New System Developed to Assess Effects of Invasive Alien Plants on Fire Regimes and Prioritize Them for Control

With increasing invasions by alien plants and threats posed to fire regimes and native ecosystems, research by the U.S. Geological Survey (USGS), in collaboration with other scientists from North America, Australia, and South Africa, indicates that effective management requires an understanding of the mechanisms that promote invasion and lead to subsequent ecological impacts. In the July issue of the journal BioScience, the scientists provide a multi-phase model describing the interrelationships between plant invaders and fire regimes, recommend ways to restore pre-invasion fire regime properties, and examine costs and probabilities of successful prevention or mitigation efforts.

“The management of plant invasions and fire are two of the most significant challenges facing land managers in the United States, yet there is relatively little scientific information available on the ecological interrelationships between these two fields of study,” said Matthew L. Brooks, a USGS research botanist in Henderson, Nev., and lead author of the article.

“Although the ability of plant invasions to increase fire hazard and cause ecological damage are widely known, such as cheatgrass in the Intermountain West,” noted Brooks, “plant invasions can also suppress various aspects of the fire regime, which may have just as serious ecological consequences.”

Plant invasions can affect native ecosystems by changing fuel properties, say the authors, and in turn affecting fire behavior, and ultimately altering fire regime characteristics such as frequency, intensity, extent, type, and seasonality of fire. If changes in the fire regime subsequently promote the dominance of the invaders over native species, then an invasive plant/fire regime cycle may become established.

As more ecosystem components and interactions are altered, restoration of pre-invasion conditions becomes more difficult, Brooks emphasized. “This means,” he said, “that managers need to realize that restoration may require managing fuel conditions, fire regimes, native plant communities and other ecosystem properties, in addition to the invaders that caused the changes in the first place.”

In terms of management implications, the authors note that:

• Plant invasions can either promote or suppress fire by altering fuel characteristics.
• Fuel changes occur directly via the biomass produced by the invaders, and indirectly through the invaders’ effects on native plants.
• Restoration of pre-invasion ecosystem characteristics may require drastic measures if fire regimes have been altered.

For additional information about this study on the effects of invasive alien plants on fire regimes, contact these USGS scientists.

Matt Brooks, 702-564-4615, matt_brooks@usgs.gov

Jim Grace, 337-266-8632, jim_grace@usgs.gov

Jon Keeley, 559-565-3170, jon_keeley@usgs.gov

David Pyke, 541-750-7334, david_a_pyke@usgs.gov

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