For decades, large portions of the semi-arid sagebrush ecosystem have been experiencing increased frequency and extent of wildfire, even though small, infrequent fire is a natural disturbance in this ecosystem (Baker, 2006). Increased wildfire is threatening the existence of sagebrush ecosystems and the wildlife species that depend upon them (Baker, 2006; Coates et al., 2016). Increased wildfire in sagebrush ecosystems is often driven by invasive annual grasses, especially cheatgrass, Bromus tectorum (L.). Invasion can initiate a trajectory toward a “grass-fire cycle”, in which cheatgrass increases fine fuel loadings that promote fire, and native plant species do not recover quickly after fire, leading frequently burned sites to transition to monocultures of cheatgrass (Brooks et al., 2004). Although cheatgrass has been extensively studied in the sagebrush steppe, less attention has been given to the organisms that would have filled the interspaces that cheatgrass replaces, namely, biological soil crusts (“biocrusts”). Semi-arid environments are characterized by sparse cover of vascular plants and substantial cover of biocrusts (Belnap & Lange, 2001). Biocrusts contain organisms that live on the soil surface and include lichens, mosses, and light algal crusts (including cyanobacteria). Although biocrusts were included in some of the first descriptions of the vegetation in the region (Flowers, 1934), biocrusts are rarely included in contemporary studies of sagebrush ecosystems. Comprehensive community studies have concluded consistent negative relationships between abundance of biocrusts and annual invasive grasses, specifically cheatgrass (Condon & Pyke, 2018a,b; Daubenmire, 1970). We postulate that biocrusts, and particularly lichens, facilitate a pattern of small, infrequent, low intensity fire given their association with reduced fine fuels (cheatgrass).
Observations of the response of biocrusts to fire as a sole disturbance are rare. For example, grazing by livestock is the primary land use in sagebrush ecosystems and biocrusts are lost to the compound disturbances of grazing and fire (Condon & Pyke, 2018a). Researchers face great challenges in identifying sites for study where fire is not coupled with grazing, perhaps because cattle preferentially use burned areas (Clark et al., 2014). Conversations in the literature speak to the difficulty in separating the effects of these disturbances on biocrusts (O'Connor & Germino, 2020; Root et al., 2020).
We surveyed a wildfire in October of 2021 outside of Boise, Idaho, that burned 15–20 acres of intact biocrusts the previous month (personal communications Rosentreter, October 20, 2021; Condon & Coates, 2022). This small fire occurred on private land and was not named. The area had not experienced grazing by livestock since 1984 and prior to the fire, it was free of other anthropogenic disturbances.