Enhancing Native Forb Establishment and Persistence Using a Rich Seed Mixture


Address correspondence to R. L. Sheley, email roger.sheley@oregonstate.edu


Establishing native forbs is crucial for invasive plant management and restoring a desirable plant community. Our objectives were to determine (1) if increasing forb seed density results in increased forb establishment; (2) if a species-rich mixture of forbs has greater establishment and survivorship than a single species; and (3) if mixtures of forbs are more competitive with Spotted knapweed (Centaurea maculosa) than a forb monoculture. To test our first two objectives, we seeded monocultures of Purple coneflower (Echinacea angustifolia), Arrowleaf balsamroot (Balsamorhiza sagittata), Annual sunflower (Helianthus annuus), Dotted gayfeather (Liatris punctata), Western white yarrow (Achillea millefolium), Sticky geranium (Geranium viscosissimum), as well as a mixture of all forbs. Pots were seeded at 800 or 2,000 seeds/m2 and watered twice or thrice weekly. The highest seed density produced the highest plant density, which averaged 4.35 plants/pot. The density of the mixture was similar to the mean density seen for individual species, and it doubled in response to the highest seed density. To test our third objective, Spotted knapweed and Purple coneflower were arranged in an addition series matrix with a maximum total density of 4,000 seeds/pot. We found that the forb mixture was seven times more competitive with Spotted knapweed than Purple coneflower alone. Using a mixture of forbs rather than a single species enhances forb establishment in various and unpredictable environments because the mixture possesses a variety of traits that may match year–year and site–site conditions. Once established, the mixture may have a greater chance of persisting than a monoculture.