Determining the most efficient and effective large-scale native seeding techniques in degraded prairies

Background/Question/Methods

Today, native grasslands are one of the most threatened ecosystems in the United States. Native prairie habitats have been nearly extirpated from the Pacific Northwest and are the most endangered ecosystem in Washington State. Past efforts to restore these landscapes have focused primarily on outplanting containerized seedlings of native plant species important for rare butterflies, an extremely labor- and resource-intensive approach. Large-scale seeding of these species may be a viable option to increase efficiency, although it is unknown which seeding techniques are most effective for germination and establishment. Because seed availability is often a limiting factor in large-scale restoration, it is also important to evaluate seed application rate to determine the lowest rate that provides the desired density of adult plants. We assessed three seeding techniques (drill, broadcast, hydroseed) and five seed application rates (0, 350, 700, 1050, 1400 seeds/m²) on germination and establishment of three native butterfly resource species (Festuca roemeri, Eriophyllum lanatum, Erigeron speciosus) in a large-scale, spatially-replicated experiment in western Washington. Treatments were applied in a 3 x 5 randomized block design within each of three sites, with three replicates per site. The experimental units were strips, sized such that operationally realistic equipment could be used (at least 84 m²). We evaluated these methods in terms of their ecological and economic costs and benefits.

Results/Conclusions

Seeding technique did not affect germination rates at most sites and for most species, suggesting that the least expensive method (broadcast seeding) is appropriate for large-scale restoration. Seed application rate and germination were positively correlated, however, seeding at the highest rate (8lbs/acre) did not provide any added benefit over seeding at 6lbs/acre for all but one species at one site. Germination rates of all seeded species varied significantly among sites, suggesting that the presence of spatially-dependent environmental limitations on germination. Litter cover, moss cover and non-native species richness, which varied by site, were all significantly negatively correlated with germination rates, and helped explain some of the inter-site variation in germination rates. These results will help managers select for habitat variables that support native germination and establishment and utilize the most effective and efficient native seeding techniques for large-scale restoration of Pacific Northwest prairies.