Northern Prairie Wildlife Research Center
Prior to pioneer settlement the prairie fringed orchid (Platanthera leucophaea (Nutt.) Lindl.) was widespread throughout the tallgrass prairie ecosystem. An 1889 record from Kansas commented "once school children brought armfuls of the curious [orchid], . . . now they are seldom seen." (Fritz 1993). Conversion of the prairie to cropland and other human development has caused the loss of most of the original habitat. The western prairie fringed orchid (Platanthera praeclara Sheviak & Bowles) was recognized as a separate species in 1986 based on material collected by M.L. Bowles from the SNG (Minnesota Natural Heritage Program 1995). Concern about the limited number of populations of both species led to their listing as threatened species by the USFWS under the authority of the Endangered Species Act. Populations of the western prairie fringed orchid are known from 173 sites in 6 states: Iowa, Kansas, Minnesota, Missouri, Nebraska, North Dakota and the Canadian province of Manitoba (Minnesota Natural Heritage Program 1995).
|Scientific Name||Common Name|
|Platanthera praeclara||Western prairie fringed orchid|
|Tall hairy grovebur
Mingan Island moonwort
Little grape fern
|Greater prairie chicken
Candidate 2 Species
|Candidate 2 Species
Candidate 2 Species
The western prairie fringed orchid usually occurs in mesic swales or draws in tallgrass prairie, with ideal habitats being subirrigated. Such habitat is common in the SNG. Platanthera praeclara is most often found in the Carex lanuginosa- Calamagrostis stricta-Juncus balticus habitat type (Manske 1980). Sieg and Bjugstad (1994) have suggested that Poa pratensis and Euphorbia esula L. are also species of co-occurrence in swales. Sieg and King (1995) present data that suggests P. praeclara may do best in areas of reduced competition, but requires some litter. It is not uncommon to see plants in disturbed areas such as roadside ditches and soil borrow sites. However, frequent disturbance such as tillage will not allow establishment of the plant. Bowles (1983) has suggested that disturbances, such as fire or grazing, may be needed to open microsites for the establishment (germination) of new plants. The orchids begin growth in early May. Flowering occurs from late June through the much of July. Flowers are evidently pollinated by a few species of hawkmoths of the family Sphingidae. The flower structure is such that only those species of hawkmoths with properly spaced eyes and compatible tongue lengths can pollinate the flower (Fritz 1993). If pollination occurs, the inferior ovary develops into a slender, angled capsule filled with thousands of dust-like sized seeds. In the fall, the capsule splits and the seeds are scattered by the wind. It is believed that the western prairie fringed orchid depends upon a mycorrhizal association to become established and grow. Bjugstad-Porter (1993), in a study of SNG orchids, isolated the mycorrhizal symbiont Rhizoctonia, a common mycorrhizal fungi of terrestrial orchids.
How to manage orchids?
The question of how to manage the areas that support the remaining populations of the western prairie fringed orchid is logical and important. The main limiting factor for the orchid is its dependency upon the limited habitat of mesic to wet-mesic tallgrass prairie (Fritz 1993). Historically, areas of tallgrass prairie which had reliable sub-surface sources of groundwater were common. However, development of farmland, roads and other forms of development have led to wetland drainage, stream channelization, ditching and shallow aquifer use which has severely depleted the orchid's habitat. These practices still occur and put some remaining orchid sites at risk. Much of the remaining orchid habitat is used for haying and/or grazing (e.g. the SNG). Many of the orchid sites are under protective ownership (governmental agency or private conservation organization). In either case, a key question is, "what management practices will be beneficial for the western prairie fringed orchid"? Manske (1995b) commented that "most any type of management practice that maintains a suitable habitat site as a grassland or prairie would have some redeeming benefits for the fringed orchid." He bases this on the observation that the fringed orchid has coexisted in suitable habitats that have been ecologically managed by defoliation by grazing, fire and or mowing for many years.
Unfortunately there is more unknown than known about the life history and ecological needs of the western prairie fringed orchid. Sieg and King (1995) studied the western prairie fringed orchid population in the SNG to learn more about the life history and the influence of management regimes and environmental factors. Population characteristics relative to 5 management practices were examined: grazed-rotational, grazing season-long, no grazing, grazed/burned, and ungrazed/burned. They found the total number of orchid plants showing aboveground growth to differ between years, but not between management practices. This is good news in that is supports Manske's (1995b) contention that managing for healthy tallgrass prairie, regardless of the method, will allow the orchid to be a component of the ecosystem. At the same time the absence of any orchid density differences between systems fails to support Bowle's idea that seasonal mowing, grazing or burning enhances orchid colonization. Further long term research examining experimental manipulation is needed before conclusions can be drawn about the management practices of mowing, burning or grazing. Most (73%) of the P. praeclara individuals observed during the 5-year study were in the vegetative state. Nonflowering may be the result of inadequate moisture the preceding growing season (Bowles 1983). Sieg and King (1995) found the number of flowering individuals to be lowest in years with low precipitation. Over 60% of the fringed orchid individuals observed each year were new, with the exception of 1994 when only 33% were new. Once absent, few P. platanthera individuals reappeared the following year (Sieg and King 1995). An average of 88% of the fringed orchid individuals that were absent in 1 year between 1991 and 1993 were also absent the following year. For individuals absent 2 years , an average of 92% were absent the third year. The authors believe the low number of originally marked Platanthera praeclara individuals that reappeared aboveground in subsequent years suggests that this plant is short-lived, or is capable of longer periods of dormancy than previously observed. However, demographic data from Minnesota (Minnesota Natural Heritage Program 1995) do not support the idea of the western prairie fringed orchid being a short-lived species. The Minnesota data indicate that the plants are longer lived, can flower continuously each year for up to 8 years and withstand a longer duration of dormancy, 3 years or longer, than what has been found for the SNG plants.
The rate of recruitment of new individuals into the population by seed production and germination needs to be studied. If having ripe seeds each year is vitally important, then management practices which allow some seed pods to mature is important. More information is needed about the pollinators. While most agencies, organizations and private landowners see the need to restrict herbicide application, the need to restrict insecticide use may not be as easily seen (Minnesota Natural Heritage Program 1995). Any vegetation manipulation carried out by the U.S. Forest Service occurs under the guidance of the Management Guidelines, Western Prairie Fringed Orchid, Sheyenne Ranger District, Custer National Forest, 1994 (Potts 1995). While these guidelines may seem onerous to the individual permitees, they do serve the purpose of protecting a threatened species until we have more information to guide management decisions.