Smooth goosefoot (Chenopodium subglabrum) COSEWIC assessment and status report: chapter 7

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Population Sizes and Trends

Search effort

Five different sand hills, one in Manitoba and four in Saskatchewan, were visited during the week of August 23-27, 2004. Using location information from published reports and herbarium specimens, the areas surrounding active sand at each dune field were searched and the number of plants counted. At several sites so many plants were present that counting all would have been difficult and too time consuming. To estimate the potential number of plants in the area, the number of active dune fields was counted and multiplied by the range of plants counted at nearby dune fields. It was assumed these dune fields would have a similar number of plants as the nearby dune. Due to the large number of sites in Saskatchewan and Alberta, it was not possible to visit all of them. In total, 14 hours were spent searching for C. subglabrum. From August 23 to 25, 2005 the Routledge and Brandon Sand Hills were visited, with four hours spent searching the former site and eight hours at the latter.

Abundance

Populations tend to occur in discrete units clustered around active dunes. Lamont and Gerry (1998) and Robson (1999) postulated that climate may impact germination of C. subglabrum. A large number of plants were observed in 2004 suggesting that C. subglabrum germination of plants in the seed bank was stimulated by the unusually cool summer temperatures and late summer moisture. The largest populations occur in the Great and Seward Sand Hills of Saskatchewan, and in the Grassy Lake Sand Hills of Alberta. Based on the observed fluctuations in population size and recognition that at any given year there are likely some C. subglabrum seeds dormant in the seed bank, it is estimated that there are 5,275-10,100 plants in Canada. The following is an overview of populations in the three provinces of occurrence.

Alberta populations

The only Alberta sites visited in 2004 were Lost River and Empress (Elchuk, pers. comm. 2004, 2005). Most population research on C. subglabrum in Alberta was conducted in the late 1980s (Table 3). Since such a long time has elapsed since these sites were visited, the dunes may have stabilized further, reducing available habitat. In total for Alberta, two sites have been confirmed and 8 are unconfirmed. Elchuk (pers. comm. 2005) reported finding 39+ plants in the Alberta portion of the Burstall Sand Hills in 2004 in the dunes near the river where the S. Saskatchewan River curves in and out across the AB/SK border near the Red Deer Forks, south of Empress.

Saskatchewan populations

Extensive C. subglabrum survey work was done in the 1990s in the sand hills of Saskatchewan (Robson 1997a, Lamont and Gerry 1998). New populations were discovered in the Bigstick-Crane Lakes, Seward, Great and Tunstall Sand Hills (Table 4). The Dundurn, Elbow, Great and Seward Sand Hills sites were visited as recently as 2004.

¹ Calculated by adding the minimum number of plants observed or the maximum number of plants estimated at each site and rounding up or down.
² The actual current number of plants is unknown since recent data are only available from a single site and the populations are known to fluctuate in size.
³ The number in parentheses represents the number of sub-populations seen.

¹ Data obtained from the Saskatchewan Conservation Data Centre 2004 unless otherwise indicated.
² Estimated number of plants in 2004; determined by multiplying the number of dune fields present in the area by the average number of plants found at other dunes in the same area.
³ Calculated by adding the minimum number of plants observed or the maximum number of plants estimated at each site and rounding up or down.
⁴ The number in parentheses represents the number of sub-populations seen.

At the Elbow site in 2004, 288 plants were observed and another 200 or so estimated to occur in the dune field. At the Seward Sand Hills an additional 1,620 plants scattered in the three dunes not visited in 2004 are estimated to occur. In the Great Sand Hills almost 1,500 plants were counted in 2004. One of the dune fields covers about 2.56 km² and has 11 active dunes, only three of which were visited. If 330 plants (the average 2004 population size of four dunes visited in the Great Sand Hills) were at the other eight dunes, an additional 2,640 plants would have been present. If the three other sites in the Great Sand Hills where Lamont and Gerry (1998) found plants also had similar numbers of C. subglabrum, there would be another 990 plants. For Saskatchewan, there are 24 extant sites known, two unconfirmed populations (Beaver Creek East and Patience Lake) and five sites likely extirpated (Broderick, Dunblane, Bridgeford, Head of Qu’appelle and McMahon). Elchuk (pers. comm. 2005) also reported finding plants at three sites within the Burstall Sand Hills within Saskatchewan but no numbers of plants are available.

Manitoba populations

The size of the population at Oak Lake (discovered in 1959) was not recorded when the plant was collected. In August of 2004, 19 individuals were found over an 800 m² area in the Routledge Sand Hills on a dune ridge with Tradescantia occidentalis. In 2005, 68 plants were observed at this locality. Since the entire area of active sand in the Routledge Sand Hills was not visited, it is possible that additional plants were present. The sand dunes in Spruce Woods Provincial Park were also searched for C. subglabrum by Manitoba Conservation Data Centre staff in August 2004 but no individuals were found. However, in 2005 a small population of nine plants was located (The Manitoba Museum voucher specimen catalogue # 37859). Given the potential habitat, there are probably at least 75-100 plants in Manitoba.

Fluctuations and trends

Due to the annual nature of this species, the population numbers fluctuate widely in response to climatic conditions. Data collected in 2004 support this hypothesis. At several sites fewer than 50 individuals were found in the late 1990s but several hundred were observed at the same sites in 2004. In Manitoba, there was a 45-year period during which no C. subglabrum was observed despite several surveys in the past 10 years by University of Manitoba and Manitoba Museum staff. A number of focused searches for the plant were made recently by the Manitoba Conservation Data Centre within the Routledge Sand Hills in 2002 (Reimer and Hamel 2003), and throughout southwestern Manitoba in 2000 (Manitoba Conservation Data Centre 2001).

Population fluctuations make it difficult to accurately estimate the number of plants and the vulnerability of populations. In 2004 there were an estimated 8,400 plants growing in Canada; in other years only a few hundred to several thousand plants were observed. However, even though plants may not be growing at a site in a given year, seeds are likely present in the seed bank.

Rescue effect

The range of C. subglabrum extends into the northern United States. Surveys for C. subglabrum in the Little Missouri National Grasslands of North Dakota in 2002 found about 1,000 plants (Schmoller 2002). This site is approximately 350 km southwest of the Manitoba population. These plants were growing on sandy cliffs along riparian areas and sand bars, rather than sand dunes where most of the Canadian plants grow. The high CDC rarity rank given to this species by all the states where it occurs suggests that it is not common in the United States. Plants that grow in the United States could likely survive in Canada since the annual habit of C. subglabrum would increase its ability to survive our colder winters.