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Comparing seed germination in western prairie fringed orchid (Platanthera praeclara Sheviak and Bowles) seeds planted in grazed and ungrazed plots.

The western prairie fringed orchid (Platanthera praeclara Sheviak and Bowles) of the family Orchidaceae has been known to inhabit the Sheyenne National Grasslands in southeastern North Dakota for years. The plant has been federally listed as threatened since 1989 and preserving this remnant population of the orchid is a high priority. The impact of current management regimes, particularly cattle grazing, on the orchid population is unknown.

This study was designed to collect data on the impacts of grazing on the orchid population in the Sheyenne National Grassland. The hypothesis for this study was that cattle grazing in orchid habitat may create disturbances that may improve orchid seed germination (1). Study objectives were to determine stages of seed germination and document numbers of germinating seeds, protocorms, and seedlings in two grazed versus two ungrazed plots.

Seed packets enclosing 0.0005 grams of seeds (about 400-500 seeds) were constructed using plankton netting and plastic slide cases (2). In October of 2003 approximately 10 packets were placed at random in each of two ungrazed swales and another 10 packets in each of two grazed swales, with each packet buried 1 centimeter deep. Seed packets were retrieved in October of 2004 and each packet's contents were transferred to agar plates for examination under a dissecting microscope. Developmental stages leading up to the young seedling stage were assessed and documented.

Results showed 11% of seeds in both grazed and ungrazed plots achieved some development, whereas 89% showed none. Observable differences were evident but z-tests of proportions between the two samples for four developmental categories showed no significance at the 95% confidence level.

Since seed germination is only a small part of the P. praeclara lifecycle, additional studies are critical to further understand the impacts of grazing on the orchid population.

1. Bowles M.L. Natural Areas Journal 3, 14-37, 1983.

2. Rassmussen HN, Whigham DF. American Journal of Botany, 80:1374-1378, 1993.

Mindy Anderson *, Bridget O'Brien, and Bonnie Alexander Department of Biology, Valley City State University, Valley City
Comparison of seeds swelling, rupturing seed coat,
and developing 1st leaf in grazed vs. ungrazed plots

Swollen & Rupturing Seeds

Ungrazed Plots Grazed Plots

 640 921

One leaf Seedling Development

Ungrazed Plots Grazed Plots

 15 7

Note: Table made from bar graph.
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Title Annotation:Collegiate Communication--Undergraduate
Author:Anderson, Mindy; O'Brien, Bridget; Alexander, Bonnie
Publication:Proceedings of the North Dakota Academy of Science
Geographic Code:1U4ND
Date:Apr 1, 2005
Words:374
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