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Management Considerations for the
Western Prairie Fringed Orchid

Llewellyn L. Manske PhD
Associate Range Scientist
North Dakota State University
Dickinson Research Extension Center

 

Western prairie fringed orchid (Platanthera praeclara) is a terrestrial orchid that has been listed as a federally threatened plant species since September 1989 under the Endangered Species Act of 1973 as amended in 1988 because of its potential extinction primarily due to loss of habitat. It is currently known to be extant on 129 sites in 39 counties of seven states and one Canadian province.

The viability of the orchid population will depend on the prevention of loss of habitat to urban development and conversion of grassland to plowed cropland and will depend on the success of the type of management used to manipulate the habitats where extant populations are found.

No scientific data exists at the present time that clearly shows the most beneficial management practices for the fringed orchid. Research on management techniques that are beneficial for the fringed orchid should have a very high priority. Very many questions need to be answered through research before we will know the best management techniques. We do not know the importance of the symbiotic relationships with mycorrhizal fungi and rhizosphere micro-organisms in the life history of the fringed orchid. We do not know the importance of vegetative reproduction in relation to sexual reproduction in the continuation of the fringed orchid at a site. We do not know how much sunlight is needed by the fringed orchid and the effects of shading and competition for sunlight from other plants. We do not know the environmental conditions needed to enhance seed germination and seedling growth. We do not know the mechanisms that control the fringed orchid to change from its saprophytic stage to its photosynthetic stage.

We do not know how long it can stay saprophytic. Some types of orchids are known to be able to remain saprophytic with no aboveground leaves or flowers for up to 14 years. Knowledge of the conditions and triggering mechanisms that control these life form changes in the fringed orchid would be extremely important. These and several other key questions need to be answered before management can be specifically recommended to benefit the fringed orchid. During the interim period until scientific research results point to the beneficial management techniques we must rely on current scientific knowledge and good empirical observations to guide us with management recommendations.

Management that is known to be detrimental to the fringed orchid on suitable habitat sites is annual cultivation for crop production. The fringed orchid can not exist in areas that are annually managed by agronomic practices that disturb the soil by tillage. Bowles and Duxbury (1986) credited the conversion of the fringed orchid habitat - "virgin" prairie to intensive agriculture-cropland as the primary reason for the decline of the fringed orchid population in North America.

Initial interim management for the fringed orchid should be to provide a mechanism and assurance that known extant sites with orchids should be free of annual agronomic practices with soil tillage and that they remain as grasslands or prairie. All other management recommendations are secondary to this. 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. The primary concern is to maintain the site as suitable habitat, then through scientific research develop the management to be specifically beneficial for the fringed orchid.

Management practices that are beneficial for the fringed orchid and the other plants on a dry mesic or mesic site dominated by big bluestem and little bluestem will be different than the management practices designed to benefit the fringed orchid and other plant species on a wet-mesic or seasonally hydric sedge meadow dominated by sedges and spikerushes. The fringed orchid is a member of a complex plant community. Management practices that are directed to be beneficial for the fringed orchid that are not also beneficial for the entire plant community will eventually be negative for the fringed orchid. Management that is known to work and be beneficial for various habitat types should be the management that is used initially to manage the known sites for the fringed orchid. The fringed orchid has coexisted in suitable habitats that have been ecologically managed by defoliation by grazing, fire, and/or mowing. The variations of timing, frequency, and combinations of these three defoliation techniques can give different effects in different habitat types.

Grazing

Several extant sites have long histories of fringed orchids coexisting with grazing. We do not know the timing of grazing periods that enhance the fringed orchid nor do we know the periods that grazing would be detrimental to the fringed orchid. We do not even know if cattle actively graze and consume fringed orchids or not. We do not know the extent that other herbivores use the fringed orchid as forage. Several observations have been made of orchid plants with some or all the flowers removed. A few observations have been made of domestic cattle and deer eating flowers. Removal of flowers would terminate seed production for that plant. If all the flowers of all the plants at a site were removed it would eventually cause propagation problems if viable seeds were not stored in the soil and if vegetative reproduction were not strong. Occasional removal of a few flowers by cattle and other herbivores should not cause propagation problems for a population. Rotational grazing plans can be developed that has grazing periods that allow orchids in some pastures to develop their flowers to seed if it is shown through research that cattle cause a problem in flower development.

The effects on an orchid plant from partial or complete defoliation by grazing are not presently known. Removal of reproductive parts at early and mid phenological stages of development by grazing of grass species stimulates vegetative growth of that plant. It is not known if this phenomenon occurs in all monocots or if it occurs in the fringed orchid.

Recent research developments by Coleman (1983) and McNaughton (1983) have shown grazing to be beneficial to grassland ecosystems by stimulation of mycorrhizal fungi and rhizosphere activity that results in rapid nutrient cycling and changes in physiological activities in the plants. The higher the plant species is in the successional scale in the grasslands the greater its obligation to mycorrhizal fungi and rhizosphere activity and the greater its evolutionary advances of physiological adaptations to produce after defoliation. This has developed to a point that lack of defoliation causes reductions in productivity. Properly timed defoliation by grazing can increase vegetative reproduction (tillering), increase plant density, and increase net primary productivity for the ecosystem. The period that shows greatest increases in physiological activity from defoliation by grazing in grass plants is after the third leaf stage and before flower anthesis which is a period of fast growth activity. This period coincides with activity periods of soil organisms and this is the period that shows the greatest potential to stimulate increased activity of the soil micro-organisms.

