Dynamics of a threatened orchid in flooded wetlands

Abstract

One of the three largest metapopulations of the western prairie fringed orchid (Platanthera praeclara) occurs on the Sheyenne National Grassland, in southeastern North Dakota. Our study was initiated in 1993 to quantify the effect of flooding on individual orchid plants. In 1993, 66 plants (33 flowering and 33 vegetative) growing in standing water were permanently marked; their status was checked at the end of the growing season in 1993 and in subsequent growing seasons (1994-1996). Most (70%) of the flowering plants persisted through the 1993 growing season. Those that did not were shorter (P = 0.001) and had a higher percentage of their stalk submerged through the growing season (P < 0.02). Only one vegetative plant persisted through the 1993 growing season. The ability of flowering plants to persist in standing water was attributed to their greater height which allowed some portion of the plant to remain above the water and produce photosynthates needed to produce next season's shoot bud and immature root system. Flowering plants persisted through the first growing season with as much as 75% of their stalk submerged in water. In 1994, only four plants reappeared; in 1995 only one plant reappeared aboveground. None of the plants that did not persist through 1993 reappeared in 1994 or 1995. By 1996 none of the marked plants were observed aboveground. Although flooding is detrimental, especially to the survival of vegetative plants, its impact must be viewed in a larger context and include data from several years. It is likely that flooding creates suitable moisture conditions on higher landscape positions, provides an important mechanism for seed dispersal, and is one of several natural catastrophic events that plays a significant role in perpetuating these wetland systems and associated species.

Citation

Sieg, Carolyn Hull; Wolken, Paige M. 1999. Dynamics of a threatened orchid in flooded wetlands. In: Springer, Joseph T. ed. The central Nebraska loess hills prairie: Proceedings of the Sixteenth North American Prairie Conference. Kearney, NE: University of Nebraska. p. 193-201.