Climbing prairie rose (Rosa setigera) COSEWIC assessment and status report addendum: chapter 10

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Population sizes and trends

Previously known populations appear to be in a decline of about 38%, with about a 21% decline in numbers of individuals, from the comparative data of the 1984 report and 2000/01 surveys. There are several core populations that likely are providing fruit and seeds for establishment of smaller and outlying populations on suitable open habitats. After the completion of the second year of fieldwork, a map of additional populations was provided by Paul Pratt of the city of Windsor, from records compiled in 1992 (Essex Region Conservation Authority [ERCA], 1992). On this map are six sites with multiple occurrences noted at the eastern limits of the Windsor boundary, plus others with listed presence to the south. Of the intensively surveyed sites and other records, including the above, it is estimated that there are currently about 145 reproductive individuals (This includes the 64 recorded in Table 1 below plus an estimated additional 81 plants in the unsurveyed sites [2 per site for the 18 Ambrose (1984) and NHC (2000) records, 3 per site in the 15 ERCA (1992) sites around Windsor] for a total estimate in known sites of 145). There are likely another 50 individuals in undocumented populations near core reproductive populations, based on undocumented observations of occurrences in nearby habitats by a local field ecologist (G. Waldron, pers. comm.) and the author’s own observations in sites on Pelee Island.

With clonal spread within populations it is not possible to obtain accurate counts of genetic individuals with only field observations; however, when clusters of rose crowns were observed in a population they were considered to be clones and in such situations a multi-crowned cluster is counted as an individual. When the species has occupied a site with a long history of being open the clusters become less clear, such as at the Stone Road Alvar where periodic droughts and fires have maintained its open character. The presence of fruiting in this dioecious species gives a clue that more than one individual is present in isolated populations, such as the one in Middlesex County (no. 53). However, even this is problematic, since dioecious species typically show a small percentage of hermaphroditic individuals (e.g., Ptelea trifoliata, Ambrose et al., 1985).

The sites surveyed are tabulated in Table 1. The site numbers in the table refer to the detailed list of all recently known populations (since 1980). It lists both sites for which there were abundance data suitable for comparison in 2000/01 shown here, as well as other reports without data. Records received at the Natural Heritage Information Centre (NHIC) after the 1984 status report were compiled and the Windsor records are listed in the middle column.

TH = Threats: S/S, succession/shade; ID, incompatible development; IM, inappropriate management; all-terrain vehicle (ATV), ATVs making trails through habitat; IE, invasive exotics. Extirpated = none observed and habitat altered; extirpated? = none observed but habitat intact.