Invasive plants—weeds—sure have been busy. They systematically infiltrate millions of acres every year, selfishly soak up precious water supplies, forever alter wildlife habitats and quietly invade our backyards. In fact, the economic impact of invasive plants and weeds in the U.S. has been estimated at $34.7 billion annually, according to a recent Cornell University report.

Now, add increasing the frequency and intensity of wildfires to the list of the destructive talents of these insidious invaders.

How Do They Do It?
In the western states, where wildfires are most prevalent, the encroachment of resilient, invasive plants has paved the way for a succession of rampant rangeland and desert wildfires. Two culprits that play major roles in stoking the flames of these reoccurring western wildfires are Cheatgrass and Red Brome.

Where the dry, feathery foliage of the winter annual Cheatgrass is abundant, wildfires flare up more often. This invasive plant acts like highly flammable kindling, fueling the ignition of rangeland fires to a roaring blaze. And, parts of Arizona’s picturesque Sonoran desert are actually bursting into flames with alarming frequency thanks to the spread of Red Brome, another non-native annual grass. Red Brome is a prime source of fires engulfing native vegetation, such as Palo Verde trees and various cacti, hallmarks of this desert habitat.

"These invasive plants can take over natural areas that once were home to a diverse variety of plant species," says Steven A. Dewey, Ph.D., Extension Invasive Weed Specialist at Utah State University and wildfire expert. "The spread of invasive plants such as Cheatgrass and Red Brome across a western landscape can lead to more expansive and more frequent fires. Charred lands in turn are left wide open for an unchallenged invasion of annual, invasive plant species. And so the cycle continues, intensifying as it goes."

Dr. Dewey recently was named Weed Science Subject Matter Liaison to the Environmental Protection Agency (EPA) by the Weed Science Society of America. In this newly created position, he will be instrumental in providing scientific information on invasive weed management to the EPA, including methods to lessen the role of invasive weeds in wildfires.

The Effects Of Wildfires Can Linger

• Fire-fueling invasive plants actually have increased the occurrence of wild fires in some areas from a natural frequency of every 60 to 100 years to an alarming 3 to 5 years.
• Recurring fires can have a devastating effect on native plant species that are critical components of wildlife habitats, endangering animal species that rely on those habitats.
• In many areas, the increased severity and frequency of wildfires driven by invasive plants are eliminating the natural assortment of native plant species. Large areas of land are becoming more homogenous—home to merely a few plant species. "One of the advantages of a diverse plant population is the different ways in which various plant species react to fire," says Dr. Dewey. "Those species that are not as combustible, such as perennial bunch grasses and forbs, can act as buffers, helping to contain naturally occurring wildfires so they don't spread out of control."

How Invasive Plants Take Over

• Overgrazing or other human-caused disturbance of rangelands leaves bare areas that are quickly filled in by invasive plants.
• Invasive plants produce countless seeds that travel by wind, animals or people, eventually settling in bare areas where they quickly establish themselves and spread.
• Because of their fast growing cycles, invasive annual plants mature and then wither long before winter, usually at the height of summer heat, posing major wildfire threats.
• Suppressing small-scale fires that nature commonly uses to remove dried, dead plants can lead to the buildup of excessive dead plant material that fuels more intense wildfires.
• Variances in weather patterns, either severe drought or excessive rainfall, which affect natural plant growth patterns, can lead to an invasive plant population explosion.

What Can Be Done?
"The integration of herbicides to control invasive plants, proper grazing management, controlled burns to remove plant debris buildup and revegetating degraded sites with native plants all can lead to rejuvenated rangeland ecosystems," says Dr. Dewey. "Healthy, native landscapes are better able to resist invasion of nonnative plants, thus restoring a more natural, prolonged wildfire frequency."

The more we learn about the far-reaching effects of invasive plants and weeds, the more able we are to work together to conquer the problems they cause. Contact your state's department of natural resources to find out more about invasive species in your area or log on to http://www.wssa.net.

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About the Weed Science Society of America:
The Weed Science Society of America, a nonprofit professional society, was founded in 1956 to encourage and promote the development of knowledge concerning weeds and their impact on the environment. The Weed Science Society of America promotes research, education and extension outreach activities related to weeds, provides science-based information to the public and policy makers, and fosters awareness of weeds and their impacts on managed and natural ecosystems. For more information, visit http://www.wssa.net.