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dry years, the length of the flowering season may be reduced. Erigeron decumbens var. <br /> decumbens is difficult to spot during field surveys outside of the flowering season. <br /> Reproductive Biology and Breeding System: Breeding system is not known; observations <br /> indicate that E. decumbens is probably insect pollinated; vegetative propagation in the strict <br /> sense does not occur (Clark et al. 1994) except to the extent that large individuals may break <br /> up into smaller units as the centers die out. <br /> Pollinators: Not documented, but likely pollinators include solitary bees and syrphid flies <br /> (Clark et al. 1994). <br /> Seed /fruit Dispersal and Establishment Mechanisms: Achenes are primarily wind <br /> dispersed (Clark et al. 1994). Seedlings are observed primarily in small areas of bare soil <br /> that form suitable microsites; at Willow Creek, seedlings tend to be more abundant (or <br /> evident) the year following a prescribed burn. A caveat: seedlings are difficult to distinguish <br /> from seedlings of Aster hallii. <br /> Potential Habitat Modifications: The largest known population of Erigeron decumbens var. <br /> decumbens, which was discovered in west Eugene in 1986, was destroyed that same year <br /> when the prairie was converted to grass seed production. Presumably many of the other <br /> historical sites that appear to no longer be extant were also lost to agriculture. In some <br /> populations, invasion of woody species has reduced the suitability of habitat for this species; <br /> at Willow Creek populations have declined in native wet prairie invaded by Fraxinus latifolia <br /> (Oregon ash) and Pyrus communis (pear). Prescribed burns and manual tree removal may <br /> benefit E. decumbens. At Willow Creek, E. decumbens has typically decreased in numbers <br /> the first year after prescribed burns, but numbers have increased in subsequent years as <br /> seedlings established and are recruited into the population. Manual tree removal in E. <br /> decumbens habitat was initiated in 1994, and this is too recent to make conclusions regarding <br /> the long -term response. <br /> Herbivory, Seed Predation and Disease: Sap sucking insects (Hemiptera), a bruchid seed <br /> predator (Coleoptera), and thrips and mites have been collected on E. decumbens; it is not <br /> known if these arthropods are damaging (Clark et al. 1994). <br /> Impacts of Exotic Plants: Agrostis tenuis, Anthoxanthum odoratum, Brachypodium <br /> sylvaticum, Festuca arundinacea, Phalaris arundinacea, Chrysanthemum leucanthemum, <br /> Daucus carota, Hypochaeris radicata, and Plantago lanceolata are specific non - native plant <br /> species that have been reported as degrading the native prairie habitat and may be excluding <br /> E. decumbens through competition (Clark et al. 1994). <br /> 3) Scientific name: Horkelia congesta Dougl. ex Hook. ssp. congesta <br /> 7 <br />