Blunt-lobed woodsia (Woodsia obtusa) COSEWIC assessment and status report: chapter 8
Limiting Factors and Threats
At a large scale, the major limiting factor for this species would appear to be the availability of suitable calcareous habitat; calcium requirement has been shown for W. obtusa (Bryan and O’Kelley 1967). However, at a small scale, it is more likely that microclimate is a limiting factor. The south facing rocky slopes whereblunt-lobed woodsia is found in Canada are extremely xeric suggesting that water availability is probably crucial. Ongoing research (Wild, unpubl. data) has shown that the addition of water to natural soils containing W. obtusa spores greatly increases germination and fertilization rates. Peck and Peck (1986) increased fertilization and subsequent sporophyte development by 83% (from 13% to 96%) by simply adding water to blunt-lobed woodsia gametophytes. This suggests that the lack of water in the Canadian habitats of blunt-lobed woodsia probably contributes to low recruitment and establishment rates.
The main anthropogenic threats occur at the largest population (Westport-Sand Lake). Evidence of former dumping of refuse from the trailer park over the fern site is still evident but no recent dumping had been noted in 2005 (S. Thompson, pers. comm. 2007). Brush clearing and tree removal along the top edge of the slope resulted in minimal habitat disruption around the ferns when the branches were thrown down the slope over the ferns. More importantly, however, the opening of the canopy has likely resulted in promoting the establishment and spread of common buckthorn (Rhamnus cathartica), an aggressive invasive alien shrub that could significantly alter the fern’s habitat and the fern’s survival. The establishment of the buckthorn in the area may have resulted from the increased bird activity around bird feeders set up at the trailer park; this would have resulted in a greater chance for buckthorn seeds to be deposited in the area through bird droppings (S. Thompson, pers. comm. 2007).