July 25, 2011
"Large, severe fires are normal for this ecosystem. It has burned this way about every few hundred years for thousands of years. But if the current relationship between climate and large fires holds true, a warming climate will drive more frequent large fires in the Greater Yellowstone Ecosystem in the future," explains Monica Turner in a press release. An ecologist with the University of Wisconsin-Madison, Turner has worked in the Greater Yellowstone area for over two decades.
Using past data as well as modeling, the study found that hotter, drier conditions in the western US will quickly turn big fires from a somewhat common occurrence to an annual one in the Yellowstone ecosystem. In fact, they predict by 2050 big fires will hit the Yellowstone ecosystem every year, leading to an estimated 100,00 hectares (247,105 acres) burning annually. Fire rotation—the time an area has to recover from fire impacts—will increase to less than 30 years, which will make it very difficult for some tree species to thrive. Prior to this, average fire rotation has been between 100-300 years.
"What surprised us about our results was the speed and scale of the projected changes in fire in Greater Yellowstone," says lead author Anthony Westerling with the University of California, Merced. "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."
Lodgepole pines, a mainstay species in Yellowstone, could be replaced by aspen and Douglas fir. The ecosystem may even 'flip' from one dominated by conifers to one dominated by open woods, shrubs and grass.
"More frequent fires will not be catastrophic to the area—Yellowstone will not be destroyed—but they will undoubtedly lead to major shifts in the vegetation," says Turner. "It is critical to keep monitoring these forests and study how they respond to future fires."
More frequent fires will also eventually burn themselves out, say experts. If the ecosystem changes significantly, fire will have less fodder to burn and will subside, but the changes to the ecosystem are likely to remain or even go in ways unexpected.
"Our research after the immense 1988 fires revealed surprises and tremendous resilience in Yellowstone's ecosystems, and Yellowstone is likely to surprise us again in the future," Turner says. "It is an incredibly valuable natural laboratory for studying how natural ecosystems adapt to changing environmental conditions."
Already the western US is experiencing a number of climate change-induced impacts: warming of less than 2 degrees Fahrenheit has increased fire in some areas and led to earlier spring snowmelts.
CITATION: Anthony L. Westerling, Monica G. Turner, Erica A. H. Smithwick, William H. Romme, and Michael G. Ryan. Continued warming could transform Greater Yellowstone fire regimes by mid-21st century. PNAS. www.pnas.org/cgi/doi/10.1073/pnas.1110199108.
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