Biological soil crusts (BSC) are communities of cyanobacteria, algae, lichens, and bryophytes which adhere to soil surfaces in drylands worldwide. BSCs are fundamental to desert ecosystems. They stabilize soils and decrease landscape erosion, fix nitrogen and carbon, and help to retain water on the soil surface and increase infiltration. Predictions of heightened aridity and elevated temperatures along with increased fire return frequency, due to exotic plant invasion, have increased concern about wildfires across the western United States over the past half century. While we know wildfires can have dramatic and lasting effects on the landscapes and vascular plant communities, the ecological effects of wildfire disturbance to BSCs are poorly understood. BSCs may be especially vulnerable to wildfires due to their slow growth rates and high sensitivity to physical disturbance. Here we describe results from a fire chronosequence study where we assessed burned and unburned BSC communities following fires across the five deserts of North America (Great Basin, Colorado Plateau, Mojave, Chihuahuan, and Sonoran). For each desert, we surveyed two burned sites (“old fire”, which was ~30 years since the fire occurred and a “new fire”, which was ~15 years since the fire occurred) and two associated unburned (control) sites.
Results/Conclusions
Our results show that BSC communities vary dramatically across deserts regardless of fire history. Cooler deserts (Great Basin and Colorado Plateau) were most prone to wildfires and, in the absence of fire had the most abundant BSC coverage with the highest proportions of well-developed BSC (i.e., lichen and moss-dominated biocrusts), whereas warmer deserts, which were less prone to wildfires (Mojave, Chihuahuan, and Sonoran) have less BSC coverage. Generally, across deserts, unburned sites contained more well-developed BSC, while burned sites generally lacked lichens, mosses, and darkly-pigmented cyanobacteria, but contained varying amounts of earlier development BSC (i.e., lightly-pigmented cyanobacteria). Nevertheless, the cooler deserts showed the highest signs of BSC community recovery following fire, whereas the warmer deserts showed less evidence of recovery. We also found that BSC recovery under the canopy of shrubs was greater than the recovery observed in the open interspace among vascular plants, indicating the importance of the presence of shrub canopies for reestablishing BSCs after fire disturbances. Our findings emphasize that fire significantly affects BSC communities differently depending on climate and habitat and the pace and trajectory of recovery following desert fire varies across desert types of North America.