation and aridity to better understand the spruce beetle outbreaks. The team found that another effective predictor of drought conditions was summer “vapor pressure deficit,” a measurement of atmospheric dryness, said Veblen.
In the new study, the researchers were particularly interested in “radial growth” rates of tree rings from sub-canopy trees of various species in the study areas that thrived following outbreaks. One hallmark of spruce beetle outbreaks is that slow radial growth rates in such areas are followed by extremely rapid radial growth rates, an indication smaller trees flourish in the absence of the larger spruce trees because of decreased competition for water and increased opportunities for photosynthesis, said Hart.
The area of high-elevation forests affected by spruce beetles is growing in the West, Hart said. “In 2012, U.S. Forest Service surveys indicated that more area was under attack by spruce beetles than mountain pine beetles in the Southern Rocky Mountains, which includes southern Wyoming, Colorado and northern New Mexico,” she said. “The drought conditions that promote spruce beetle outbreak are expected to continue.”
Spruce beetles have even hit Alaska.
One big concern about spruce beetle outbreaks is their effects on headwater streams that are important for water resources, said Veblen. “In the short term, trees killed by spruce beetles will lead to less water use by trees and more water discharge into streams. But in the long term, the absence of the trees killed by beetles may lead to less persistence of snow and earlier runoff.”
Veblen said it might seem counterintuitive to some that spruce-fir subalpine forests in Colorado are larger by area than lodgepole/ponderosa pine forests. “It is probably because spruce and subalpine forests are found in more remote areas not as visible to most people,” he said. “But potentially, the current spruce beetle outbreak could affect a larger area than the mountain pine beetle outbreak.”
The study had its beginnings in 1986, when Veblen and his students began compiling spruce and subalpine fir tree rings from various study sites in the Colorado mountains. Tree rings from individual trees — which carry information about weather, climate and even events like volcanic eruptions — can be matched up and read with rings from other trees, much like the pages of a book, from year to year and even from season to season.
-CU-
CU study: Melting glaciers are largely responsible for sea level rise
May 16th
While 99 percent of Earth’s land ice is locked up in the Greenland and Antarctic ice sheets, the remaining ice in the world’s glaciers contributed just as much to sea rise as the two ice sheets combined from 2003 to 2009, says a new study led by Clark University and involving the University Colorado Boulder.
The new research found that all glacial regions lost mass from 2003 to 2009, with the biggest ice losses occurring in Arctic Canada, Alaska, coastal Greenland, the southern Andes and the Himalayas. The glaciers outside of the Greenland and Antarctic sheets lost an average of roughly 260 billion metric tons of ice annually during the study period, causing the oceans to rise 0.03 inches, or about 0.7 millimeters per year.
The study compared traditional ground measurements to satellite data from NASA’s Ice, Cloud and Land Elevation Satellite, or ICESat, and the Gravity Recovery and Climate Experiment, or GRACE, missions to estimate ice loss for glaciers in all regions of the planet.
“For the first time, we’ve been able to very precisely constrain how much these glaciers as a whole are contributing to sea rise,” said geography Assistant Professor Alex Gardner of Clark University in Worcester, Mass., lead study author. “These smaller ice bodies are currently losing about as much mass as the ice sheets.”
A paper on the subject is being published in the May 17 issue of the journal Science.
“Because the global glacier ice mass is relatively small in comparison with the huge ice sheets covering Greenland and Antarctica, people tend to not worry about it,” said CU-Boulder Professor Tad Pfeffer, a study co-author. “But it’s like a little bucket with a huge hole in the bottom: it may not last for very long, just a century or two, but while there’s ice in those glaciers, it’s a major contributor to sea level rise,” said Pfeffer, a glaciologist at CU-Boulder’s Institute of Arctic and Alpine Research
ICESat, which ceased operations in 2009, measured glacier changes using laser altimetry, which bounces laser pulses off the ice surface to determine changes in the height of ice cover. The GRACE satellite system, still operational, detects variations in Earth’s gravity field resulting from changes in the planet’s mass distribution, including ice displacements.
GRACE does not have a fine enough resolution and ICESat does not have sufficient sampling density to study small glaciers, but mass change estimates by the two satellite systems for large glaciated regions agree well, the scientists concluded.
“Because the two satellite techniques, ICESat and GRACE, are subject to completely different types of errors, the fact that their results are in such good agreement gives us increased confidence in those results,” said CU-Boulder physics Professor John Wahr, a study co-author and fellow at the university’s Cooperative Institute for Research in Environmental Sciences.
Ground-based estimates of glacier mass changes include measurements along a line from a glacier’s summit to its edge, which are extrapolated over a glacier’s entire area. Such measurements, while fairly accurate for individual glaciers, tend to cause scientists to overestimate ice loss when extrapolated over larger regions, including individual mountain ranges, according to the team.
Current estimates predict if all the glaciers in the world were to melt, they would raise sea level by about two feet. In contrast, an entire Greenland ice sheet melt would raise sea levels by about 20 feet, while if Antarctica lost its ice cover, sea levels would rise nearly 200 feet.
The study involved 16 researchers from 10 countries. In addition to Clark University and CU-Boulder, major research contributions came from the University of Michigan, the Scripps Institution of Oceanography in San Diego, Trent University in Ontario, Canada, and the University of Alaska Fairbanks.
Built by Ball Aerospace & Technologies in Boulder, NASA’s ICESat satellite was successfully operated from the CU-Boulder campus by a team made up primarily of undergraduates from its launch in 2003 to its demise in 2009 when the science payload failed. The students participated in the unusual decommissioning of a functioning satellite in 2010, bringing the craft into Earth re-entry to burn up. ICESat’s successor, ICESat-2, is slated for launch in 2016 by NASA.
-CU media release-
