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.
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).
Erigeron decumbens is an early successional species that is dependent on flooding and fire to maintain open prairie habitats (Kagan and Yamamoto 1987). Fire prevents native shrubs and trees from encroaching and out-competing shade intolerant plants, such as the Willamette Daisy.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).
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