It’s AGU week in San Francisco, of course that means the annual barrage of science by press release. I was struck by this juxtaposition of two press releases at Eurekalert this morning. Note the headlines of the screencap below:
Here are the two releases in full:
The top one:
Team of scientists predicts continued death of forests in southwestern US due to climate change
(Santa Barbara, Calif.) –– If current climate projections hold true, the forests of the Southwestern United States face a bleak future, with more severe –– and more frequent –– forest fires, higher tree death rates, more insect infestation, and weaker trees. The findings by university and government scientists are published in this week’s issue of the Proceedings of the National Academy of Sciences (PNAS).
“Our study shows that regardless of rainfall going up or down, forests in the Southwest U.S. are very sensitive to temperature –– in fact, more sensitive than any forests in the country,” said first author Park Williams, postdoctoral researcher in the Department of Geography at UC Santa Barbara. “Forests in the Southwest are most sensitive to higher temperatures in the spring and summer, and those are the months that have been warming the fastest in this area.”
Past forest studies have shown that warmer temperatures are associated with wildfires and bark beetle outbreaks. “We found that up to 18 percent of forest area in the Southwest –– millions of acres –– has experienced mortality due to severe wildfires and bark beetle outbreaks in the last 20 years,” said Williams.
Co-author Joel Michaelsen, a professor of geography at UCSB, said: “In order to carry out this research project, Park Williams assembled a very comprehensive data set of over 1,000 tree ring chronologies from all across the United States.” Michaelsen is a dendroclimatologist –– a scientist who studies climate using analysis of tree rings.
“Instead of using the chronologies to reconstruct past climate patterns, as is usually done in dendroclimatic work, the relationships between growth and climate were used to study possible impacts of future climate change on forest health,” said Michaelsen. “One noteworthy finding was that tree growth throughout the Southwestern U.S., while quite sensitive to precipitation variations, is also negatively impacted by warmer temperatures. This is an important result, because predictions of future warming in the region are considerably more certain than any predictions of precipitation change.”
Researchers found that historic patterns of vegetation change, insect outbreaks, fire activity, runoff, and erosion dynamics show that landscapes often respond gradually to incremental changes in climate and land-use stressors until a threshold is reached, at which time there may be dramatic landscape changes, such as tree die-offs or episodes of broad-scale fire or erosion. They also found that the stressors that contribute to tree mortality tipping points can develop over landscape and even sub-continental scales.
Co-author Christopher Still, an associate professor of geography at UCSB, said: “These predicted large-scale changes in forest cover and composition (i.e., types of tree species present) will have large implications for everything from snowpack and the river flows that our society depends on, to the intensity and frequency of fires, to the visual appearance of these landscapes that drives much of the tourism in this region.”
Added co-author Craig D. Allen of the U.S. Geological Survey: “Such big, fast changes in Southwest forest vegetation could have significant effects on a wide range of ecosystem goods and services, from watershed protection and timber supplies to biodiversity and recreation. These emerging vulnerabilities present increasingly clear challenges for managers of southwestern forests to develop strategies to mitigate or adapt to the coming changes, in order to sustain these forested ecosystems and their benefits into the future.”
Forests help retain rainwater and keep it from flowing down mountains immediately, noted Williams in explaining the importance of forests to landscapes and rivers. “When forests disappear,” he said, “water runs downhill more quickly and takes the upper layers of soil with it.”
According to Williams, the erosion makes it harder for future generations of trees to establish themselves and makes it more difficult for people to capture storm water as it flows from the mountains. In addition, erosion increases the amount of sediment flowing in rivers and settling in lakes, and causes water to remain in the forest long after the rain.
The paper also points to the many implications of these changes for future management and use of Southwest forests.
The scientific article is part of a special PNAS feature edition called “Climate Change and Water in Southwestern North America.”
Note to editors: Park Williams is available by e-mail at email@example.com. Christopher Still is available at (805) 450-3070, or by e-mail at firstname.lastname@example.org. For downloadable images see: http://www.ia.ucsb.edu/pa/display.aspx?pkey=2387
The American Geophysical Union (AGU) will hold a press conference on these findings at 5 p.m. today at the Moscone West Building, room 300, in San Francisco. Park Williams and other scientists will present results. To register for the press conference, please contact The AGU at email@example.com.
The bottom one:
Contact: Sherri Eng
USDA Forest Service, Pacific Southwest Research Station
Drought and rising temperatures weaken southwest forests
ALBANY, Calif.—Forests in the southwestern United States are changing and will face reduced growth if temperatures continue to rise and precipitation declines during this century, according to a study conducted by a team of scientists from the U.S. Forest Service; University of California, Santa Barbara; U.S. Geological Survey; and University of Arizona. Their findings were released today in the Proceedings of the National Academy of Sciences (PNAS) special issue on climate change.
Using tree-ring data and climate models, the team determined that rising temperatures and declining precipitation has led to an overall lower fitness of forests in the Southwest. This weakening of forest health has led to the trees’ inability to survive wildfires and stave off bark beetle attacks. Fire and bark beetles caused high levels of mortality in 14-18 percent of forest areas in the Southwest, according to the scientists, who examined the tree rings of piñon pine, ponderosa pine and Douglas fir.
“These results have been observed previously on a case-by-case basis, but our demonstration of the pervasive effects of warming and drought should better enable water and land managers to prepare for climate adaptation in coming decades,” says Connie Millar, a research climate ecologist with the U.S. Forest Service’s Pacific Southwest Research Station, who co-authored the study.
Scientists analyzed annual tree-ring width data from 853 tree populations located throughout the continental United States. Of those, 235 samples represented trees located in Arizona and New Mexico. These samples were compared to each other in order to identify trends on how certain climatic conditions affect tree growth.
The projected continuing decline of these forests could mean significant ecosystem changes if the Southwestern forests continue to be impacted by wildfires and insect attacks. Drier and hotter climate conditions will continue to favor shrublands, chaparral and other invasive species.
These findings may be useful in helping forest managers make key decisions about how to adapt to climate change. The study highlighted the most vulnerable areas and suggested fuels treatment, focused fire-suppression efforts, intensive use of insect-aggregating hormones, and early detection-rapid response for invasives elimination as ways to protect high-priority areas.
The protection and preservation of forests in the Southwest is particularly important because they help maintain the area’s watershed which feeds into the Colorado River. An altered hydrologic regime could cause a cascade of effects on everything—and everyone—dependent on the river’s water supply.
The study, “Forest Responses to Increasing Aridity and Warmth in the Southwestern United States” will be available at: www.pnas.org/site/misc/special.shtml
The Pacific Southwest Research Station is headquartered in Albany, Calif. The station develops and communicates science needed to sustain forest ecosystems and other benefits to society. It has laboratories and research centers in California, Hawaii, and the United States-affiliated Pacific Islands and employs about 50 scientists. www.fs.fed.us/psw/.
Obviously, these two gals never talk to each other, but the result is comical. With such dueling messages, is it any wonder the public is getting battle fatigued?