Justin Valliere / UC Riverside
Nitrogen levels increase along with proximity to Los Angeles. Researchers at UC Riverside, the National Parks Service and the U.S. Forest Service are studying how high levels of nitrogen are affecting plant diversity in the Santa Monica Mountains.
Preliminary findings released Tuesday from a study in the Santa Monica Mountains show that air pollution may be increasing fire danger in the mountain range.
Researchers from the National Park Service, University of California Riverside and the U.S. Forest Service have been monitoring atmospheric nitrogen at 10 sites in the Santa Monica Mountains for two years. Nitrogen is a byproduct of gas combustion and a major component of smog. Researchers attribute nitrogen depositing out of the air in the area to vehicle emissions.
Data that was analyzed after the first year of a three-year study show that a gradient of nitrogen levels exist across the test area, increasing from west to east. Atmospheric nitrous oxide levels at the eastern edge of the study range are at levels more than three times higher than those found at places along the western edge.
“Nitrogen enrichment into ecosystems is probably the third largest global change driver and driver of loss of biodiversity that we face on the planet,” said Irina Irvine, a wildlife ecologist for the National Park Service at the Santa Monica Mountains National Recreation Area.
Two locations identified as having lower levels of atmospheric nitrogen were experimentally given added levels of nitrogen and monitored. Keystone native plants declined at higher nitrogen levels, while invasive grasses thrived.
As exotic species out-compete native plants, that could increase potential fire danger, as native species are more fire resistant.
“If your cigarette butt or your backfire hit a coastal sage scrub plant or a chaparral plant, it’s probably got more moisture involved in its tissues. It’s going to be a little bit harder to ignite,” Irvine said. “But if you’ve got a bunch of grasses there, then off you go to the races.”
Irvine said that further research will be done to try to quantify the increase in fire danger as a result of high nitrogen pollution. The three-year, $100,000 study is intended to allow scientists to understand the “critical load” point at which pollution causes harmful changes to the range’s ecosystem.
Nitrogen is a key component in fertilizer, but Irvine said not all plants benefit from it.
“It was wonderful for the people of earth to have all of this nitrogen available for their farms and to increase productivity,” Irvine said. “The downside is that nitrogen enrichment in pretty much every ecosystem that it’s been tested in results in a dramatic loss in biodiversity.”