Conservation introduction of a locally extinct fern species in Estonia during 1998-2008

Summary

Woodsia ilvensis, a circumpolar fern historically rare in Estonia and unrecorded there since 1977, was declared naturally extinct in the country by 2005 after researchers found no surviving individuals at any of its four historic sites during surveys spanning 1994 to 2006, two of which had been destroyed when the stone fences the fern depended on were removed. Tallinn Botanic Garden identified a substitute habitat on the small island of Prangli by using a related fern, Asplenium septentrionale, still surviving there as an indicator of suitable calcium-free rocky conditions, and selected the unoccupied north-facing side of the same old churchyard stone wall for the reintroduction trial. Lacking any local spore source, plants were grown in the laboratory from wild-collected spores obtained through botanical garden exchanges with Finland, raised for two years in leaf-mold and sand mixtures under minimal-maintenance shaded conditions, then planted out onto the stone wall in two cohorts, two-year-old individuals in 1998 and five-year-old individuals in 2001, with no follow-up watering or management. Some plants died in the first two years, but the survivors have persisted and grown for over a decade, tolerating seasonal drought by curling and later regreening their fronds, and reliably producing viable spores confirmed through germination testing; however, no natural seedling recruitment or spread has been observed after eleven years. The project rates itself Partially Successful, concluding the habitat can sustain planted individuals long-term but that establishing a truly self-propagating population will require repeated, gradual plantings rather than a single introduction event.