Small-flowered sand-verbena COSEWIC assessment and status report: chapter 7
Population Sizes and Trends
In 1992, the total Alberta population of small-flowered sand-verbena was estimated to be under 1000 plants (Smith and Bradley 1992). At that time, the population was distributed amongst the southeastern Alberta localities as follows: Lost River – 200 plants, Bow Island – 265 plants, Purple Springs – 30 plants, Bull Pound – less than 100 plants, Wolf Island – 110 plants. Population data were collected by Wallis and Wershler (1988) during the 1987 field season. Johnson (1975) surveyed the Bull Pound area. The Suffield National Wildlife Area site was examined in 1994 (Macdonald 1997). At that time only one plant was found in the area.
There are no population data available for the Saskatchewan site (collected 1981) but fewer than 10 plants were noted at the time of the collection (pers. comm. From V. Harms, University of Saskatchewan to E. Haber, COSEWIC).
In 2001, the author resurveyed all known Canadian small-flowered sand-verbena sites, with the exception of the Suffield Wildlife National Area site (Macdonald 1997). The survey was undertaken during the months of July and August. Sites were surveyed later in the season since the distinctive three-winged, peach-colored fruit is the most recognizable feature of the species. The Bow Island and Bull Pound sites were surveyed on three separate occasions (early July, mid-July, early August) in an attempt to find specimens. All other sites were surveyed once in mid-July and again in early August. In all cases the site was identified on topographic maps, located in the field and suitable habitat examined. In the case of the Lost River site a one kilometre area both up and downstream from the original site was investigated for suitable habitat occurrences. In the case of the Purple Springs site the entire area of the partly-stabilized dune ridges in the small dune field was investigated. There was no suitable habitat found at or near the Wolf Island site. Surveys were intensive and extended beyond the original site to include surrounding areas in an attempt to locate other potential habitat.
During fieldwork conducted in the 2001 field season only one plant was found along a sandy road cut at the Bow Island site in Alberta. This was the only specimen of small-flowered sand-verbena located during 2001.
Field data were noted as follows:
Bow Island – 1 plant along an area of artificially exposed actively blowing sand along a road cut in an operating oil and gas field. Although the surrounding area was extensively surveyed no additional specimens were found. This area represented the most extensive zone of actively blowing sand in the oil field associated with the Bow River. Small scattered areas of sand, no more than a square metre of area at most, were found throughout the northeastern areas of the oil field. No specimens of small-flowered sand-verbena were found in any of these areas.
Lost River – no remaining suitable habitat. In 2001, the area was surveyed one kilometer up and downstream from the original location along the course of the Lost River. Small-flowered sand-verbena was previously located at this site in 1975, 1977 and 1987. There is a possible extirpation of the species at this site.
Purple Springs – small dune field of three separate sand dune ridges with scattered small areas of open sand. No specimens were found. Plants may be located at this site in a non-drought year but there is little available habitat for the species at this site.
Wolf Island – this site is now totally stabilized by prairie vegetation and has likely been lost as a possible location for small-flowered sand-verbena.
Bull Pound – areas of open sand exist which might provide suitable habitat in a non-drought year but no specimens were found during the 2001 survey.
Suffield National Wildlife Area – one plant found in 1994 (Macdonald 1997). No other specimens found during the survey of the wildlife area.
Saskatchewan site on the South Saskatchewan River just east of the Alberta border – no specimens found. There is apparently no suitable habitat but a more extensive search should be conducted down river during a non-drought year.
Small-flowered sand-verbena apparently occurs as individual or very small populations along the course of the South Saskatchewan River from the confluence with the Oldman and Bow Rivers to the Saskatchewan border. Only very small patches of available habitat now remain, which undoubtedly limits population size and any chance of small-flowered sand-verbena expanding its range into new territory.
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