The disturbance of soil carbon and nitrogen in big sagebrush ecosystems after mastication treatment

Big sagebrush (Artemisia tridentata) is the dominant plant species in sagebrush steppe ecosystems across western North America. Like other dryland shrub-dominated ecosystems, there are higher soil carbon and nitrogen concentrations found underneath sagebrush, in elevated mounds of soil called hummocks, creating an “island of fertility” effect that establishes important spatial heterogeneity. Shrub removal practices, including mechanical shrub mowing or “mastication”, are commonly used to increase grass forage for livestock and wildlife grazing. We examined the effects of mastication on soil carbon and nitrogen pools and their spatial distribution, using a chronosequence (2005, 2007, 2012, 2019) of treatments with paired controls. At each site, we took soil samples from under sagebrush (live, dead, and masticated), under perennial grass, and in bare ground. Our results suggest that soil organic matter pools decrease after mastication treatment and do not recover to pre-treatment levels after 17 years. Shrub removal, hummock disruption, and slow shrub recovery mean these losses are largest under shrubs. This study contributes to our knowledge of how common land management practices impact ecosystem C storage and distribution.