Technical Report

 

Regeneration biology of Erigeron decumbens var. decumbens, an endangered plant of the Willamette Valley Public Deposited

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  • Erigeron decumbens var. decumbens, the Willamette daisy, is known only from the Willamette Valley of Oregon. Herbarium records, from the 1800's until 1934, indicate that the Willamette daisy was once common and widely distributed throughout the Willamette Valley (Clark et al. 1993). However, between 1934 and 1980, this taxon was not observed or collected and was considered to be extinct until its discovery in 1980 at Willow Creek (Lane County) by James Kagan, and at Finley National Wildlife Refuge (Benton County) by Robert Meinke (Clark et al 1993). Presently, Erigeron decumbens var. decumbens populations are found in both wetland and upland prairies. The wetland prairies have seasonally flooded hydric soils often characterized by an abundance of Deschampsia cespitosa (tufted hairgrass). The upland prairies, in contrast, have well-drained soils and are characterized by a mix of native bunch grasses, including Festuca rubra (red fescue), Bromus carinatus, and Elymus glaucus. Scattered Quercus garryana (white oak) are often present. Both the upland and wetland prairies are believed to have been maintained by fires set by indigenous people to increase abundance of food plants and for ease of hunting (Toepel 1991). The frequent fires prevented the establishment of woody species. Since the arrival of settlers in the mid-1800's, large-scale fires have been prevented, allowing the encroachment of trees and shrubs onto the prairies. Now, these prairies, both wetland and upland, are considered among the rarest of western Oregon's ecosystems. Historically, Willamette daisy populations were destroyed by housing and industrial development, farming, grazing of livestock, and secondary succession. Today, survival of remaining Erigeron decumbens var. decumbens populations is threatened by urban development, increases in cover of woody species, and competition from weedy non-native species. There are currently 18 remaining known populations of Erigeron decumbens var. decumbens in six distinct areas of the Willamette Valley. The northern- and western- most population at Grand Ronde is approximately 100 km from the southernmost population at Goshen. Grand Ronde is about 70 km west of the easternmost population near Silverton. Erigeron decumbens var. decumbens is federally listed as a Category 1 Candidate (U.S. Fish and Wildlife Service 1990) and as Endangered under Oregon State Law.
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  • Companion Report: Demography and Reproduction of Erigeron decumbens var. decumbens, 1993-1994 Field Studies
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  • Prepared for Oregon Department of Agriculture, Plant Conservation Biology Program, 635 Capitol Street NE, Salem, Oregon

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