Bromus tectorum Response to Fire Varies with Climate Conditions
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The invasive annual grass Bromus tectorum (cheatgrass) forms a positive feedback with fire in some areas of western North America’s sagebrush biome by increasing fire frequency and size, which then increases B. tectorum abundance post-fire and dramatically alters ecosystem structure and processes. However, this positive response to fire is not consistent across the sagebrush steppe. Here, we ask whether different climate conditions across the sagebrush biome can explain B. tectorum’s variable response to fire. We found that climate variables differed significantly between 18 sites where B. tectorum does and does not respond positively to fire. A positive response was most likely in areas with higher annual temperatures and lower summer precipitation. We then chose a climatically intermediate site, with intact sagebrush vegetation, to evaluate whether a positive feedback had formed between B. tectorum and fire. A chronosequence of recent fires (1–15 years) at the site created a natural replicated experiment to assess abundance of B. tectorum and native plants. B. tectorum cover did not differ between burned and unburned plots but native grass cover was higher in recently burned plots. Therefore, we found no evidence for a positive feedback between B. tectorum and fire at the study site. Our results suggest that formation of a positive B. tectorum-fire feedback depends on climate; however, other drivers such as disturbance and native plant cover are likely to further influence local responses of B. tectorum. The dependence of B. tectorum’s response to fire on climate suggests that climate change may expand B. tectorum’s role as a transformative invasive species within the sagebrush biome.
KeywordsBromus tectorum cheatgrass fire Idaho National Laboratory positive feedback sagebrush
We would like to thank Gonzales-Stoller Surveillance, LLC and the Idaho National Laboratory (DOE) for access to the site. We would also like to thank Roger Blew, Amy Forman and others at Gonzales-Stoller Surveillance, LLC who helped the project run smoothly. Comments by two anonymous reviewers improved the manuscript. Funding for this project came from Gonzales-Stoller Surveillance (GSS-0300-1100008). KT and BDM were additionally funded by NSF-WildFIRE PIRE, OISE 09667472.
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