Native sagebrush ecosystems in the Great Basin (western USA) are often invaded following fire by exotic Bromus tectorum (cheatgrass), a highly flammable annual grass. Once B. tectorum is established, higher fire frequencies can lead to local extirpation of Artemisia tridentata ssp. vaseyana (mountain big sagebrush) and have cascading effects on sagebrush ecosystems and the species that depend on them. We conducted a landscape-scale observational study to examine the distribution and cover of B. tectorum and A. tridentata 6 years after a large wildland fire. We used structural equation models to quantify the interacting influences of pre-fire tree canopy cover, perennial species cover, distance from potential seed source, and site environment on post-fire cover of B. tectorum and A. tridentata. Results confirmed a hypothesised negative effect of pre-fire tree canopy cover on post-fire cover of A. tridentata. Site- and landscape-level abiotic factors influenced pre-fire tree canopy cover, which, in turn, influenced the probability of rapid recovery to A. tridentata. However, B. tectorum cover was primarily influenced by a positive effect of incident solar radiation and a negative effect of perennial herbaceous species cover. Restoration efforts to reduce tree canopy cover should be limited to productive sites with sufficient cover of perennial herbaceous species to facilitate site recovery.
Biological soil crusts contribute to ecosystem functions and occupy space that could be available to invasive annual grasses. Given disturbances in the semiarid shrub steppe communities, we embarked on a set of studies to investigate restoration potential of mosses in sagebrush steppe ecosystems. We examined establishment and growth of two moss species common to the Great Basin, USA: Bryum argenteum and Syntrichia ruralis from two environmental settings (warm dry vs. cool moist). Moss fragments were inoculated into a third warm dry setting, on bare soil in spring and fall, both with and without a jute net and with and without spring irrigation. Moss cover was monitored in spring seasons of three consecutive years. Both moss species increased in cover over the winter. When Bryum received spring irrigation that was out of sync with natural precipitation patterns, moss cover increased and then crashed, taking two seasons to recover. Syntrichia did not respond to the irrigation treatment. The addition of jute net increased moss cover under all conditions, except Syntrichia following fall inoculation, which required a second winter to increase in cover. The warm dry population of Bryum combined with jute achieved on average 60% cover compared to the cool moist population that achieved only 28% cover by the end of the study. Differences were less pronounced for Syntrichia where moss from the warm dry population with jute achieved on average 51% cover compared to the cool moist population that achieved 43% cover by the end of the study. Restoration of arid land mosses may quickly protect soils from erosion while occupying sites before invasive plants. We show that higher moss cover will be achieved quickly with the addition of organic matter and when moss fragments originate from sites with a climate that is similar to that of the restoration site.
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