UC Merced

UC Merced study: Climate change could 'profoundly' change Yellowstone ecosystem

An increase in wildfires blamed on climate change could rapidly and profoundly alter the greater Yellowstone ecosystem, according to a study written by environmental engineering and geography professor Anthony Westerling of UC Merced.

The study by Westerling and his colleagues, which will be published online this week in the Proceedings of the National Academy of Sciences, suggests that the expected rising temperatures caused by climate change could increase the frequency of large wildfires in Yellowstone to an unprecedented level, according to a news release from the university.

The projected increase in fires would probably cause a major shift in the greater Yellowstone ecosystem, with fewer dense forests and more open woodland, grass and shrub vegetation.

The change could happen by 2050, Westerling theorizes, with forests becoming younger, the mix of tree species changing and some forests failing to regenerate after repeated fires. That would affect the region's wildlife, hydrology, carbon storage and aesthetics, the news release said.

"What surprised us about our results was the speed and scale of the projected changes in fire in greater Yellowstone," Westerling said. "We expected fire to increase with increased temperatures, but we did not expect it to increase so much or so quickly. We were also surprised by how consistent the changes were across different climate projections."

For their study, the researchers compiled climate data from 1972 to 1999 and examined it in relation to the occurrence and size of large wildfires in the northern Rocky Mountains over the same time period.

Using the resulting statistical patterns, Westerling and his co-authors projected how climate change would affect greater Yellowstone fires through 2099.

In the researchers' simulations, years with no large fires, common in the recent past, become rare by 2050 and are all but eliminated after 2050. The projections show that after 2050, the average annual area burned is about 100,000 hectares, or nearly 400 square miles. By 2075, the average yearly burn exceeds that of the historic season of 1988, when fires claimed more than 1,200 square miles.

Westerling cautioned that the models used in the study will not work once the increase in fires creates a fundamental change in the ecosystem. As the landscape changes, the relationships between climate and fire would change as well.

Westerling and his co-authors said warming alone is likely to lead to a decline in suitable habitat for tree species currently found in greater Yellowstone, and the projected increase in frequency and severity of wildfires could accelerate that process to a tipping point at which the trees may no longer regenerate. This could cause some forested areas to be converted to woodland or nonforest. Similar changes might be expected in other subalpine or boreal forests.

Westerling's co-authors on the study were Monica Turner, the Eugene P. Odum professor of ecology at the University of Wisconsin at Madison and a member of the National Academy of Sciences; Erica Smithwick, an assistant professor of geography and ecology at Pennsylvania State University; Mike Ryan, a research ecologist in the U.S. Forest Service; and Bill Romme, professor emeritus at Colorado State University.