Abstract
Fire and invasions by nonnative plants can change the structure and function of ecosystems, and independent effects of each of these processes have been well studied. When fire is restored to areas where it has been excluded and the native plant communities have been invaded by nonnative species, changes in vegetation structure and composition are likely to alter the fire regime. These changes, in turn, might alter the effects of fire on wildlife and wildlife habitat. In this paper, we develop a framework to evaluate whether fire and plant invasion act as independent, additive processes, or whether applying fire in invaded areas results in novel effects on wildlife. We explore changes in abundance of three small mammal species in response to experimental fires set along a gradient of dominance by Lehmann lovegrass (Eragrostis lehmanniana), an African bunchgrass that has invaded semidesert grasslands of the southwestern USA. For two of three species of small mammals, the effect of fire on abundance varied with the degree of invasion, suggesting a fire × invasion interaction. In systems dominated by nonnative plants, fire can function differently than it did prior to invasion, especially for animals with habitat requirements that match conditions created by the invading plant species. Consequently, prescriptions for restoration fires will need to consider the novel effects of fires on native plants and animals in areas where the plant community has changed.
Highlights
Grasslands are among the most endangered plant communities in North America, in part due to invasions by nonnative plants (Noss et al 1995)
Managers should know whether changes in structure and composition of the plant community due to invasions by nonnative plants alter the way that fire functions to affect animal populations and their habitats. We suggest that this question is addressed most appropriately as one of interaction: does the effect of fire vary with the degree of invasion by nonnative plants?
For two of the three, the effect of fire on abundance varied with the degree of nonnative plant invasion (Table 1, Figure 2)
Summary
Grasslands are among the most endangered plant communities in North America, in part due to invasions by nonnative plants (Noss et al 1995). Invasions alter the structure and composition of grassland plant communities by reducing heterogeneity and structural complexity, reducing space among plants, and often increasing biomass relative to native plant communities (Brooks et al 2004, Geiger 2006) These alterations affect the ability of invaded areas to function as habitat for animals (D’Antonio and Vitousek 1992). Managers should know whether changes in structure and composition of the plant community due to invasions by nonnative plants alter the way that fire functions to affect animal populations and their habitats We suggest that this question is addressed most appropriately as one of interaction: does the effect of fire vary with the degree of invasion by nonnative plants?.
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