Bird's-foot violet (Viola pedata) COSEWIC assessment and status report: chapter 9
Population Sizes and Trends
At the time of the original designation of this species in 1990, Viola pedata was extant at three locations (Hutchison and Kavanagh, 1994; Kavanagh et al., 1990; Oldham, 1996; Oldham, 2001). There were nine historic records that had not been seen since before 1950. Most of these latter populations had been searched for unsuccessfully prior to the 1990 status report preparation. Two additional historic records date to between 1950 and 1965. Extensive searches had been conducted in these two areas but no Viola pedata was found at either location. Between 1965 and the 1990 Status Report, no new locations were found.
Between the time of the COSEWIC designation of this species in 1990 and the present fieldwork in 2001, two historic records that were thought to be extirpated were relocated. The following five sites are considered extant.
Brantford: in 1987 there were about 3300 plants in six subpopulations (Site 2 on Figure 3). Some of these subpopulations were thought to be at risk from housing development (Kavanagh et al., 1990). Fieldwork on 21 September 2000 by Melinda Thompson and Don Kirk found that two of the subpopulations had been eliminated by new housing and the other four subpopulations had been reduced to about 100 plants.
Forestville: in 1987 this record was considered to be extirpated as it had not been seen since 1937 (Kavanagh et al., 1990) and it was not found during inventories of Haldimand-Norfolk natural areas (Gartshore, et al., 1987). A small population was relocated by Mary Gartshore in 1994 (Site 3 on Figure 3). The author and Mary Gartshore searched the site on 10 July 2001 but found only a single plant in a very small forest opening.
St. Williams Forest Station: a small population was found across the road from Turkey Point Provincial Park in 1987 (Site 12 on Figure 3). As the result of fieldwork on 9 and 14 May 2001 by Bill Draper and on 10 July 2001 by Mary Gartshore and the author, a total of about 183 plants were found in six adjacent subpopulations. Less than 200 metres separate this site from plants in Turkey Point Provincial Park on the other side of County Road 10.
Turkey Point Provincial Park: about 10 300 plants were seen in the Park in 1987 (Kavanagh et al., 1990). Fieldwork on 11 July 2001 by the author estimated about 6500 plants in eight subpopulations (Site 12 on Figure 3). Most plants (about 6000) occur in one subpopulation. The other seven subpopulations consist of from six to 300 plants. Due to the very dry conditions in Southern Ontario in 2001, many bird’s-foot violets may have entered early dormancy so the population may not have declined since 1987 as the numbers suggest.
Vittoria: in 1987 this record was considered to be extirpated as it had not been seen since 1936 and it was not found during inventories of Haldimand-Norfolk natural areas (Gartshore, et al., 1987). A small population was relocated by Mary Gartshore and Sam Brinker in 2000 (Site 13 on Figure 3). The author and Mary Gartshore searched the site on 10 July 2001 and found nine plants. The population is very precarious near the top edge of an eroding embankment.
The following nine sites have likely been extirpated. None of these old records have information about population size.
Backus Woods: this record is based on a collection made in 1963 (Site 1 on Figure 3). Despite extensive inventory work in this area by Steve Varga in 1985 and more recent searches, bird’s-foot violet has not been seen again in this area.
London: last seen here in 1890 (Site 4 on Figure 3). No new sightings despite surveys of Environmentally Sensitive Areas (ESA’s) of Middlesex County.
Niagara-on-the-Lake: last seen here in 1906 (Site 5 on Figure 3). Remnant habitat was searched in 1988 in this area by Steve Varga and others but no sightings were made.
North of Normandale: last seen here in 1960 (Site 6 on Figure 3). Not found during inventories of Haldimand-Norfolk natural areas (Gartshore, et al., 1987).
Normandale: last seen here in 1928 (Site 7 on Figure 3). Not found during inventories of Haldimand-Norfolk natural areas (Gartshore, et al., 1987).
Paris: last seen here about 1900 (Site 8 on Figure 3). Not found despite an extensive search of the area in 1989 (Kavanagh et al., 1990).
St. Williams: last seen here in 1939 (Site 9 on Figure 3). Not found during inventories of Haldimand-Norfolk natural areas (Gartshore, et al., 1987).
Sarnia: last seen here in 1909 (Site 10 on Figure 3). Not found despite extensive searches of the area in 1959 and 1961 by L. Gaiser, and by Dorothy Tiedje in 1970’s and 1980’s (D. Tiedje, pers. com., 2001).
Simcoe: last seen here in 1905 (Site 11 on Figure 3). Not found during inventories of Haldimand-Norfolk natural areas (Gartshore, et al., 1987).
Numbers refer to sites and populations discussed in text. Extant populations are present at sites 2, 3 12 (representing 2 nearby sites) and 13.
At the time of the original status report, the total Canadian population of Viola pedata was thought to be about 13 600 plants at three locations (Kavanagh et al., 1990). Based on fieldwork in 2000 and 2001, the Canadian population is estimated to be about 6 800 plants at five locations. It is estimated that about 5000 of these plants are of reproductive age. Population counts and estimates--especially at Turkey Point Park--may be low due to the extremely dry conditions in the summer of 2001. Considering that the population size for the extensive Turkey Point site was derived as an estimate based on an extrapolation from sample areas searched and in view of the difficulty in distinguishing this species from other drought stressed plants, the population size for this locality may have been underestimated. Population counts for smaller sites were based on actual observed individuals throughout the locality and are therefore a better estimate of population size. Taking this difficulty in estimating the size of a large population such as that at Turkey Point into consideration, the Ontario population of bird’s-foot violet has declined by about 25-50% since the 1990 status report.
The Ontario populations are isolated from the main range of the species in the United States (refer to Figure 2). If bird’s-foot violet populations were to become extirpated in the province, the United States populations likely could not recolonize Canadian sites through natural dispersal mechanisms because these are effective only for short-range dispersal of seeds and because of the discontinuity of habitat.