Submitted to: Restoration Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2006
Publication Date: 12/1/2006
Citation: Sheley, R.L., Half, M.L. 2006. Enhancing native forb establishment and persistance using a rich seed mixture. Restoration Ecology 14(4):627-635.. Interpretive Summary: In prior studies, we found that broadleaved forbs were important to maintaining the basic health of plant communities and maintaining some resistance to invasive by weeds. In this study, we tried to improve our ability to establish forbs in weed infested areas. The objectives were to determine 1) if increasing seeding rates would provide for better forb establishment, 2) if using many species of forbs, rather than a single forb would best establish forbs, and 3) if a mixture of forbs is more competitive with spotted knapweed than a single forb species. The highest seeding rate produced the highest forb densities. The mixture of forbs provided consistent forb establishment in a variety of environmental conditions and was more competitive with spotted knapweed than a single species. This study suggests using a mixture of forbs, rather than a single species will enhance the likelihood of establishment in various and unpredictable environments because the mixture has a variety of plant traits that may match year-year and site-site environments, and once established, the mixture may have greater chance of persisting than seeding a single species.
Technical Abstract: Introducing and establishing desirable competitive forbs is crucial for successful invasive plant management and the re-establishment of a desirable plant community. The objectives of this study were to determine: 1) if increasing forb seeding rates would yield an increase in forb establishment, 2) if a rich group of forbs would yield greater establishment and survivorship than that of a single species, and 3) if a mixture of forbs is more competitive with spotted knapweed than a forb monoculture. We hypothesized that high forb densities would occur at the highest seeding rate. We also hypothesized that seeding a rich mixture of forbs would establish at a density equal to or greater that the average densities of all the species seeded as monocultures, regardless of watering frequency because species with varying traits would average their response in varying moisture regimes. Monocultures of purple coneflower, arrowleaf balsamroot, annual sunflower, dotted gayfeather, western white yarrow and sticky geranium and a mixture of all forbs were used to test emergence of each individual species and the combination of all forbs at two densities (800 and 2000 seeds/m2) and two water frequencies (twice and thrice/week) with a background density of 2000 spotted knapweed seeds/m2. Pots were arranged in a split-split plot design and replicated 10 times in a growth room. Plants were allowed to grow for 62 days before each species density were counted. The highest seeding rate produced highest plant density, which averaged 4.35 plants/pot, regardless of watering frequency. The mixture yielded about average of the individual plant density and about doubled in response to the highest seeding rate, but was not influenced by watering frequency. Our final hypothesis stated that a mixture of forbs would be more competitive with spotted knapweed than a monoculture of purple coneflower. Spotted knapweed, purple coneflower, and a mixture of associated forbs (arrowleaf balsamroot, annual sunflower, dotted gayfeather, western white yarrow, and sticky geranium) where used as model system. Spotted knapweed and purple coneflower were arranged in an addition series matrix. Fall 2002, 5 densities (0, 100, 400, 700, and 1000 seeds/pot) of both species were seeded and completely randomized and replicated 4 times in a growth chamber. Plants were allowed to grow for 85 days before harvesting. Multiple linear regressions predicting biomass was calculated using initial and final densities of both species as independent variable. Our data indicated that the forb mixture was 7 times more competitive with spotted knapweed than purple coneflower alone when using initial density, but not when using final density as the independent variable. This study suggests using a mixture of forbs, rather than a single species will enhance the likelihood of establishment in various and unpredictable environment because the mixture possesses a variety of traits that may match year-year and site-site environments, and once established, the mixture may have a greater chance of persisting than a monoculture.