White meconella (Meconella oregana) COSEWIC assessment and status report: chapter 4

Distribution

Global range

The global range of Meconella oregana is restricted to southwestern British Columbia and to Washington, Oregon and California in the United States (NatureServe 2003). The distribution of populations is highly scattered and there are large discontinuities between populations (Figure 2).

Figure 2. Global distribution of Meconella oregana.

Figure 2. Global distribution of Meconella oregana.

The historic range is probably consistent with the current range with the populations in British Columbia representing the northern extent of the range. U.S. sources state that it is difficult to determine whether the patchy distribution is due to scattered populations or differences in collection effort because this plant is easily overlooked (Rush et al. 1999; East Bay Chapter, California Native Plant Society 2004; Washington Natural Heritage Program 2004).

Canadian range

The Canadian range is small and wholly contained within the distributional limits of Garry oak (Quercus garryana). Twenty-four records held by the BC Conservation Data Centre (Penny, pers. comm. 2004) amount to 15 discreet locations between Victoria and Port Alberni, Vancouver Island (Figure 3). Nine of these 15 locations did not yield an extant population during fieldwork in the spring of 2004 (writer’s observations). Three of the nine locations are described with very low precisions, but are now deemed to be lost to residential development. One additional location has lost its population due to industrial development and one location known from a 1910 collection has not been visited (privately owned island).

Figure 3. Distribution of Meconella oregana in British Columbia.

Figure 3.  Distribution of Meconella oregana in British Columbia.

The extent of occurrence in Canada is estimated at under 2,500 km². The area of occupancy is extremely small as the majority of examined subpopulations each cover only between 0.25 and 12.00 . The total area of occupancy in Canada is estimated at between 50 and 100 m² (0.005 to 0.01 ha), based on fieldwork by the writer in 2004.

As it is difficult to determine absence of Meconella oregana with certainty, it will be equally difficult to compare the historic and present range of the species. According to recent surveys the extreme points of the Canadian range are still occupied, with the exception of some of the southeastern, now urban stations. However, populations in several of the intermediate points of occurrence could not be confirmed, indicating the beginning fragmentation of the range.

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