Orchids: Indicators of healthy ecosystems
By Bruce Rittenhouse

“Orchids can give managers information on whether an ecosystem is healthy and functioning. This is because many species … require stable habitat conditions and are sensitive to human-caused disturbances.”

ORCHIDS, WITH AS MANY AS 35,000 SPECIES, comprise approximately one tenth of the world’s flowering plants. Though their greatest diversity occurs in the tropics, they are found worldwide in a wide range of habitats, including arctic tundra. In the National Park System, orchids number approximately 200 species occurring in 145 units. These park sites range from Noatak National Preserve, north of the Arctic Circle, Alaska, with 1 orchid species, to Everglades National Park, Florida, which has the greatest number of species, 42. Ironically, Hawaii, though tropical, has only 3 native orchid species while Alaska has 29. National parks in the Appalachian Mountains and upper Midwest exhibit a high diversity of orchid species. Summer coralroot (Corallorrhiza maculata), known from 43 parks, occurs in the most national parks.

Orchids have adapted several biological strategies unique to the plant kingdom. For example, their seeds lack nutritive materials and cannot successfully germinate naturally without a fungal host. Following germination, orchid seedlings maintain contact with a fungus for successful establishment. This strategy allows them to persist in less than ideal habitats, such as tropical forest canopies and nutrient-poor soils.

This group of plants has also evolved several intricate and deceptive pollination systems. For example, the pink lady’s-slipper (Cypripedium acaule), which occurs in 32 national parks in eastern North America, is pollinated by the bumblebee. Lured into the flower by its color and scent, the bee becomes trapped and must first deposit pollen on the stigma before it can pick up more pollen, escape, and repeat the process in other flowers.

Some orchid species use the strategy of prolonged dormancy and do not produce any aboveground tissue for a year or more. The threatened small whorled pogonia (Isotria medeoloides) is able to remain dormant for two or more growing seasons. Reasons for this adaptation are not well understood but may be related to specific environmental conditions or previous reproduction success. This strategy allows orchids to survive periods of nonoptimal environmental conditions such as drought.

Copyright Loyal Mehrhoff

Small whorled pogonia (Isotria medeoloides) is a federally listed threatened orchid species that occurs at Prince William Forest Park, Virginia, and Blue Ridge Parkway, Virginia and North Carolina. Its preservation in these parks depends in part on protecting the habitat that supports it and not disclosing its locations.

Copyright Loyal Mehrhoff

Round-leaf orchid (Amerorchis rotundifolia) occurs in the northeastern and upper midwestern states, including Voyageurs and Isle Royale National Parks. Like many orchids, this species experiences periods of prolonged dormancy to conserve resources in nonoptimal growing conditions.

Copyright Loyal Mehrhoff 

Mountain lady’s-slipper (Cypripedium montanum) inhabits the mountainous regions along the West Coast and northern Rocky Mountains, including Glacier and Yosemite National Parks. This species apparently responds favorably to prescribed fires. 

Four orchid species occurring in national parks are listed under the Endangered Species Act. Small whorled pogonia is known from Prince William Forest Park (Virginia) and Blue Ridge Parkway (Virginia and North Carolina). Hawaii bog orchid (Platanthera holochila) occurs at Haleakala National Park. Ute ladies’-tresses (Spiranthes diluvialis) is known from Dinosaur National Monument (Colorado and Utah), Lake Roosevelt National Recreation Area (Washington), and historically Capitol Reef National Park (Utah). Western prairie fringed orchid (Platanthera praeclara) occurs at Pipestone National Monument (Minnesota).

The National Park Service is working under a cooperative agreement with the Center for Plant Conservation (CPC) to collect seeds for all federally listed plant species in national parks, including the four listed orchid species. Participating botanical gardens and arboretums are beginning to work with parks where listed plant species occur to collect seeds under sampling guidelines developed by botanists to ensure that a genetic representation of the species is gathered. These seeds will be stored at the National Center for Genetic Resources Preservation in Fort Collins, Colorado. The objective of this project is to store these seeds for potential reintroduction or augmentation of populations to help achieve future recovery goals. The project began in 2004 and will continue through 2006.

Dinosaur National Monument recently mapped the geomorphic resources along the Green River to determine the relationship between high water discharges from Flaming Gorge Dam and the distribution of the threatened Ute ladies’-tresses in the monument. Surveys indicate a strong correlation between the floodplain and the orchid’s presence. Results from this project were used for an environmental impact statement to establish times and patterns for future discharges of dam water to protect endangered fish, which would also improve habitat for the orchid.

Though they are not the dominant vegetative component in most areas, orchids can give managers information on whether an ecosystem is healthy and functioning. This is because many species in North America require stable habitat conditions and are sensitive to human-caused disturbances. Conversely, certain natural disturbances such as fire may benefit some orchid species. Because of this sensitivity, orchids may be viewed as the “canary in the coal mine,” that is, indicators of healthy, functioning ecosystems, and would be good candidates as ecological vital signs for resource monitoring. Their survival or death following a disturbance may indicate whether certain disturbances are within the range of natural conditions or require management intervention.