Eastern Prairie Fringed Orchid Habitat Model

Eastern Prairie Fringed Orchid Habitat Model
go to: USFWS Gulf of Maine Watershed Habitat Analysis
go to: Species Table
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Draft Date:
March 2001

Species:
Eastern prairie fringed orchid, Platanthera leucophaea (also know as Habenaria leucophaea leucophaea; Gleason and Cronquist 1991).

Use of Study Area Resources:
The eastern prairie fringed orchid is a federally endangered herb (family: Orchidaceae) which grows in wet calcareous meadows (Hinds 1983), wet prairies, and rarely in bogs and marshes (Gleason and Cronquist 1991). Its known occurrence in the study area is limited to a single sphagnum - arborvitae bog (Crystal Bog) in Maine's Aroostook County (Brower 1977). The orchids grow in a calcareous fen (LIttle Crystal Fen; Stockwell 1994, Maine Department of Conservation 1999) within the bog. The known extant population is currently around a dozen plants. An exact count is difficult since individual plants may go into dormancy for one or more seasons. At least one other blooming plant was found several years ago in another part of the bog, by a photographer who refused to disclose the location. Accordingly, one or more undocumented additional populations probably exist in this 4000 acre bog.

Habitat Requirements:
Typical habitat in most of this orchid's midwestern range is wet tallgrass prairie; relict eastern populations mostly occur in "wet sedge meadows "(USFWS webpage). In Maine, its easternmost occurrence, the sphagnum bog microhabitat described by Brower (1977) is open with: "scattered groups of arborvitae, with a few young larch coming in. Neighboring plants are sedges, bog birch, shrubby cinquefoil, bog laurel, sheep laurel and other sphagnum bog plants. That portion of the big bog is quite wet, and with standing water at times...This orchid (grows) somewhat above the general bog in one of the somewhat elevated areas of mixed bushes." Suitable soils for these plants range from calcareous fine silt loam to coarse sand mineral soils, but in Maine consist of hydric organic soils of bogs or fens, of either acid or neutral pH (Bowles 1983).

Pollination and reproduction: The mid-July flowers of the eastern prairie fringed orchid are creamy-white to whitish-green, and fragrant (Brower 1977). Hawkmoths (Sphingidae) have been credited as this plant's primary pollinator: Xylophanes tersa and Eumorpha achemon are confirmed pollinators; Sphinx eremitis have been collected with orchid pollen; Manduca sexta, and Manduca quinquimaculata have been observed visiting flowers at dusk (Bowles 1983) and may also be effective pollinators.

P. leucophaea reproduces by windblown seed (Bowles 1983), or may regenerate quasi-vegetatively by forming a perennative bud on the plant's thick, spindle shaped root, which develops into new root stock the following season (Dressler 1981 in Bowles 1983). Seed germination and successful vegetative regeneration both require favorable soil-inhabiting fungi/mycorrhizae to facilitate nutrient uptake (Bowles 1983).

Limiting factors: Factors which appear to be limiting to this species include shading by shrubs or forest canopy (Bowles 1983), invasions of purple loosestrife or reed canary grass (USFWS 1991/Midewin National Tallgrass Prairie webpage), grazing on flowering stems by deer (Bender 1988 and Stoutamire 1996 on Midewin National Tallgrass Prairie webpage), feeding on flowers and fruit by conehead grasshoppers (Harrison 1988 on Midewin National Tallgrass Prairie web page) and fires during the growing season (Bowles 1983). Fires during the dormant season may be beneficial. Fires early in the growing season may stimulate flowering, possibly by creating warmer soil conditions or enhancing conditions for beneficial soil fungi, whereas late season fires may damage flower buds that have set for the next growing season (Bowles 1983).

Growth of competing plants, and frequency and intensity of fires, are affected by soil and groundwater levels. Hydrology of Crystal Bog was altered in the past by construction of a railroad embankment. Further reduction of or increase in water supply to the bog thus would likely affect the orchid either directly, or indirectly. Similarly, changes in nutrient levels or pH could affect the survival of eastern prairie fringed orchids at this location.

Disturbance
This plant is probably most threatened by the botanically curious. It is small and inconspicuous when not in bloom and therefore easily damaged by foot traffic.

Model/Mapping
Occurrence information was provided by the Maine Natural Areas Program. The wetland conditions at the documented orchid location in Maine and conversations with biologists/botanists who have been to the site (K. Stockwell, S. Gawler both Maine Natural Areas Program) were used to select NWI wetland polygons including the site being used by the orchid. This occurrence matched adjoining palustrine scrub-shrub (PSS) patches, one a mixture of type 1 (broad leaved deciduous) and type 4 (needle leaved evergreen), the other just type 4. Botanists advised that type 4 is preferred. Accordingly the occurrence area within the bog mapped as PSS4 was scored 1.0, nearby polygons mapped as PSS1 were scored 0.7, and the more generally characterized PSS7 (evergreen) were scored 0.3 if they had a water regime of B (saturated) or E (seasonally flooded, saturated). Habitat was mapped only within or close enough to the main portion of the bog to benefit from colonization by wind-borne seed.

Sources:
Bender, J. 1988. Element stewardship abstract for Platanthera leucophaea. The Nature Conservancy, Arlington, VA.

Bowles, M.L. 1983. The tallgrass prairie orchids Platanthera leucophaea (Nutt.) Lindl. and Cypripedium candidum Muhl. ex Wild.: some aspects of their status, biology, and ecology and implications toward management. Natural Areas Journal 3(4):14-37.

Brower, A.E. 1977. The Prairie White Fringed Orchid (Habenaria leucophaea Nutt.) in Maine and its relevance to the Critical Areas Program. Planning Report 34, State Planning Office, Augusta, ME.

Gleason, H.A. and A. Cronquist. 1991. Manual of Vascular Plants of Northeastern United States and Adjacent Canada, 2^nd ed. N.Y. Botanical Garden, Bronx, NY. p 858.

Hinds, H.R. 1983. The Rare Vascular Plants of New Brunswick. A Canadian contribution to the UNESCO program on man and the biosphere. National Museum of Natural Sciences, Syllogeus No. 50. 97 pp.

Maine Department of Conservation. 1999. Rare Plant Fact Sheet: Platanthera leucophaea (L.) Lindl. Prairie White-fringed Orchid, Natural Areas Division, Augusta, ME. 2pp.

Midewin National Tallgrass Prairie webpages: http://www.fs.fed.us/mntp/speciesreintro/, downloaded 11/05/99

Stoutamire, W. 1996. Seeds and seedlings of Platanthera leucophaea (Orchidaceae). Pages 54-61 in Carol Allen (ed.) North American native terrestrial orchids, propagation and production. Conference Proceedings March 16-17, 1996.

Stockwell, K. 1994. Platanthera leucophaea - Eastern Prairie Fringed Orchid. Little Crystal Fen, Crystal, Maine. Manuscript, The Nature Conservancy. 6pp.

USFWS. 1991. Recovery plan for the eastern prairie fringed orchid Platanthera leucophaea (Nuttall) Lindley. U.S. Fish & Wildlife Service. Twin Cities, MN.

USFWS webpage: http://ifw2es.fws.gov/Oklahoma/orchid2.htm downloaded 11/05/99 "Information current as of March 1992."