Role of Dispersal Timing and Frequency in Annual Grass—Invaded Great Basin Ecosystems: How Modifying Seeding Strategies Increases Restoration Success

Abstract

Abstract. Seed dispersal dynamics strongly affect plant community assembly in restored annual grass—infested ecosystems. Modifying perennial grass seeding rates and frequency may increase perennial grass establishment, yet these impacts have not yet been quantified. To assess these effects, we established a field experiment consisting of 288 plots (1 m2) in an eastern Oregon annual grass—dominated shrubsteppe ecosystem. In this study, the amount, timing, and frequency of perennial grass seeding events, soil moisture availability, and annual grass seed bank density were manipulated. We found that more frequent perennial grass seeding events combined with high perennial grass seeding rates produced the highest perennial grass density and biomass 2 years following seeding. However, we also found that if annual grass seed density was 1500 seeds · m-2 or higher, perennial grass density and biomass decreased, regardless of seeding strategy. Because of this finding, it appears that a threshold is crossed between...