Rosy owl-clover (Orthocarpus bracteosus) COSEWIC assessment and status report: chapter 7

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Population Sizes and Trends

There are nine historic collections for Orthocarpus bracteosus in Canada, all in the Victoria area, but it is uncertain as to how many of these, in fact, represent distinct populations due to the vague location data. One population is currently extant on Trial Island. The earliest record from Trial Island (1976) did not include an estimate of population size.  The Trial Island population consisted of about 40 plants in 1998, at least 150 plants in 1999, 940 plants in 2001 and about 300 plants in 2002. Plants were present in 2003 but no counts were made. Atsatt (1970) observed that patterns of abundance and distribution in populations of grassland Orthocarpus show sizeable year-to-year fluctuations within sites. Wide population fluctuations are typical in many other annual species (Harper 1977) and such fluctuations may obscure population trends – particularly if the increase in shoot numbers occurs through seed bank depletion. The total number of mature plants has varied in recent years from 40 to nearly 1000.