Enhancing native forb establishment and persistance using a rich seed mixture

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: 1) To measure germination, dormancy, and viability of six native forbs, 2) To determine whether increasing forb seeding rate will yield an increase in forb establishment, 3) To examine the effects of a species mixture versus a single species on establishment and survival of desired species, and 4) To determine whether a mixture or a monoculture of forbs is more competitive with spotted knapweed. We hypothesized that high forb densities will occur at the highest seeding rate. We also hypothesized that seeding a species rich mixture of forbs will establish average densities of all the species seeded as monocultures, regardless of water frequency. Monocultures of purple coneflower, arrowleaf balsamroot, annual sunflower, dotted gayfeather, western white yarrow, sticky geranium and a mixture of all forbs were used to test emergence at two seeding densities, two watering frequencies and all were seeded with a background density of spotted knapweed. The highest seeding rate produced the highest plant densities, regardless of water frequency. The mixture yield about average of the individual plant densities 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 will be more competitive with spotted knapweed than a monoculture of purple coneflower. Spotted knapweed, purple coneflower, and a mixture of associated forbs were used as a model system to test our hypothesis. Multiple linear regressions predicting biomass was calculated using initial and final densities of both species. The forb mixture was 7 times more competitive with spotted knapweed than purple coneflower alone when using initial density. 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 group possesses a variety of traits that may match year to year and site to site environments, and once established the mixture may have a greater chance of persisting than a monoculture.