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COSEWIC assessment and update status report on the American Columbo in Canada

Population Sizes and Trends

Search Effort

In 2004 the writers surveyed nine populations (2, 3, 5, 8, 9, 10, 11, 14 and 17; see Table 1) over six days in the field between July 13 and July 30, 2004. They succeeded in locating plants and conducting censuses at all but populations 5 and 17. Populations 8 and 11 were revisited on August 13 and population 12 was also visited on this latter date. No additional plants were located at sites 8 and 11 and none were seen at site 12. It may have been too late in the season by this time.

Table 1: Summary of Canadian Frasera caroliniensis Populations
SiteLast ObservationNumber of PlantsCommentThreats
1 Innerkip1918UnknownNever relocated; vague location data 
2 Glen Morris2004862Three subpopulations; population apparently increasing, but may be a result of great search intensity in 2004Invasive plant species: Melilotus, Rhamnus. Habitat protected
3 Blue Lake2004745Private landowner interested in protecting this population; numbers increasing as a resultA variety of invasive plant species; historically grazed, managed as picnic area.
4 Brantford1930UnknownNever relocated, vague location data 
5 Oriskany Sandstone Formation1989“Several”No plants found in 2004Heavily impacted by recent logging andAlliaria officinalis
6 Selkirk Provincial Park2004105Plants scattered in several locations at this site. Population stable since 1997, when >100 plants were noted.Canopy closure may be shading plants; Invasive species: Rosa multiflora, Rhamnus spp. Habitat protected.
7 Borer’s Creek1989(less than 10 plants none flowering)Incidental observation by D. KirkHabitat protected.
7 Borer’s Creek2005noneDirected 2 hour search at same UTM none found D. Kirk/R. HayHabitat protected.
8 Clappison Escarpment Woods2004513 total: two subpopulations of 329 and 184 plants10 observations since 1950, all indicating a sizable population, although we failed to locate one of the two subpopulations in 2004 (may have left it too late in the season).Habitat may be developed in future
Bridgeview2004(329) slope:  168  hydro line:  161 plantsP. O’Hara/J. Ambrose later C.J. Rothfels, E.C. Oberndorfer, P. O’Hara, S. Rehman (somewhat separate from other obs. at this EO)Small trails, some dumping, invasive species:Alliaria, Cynanchum, Rhamnus, Lonicera.
Snake Road2004(184)Dense shrub-thicket.Many invasive species
Snake Road200519 vegetative plants none floweringDirected search by R. HayMany invasive species
9A Hendrie Valley2004153Population first reported in 1937. Apparently stable.Erosion, informal trail, Rhamnus cathartica, Alliaria officinalis
9B Hendrie Valley2005120, 18 in flowerNewly discovered, ca. 200 m from Hendrie Valley AThis habitat is protected, but the owner has no capacity for management
10 Sassafras Woods2004531ca. 50% decline since 1990Some human disturbance, invasive species present.
10 Sassafras Woods2005100sHundreds of vegetative plants, too difficult to count due to withered leaves, 5 with flowering stalks D. Kirk/R. HayRecent logging in the area, site may be developed in future.
11 King Road East2004204500 plants recorded in 1982. The 2004 plants are from a new subpopulation; the original population could not be located (perhaps too late in the season).Erosion and Melilotus alba; future industrial development expected to destroy site
12 King Road West1986270No plants found in August 2004. Search may have been too late in the season.Future industrial development expected to destroy site
(Hanson Brick Yard) same site as above20053 flowering stalksrosettes too difficult to count - very withered D. Kirk/R. HayFuture industrial development expected to destroy site
13 Hamilton1933UnknownNever relocated, vague location data 
14 Sixteen Mile Creek200467First documented in 1966; no previous population estimatesInvasive plants: Alliaria, Hesperis; informal trails, refuse dumping.
15 Fifteen Mile Creek1987UnknownLocation and abundance data unavailable 
16 Short Hills Provincial Park19981?Few details with 1998 report. ca. 1000 plants seen in 1995.Protected habitat, no on-site staff for management.
16 Short Hills Provincial Park20051000 estimateapprox. 500 plants in wooded area, plus hundreds in open area 14 flower stalks D. Kirk/R. HayProtected habitat, no on-site staff for management.
17 Twelve Mile Creek1956UnknownNo plants found in 2004, despite considerable search effort.Good habitat, but lots of invasive Rosamultiflora
18 St. Davids1897UnknownPossibly extirpated – vague location data and no sightings in more than a century 
19 Queenston Heights1911UnknownProbably extirpated 
20 Sarnia1896UnknownNever relocated, probably extirpated 
21 Cartwright Property2005287 plants, 24 in flowerA. Ernest, Hamilton Naturalists Club PropertyHabitat protected with volunteer management.
22 Cootes Paradise200512 plants, 6 in flowerNewly discoveredHabitat protected, but the owner has no capacity for management

Note: Data from several sites for 2005 were provided, subsequent to the completion of the report, by the Natural Heritage Information Centre, Peterborough, ON.

