Will cheatgrass dominate a site in the first growing season following fire where native perennial grasses are depleted?

Response of cheatgrass (Bromus tectorum) the first growing season on a depleted site following fire depends on seed source.  Abundance of post-fire cheatgrass seed is directly related to:

  1. the amount of seed in the seed-pool prior to the fire
  2. the amount seed combusted by fire, which is largely related to the abundance and types of surface fuels, primarily shrubs (Miller et al. 2014).

Following fire on a cheatgrass-dominated site with few shrubs (photo below) the majority of cheatgrass seed would not be combusted.  Fuels are very light resulting in limited combustion of surface litter and seed.  If 15% or more shrub cover was present, much of the cheatgrass seed is usually combusted allowing a one-year window to seed the depleted site.

Little cheatgrass seed is combusted during a fire where light fine fuels are the primary fuels and shrubs are largely absent (photo by Nolan Preece).
Fast moving low severity fire resulting in most of the organic matter including cheatgrass seed remaining on the surface. Greater woody plant cover would have increased the combustion of cheatgrass seed (photo by Rick Miller).
A high severity fire resulted in nearly 100% combustion of surface litter, including cheatgrass seed. Native annuals can often dominate in the first year. Cheatgrass may or may not dominate in year 2 or 3, depending on seed source. The native annual forb ground smoke (Gayophytum sp.) is the dominate annual in the first year following a high severity wildfire in Utah (photo by Rick Miller).