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Coating seeds with amendments to increase germination, emergence, and establishment is a promising strategy for dryland restoration. Seed coatings containing fungicides offer a potential solution in regions where fungal pathogens cause seed mortality during the winter stratification period between late fall seeding and spring germination. The effectiveness of the fungicide treatment, however, may be dictated by weather and within‐site microenvironment. We tested how fungicide coating influenced seedling emergence of native grasses within sagebrush stands by planting untreated seeds and seeds coated (encrusted) with and without active fungicide ingredients in furrows that extended from the canopy edge of sagebrush plants (Artemisia tridentatassp.wyomingensis) into the interspace. This was replicated at four sites across the Intermountain West in two successive years. We planted two native grasses, bottlebrush squirreltail (Elymus elymoides) and bluebunch wheatgrass (Pseudoroegneria spicata). Emergence was extremely low in both years, with a complete seeding failure (i.e. zero emergence) at two sites in the first year and three sites in the second year. At one site where emergence was sufficient for statistical analysis: (1) the coating on the fungicide and blank treatments inhibited emergence under anomalously dry conditions and (2) across seed treatments, proximity to a sagebrush canopy slightly increased seedling emergence. The variable emergence patterns across sites and years (i.e. the highest emergence was for the site–year combination with the lowest precipitation) highlight the sensitivity of seeding outcomes to, and dependence of fungicide seed coatings on, site conditions, and the necessity of repeating experiments across different weather years.

 

Abstract Reducing invasive species abundance near the leading edge of invasions is important for maintaining diverse, high-functioning ecosystems, but it can be hard to remove invasives present at low levels within desirable plant communities. Focusing on an invasive annual grass, Bromus tectorum , near the edge of its range in the southern Colorado Plateau, we used an observational study to ask what plant community components were associated with lower levels of B. tectorum , and a manipulative experiment to ask if targeted spring grazing or seeding native competitors were effective for reversing low-level invasion. The observational study found that higher C 3 perennial grass cover and shrub cover were associated with lower B. tectorum abundance, and adult Poa fendleriana and Pascopyrum smithii plants had the fewest B. tectorum individuals within 50 cm. Our manipulative experiment used a randomized, hierarchical design to test the relative effectiveness of seeding native perennial grasses using different spatial planting arrangements, seeding rates, seed enhancements, and targeted spring grazing. Two years after seeding, seeded species establishment was 36% greater in high seed rate than unseeded plots, and high rate plots also had lower B. tectorum cover. One season after targeted spring grazing (a single, 2-week spring-grazing treatment 17 months post-seeding), grazed paddocks displayed trends towards higher seeded species densities and lower B. tectorum biomass in certain seeding treatments, compared to ungrazed paddocks. Results suggest high rate native grass seedings may be effective and short-duration spring grazing should be further evaluated as potential tools for preventing ecosystem conversion along invasion fronts.