Propagule pressure and priority seeding effects on the demography of invasive annual and native perennial grass species

Authors: SCHANTZ, MERILYNN - Oregon State University; Sheley, Roger; JAMES, JEREMY - University Of California Agriculture And Natural Resources (UCANR)

Submitted to: Plant Ecology & Diversity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2019
Publication Date: 5/13/2019
Citation: Schantz, M.C., Sheley, R.L., James, J.J. 2019. Propagule pressure and priority seeding effects on the demography of invasive annual and native perennial grass species. Plant Ecology & Diversity. 12(2):139-150. https://doi.org/10.1080/17550874.2019.1613696.
DOI: https://doi.org/10.1080/17550874.2019.1613696

Interpretive Summary: Native perennial grass recruitment is generally low when seeding into annual grass invaded ecosystems. Quantifying seedling success at differing annual and perennial seeding rates and seeding times should allow us to identify the native perennial grass seeding rates and seeding times necessary to produce stable native perennial grass communities in annual grass ecosystems. Furthermore, this research should allow us to pinpoint the growth stages most vulnerable to mortality. In this study, we evaluated how annual and perennial grass seeding time, seeding rates, and water availability affected annual and perennial grass performance through their life history (germination to adult). We found that plant community assembly following restoration of annual grass invaded ecosystems was driven by the growing conditions in the first growing season as opposed to seeding inputs.

Technical Abstract: Restoring native plant community structure and function in annual grass invaded ecosystems is fundamental to fostering natural successional cycles. Systems-based management approaches, which track plant growth through time, can be a valuable restoration management tool, especially when existing ecosystem properties (e.g. water availability), and management inputs (e.g. seeding time and rate) differ. We used a systems-based management approach to quantify limiting growth stages in seedling life history and the transitions among life history stages when seeding time and rate, and water availability differed. In an eastern Oregon shrub-steppe ecosystem, we seeded perennial grasses in autumn, spring, or seeding half of the perennial grasses in autumn and the remaining half in spring. Annual and perennial grass seeding rates were 150, 1,500, 2,500, or 3,500 seeds m-2. Adding water in combination with the lowest annual and the highest perennial grass seeding rates produced the highest perennial grass density at 46.6 ± 6.5 perennial grasses m-2. However, perennial grasses had the highest density following the first growing season at 57.7 ± 9.5 plants m-2, yet by the second growing season perennial grass density was highest at 15.7 ± 1.7 plants m-2 when seeded in autumn. While a systems-based management approach to restoration may increase native perennial grass density in annual grass systems; we found that plant community assembly following restoration of annual grass invaded ecosystems is likely driven by the growing conditions in the first growing season as opposed to management inputs.