Donald Kirk and Rebecca Hay searched site 12 in 2005 and found 3 flowering stalks and an indeterminate number of vegetative rosettes. The authors also discovered two new populations in 2005, one in the Cootes Paradise sanctuary of Royal Botanical Gardens (#22) and one in the Cartwright nature sanctuary, recently acquired by the Hamilton Naturalists’ Club (#21; Rothfels, 2005). Additional population data were collected at four other sites in 2005 (9, 10, 12, 16), and no plants could be found at a fifth site (7), which is now presumed extirpated.

Populations were censused by intensively searching potential habitat at each site, and the population estimates presented are the result of a direct count of plants. This method provides valuable baseline data, but several limitations make it difficult to accurately assess population trends. First, and most critically, the majority of previous population assessments were conducted in a haphazard manner, as the observers were usually documenting Frasera caroliniensis populations only incidentally in the course of fieldwork in service of other objectives. For example, the writers found considerably more plants at population 2 in 2004 than had been previously documented; it is difficult to determine if this represents an actual increase in this population, or only reflects a greater search effort in the 2004 survey.

A second confounding factor is the reproductive biology of Frasera caroliniensis. As a monocarpic perennial with synchronous flowering, a large proportion of any population will bloom and die the same year, producing a temporary decline in numbers. Single-season surveys may therefore underestimate plants at populations that have recently flowered. This may have been the case at population 10, where the writers recorded approximately half the numbers that were seen in 1990.

The only way to address these issues is to establish regular, ongoing population monitoring. This is beyond the scope of status assessment, but is usually incorporated in recovery planning.


Abundance

With the above limitations in mind, the present data do provide a good basis for assessing the abundance of Frasera caroliniensis in Canada. Using the writers’ own data and that available in the Natural Heritage Information Centre database, the total Canadian population of vegetative rosettes was 3919 in 2004. More limited fieldwork in 2005 revealed a total of 70 flowering shoots at 6 populations, as noted in Table 1.

Assessing population structure of this species in Canada is difficult. Frasera caroliniensis has essentially three age classes, seedling, juvenile and reproductive adults. However, we are unable to accurately predict when an individual will make the transition from juvenile to adult. This leaves superficial categorization into size classes as the only tool for field biologists. Most of the populations surveyed appeared to consist primarily of individuals of approximately the same size. The only exception was Clappison Escarpment Woods, where plants demonstrated a range of different sizes. None of the previous records available from the NHIC contain any indication of size or age structure. Since only rosettes of living plants were counted and there was no way of determining which rosettes might have been sufficiently mature to produce flowers the following year, the actual number of mature and potentially reproductive individuals for 2004 is unknown and a total of only 70 flowering shoots were recorded at 6 populations/subpopulations in 2005. It is impossible to determine, with the present data, how many vegetative shoots, in addition to those flowering, might be considered sufficiently mature to be counted as mature individuals.

The estimated total number of plants in 2005 is in the order of perhaps 4200, with all but a few being vegetative.


Fluctuations and Trends

Of all the recently located populations, perhaps four should be considered stable: 6, 8, 9, and 16. Two populations may be increasing: 2 and 3. However, this increase may be an artifact of greater search intensity in 2004, as mentioned above. Population 10 is relatively large, but recent surveys suggest large fluctuations between years. More detailed population monitoring is required to clarify the status of this population. Similarly, the Cartwright population (21) is large, but as it is newly discovered we have no basis for assessing population trends. The landowners for populations 11 and 12 intend to expand industrial development at those sites in the future, and similar activities have destroyed most of these populations over the past twenty years.

Nine historic populations dating from 1896 to 1956 are likely extirpated (1, 4, 5, 7, 13, 17, 18, 19, 20). The three remaining populations are small (14, 22) or of uncertain status (15). The historic loss of nine populations represents about a 41% decline over the past century.

In summary, of the ten large F. caroliniensis populations in Ontario, only half are in protected areas (2, 6, 9, 16, and 21), and two face extirpation in the near future (11, 12). The others are vulnerable to a change in land ownership or a change in the priorities of the current land owners. However, the density of populations in southwest Halton, and the existence of extensive potential habitat along the Niagara Escarpment suggest that further populations may await discovery.


Rescue Effect

Natural dispersal of Frasera caroliniensis from the United States of America into Canada is likely exceedingly rare, if it occurs at all. The Niagara River, Lake Erie, and the Detroit River provide serious barriers to plants that do not have any obvious adaptations to bird-dispersal. In any case, habitat loss is a far more pressing concern for this species than limited recruitment.