Identifying herbicides compatible with biological soil crusts for land management: effects differ by mechanistic family

Dryland degradation is a global problem, destabilizing ecosystems and disrupting coupled human-natural systems in arid regions. Degradation, caused by livestock grazing, wildfire, vehicles, construction, climate perturbances, and other surface disturbances, open space for invasive plants to establish while damaging soils, biological soil crusts (biocrusts), and vascular plant communities. Due to the scale of invasive plant infestations and the cost of mechanical control, invasive plants are commonly treated with herbicides, but little is known about the consequences of herbicides on biocrust. Biocrusts are communities of biota that aggregate the soil surface and provide ecosystem services, including mitigating soil erosion and fixing nitrogen, making biocrust a promising and emerging tool to counteract degradation. To test biocrust compatibility with standard herbicide treatments, we conducted a organisms (mosses and the lichens Placidium/Clavascidium and Enchylium). We found that response varied based on the herbicide mechanistic family, with the magnitude of response varying for biocrust organisms. Mosses treated with amino acid disrupters (glyphosate and imazapic) had 65–75% less health tissue area than controls after 3 months. Surprisingly, mosses treated with synthetic auxins (2,4-D and aminopyralid) had a similar or slightly greater healthy area. Blue dye and surfactants had no effect on any tested biocrust organism. This greenhouse study suggests that through careful selection of herbicides, biocrust restoration could be simultaneously used with herbicide treatments of invasive plants to improve soil health.