Counting orchids: 40 years of monitoring

By Edwin Morelli

Sparrow's-egg Lady's-slipper, a rare orchid species at Pukaskwa National Park, has been monitored since 1979. The population has been declining in the park, leading staff to investigate potential explanations.

Sparrow's-egg Lady's-slipper is an herbaceous perennial plant and ranges from Alaska to northern Montana and the shores of James Bay; it is one of the few orchid species known to grow within the Arctic Circle.  Pukaskwa National Park is home to a disjunct population of Sparrow’s-egg Lady's-slipper orchids. These orchids have a unique life cycle, as seeds and seedlings are dependant on a symbiotic fungus until they produce a stalk several years after sprouting. Once the stalk grows above-ground, Lady’s-slippers reproduce asexually underground, creating new clones close to the parent plant. Lady’s-slippers may take as many as 15 years before they begin to flower, limiting their ability to produce new plants by seed.

Staff have performed counts of Sparrow’s-egg Lady’s-slippers within the park since 1979. A recent analysis found that Sparrow’s-egg Lady's-slipper has declined by 63% since then, with only 162 plants remaining, and 11 of the 20 historical colonies having disappeared within the park. As several of the remaining colonies have less than 15 plants each, there is concern that more colonies will be lost in the future. In response to this, we examined possible factors that may be contributing to this decline, and identified three potential factors:

1. Dune stabilization: The habitat where Sparrow’s-egg Lady’s-slipper occurs is currently changing through natural succession to forest.These ecosystem changes may be contributing to a lack of plant survival or establishment.
2. Climate change: Pukaskwa National Park is at the southern extent of the range of Sparrow’s-egg Lady’s-slipper. Long-term trends for the region include an increase in air temperature and changes in precipitation regimes. It is possible that climatic conditions will no longer be suitable for this plant to survive and reproduce.
3. Human impacts: These sensitive plants have been given special protection to limit the potential for human disturbance. Despite these efforts, it is possible that some individuals and colonies of Sparrow’s-egg Lady’s-slipper may have been inadvertently trampled by visitors or staff.

Determining the exact causes of decline is difficult as little is known about the habitat requirements and factors contributing to the successful survival and reproduction of Sparrow’s-egg Lady's-slipper. Pukaskwa National Park aims to collaborate with partners to better understand this plant and help its population recover. Please note that this sensitive population grows in a restricted location; please contact pukaskwaont@pc.gc.ca to set-up an accompanied viewing.

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