Wildfire and Invasive Plants

The severity of wildfires in recent years has increased public awareness and concern about a fuel build-up in western U.S. forests. Federal land management agencies are responding by greatly expanding programs to reduce hazardous fuels. However, scant information exists on the efficacy of fuel treatments for mitigating wildfire severity. There is even less information regarding the influence of fuel treatments on second-order fire effects, such as non-native plant invasions. USGS scientists Geneva Chong and Tom Stohlgren have teamed with Colorado State University colleagues Phil Omi, Erik Martinson, Mohammed Kalkhan, and Molly Hunter to examine the spatial interactions among forest fuels, wildfire, and invasive plants.

The Cerro Grande Fire near Los Alamos, New Mexico, provided a unique opportunity to initiate the research, which involves assessing pre-fire stand conditions, burn severity, vegetation (both native and non-native plant species), and post-fire flammability. This information will be used to develop models that predict fire severity using satellite imagery and existing field data.

Some of the Cerro Grande Fire burned mature, dense forest stands that were "protected" by over a half-century of fire suppression. Other areas were previously treated with mechanical thinning and/or prescribed burning. Preliminary results suggest that wildfire severity was significantly lower in thinned stands than in adjacent untreated stands. Other results imply that under extreme fire conditions, stand density (the number of trees per unit area) may be more important than surface fuel load (ground litter) in determining fire behavior and effects in ponderosa pine forests.

Results from vegetation sampling in 2001 indicate that non-native plant species are most prevalent in severely burned stands of ponderosa pine, much less prevalent in stands that were both thinned and burned, and lowest in unburned stands. To learn whether this pattern is typical throughout the West, other wildfire areas in western states will be assessed over the next few years.

USGS scientists are coordinating their research and combining their results under a USGS Venture Capital project, "The Ecological, Hydrological, and Geological Consequences of Burn Severity and Social Application of those Results". This work complements ongoing USGS research on invasive plants, animals, and wildlife diseases, and has helped to engage long-term partnerships in invasive species science with NASA Goddard Space Fight Center, the EROS Data Center, many USGS research centers, and other DOI bureaus. Results from this combined effort will allow land managers to predict likely outcomes of wildfire based on the relationship between fuel loads, stand density, burn severity, and non-native plant invasions across the western U.S.

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For more information, contact:

• Geneva Chong
• Tom Stohlgren