Post-fire abundances of soil cyanobacteria relate more to variations in sparse tree cover and soil properties than to fire history, in semiarid shrub steppe

The frequency and extent of wildfire are increasing globally, and understanding the ecosystem impacts of fire can help guide management of burned areas. Cyanobacteria are widespread in surface soils of semi-arid and arid rangelands and confer soil stabilization and resistance to exotic-plant invasions. We examined the probability of encountering cyanobacteria of the order Oscillatoriales in 2022, via microscopic counts of rewetted soils in the lab, following nine recent wildfires that burned as recently as 2012–2017 and up to four times repeatedly until then, in the northern Great Basin of the western U.S. Much of the variability in Oscillatoriales was attributed to the identity of the wildfire, i.e. unexplained variation. Tree cover estimated from gridded satellite-based models was scarce before and especially after fire yet was the second-most predictive covariate. Estimated cover of Oscillatoriales (lab derived) was 0.48 where trees were absent compared to 0.42 where tree cover was detected in the 30-m pixel surrounding soil samples. Presence of sand conferred nearly the opposite effect, which was counter to expectations but could be related to reduced vegetative cover on coarser soils. Other site factors including climatic precipitation and soil fertility were also predictive of Oscillatoriales. Cyanobacteria are considered to be cosmopolitan, i.e. ubiquitous in soils, but these spatial patterns of Oscillatoriales indicate relationships to landscape factors that have not been considered before. Understanding these relationships could aid land managers in identifying post-fire conditions most favorable to soil stabilizing cyanobacteria, which, in turn, could help achieve management goals of moderating soil erosion and additional invasion of fire-promoting exotic plants.