USDA Forest Service Pacific Southwest Research Station
CALIFORNIA – ALBANY-ARCATA-DAVIS-FRESNO-PLACERVILLE-REDDING-RIVERSIDE – HAWAII-HILO
SCIENCE THAT MAKES A DIFFERENCE
http://www.fs.fed.us/psw/
For Immediate Release: Dec. 13, 2010
Contact:
Sherri Eng, PSW Research Station Public Affairs, sleng@fs.fed.us; (510) 559-6327
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: http://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.
http://www.fs.fed.us/psw/.
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