|SCHANTZ, MERILYNN - Oregon State University|
|JAMES, JEREMY - University Of California Agriculture And Natural Resources (UCANR)|
Submitted to: Western North American Naturalist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/30/2015
Publication Date: 3/1/2016
Citation: Schantz, M.C., Sheley, R.L., James, J.J., Hamerlynck, E.P. 2016. Role of dispersal timing and frequency in annual grass-invaded Great Basin ecosystems: how modifying seeding strategies increases restoration success. Western North American Naturalist. 76(1):36-52. doi: 10.3398/064.076.0106.
Interpretive Summary: Restoring invaded rangeland with desired species is the only viable long-term strategy for managing rangeland pest plants. However, it is very difficult to get seedlings to emerge and establish during restoration. In an attempt to overcome this barrier to restoration, tested seeding rates, frequency of seeding, and seasons of seeding in various combinations. We found increasing the frequency of perennial grass seeding to autumn and spring or delaying perennial grass seeding until spring produced higher perennial grass density and biomass than seeding in autumn alone. Increasing perennial grass seeding rates also increased perennial grass density and biomass, especially when seeding frequency and water availability was higher. These guidelines should improve our ability to successfully establish desired plants on degraded rangeland.
Technical 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 requency of perennial grass seeding events, soil moisture vailability, 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 150 and 1500 annual grass seeds · m-2. Adding water in the first growing season initially facilitated perennial grass establishment but only produced higher perennial grass density following the second growing season when annual grass density was lowest. Assessing the existing annual grass seed bank prior to seeding can likely forecast restoration outcomes because high annual grass seed densities likely interfere with and reduce perennial grass recruitment. In addition, if annual grass seeding density is 1500 seeds · m-2 or lower, modifying the temporal patterns of perennial grass seed arrival will increase the likelihood that a perennial grass seed finds a safe-site.