Recent invasions by grasses have increased the amount and continuity of fuels which has increased the frequency of fire in a variety of ecosystems including the semi-arid shrublands of North America. In sagebrush steppe of the Great Basin fires were historically less frequent than they are today, occurring every 30 to 100 years. However, the expansion of invasive annual grasses during the 1900’s has decreased fire return intervals to <5 years in many areas, beyond the point where native shrubs can recover. Fire and invasive annual grasses are now considered primary threats to the conservation of native plants and animals and the maintenance of ecosystem integrity in the Great Basin and other deserts of North America. Preventing invasive annual grass invasions and decreasing fire return intervals to restore native plant communities has repeatedly been identified by land management agencies as a high priority research need.

Variable soil heating during fire creates variable effects on the landscape that can influence the dominance of invasive grasses, and may alter the effectiveness of postfire seeding treatments designed to control them. Fires can kill plants and seeds directly by either consuming them or exposing them to lethal temperatures. Spatial variation in the composition of the surviving seedbank can have significant effects on immediate postfire plant succession, and may affect the postfire growth and reproduction of cheatgrass.

Fire can also affect plants indirectly by altering soil nutrient levels. Soil nutrient levels can either increase or decrease after fire, which should affect the relative productivity of invasive annual grasses such as cheatgrass, especially in ecosystems with naturally low soil nutrient levels. Invasive grasses respond positively to naturally high, or artificially increased, levels of nitrogen and phosphorous in desert regions. Phosphorous may be particularly limiting to plant growth in soils where levels of CaCO₃ are high, binding much of the phosphorous pool that would otherwise be available to plants. Where soil CaCO₃ is low and available phosphorous is high, nitrogen is likely to be the primary limiting soil nutrient. Thus, soil fertility should significantly affect growth and reproduction of cheatgrass, and may affect the ability of seeded species to suppress cheatgrass. The relationships between soil heating during fire and availability of soil nitrogen and phosphorous are currently under investigation, but the effects of soil nutrients on the ability of postfire seeding treatment to reduce dominance of invasive grasses remain to be tested.

In mature sagebrush steppe, fuel loads vary between shrubs and intershrubs, resulting in a spatially heterogeneous pattern of soil heating during fire, and variable ecological effects across the landscape after fire. Given a postfire landscape that varies in the spatial distribution of the surviving soil seedbank and in soil nutrient availability, the establishment rates of seeded species and their effects on cheatgrass will likely vary. For example, the benefits of high soil nutrient levels to cheatgrass may improve its ability to compete with the seeded species, potentially affecting their ability to reduce cheatgrass growth and reproduction. High density and diversity of native species in the postfire soil seedbank may also reduce establishment rates of both seeded species and cheatgrass due to heightened competition for limiting resources.

Land managers need to know the postfire soil conditions where seeding will be most effective, and what types of species they should include in seed mixes. Introduced grass species are most often used, largely because they are inexpensive, readily available, and grow fast. Introduced species can compete better, compared to natives, with cheatgrass, but more comprehensive analyses are needed to compare their relative effectiveness given the potentially wide range of postfire soil conditions. In addition, legumes such as dryland alfalfa are often included along with grass species in seed mixes, although their ability to increase soil nitrogen levels may actually benefit cheatgrass, but this hypothesis needs to be tested. The initial effects of postfire seeding may have negative effects on resident native species through increased competition for limiting resources, but the long-term effects may be beneficial for natives if seeding can suppress cheatgrass and prevent recurrent fire.