Ch. Sieg et Rm. King, INFLUENCE OF ENVIRONMENTAL-FACTORS AND PRELIMINARY DEMOGRAPHIC-ANALYSES OF A THREATENED ORCHID, PLATANTHERA-PRAECLARA, The American midland naturalist, 134(2), 1995, pp. 307-323
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.