INFLUENCE OF ENVIRONMENTAL-FACTORS AND PRELIMINARY DEMOGRAPHIC-ANALYSES OF A THREATENED ORCHID, PLATANTHERA-PRAECLARA

In 1987, 160 individual Platanthera praeclara Sheviak and Bowles were permanently marked on 16 transects on the Sheyenne National Grassland, in southeastern North Dakota. They were located on five sites that re presented five management regimes: (1) grazed-rotational; (2) grazed-s eason long (5.5 mo); (3) ungrazed; (4) ungrazed and burned, and (5) gr azed and burned. By 1994, only 4% of the originally marked Platanthera praeclara individuals were observed; however, numbers did not differ (P = 0.13) among sites. Beginning in 1990, all Platanthera praeclara i ndividuals in belt transects on each site were marked and counted, and demographic data were recorded. Total orchid density differed (P = 0. 04) among sites, but not with a consistent pattern among years (P = 0. 001). In some years, Platanthera praeclara density was positively corr elated with surface soil moisture. Preliminary demographic analyses in dicate that Platanthera praeclara may be short-lived and that absent p lants rarely reappear. Cluster analysis indicated that the most common vegetative community supporting Platanthera praeclara was dominated b y Poa pratensis L. and Juncus balticus Willd., although Platanthera pr aeclara density on the Sheyenne National Grassland was most highly cor related with cover of Calamagrostis stricta (Timm.) Koel.