Climate change in arid lands has very likely increased the size and number of forest fires, insect outbreaks, and tree mortality in the western and southwestern U.S., and is projected to cause changes in other natural processes, according to a panel of University of Arizona scientists.
Extensive forest areas of the Southwest have undergone great changes over the past century as a consequence of livestock grazing, logging, road building, and fire suppression, said Thomas Swetnam, director of the UA's Laboratory for Tree-Ring Research.
These changes include increased forest densities and fuels, leading to wildfires of extraordinary severity, Swetnam said.
He was among the experts to speak during a conference, "Adaptation to Climate Change in the Desert Southwest: Impacts and Opportunities," being held at the Westward Look Resort today and Friday.
Sponsored by several several UA units and departments, the conference brought together scientists and other experts from across the nation to discuss the issue of climate change in the Southwest.
Some forest and woodland ecosystems are capable of recovering from high severity fire, while others are not; observations and studies in ponderosa pine forests indicate that many areas that have been burned in severe fires have converted to grasslands or shrub fields, Swetnam said.
Adapting to climate change will require the careful restoration and management of forests and woodlands to increase the resiliency of these ecosystems to wildfire events and other disturbances, he added.
The response to a loss of tree cover and loss of roots within a burned area is "a more flashy" watershed; rain does not soak into the ground as well as it normally does, resulting in more runoff and increased prospects of floods, said Holly Hartmann, a UA associate research scientist and director of the Arid Lands Information Center.
"With those kinds of impacts, you have to think about how to respond to extreme events" other than warmer temperatures or drought, Hartmann said.
In addition, climate change in arid lands will create physical conditions conducive to wildfire, and the proliferation of exotic grasses will provide fuel, thus causing fire frequencies to increase in a self-reinforcing fashion, said David Breshears, professor in the UA School of Natural Resources.
In arid regions where ecosystems have no co-evolved with a fire cycle, the probability of loss of iconic megaflora, such as saguaro cacti and Joshua trees, is likely, Breshears said.
Higher temperature, increased drought, and more intense thunderstorms will very likely promote the invasion of exotic grass species in arid lands and increase erosion, he said. Furthermore, these climate changes are expected to decrease the vegetation cover that protects the ground surface from wind and water erosion.