Seeding and transplanting rare Willamette Valley prairie plants for population restoration
Prairies and oak savannah habitats once dominated the valleys and foothills in western Oregon and southwestern Washington. Fire suppression, invasive species, and habitat loss have substantially reduced the quantity and
Prairies and oak savannah habitats once dominated the valleys and foothills in western Oregon and southwestern Washington. Fire suppression, invasive species, and habitat loss have substantially reduced the quantity and quality of this habitat. Several plant species of this ecosystem are considered rare, threatened or endangered. Their survival may depend reintroduction and population augmentation, as well as habitat protection and targeted management. Here we report findings from a series of experiments which tested the best methods for reintroducing or augmenting 5 rare species: Aster curtus, Erigeron decumbens ssp. decumbens, Horkelia congesta ssp. congesta, Lomatium bradshawii, and Lupinus sulphureus ssp. kincaidii. This executive summary condenses 5 years of research at 7 sites into straight forward recommendations for each species. Detailed experimental results showing how we arrived at these recommendations can be found in the succeeding chapters.
The goal of this study was to establish reintroduction protocols for five rare prairie species of western Oregon:
- Aster curtus (white-top aster)
- Erigeron decumbens (Willamette fleabane)
- Horkelia congesta (Sierra horkelia)
- Lomatium bradshawii (Bradshaw’s desert parsley)
- Lupinus sulphureus ssp. kincaidii (Kincaid’s lupine)
Summary of experimental methods
Experiments were conducted at seven study sites within the West Eugene Wetlands–1135 Terry St., Beaver Run (including the Rosy unit), Balboa, Coble/Turtle Swale, Greenhill Road, Isabelle, and Oxbow West – from 1999 to 2004. Experiments tested the following factors:
- Planting method
- Seed scarification
- Direct seeding
- Planting date
- Source population
- Environmental factors
- Wetland vs upland (Kincaid’s lupine only)
- Topographic position (microsites within wetlands)
- Density of competing vegetation
Recommendations for reintroduction/augmentation are described below:
- A. curtus: Transplant in fall in wetland sites outside of vernal pools. With this protocol, up to 42% of transplanted Aster curtus survived 4 years. Direct seeding is not recommended; it produced only 1-2 % establishment. Fertilizer reduced survivorhips at one site but increased flowering at another. Overall, we recommend fertilizing only in low competition environments.
- E. decumbens: Transplant in spring in wetland sites outside of vernal pools without fertilizer. This protocol yielded establishment rates of up to 55% after 4 years. Direct seeding produced <0.5% establishment and is not recommended.
- H. congesta: Transplant without fertilizer in wetland sites outside of vernal pools in spring. Success rates with this method ranged from 38% to 83% survival after 4 years. Direct seeding can produce a few recruits; however seeding was only marginally effective (up to 4% establishment when combined with weeding).
- L. bradshawii: Seed in wetlands without fertilizer in fall after removing or reducing competing vegetation. This protocol produced up to 37% establishment after 4 years. Transplanting works well in fall without fertilizer, especially in wetter sites with weeds eliminated. However, the gain in establishment (40-70% after four years) may not outweigh the increased labor involved.
- Lupinus sulphureus ssp. kincaidii: Success rates for this species are variable, and likely depend on seasonal climate and local site characteristics such as abundance of weedy vegetation, soil type and hydrology, and soil microorganisms (mycorrhizae and/or Rhizobium). Our best recommendations to date are to seed in fall in upland sites with little competing vegetation, especially grasses and aggressive weeds. Transplanting may work, but only in well-restored native prairie with minimal weed densities, especially grasses and aggressive weeds. No fertilization is necessary but Rhizobium may increase flowering in the long term.
In addition to the species specific recommendations, we stress the importance of site selection and site preparation. Sites for reintroduction should be similar to habitats where the species currently thrives, and weed abundance should be kept low. Reintroducing species to multiple sites provides the best potential for species recovery.
All five of these rare species can be successfully reintroduced or increased in abundance using the protocols described above. Seedlings were observed near some E. decumbens and H. congesta transplants after four years and new seedlings have appeared in L. bradshawii seeding plots after five years, suggesting that viable seed can be produced in a new population within a short time period. Fender’s blue butterfly eggs were observed on both seeded and transplanted populations of L. sulphureus ssp. kincaidii, thus both propagation methods produce acceptable lupine habitat for the butterfly.