Survival of the western prairie fringed orchid at Pipestone

THE WESTERN PRAIRIE FRINGED ORCHID (Platantherapmeclara) is an erect perennial herb with a show inflorescence or flower stalls reaching up to 75 centimeters (29.6 in.) in height and producing 5-25 white flowers (Sheviak and Bowles 1986) (fig. 1, below). The orchid once grew throughout the western tallgrass prairie but is now restricted to remnant sites in six states and southern Canada. It has declined because of the drainage and direct loss of habitat resulting from agricultural expansion, and was listed as a federal threatened species in 1986 (U.S. Fish and Wildlife Service 1996). Because of the shallow soil and altered hydrology of its habitat in Pipestone National Monument, the western prairie fringed orchid may be prone to greater moisture stress and lower survival than plants growing in other orchid habitat with deeper soils and intact hydrology. To determine if lower survival of orchid plants occurs in the monument, we compared the survival of orchid plants at Pipestone with the survival of another population of these plants at Sheyenne National Grassland in southeastern North Dakota (Sieg and King 1995). Sheyenne National Grassland protects one of the largest populations of the orchid in deep-soiled habitat that is usually wet but can be dry or flooded. Pipestone and Sheyenne are similar in general soil type (mesic loam), climate (total amount and distribution of precipitation), and management (prescribed burns and no cattle grazing in orchid habitat); they differ in soil depth and hydrology. Lower survival of orchid plants at Pipestone than that at Sheyenne would suggest the population at Pipestone would benefit from restoration of the natural hydrology. However, because of the extent and depth of channelization of Pipestone Creek in the monument and upstream, the only feasible response may be changes to the management regime (e.g., prescribed fire) in the orchid habitat.