Fragrant popcornflower (Plagiobothrys figuratus) COSEWIC assessment and status report: chapter 7

Population Sizes and Trends

Search effort

The authors spent 3 days in 2002 surveying historical and potential sites on Hornby Island (e.g., Helliwell Provincial Park) and Vancouver Island. Unfortunately, aside from the Hornby Island site, most historical records for fragrant popcornflower lacked sufficient locality information to be properly investigated (Table 1). However, all appeared to have originated from localities that have now since been developed. Consequently, we focused subsequent search efforts on several areas near Nanaimo with some of the likeliest remaining habitat (i.e. spring ephemeral meadows on shallow soil over smooth sandstone, with spring seepage). Three areas were surveyed: White Rapid Road; Harewood Plains; and Harmac Meadows, near Cedar. These searches were all unsuccessful. One historical record, Lazo Point near Comox, was not surveyed (Table 1).

Given the showy bloom of fragrant popcornflower, and the fact that most historical records appear to originate from areas that are now well populated and/or partially urbanized, it seems unlikely that this species, if still present, would continue to have been overlooked on southeastern Vancouver Island for the past 25 years. This, combined with the recent loss of habitat to residential development, leads us to believe that there is a strong likelihood this species has now been reduced in Canada to a single remaining population fragment at Hornby Island.

Abundance

There are 12 historical records for fragrant popcornflower in Canada. All are pre-1987 and the majority are more than 65 years old (Table 1). No abundance data are associated with these records, but the total population size was likely substantial as this species has the ability to form dense mats and may cover its habitat in some wet prairies and vernal pool systems (NatureServe 2005).

Prior to 2005, the last confirmed sightings of fragrant popcornflower at Hornby Island date from 1986. Population size at this time is unknown but may have numbered in the hundreds. The photograph in Figure 4, taken by the third author in 1968 before rare plant tracking was introduced, shows about 100 flowers in a densely flowered patch. This patch represented just a proportion of the plants present at the time (H. Roemer, pers. obs.).

In 2005, the Hornby Island population appeared to contain just a single flowering plant (R. Martin, pers. comm. 2006). It is unknown at present whether this reflects the true population size, or whether the species persists underground as dormant seeds. There were no plants observed in 2006 at this location (R. Martin, pers. comm. 2006) but a seed bank may still exist in the soil.

Figure 4. Fragrant popcornflower on Hornby Island, B.C. in 1968. Note density of patch. Photo courtesy of H. Roemer.

Figure 4. Fragrant popcornflower on Hornby Island, B.C. in 1968. Note density of patch.

Fluctuations and trends

The data associated with the British Columbian records of fragrant popcornflower are insufficient to express fluctuations, although the trend to a total decline is unquestionable. Data from one population on Galiano Island of Plagiobothrys tenellus, another annual species at risk in British Columbia, indicates that this species appears to undergo extreme fluctuations.

Rescue effect

The nearest populations of fragrant popcornflower outside Canada occur in the southern Puget Trough region of Washington State where current population status is not tracked (Washington Natural Heritage Program 2003). The distance to the closest U.S. population is approximately 450 km. This distance is such that natural interchanges between the U.S. and Canadian populations, genetic or otherwise, are highly unlikely. Hence, rescue effects originating from south of the border are unlikely to be a factor. On the other hand, these southerly populations could potentially serve as an important source of seed for manual reintroduction onto Vancouver Island. Whether or not artificial introductions of fragrant popcornflower from south of the border would be genetically adapted to survive in Canada is, however, unknown.

Page details

Date modified: