Study suggests air pollution in the Santa Monica mountains is harming native plants, increasing fire risk

January 28, 2014 by Iqbal Pittalwala
Interns measure plots of California sagebrush that have been injected with various levels of nitrogen as part of a three-year study to learn how air pollution is impacting native plants and fire risk. Credit: National Park Service

(Phys.org) —Initial results from experiments conducted in the Santa Monica Mountains by a botanist at the University of California, Riverside and her colleagues indicate that high levels of nitrogen may adversely impact native plants and, by extension, increase the risk of wildfire.

The researchers measured levels at ten sites throughout the Santa Monica Mountains and found significantly higher in the eastern end, closer to Los Angeles.

Generally attributed to vehicle emissions in the Santa Monica Mountains, deposition is the air pollution from industry, agriculture and transportation that settles out of the atmosphere and onto the earth's surface.

The study is helping the scientists better understand how high nitrogen levels affect native vegetation and what that might mean for fire risk in such a fire-prone region.

"Invasive annual grasses from the Mediterranean have a greater growth response to nitrogen than most native species, and are crowding out ," said Edith Allen, a professor of plant ecology and cooperative extension specialist at UC Riverside, and the principal investigator for the study. "Grasses also produce fine, flashy fuels that cause more frequent and larger fires, promoting vegetation-type conversion from native shrubland to exotic annual grassland."

The preliminary results are from the first year of a three-year study undertaken by Allen, Irina Irvine, a restoration ecologist for Santa Monica Mountains National Recreation Area, and Andrzej Bytnerowicz and Mark Fenn of the U.S. Forest Service.

At the two sites with the best air quality, the researchers added various levels of into experimental plots of coastal sage scrub to simulate pollution levels found throughout the mountains. They found that the higher levels of nitrogen led to a decline in native shrub seedlings and an increase in nonnative grasses.

Other studies in Australia and California have demonstrated a link between nonnative grasses, also known as "flashy fuels," and larger and more frequent wildfires.

"The recent fire of May 2013 burned our research plots, but provides an opportunity to learn how invasive grasses compete with native seedlings establishing post fire under nitrogen deposition," Allen said. "The data will enable us to determine critical loads of to help set clean air regulations to protect native ecosystems."

Coastal sage scrub once covered much of coastal California and is now an endangered habitat type, primarily due to development.

Explore further: Clean Air Act has led to improved water quality in the Chesapeake Bay watershed

More information: "Effects of nitrogen deposition and empirical nitrogen critical loads for ecoregions of the United States." Linda H. Pardo, Mark E. Fenn, Christine L. Goodale, Linda H. Geiser, Charles T. Driscoll, Edith B. Allen, Jill S. Baron, Roland Bobbink, William D. Bowman, Christopher M. Clark, Bridget Emmett, Frank S. Gilliam, Tara L. Greaver, Sharon J. Hall, Erik A. Lilleskov, Lingli Liu, Jason A. Lynch, Knute J. Nadelhoffer, Steven S. Perakis, Molly J. Robin-Abbott, John L. Stoddard, Kathleen C. Weathers, and Robin L. Dennis. Ecological Applications 2011 21:8, 3049-3082

Related Stories

Impacts of plant invasions become less robust over time

November 20, 2013

Among the most impressive ecological findings of the past 25 years is the ability of invasive plants to radically change ecosystem function. Yet few if any studies have examined whether ecosystem impacts of invasions persist ...

One tree likes seabird poop, the next prefers fresh air

January 24, 2014

Off the west coast of Peru, seabirds deposit thick layers of guano that accumulates on the ground because of the lack of rain. Guano has historically played a key role in agriculture worldwide because it is rich in plant ...

Recommended for you

New study sheds light on end of Snowball Earth period

August 24, 2015

The second ice age during the Cryogenian period was not followed by the sudden and chaotic melting-back of the ice as previously thought, but ended with regular advances and retreats of the ice, according to research published ...

Earth's mineralogy unique in the cosmos

August 26, 2015

New research from a team led by Carnegie's Robert Hazen predicts that Earth has more than 1,500 undiscovered minerals and that the exact mineral diversity of our planet is unique and could not be duplicated anywhere in the ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.