Erigeron decumbens var. decumbens
|Willamette daisy, Willamette Valley daisy, Williamette fleabane|
|Edward Guerrant, Ph.D.|
The following Participating Institutions are custodians for this species in the CPC National Collection:
Rae Selling Berry Seed Bank & Plant Conservation Programs
The conservation of Erigeron decumbens var. decumbens is fully sponsored.
Edward Guerrant, Ph.D. contributed to this Plant Profile.
Today, less than one present of Prairie land in the Willamette Valley remains in western Oregon and southwestern Washington. Consequently, the once common Willamette daisy (Erigeron decumbens ssp. decumbens) has nearly become extinct.
Not seen since 1934, Erigeron decumbens ssp. decumbens was thought extinct until 1980, when two populations were discovered. Although more populations have subsequently been found, this species continues to be at risk. In 1986 the largest population ever known (>6000 plants) was destroyed by plowing. The current 18 populations contain a mere 7500 plants, and only 4 of these remaining populations are on federal or city land and therefore legally protected from development.
Post-colonization land use practices are responsible for the destruction and fragmentation of the oak-savanna ecosystem. Both flooding and occasional fires helped to preserve the prairie habitat. The Native Americans that initially made the Willamette Valley their home managed prairies by setting fires in order to increase the abundance of food plants and for ease of hunting. This kept ash, rose, blackberry, conifers and other woody species from invading.
Since European settlement, vast tracts of Willamette Valley Prairie have been converted to agricultural production or human habitation. Due to fire suppression efforts, much of the remaining areas have been converted to dense thickets of brush or trees. The Willamette daisy has not been found in any areas currently grazed or farmed, but is sometimes found in places that were formerly grazed or farmed, providing encouragement that restoration efforts could be successful.
Distribution & Occurrence
Heavy soils in seasonally wet native or dry upland prairie grasslands (Meinke 1982; Kagan and Yamamoto 1987).
Associated species include Aster hallii, Festuca sp., Danthonia sp., Rhus diversiloba, Hypericum perforatum, and Aira caryophyllea (Meinke 1982).
|As of 1993: 18 populations were known, with two on federal land and two on city owned land. These four populations are the only legally protected from development. Since it is difficult to distinguish genetically distinct plants, "clumps" of plants were counted. There were approximately 7500 clumps observed in 1993. Populations ranged in size from 1 individual to 2080 "clumps" (Clark et al. 1993).|
Conservation, Ecology & Research
This rare species spreads vegetatively via rhizomes over very short distances about 4 inches (<10cm) (Kaye 2000). Since plants often grow in clumps, it is often difficult to distinguish individuals. Sexual reproduction is facilitated by pollination by insects, including the field crescent butterfly, sweat bees, and a syrphid fly. Seeds are dispersed by wind, but the small size and number of pappus bristles leads to more localized dispersal (Kagan and Yamamoto 1987).
Laboratory testing reveals that scarification stimulates germination. The mechanism for seed coat scarification in the wild is unknown, but researchers hypothesize that soil microbes may break down the coat during the winter (Clark et al, 1997). Most germination of E. decumbens seeds occur in April and May (Clark et al. 1997). Flowering in concentrated in June and early July, and seeds are dispersed in mid to late July (Ingersoll et al. 1995).
Unmonitored burning (infrequent, hot fires) (Meinke 1982).
Secondary succession (Kagan and Yamamoto 1987).
Road construction and maintenance (Clark et al. 1993).
Invasive non-native plants, especial
Germination trials. Results indicated that scarification is required for germination (Clark et al. 1995). Other studies show that cold stratification can be used instead of scarification.
Erigeron decumbens ssp. decumbens can be propagated using above stem cuttings, but success rates for establishment are much higher when vegetative cuttings include a small amount of rhizome tissue. Rhizome cuttings had survival rates if 67% at eight weeks and 33% at 26 weeks (Clark et al. 1997).
Propagation and transplantation studies. Erigeron decumbens ssp. decumbens produced few seedlings when directly seeded, even at high density seeding (60 seeds/m2). Encouragingly, transplants had fairly high survival rates, ranging from 33% to 70%, depending on source population and fertilization treatment (Kaye et al. 2000). These transplantation rates were much higher than a previous study had found (Clark et al., 1997). Researchers from the first study noted that roots developed slowly and their high mortality rates were caused by desiccation.
Monitoring and Management studies:
A five-year demographic study at three different sites did not help researchers identify optimal environmental conditions, due to a lack of gradient in environmental conditions. In most years, populations from both upland and lowland sites had similar reproductive output (Finley 1998). The five-year monitoring study did reveal a possible trend towards fewer reproductive plants and greater mortality at one site during the final year of monitoring (Finley 1998).
Experimental burning over a four-year period at a Research Natural Area found that plants were negatively affected by burning in the first year. However, results were positive in subsequent years, as crown area and flowering increased relative to unburned plants (Connelly and Kauffman 1991, Finley and Kauffman 1992 in Clark et al. 1993).
Germination trials at The Berry Botanic Garden resulted in 78% germination of apparently good seeds when subjected to eight weeks of cold stratification followed by alternating 50F/68F (10C/20C) and 60% when apparently good seeds were subjected to eight weeks of cold stratification followed by constant 68F (20C). Seeds not cold stratified did not germinate (BBG File).
Germination trials conducted. Germination was essentially zero with no cold treatment, and increased steadily with the duration of cold stratification. Twelve weeks of cold stratification yielded germination from 13% to 44% depending on seed source. Since this species' small seed size makes manual scarification difficult, cold stratification may be a more effective method when germinating large numbers of seed (Kaye and Kuykendall 2000).
Germination and viability studies. Addition of Gibberellic acid (GA) (a plant hormone that plays a role in the regulation of seed germination and dormancy) increased germination rates in scarified seeds from 1993. Scarified seeds from 1994 did not have the same response. One hypothesis is that the 1993 seeds underwent after-ripening and were more receptive to GA. There was not an increase in germination rate with GA addition for either seeds that were not scarified or those that had received cold treatment (Clark et al. 1997).
Seed viability studies. The viability of E. decumbens seeds that appeared to have a developed embryo ranged from 60-70%. However, overall production of seeds with embryos was only between 2-19% of total seed production. Seed viability did not decline after one year of storage (Clark et al. 1997).
Manual and mechanical removal of encroaching trees (Kagan and Yamamoto 1987).
Base-line data is being collected to determine effects of future management treatments such as mowing and burning on BLM land (Kaye 2000).
Seed from at least 5 of the 18 locations are stored at The Berry Botanic Garden.
Determine if low rate of filled seed production is a consistent pattern and investigate what factors influence production of viable seed (Clark et al. 1997).
Determine seed scarification mechanism in the wild to develop a practical method for laboratory scarification and assist in restoration efforts (Clark et al. 1997).
Determine appropriate frequency of prescribed burning (Clark et al. 1993).
Determine extent of clonality via genetic analysis.
Seed viability testing, germination temperature and condition optimization, and methods of transplantation (Finley et al. 1995).
Meinke, R.J. 1982. Threatened and Endangered Vascular Plants of Oregon: An Illustrated Guide. Portland, Oregon: U.S. Fish & Wildlife Service, Region 1. 326p.