Long-term population dynamics of seeded plants in invaded grasslands

Authors: Rinella, Matthew - Matt; MANGOLD, JANE - Montana State University; Espeland, Erin; Sheley, Roger; JACOBS, JIM - Natural Resources Conservation Service (NRCS, USDA)

Submitted to: Ecological Applications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/14/2011
Publication Date: 6/1/2012
Citation: Rinella, M.J., Mangold, J.M., Espeland, E.K., Sheley, R.L., Jacobs, J. 2012. Long-term population dynamics of seeded plants in invaded grasslands. Ecological Applications 22(4):1320-1329.

Interpretive Summary: Many studies are evaluating seeding of desirable species as a method for combating invasive grassland weeds. Seeding is expensive, so to be economically viable, seeded species must persist, grow and suppress grassland invaders for long periods of time. Unfortunately, because seeding studies usually last only a few years, little is known about seeded species performances over the long term. In an exceptionally long study, we measured seeded species and grassland invaders out to 15 years after seeding. We found that some seeded populations remained very small for six or more years but then became highly productive and greatly suppressed the invader. Other populations maintained high densities for three or more years but then became exceedingly rare or extinct. These results show seeding sometimes provides appreciable long-term benefits, but it other times fails. The results also show that short-term data can both over- and under-estimate the lasting benefits of seeding. Short-term data do not reliably foreshadow the long-term seeding outcomes that most concern grassland managers. Additional long-term data are needed to assess the likelihood of favorable seeding outcomes. Where sites have not been greatly disturbed and plots can be relocated, we advocate re-measuring past seeding studies to increase the stores of long-term data.

Technical Abstract: In recent decades, dozens of studies have involved attempts to introduce native and desirable nonnative plant species into grasslands dominated by invasive weeds. The newly introduced plants have proven capable of establishing, but because they are rarely monitored for more than four years, it is unknown if they have a high likelihood of persisting and suppressing invaders for the long term. The lack of long term monitoring is a general problem plaguing reintroduction research on a range of taxa and ecosystems. We introduced species from seed then periodically measured plant abundances for nine years at one site and 15 years at a second site. To our knowledge, our 15-year data are the longest to date from a seeding experiment in invaded, never-cultivated grassland. At one site, three seeded grasses maintained high densities for three or more years, but then all or nearly all individuals died. At the second site, one grass performed similarly, but two other grasses proliferated and at least one greatly suppressed the dominant invader (Centaurea maculosa). For example, our point estimate suggests Thinopyrum intermedium reduced C. maculosa biomass by 93% 15 years after seeding. In some cases, data from three and less years after seeding falsely suggested seeded species were capable of persisting within the invaded grasslands. In other cases, data from as late as six years after seeding falsely suggested seeded populations were remaining small over time and would thus not suppress the invader. These results show seeded species sometimes persist and suppress invaders for long periods, but short-term data cannot predict if, when or where this will occur. Because short-term data are unreliable and long-term data are scarce, additional long-term data are needed to identify effective traits, species and practices for revegetating invaded grasslands.