Fire

Fire is a natural force in the environment. Currently Iowa, Kansas, and Minnesota have extant fringed orchid sites that are being managed exclusively with prescribed fire in early spring. The orchids seem to be able to coexist with this management. Many prairie plant species of the Tall Grass Prairie Biome Type have evolved and adapted to fire. Higgins (1986) investigated the historical records and found that the majority of lightning set prairie fires occurred in July and August and that Indian set fires peaked in April and October. Lightning set fires have had a longer historical influence on the evolutionary development of the plants than have Indian set fires. It is not known what effects defoliation by fire has on the fringed orchid at various times. Fire may play a very important role in the life cycle of the orchid by reducing competition for sunlight or altering the environment to trigger seed germination and seedling growth. Fire generally removes standing litter, warms soil temperatures, and slightly improves available nutrients. Fire is an important component of the management of tall grass prairie habitat at prescribed places and times.

It is not known at the present time if fire can be used to stimulate the mycorrhizal fungi and soil micro-organisms of the rhizosphere or not in the prairie ecosystem. Prescribed fire is generally conducted during periods of slow growth activity of the desirable plants which is also slow activity periods for soil organisms with little or no potential to stimulate increases in activity. Management of an area by fire alone without a combination of grazing or mowing during fast growth periods may eventually hurt the nutrient cycling by reducing the soil organism activity. Additional research is needed on this problem to determine the effects of fire on the soil organisms over the long term.

Mowing

Mowing is not a natural form of ecological management in the same sense as grazing and fire but the effects of defoliation by mowing trigger plants to have similar physiological responses as other forms of ecological management by defoliation. This is the reason that mowing is categorized as a type of ecological management. Mowing grasslands for habitat improvement is a desirable practice. Big bluestem and Indian grass and several other prairie plants respond very favorably to defoliation by mowing with increases in plant density. Mowing annually during the summer for hay production seems to be the most dominant type of management currently used on known extant western prairie fringed orchid sites. The orchids do coexist with this type management but observations have been made that infer that the number of plants generally remain small. We do not know the true reasons that cause this observed response. It is presently assumed that mowing prohibits mature seed production. The annual removal of the sexual reproductive portions of the orchid stop seed production for that year and may not allow for recruitment of new plants from seed in that population. The population then must depend on vegetative reproduction for the perpetuation of the population. The process of vegetative reproduction of the fringed orchid is little understood but is probably a very important component of the life history of the orchid and could be enhanced by knowing the proper times for defoliation.

We do not know the importance to a population of successfully completing sexual reproduction to ripe seeds every year. If having ripe seeds each year is vitally important then annual summer mowing management needs to be modified. Mowing before the flowering period usually causes considerable reduction in the amount of harvestable herbage. Mowing after the seeds are ripe results in considerable reduction in quality of the harvested herbage. Harvesting for hay by mowing on alternate years or every third year may be a management practice that would allow the orchids to produce seeds to completion. This type management practice of mowing every second or third year would work nicely on publicly owned land. This management practice would probably not be acceptable on privately owned land unless cattle were allowed to harvest the herbage during the other years not managed by mowing. We do not know how frequently the orchid needs to produce viable seed to perpetuate a population. Very few prairie plants need to produce seeds each year to survive. When this frequency is known from research, then we will know how often the orchids on hay meadows should be allowed to produce ripe seeds. Long term management plans should allow the orchids to produce seeds at some interval of time that is presently not known.

Annual mowing for hay production on private land may not enhance the orchid population to grow to large numbers of individuals but this would be preferable management when the alternative choice would be to manage a site with annual tillage for crop production.

Idle (No defoliation management)

Land managers have a fourth type of management as one option. This choice is to do no defoliation management. Orchids are known to exist on sites that have been managed by no defoliation (idle) for short periods of time. Idle or no defoliation management is not a good long term management for grassland and prairie ecosystems. Generally on idle areas the quality of the prairie deteriorates. Dead aboveground litter accumulates, shading of young growth reduces development, soil temperatures are altered, mycorrhizal fungi and rhizosphere activity decreases, nutrient cycles are slowed and available nutrients are reduced, net primary productivity is reduced and plant densities are decreased on long term idle prairies. Long term effects of idle management on the fringed orchid is not known but it is not good management for the other plants in the ecosystem.

Management to benefit the western prairie fringed orchid is primarily good prairie management by ecological techniques of defoliation by grazing, fire and/or mowing. The primary initial objective of management for the fringed orchid is to maintain the quality of the grassland and prairie habitats. The fine tuning of the management will be adjusted as information from scientific research is developed. The known extant sites with fringed orchids need to be managed as prairie and not managed by tillage for crop production. Literature Cited

Bowles, M.L. and A. Duxbury. 1986. Report on the status of Platanthera praeclara Sheviak and Bowles in Oklahoma, Kansas, Nebraska, South Dakota, and North Dakota. Unpublished report to the U.S. Fish and Wildlife Service, Denver, CO. 42 p. + appendices.

Coleman, D.C., C.P.P. Reid, and C.V. Cole. 1983. Biological strategies of nutrient cycling in soil systems. In: A. MacFadyen and E.D. Ford (eds.), Advances in ecological research, Vol. 13, Academic Press, New York.

Higgins, K.F. 1986. Interpretation and Compendium of Historical Fire Accounts in the Northern Great Plains. U.S. Fish Wildl. Serv. Resour. Publ. 161. 39 p.

McNaughton, S.J. 1983. Compensatory plant growth as a response to herbivory. Oikos 40:329-336.