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1990 Soiranthes diluvialis Management Plan <br /> BACKGROUND <br /> Soiranthes diluvialis is the second rarest orchid in Colorado (B.Jennings to D. <br /> Antonio, 7/22/86). It is being recommended by the U.S. Fish and Wildlife Service for <br /> federal listing as an endangered species and is expected to be listed during FY <br /> 1991. In the summer of 1986 a population of almost 5500 orchids was discovered <br /> by Bill Jennings on City of Boulder Open Space property known as Van Vleet. The <br /> particular fields have historically been hayed and grazed. <br /> The orchids grow in two irrigated fields adjacent to South Boulder Creek. The <br /> soils are of the Niwot series with mild alkalinity and moderate permeability (SCS <br /> Soil Survey, 1975). The wetter areas of the field contain tall grass species, <br /> especially prairie cordgrass (Spartina Dectinatal, yellow indiangrass (Sorghastrum <br /> nutans and big bluestem (Andropoaon gerardiil. The short-mid grass communities <br /> include, meadow fescue (Festuca Dratensis), smooth brome (Bromus inermis) and <br /> blue gramma (Bouteloua curtipendulal. The orchids appear to do best in these <br /> shorter grasses and areas of less vegetative density. <br /> From 1986 through 1990 the population decreased and fluctuated <br /> dramatically. The most recent inventory from August 1-7, 1990 reports almost 1900 <br /> orchids (E. Smith) -- a substantial increase over last year. This includes plants <br /> found in new locations. August haying and winter grazing have continued on these <br /> fields since 1987. <br /> PURPOSE <br /> The purpose of this research is to determine which, if any, of the historic <br /> agricultural practices best promote the growth of the orchid, Spiranthes diluvialis, <br /> and to evaluate potential management opportunities. Test plots will be set up and <br />