Bromus tectorum Response to Fire Varies with Climate Conditions

Abstract

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 sage-brush 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 sage-brush biome. Author contributions: Kimberley Taylor conceived of/designed study; performed research; analyzed data; and wrote paper. Tyler Brummer performed research and wrote paper. Lisa J. Rew conceived of/designed study and wrote paper. Matt Lavin contributed new methods/models and wrote paper. Bruce D. Maxwell conceived of/designed study; performed research; and wrote paper. Results for the ten climate variables that were most correlated with PCO 1 are shown in declining order of importance. temp. Temperature, precip. precipitation, min. minimum, max. maximum.

Refining the cheatgrass–fire cycle in the Great Basin: Precipitation timing and fine fuel composition predict wildfire trends

“…The rapid vegetative growth of cheatgrass suppresses growth and recovery of native perennial plants, particularly in parts of the Great Basin where precipitation and native perennial bunchgrass cover are low (Brummer et al., ). Hence, the propensity of cheatgrass to dominate following fire is highest in warmer, drier locations (Taylor, Brummer, Rew, Lavin, & Maxwell, ) as well as where prefire biological soil crust cover is low and native perennial grasses and forbs are depleted (Chambers et al., ; Shinneman & Baker, ).…”

Fire and development influences on sagebrush community plant groups across a climate gradient in northern Nevada

“…, Taylor et al. , Brummer et al. ), especially those dominated by winter precipitation with dry summers (Prevéy and Seastedt , Taylor et al.…”

“…, Taylor et al. ). Therefore, we limited our dataset to sites sampled in at least the calendar year after a fire and included time since most recent fire in our models.…”

“…Several studies have suggested that the main driver of B. tectorum abundance in the sagebrush biome is climate, with the combination of hot and dry summers positively correlated with abundance (Bradley , Taylor et al. , Brummer et al. , Larson et al.…”

Pre‐fire vegetation drives post‐fire outcomes in sagebrush ecosystems: evidence from field and remote sensing data

“…3, 4), a pattern which may be a product of competitive interactions. Certain native perennial grass species, including western wheatgrass (Pascopyrum smithii) and Sandberg bluegrass (Poa secunda), may expand after a fire due to competitive release from sagebrush, which recovers more slowly (Vale 1974, Cooper et al 2011, Davies et al 2012, Taylor et al 2014, Ellsworth et al 2016, Shinneman and McIlroy 2016, Ellsworth and Kauffman 2017, Mitchell et al 2017, Condon and Pyke 2018. Certain native perennial grass species, including western wheatgrass (Pascopyrum smithii) and Sandberg bluegrass (Poa secunda), may expand after a fire due to competitive release from sagebrush, which recovers more slowly (Vale 1974, Cooper et al 2011, Davies et al 2012, Taylor et al 2014, Ellsworth et al 2016, Shinneman and McIlroy 2016, Ellsworth and Kauffman 2017, Mitchell et al 2017, Condon and Pyke 2018.…”