Blunt-lobed woodsia (Woodsia obtusa) COSEWIC assessment and status report: chapter 7

Population Sizes and Trends

Search effort

Most search effort for this report was centred on verifying the presence and abundance of individuals at the known locations. However, ferns have been widely collected within Ontario and Quebec over many decades with the likelihood that most localities for this species are known. The recent discovery of two new populations does indicate that some potential for new discoveries is possible but is highly limited. The specific type of habitat for this species is quite scarce in southeastern Ontario and southwestern Quebec in the regions from which the species is known in Canada.

Ontario sites

Only two Ontario sites were mentioned in the original status report (Consaul 1994). Two have since been added, one of which was rediscovered in 2001 by Daniel Gagnon (UQAM), after initially finding it in 1978; the other was found by Shaun Thompson (OMNR) in 2004. All four were visited during August-September 2005.

1. Frontenac Park

This population has been visited annually since 2001. Approximately 60 individuals have been recorded there every year since 2001. Although the surrounding area appears suitable, extensive searches have failed to reveal any other colonies. Over the past four years, at least 20 person hours have been spent searching for the species at this site.

2. Westport– Sand Lake

Extensive searches in 2005 revealed approximately 500 individuals at this site. A total of eight person hours were spent searching for W. obtusa in 2005 (two people/four hours).

3. Westport– Rideau Trail

This population was found by S. Thompson in 2004. In 2005 this location contained 82 plants. Eight person hours (four people/two hours) were spent searching for the species in 2005.

4. Foley Mountain Conservation Area

Although this population was not reported in previous status reports, it has existed for at least 25 years, as it was originally discovered by D. Gagnon in 1978, and found again in 2001. Just over 200 plants were found here in 2005, after approximately eight person hours spent searching (four people/two hours).

QuebecSites

Of the four known sites from the original status report (Consaul 1994), one has still not been found despite several attempts and one has not been visited due to denial of access by the landowner. One new Quebec population was found in 2000.

5. Champlain Lookout, Gatineau Park

In 1974, this site was described as containing only a few stunted plants (Brunton and Lafontaine 1974). Several searches since 1990 have failed to find any plants at this site; more than 20 person hours have been spent attempting to find the population in recent years.  This population is likely extirpated.

6. Eardley Escarpment, Gatineau Park

This population is estimated to contain over 300 individuals of blunt-lobed woodsia. Exact counts are virtually impossible as a large number of individuals (approx. 200) occur on a steep scree slope where any attempt to get close enough for individual counts would surely be detrimental to the species and its habitat. The entire area surrounding the known sub-populations has been extensively searched a number of times over recent years. At least 40 person hours have been spent searching for the species at this site.

7. Saint-Armand, Missisquoi Co.

Requests to revisit this site were denied by the landowner; it was last visited in 2001. The location was estimated at that time to contain somewhere between 100 and 200 individuals, spread between two main colonies of approximately 25  each. Although the current situation of this population is unknown, the remoteness and abruptness of the terrain where the plants are located probably preclude any human disturbance.

8. Chemin Saint-Armand, MissisquoiCo.

This is the only known Canadian population that does not occur on a rocky southern slope. It is situated on a rock outcropping (approx. 10m long, 5 m wide and 4 m high) in an abandoned field. Originally found in 2000 by Jean Faubert, it was visited in 2005 and a total of 120 plants were found.

9. Frelighsburg, Missisquoi Co.

This population was last visited in 1993 by J. Labrecque. At that time, very few individuals were found (5-6). Attempts to contact the landowner for permission to revisit in 2005 were unsuccessful.

Abundance

The number of mature individuals found and the approximate areas occupied at the sites are given in Table 1. Counts made by the writer in 2005 represent careful actual counts of plants. These cannot, for the most part, be readily reconciled with earlier counts that were based on less extensive fieldwork by other observers.

Table 1.  Size and abundance of known Canadian populations in 2005 *
Population Approximate area Last visited Mature individuals Previously reported numbers
1. Frontenac Park, ON. 10 2005 64 47 (1990)
2. Westport – Sand Lake, ON. 2 x 500 2005 499 ~28 (1990)
3. Westport – Rideau Trail, ON. (New) 60 2005 82 ~30 (2004)
4. Foley Mtn Cons. Area, ON. 100 +
150
2005 212 ~10 (1978)
5. Gatineau Park (Champlain), QC <5 1974 <10 <10 (1974)
6. Gatineau Park (Eardley), QC 500 2005 ~300 ~200 (1972)
7. Saint-Armand, QC 2 x 25 2001 ~40 70 (1994)
8.Ch. Saint-Armand, QC (New) 50 2005 120 ~30 (2000)
9. Frelighsburg, QC <5 1993 5-6 5-6 (1993)
Total ~1930   ~1330 ~430

* Populations identified in the original report (Consaul 1994) as currently or recently verified included numbers 1, 2, 6, and 7.

Fluctuations and trends

Of the four of six populations mentioned in the original status report (Consaul 1994), three (Westport, Frontenac Park and Gatineau Park (Eardley)) have been revisited within the past year and all three have considerably higher numbers of individuals than previously reported. At all recently visited sites there was some evidence of newly established plants, suggesting that these populations are recruiting individuals. Although it seems that numbers in most populations have increased (Table 1), this is possibly due to more extensive searching as a large number of plants look well established. Differences in summer climate, from year to year, also seem to influence frond size as well as date of senescence and it would appear that 2005 was a particularly good year to search for the species. Given the perennial nature of this species, large fluctuations in population size likely do not occur.

The fact that blunt-lobed woodsia is a species that is relatively hard to identify and generally occurs on steep inaccessible slopes suggests the possibility that there are other populations yet to be discovered. The recent finding of two new populations (Ch. Saint-Armand in 2000 and Westport – Rideau Trail in 2004) in areas well known to field botanists (in Missisqoui County, QC and along the Rideau Trail, ON) would appear to corroborate this.

Rescue effect

Considering that all known Canadian blunt-lobed woodsia locations are relatively close to the United States (<100 km), it is possible that establishment of new Canadian populations from spores originating from the US populations could potentially occur over a long period of time. This is the most likely historical source of propagules for the known Canadian populations. However, the chance of a new population becoming established by long-distance spore dispersal should be considered remote, based on the very limited availability of suitable habitat and the difficulty in individual recruitment and establishment observed for this species (see below). 

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