Western Prairie Fringed Orchid Management, Ecology, and Decline at Mormon Island

Abstract

The western prairie fringed orchid (Platanthera praeclara Sheviak & M. L. Bowles; WPFO) was first detected in a vegetative state on Mormon Island in 1978 and identification was confirmed following a mass flowering event in 1982. From a high count of ~60 plants the WPFO slowly declined and has not been observed since 2000 despite flowering season surveys conducted in 15 of the last 20 years. We explore the natural history of the WPFO in the contexts of Mormon Island to establish potential causes for its apparent disappearance and evaluate the possibility it persists in some capacity. Our investigation of secondary data suggests the Mormon Island vegetation community remains relatively intact, including species associated with WPFO occurrence. Examination of the ranges of known and potential WPFO pollinators suggests that Sphinx drupiferarum, Eumorpha achemon, and Hyles lineata were the most likely pollinators at Mormon Island, and recent observations of these species indicate pollinator decline may not have been a primary factor in WPFO disappearance locally. Research demonstrates individual WPFOs can occasionally live for decades, are able to survive underground as rhizomes for periods of time, and often present above ground as just 1–3 leaves during the growing season. Additionally, the seeds may persist in the soil for a substantial period of time. The WPFO appears to tolerate a reasonably wide range of habitat conditions and management regimes but may require a relatively narrow range of circumstances to flower en masse, including above average spring precipitation in subsequent years. Mass flowering events may also be stimulated by early spring burns that precede above ground vegetative growth and subsequent rest during the growing season, but research is equivocal. Though factors such as inbreeding depression and herbicide overspray could have potentially impacted the population, based on local conditions we suggest the WPFO may persist on Mormon Island in a reduced capacity. We recommend the continuation of growing season surveys and experimentation with multi-year management strategies that could stimulate growth and flowering. Keywords: Western prairie fringed orchid, Platanthera praeclara, Management, Pollination, Ecology, Central Platte River Valley, Sphingidae