Using native grass seeding and targeted spring grazing to reduce low-level Bromus tectorum invasion on the Colorado Plateau

Lauren M Porensky,Matthew D Madsen,Elizabeth A Leger,Matthew A Williamson,Owen Baughman,Barry L Perryman

doi:10.1007/s10530-020-02397-0

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 C3 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.

Highlights

In many dry shrublands of western North America, plant community composition and structure have been drastically altered by the introduction of invasive annual grasses, including Bromus tectorum L., called cheatgrass or downy brome
This study evaluated which plant community components were associated with resistance to further B. tectorum invasion along the edge of its invasion front in the Colorado Plateau, and experimentally tested the separate and combined efficacy of five approaches that could be utilized in lightly invaded uplands to increase resistance to additional B. tectorum invasion
The best models based on AICc included C3 perennial grass cover (Table 1), and this parameter was highly significant in all averaged models (Table 2)

Summary

Introduction

In many dry shrublands of western North America, plant community composition and structure have been drastically altered by the introduction of invasive annual grasses, including Bromus tectorum L., called cheatgrass or downy brome. In the Great Basin, increased gaps between perennial bunchgrasses, increased litter, and soil disturbances have all been associated with B. tectorum invasion (Beckstead and Augspurger 2004; Chambers et al 2014; Jones et al 2015; Reisner et al 2013). Both biotic and abiotic factors can drive invasion resistance at finer spatial scales

Methods

Results

Discussion

Conclusion