Loss of habitat and declining numbers of the hawkmoth, its primary pollinator, threaten the western prairie fringed orchid's existence.
By Jenell Talley
Roses may be the flowers of choice for the love-smitten come birthdays and holidays, but the rare western prairie fringed orchid has drawn its own high level of interest from scientists, botanists, and biologists concerned for the future of this unusual plant.
A loss of the tallgrass prairie habitat that the orchid favors has caused a 60 percent drop in the flower's population over the last few decades. Listed as threatened since 1989, the orchid is found at Pipestone National Monument in Minnesota and is present throughout the tallgrass prairie region: Iowa, Minnesota, North Dakota, Kansas, Nebraska, Missouri, and Manitoba, Canada. The larger populations are found in North Dakota, Minnesota, and Manitoba.
Much of the habitat loss is the result of agricultural use. Mowing, haying, and grazing prevent the plants from flowering, stalling seed production.
Historically, the western prairie fringed orchid was recorded in South Dakota and in portions of Oklahoma, but sightings in those states have not been reported since 1970. In 1999, there were 175 known populations of the fringed orchid in North America.
"In 2003, Pipestone National Monument recorded its highest number of individual plants since monitoring began," says Gia Wagner, Pipestone's biologist-resource program manager. "A total of 221 plants were detected."
The number of individual plants varies from year to year depending on weather and site conditions-the orchids require undisturbed, wet tallgrass prairie or sedge meadow to thrive. The orchids are found with reedgrass and rushes, or in areas where such plants meet big bluestem, little bluestem, and switchgrass. According to Wagner, each of the country's orchid populations can have as few as one or as many as 1,000 plants.
Pipestone began monitoring its fringed orchid population in 1993. Wagner believes that precipitation and soil moisture play a crucial role in determining the number of individual plants detected in a given year. There have been times when park staff have found no plants in the park and other times when they recorded more than 200.
The plants at Pipestone occur within a ten-acre area closed to visitors. Their small size makes them visible from roads and trails only during flowering season, from mid-June to late July. The orchids' stalks may grow as tall as four feet, but most are one to three feet tall, comparable in height to surrounding prairie grasses. Each plant has two to five long, thick leaves and one stem with up to two dozen creamy white flowers.
The large, showy flowering stalks protruding from its stem distinguish the orchid from other plants. The flowers are narrow, only one inch wide, and fringed around the margin, giving them a feathery appearance. Each of the orchids has a three-lobed petal. The plant's floral display usually lasts about 21 days; individual flowers last up to ten days. The orchids typically live between one and seven years, depending on environmental conditions.
In addition to the loss of habitat, several factors are contributing to the species' low population numbers, according to Wagner, including the decline of another species, the nocturnal hawkmoths, the orchid's only pollinator. The moth has been affected by the loss of habitat, fragmentation, and the use of insecticides on agricultural crops.
Hawkmoths and the western prairie fringed orchid have a unique relationship. At night, the orchid's flowers increase their fragrance to attract the moths, and its petals direct the insects to its nectar supply. The orchid's nectar spur is longer than that of any North American orchid, and not surprisingly, the hawkmoth has a long tongue to match. When the moth extends its tongue into the flower's spur, pollen is brushed onto its eyes. The moth then carries the pollen to the next orchid. Without the hawkmoth, the orchid cannot be fertilized or produce seeds.
Other factors that contribute to the orchid's threatened status include over-collection of the flowers for scientific or commercial purposes, competition with non-native plants, chemical threats from herbicides used to control exotic weeds, and excessive grazing and haying.
The U.S. Fish and Wildlife Service published a recovery plan in 1999 that focuses on research needs, protection of known populations, and identification of suitable habitat. Wagner notes, however, that although such efforts may sustain the current population of orchids, it is unlikely that the species will be de-listed in the near future without major efforts to repopulate areas and protect the hawkmoths.
"Restoration efforts for the western prairie fringed orchid include monitoring populations and environmental conditions, supporting research, and education," says Wagner. "Research focused on determining the optimum hydrologic, weather, soil conditions, reproductive biology, and factors influencing the local populations of hawkmoths are all needed to provide the background information required to best manage the species and to predict how and where reintroductions might be effective."
