- Erigeron decumbens var. decumbens, the Willamette Daisy, is endemic to the
Willamette Valley of Oregon. This taxon is a Category 1 Candidate for listing under the
federal Endangered Species Act (U.S. Fish and Wildlife Service 1990) and is listed as
Endangered under Oregon state law. Herbarium records indicate that E. decumbens var.
decumbens was once widespread in prairies throughout the Valley. In 1934, however,
records ceased and E. decumbens var. decumbens was considered to be extinct until two
populations were discovered in 1980, at Willow Creek (Lane County) and Finley National
Wildlife Refuge (Benton County; Clark et al. 1993). Several populations have been
extirpated within the last decade, and there are currently only 18 known populations of E.
decumbens remaining in the Valley. Most populations are small, consisting of fewer than 50
plants, with the largest concentration of sites occurring in wetland prairies west Eugene area.
Erigeron decumbens var. decumbens occurs in both wetland and upland prairie
habitats. Willamette Valley wetland prairies are characterized by seasonally flooded hydric
soils, and are often dominated by Deschampsia cespitosa. The upland prairies occur on well-drained
soils and formerly supported a mix of native perennial bunchgrasses, such as Festuca
rubra and Elymus glaucus. Before the mid-19th century, both prairie types were probably
maintained by seasonal fires set by the native Kalapuya people (Toepel 1991, Boag 1992) to
maintain favored forage plants and to aid in hunting. The prairies of the Willamette Valley
are considered to be one of the rarest ecosystems in western Oregon, and much E. decumbens
habitat has been destroyed by agricultural/urban development and encroachment by woody
species and exotic plants.
In 1993, we were requested by the Oregon Department of Agriculture to update the
status of Erigeron decumbens var. decumbens and to initiate a long-term population
monitoring program for this taxon. Clark et al. (1993) and Ingersoll et al. (1993) found
major gaps in our knowledge of the biology and ecology of Erigeron decumbens, and
identified areas of study needed for its protection and management. In 1993, we established
permanent demographic monitoring plots, collected first-year data on population and
reproductive characteristics, and established a protocol for future monitoring (Ingersoll et al.
1993). The objectives of this monitoring program are to assess long-term population trends
of E. decumbens, particularly patterns of reproduction, recruitment, and mortality. In 1994,
we continued demographic monitoring and conducted studies of seed and vegetative
regeneration. In this report, we present and discuss the results of two years of demographic
monitoring of E. decumbens. Regeneration studies are discussed in a companion report
(Clark et al. 1995).