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Vicious cycle: Global warming feeds fire potential
Global warming may greatly accelerate the fire cycle in the desert ecosystem of North America, according to a study published today in the journal Nature.
Elevated carbon dioxide levels, the result of increased fossil fuel burning, can alter the delicate balance of grasses in desert areas, the report notes. This finding may have major implications for the biodiversity and health of desert ecosystems in the western United States.
"This could be a real problem for land managers," said Stan Smith, a professor of biology at the University of Nevada in Las Vegas and lead author of the study.
The scientists based their research on the assumption that CO2 emissions will increase by 50 percent over the next 50 years. Using free-air CO2 enrichment technology, they examined the impact of such an increase on four plant communities in the Mojave Desert ecosystem.
Both plant density and biomass increased at elevated CO2 levels, which coincided with high precipitation years. Following the 1998 El Niño rain cycle, Nevada experienced one of the worst fire seasons on record, with the loss of more than 1.5 million acres of land. "Recent studies suggest that the El Niño high rain cycle will intensify with climate change," Smith noted.
Increased CO2 especially influenced the survival of invasive plants.
Most productive among the plants studied was a non-native grass commonly known as red brome. The grass, which thrives in hotter deserts of the West and is suspected to have helped flame recent fires in the region, is a close relative of cheatgrass.
"What red brome does is provide a lot of fine fuels for fires to get started and carry through," said study co-author Bob Nowak.
"(Red brome) is capable of carrying fire across the bare zones between shrubs, and thus burn both the grasses and shrubs," Smith added. "Prior to the introduction of these exotic grasses, there were few plant species that could create such a continuous cover, and so these desert scrub ecosystems did not historically burn."
When cheatgrass and fire conspire, they continue to wipe out native grass species. With each blaze, the fire-savvy annual endures, while native species are choked out.
"The dominance of the exotic grass species bromus tectorum (cheatgrass) which has invaded many thousands of acres in western North America may be enhanced by elevated CO2 and thus alter competitive balance and the fire cycle in semi-arid shrub steppe environments," the authors write. "If these predictions are realized, biodiversity in arid and semi-arid ecosystems could be significantly reduced."
Red brome has the same potential. "The clear picture we are seeing is that this exotic annual could become much more dominant in the ecosystem and could enhance the fire cycle," Smith said.
Conservation groups also cite climate change as one of the causes behind the 2000 fire season, which ravaged more than 5 million acres in the western United States.
Smith allows that Nevada's fire cycle in relation to invasive grasses is very different from factors in the 2000 forest fires. But he, too, believes that climate change may have played a role in the recent disaster.
"In a lot of ways the experiment we're doing is a look into the future, and the future doesn't look so good," Nowak said. "What we are already seeing in the northern Nevada Great Basin with cheatgrass, we are going to see more and more in southern Nevada in the Mojave with red brome."
Copyright 2000, Environmental News Network, All Rights Reserved
Report strengthens link between pollution, global warming
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