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Effects of Fire Retardant Chemical and Fire Suppressant Foam on Shrub Steppe Vegetation in Northern Nevada

Introduction

Fire suppressant foams and fire retardant chemicals are used to contain wildland fires and control prescribed burns for habitat management. In 1988 alone, more than 19 million L of retardant were dropped from aircraft on wildland fires in the western United States (Guth and Cohen 1989). Class A foams receive widespread use in constructing fire lines for both wildfires and prescribed burns. Some 795,000 L of concentrate&#151enough to make 159 million L of foam—were sold in 1992 (C. Johnson, U.S.D.A. National Fire Sciences Laboratory, pers. comm.). These chemicals are often applied in environmentally sensitive areas that may contain endangered, threatened, or economically significant plant and animal species.

Relatively little is known about the toxicity of these chemicals to terrestrial plants and animals; even less information is available concerning effects at the community and ecosystem levels. Here, we address responses of terrestrial vegetation to fire retardant chemical and fire suppressant foam application in the Great Basin of North America.

Previous work on a mixed-grass prairie site in North Dakota (Larson and Newton 1996) indicated that the primary effect of both retardant and foam on prairie vegetation is a reduction in plant species richness. Several aspects of the Great Basin environment suggest that results may vary from those obtained in the more mesic Midwest. The Great Basin growing season tends to be divided into two peaks: an early, large response to moisture from melting snow, and a second, smaller response to precipitation from late summer storms (West 1988). Vegetation in the Great Basin is often water-limited. Many species are dormant during the hottest summer months when natural fires are most likely to occur and thus when retardant is used. Like the mixed-grass prairie, vegetation cover in the Great Basin can be nearly 100% in riparian areas. In contrast, upland areas of the Great Basin tend to be dominated by sparse bunch grasses and shrubs, with large areas of exposed soil (Daubenmire 1978, West 1988).

Fire retardant chemicals and fire suppressant foams may influence vegetation in several ways. Because fire retardants are composed largely of nitrogen and phosphorus fertilizers, we can make predictions about their effects on vegetation based on studies of fertilizers. Like fertilizers, fire retardants may encourage growth of some species at the expense of others, resulting in changes in community composition and species diversity (James and Jurinak 1979, Larson and Duncan 1982, Wilson and Shay 1990, Tilman 1987, Wedin and Tilman 1996). Differential growth may also influence herbivory; both insect and vertebrate herbivores tend to favor new, rapidly growing shoots (Stein et al. 1992). Fire suppressant foams, which are most closely aligned with soaps, have no analogous studies from which to make predictions of effect.

The objectives of this study were to determine effects of fire retardant chemical and fire suppressant foam on (1) plant growth; (2) plant species richness, evenness, and diversity; (3) plant community composition; (4) resprouting and (5) flowering of burned and unburned vegetation; and (6) activity of galling insects on that vegetation.

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