White meconella (Meconella oregana) COSEWIC assessment and status report: chapter 7

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Population Sizes and Trends

Search effort

Meconella oregana is easily overlooked and the plants are difficult to locate, except when they are in flower. The plants flower for a very short time each year and the bloom time changes considerably from year to year (e.g. from mid-March to mid-April) depending on local weather conditions (Rush et al. 1999; East Bay Chapter, California Native Plant Society 2004; Washington Natural Heritage Program 2004). In 2004 the report writer found flowering Meconella oregana from March 11 to April 10.

Of the 15 known distinct locations in Canada all but four were re-surveyed (Tables 1 and table 22). All these locations are from several to many kilometres distant from each other and represent 15 populations. Within populations, the largest distance between two sub-populations was 200 metres. Three of the four locations/populations that were not visited (all based on records between 50 and over 100 years old) are known with too low precision to locate and are also now in residential areas. The remaining location not re-surveyed (a record dated 1910) is on a privately owned island. Of the 11 surveyed locations with existing records, five yielded extant populations. These included the largest known and the most southerly and northerly populations. Three populations were composed of two to nine separate subpopulations. In addition to the populations with existing records six other locations with promising habitats were searched for new populations, none of them successfully (Table 2). Further, the report writer has been familiar with Meconella oregana for the past 30 years and has located only one new population during this time, despite frequent visits to potential locations and habitats. Similar statements could also be made for other local field botanists. It is therefore likely that the majority of Meconella occurrences in Canada are known.

Meconella searches by the report writer and associates were based on habitat recognition, as only very small segments of the landscape contain potential habitats (see “Habitat requirements”). Potential habitats were identified by a combination of physical terrain attributes (south-facing slopes, neighborhood of seepages), physiognomy (very short turf), and, later, species combination gleaned from the extant occurrences.

Over 200 of what were considered “prime microhabitats” were surveyed to detect a total of 17 subpopulations representing the 5 extant populations.

Abundance

Very little quantitative information is associated with the old Canadian records (BC Conservation Data Centre records 2004). The number for the largest population is given with “several thousand” for the year 1993. The report writer's counts for 2004 are provided in Tables 1 and table 22. These counts are considered accurate within +/-15% where the numbers are above, and more accurate where the numbers are below one thousand. Under the assumption that all Canadian populations were found, a total of only 3355 Meconella plants would result for the year 2004. All these plants are flowering individuals as no non-flowering plants appeared to occur at all, no matter how small the observed plants were. This does not mean, however, that all these plants reach viable seed-bearing status, something highly dependent on weather development after anthesis.

Fluctuations and trends

As mentioned, quantitative data for past records are too sparse to assess fluctuations properly. The largest Canadian population for which “several thousand” were reported in 1993 had 1274 plants (+/-) in 2004. The second-largest population which the writer observed for the last four years was estimated at 60, 100, 330 and 1209 individuals in these consecutive years. This would suggest that 2004 was a “good” year for Meconella. Both the 1274 and the 1209 plant populations are in habitats with distinct seepage influence and it seems possible that for plants in drier habitats the year may have been less favorable. Clearly, the populations can fluctuate considerably within a period of several years.

Table 1 shows 15 Canadian Meconella occurrences recorded over the last 129 years. Eleven of these sites were examined in the 2004 surveys by the writer, but only five could be confirmed as extant. While no absolute certainty exists that all populations were found, this still raises strong concerns about an overall downward trend for the species in Canada.

Note: In April 2005, prior to designation in May 2005, additional population data were collected by H. Roemer and M. Fairbarns. Data for 2005 indicate that there had been a decline at three of the four extant populations: Port Alberni (from 1274 to >500), Skirt Mountain (1209 to 86) and Little Saanich Mountain (from 422 to 197). No 2005 data were available for the Saturna Island population (E. Haber, Co-chair, Subcommittee for Plants and Lichens, May 1, 2005)

Rescue effect

Meconella oregana has a spotty distribution from southwestern British Columbia and across the border through Washington, Oregon and California. In the United States, the population sizes for records of Meconella oregana are not given for each location. In Washington, the population size is “thousands” at one location and ranges from about 75 to15 individuals at other locations where population size is noted (Washington Natural Heritage Program 1992; Caplow pers. comm. 2004). In Oregon, population sizes range from few plants (4-6), to about 25 plants to 50-100 plants where population size is noted (Oregon State Universitydatabase 2004). No population sizes are recorded for California (California Natural Diversity Database 2004).

Meconella oregana is rare (variously listed as S1 or S2) in Washington and very rare (S1) further south (Oregon and California). On this basis, rescue effect from the south therefore appears to be an uncertain scenario, should the Canadian populations be extirpated. In fact, the United States populations are equally likely to need “rescue” by Canadian populations.

In Washington state the nearest Meconella population on Whidbey Island is about 50 km distant from Canadian populations and it is unknown if genetic information is exchanged over such distances in M. oregana. Similar and larger distances exist between extant Canadian occurrences.