Showy phlox (Phlox speciosa): COSEWIC assessment and status report: chapter 5

Habitat

Habitat requirements

All previously known Phlox speciosa locations in Canada were surveyed in June 2003 by Ksenia Barton and Jan Teversham, but the locations from 1927 and earlier could not be relocated. In addition, four new populations were discovered. Additionally, it was found that the extent of occurrence, area of occupancy, and population sizes are substantially larger than previously suspected.

Douglas et al. (1999) summarize the habitats of Phlox speciosa in British Columbia as “dry grasslands, shrublands, and open forests in the steppe and montane zones”. In the Pacific Northwest, Phlox speciosa [spp. occidentalis] occurs “in sagebr[ush] and ponderosa pine areas” (Hitchcock and Cronquist 1973).

More specifically, Phlox speciosa occurs within the very hot, dry, interior of British Columbia’s Okanagan Valley within three biogeoclimatic units: the Okanagan Very Dry Hot Bunchgrass variant (BGxh1), the Okanagan Very Dry Hot Ponderosa Pine variant (PPxh1), and the Okanagan Very Dry Hot Interior Douglas-fir variant (IDFxh1). The extent of these biogeoclimatic units is shown in Figure 4. See Lloyd et al. (1990) and Meidinger and Pojar (1991) for descriptions of these units.

Sites typically occur on dry soils including Brunisol, Chernozem or Regosol soils, derived from morainal, colluvial, glaciofluvial, or bedrock surficial materials. Sites sometimes exhibited signs of moderate erosion. The populations occur on open sites, such as areas of widely spaced bunchgrasses where big sagebrush (Artemisia tridentata) is a characteristic element, and in open ponderosa pine (Pinus ponderosa) and Douglas-fir (Pseudotsuga menziesii) forests with 25% canopy closure or less.

Locations were recorded using a GPS unit, then mapped onto a topographic base to determine location elevations. Plants occur within an elevational range of 700-1100 m where they are found on slopes and level sites. Sloping sites tend to be somewhat protected from direct sunlight, and have aspects ranging from 285°-135°.

In general, at sites with the required climate and elevational range, Phlox speciosa occurs within a variety of habitats including areas subject to various disturbances, including: roadcuts, logging, soil disturbance, moderate cattle grazing, deer trampling, and the proliferation of introduced species.

Not all areas of seemingly appropriate habitat in close proximity to patches ofPhlox speciosaare apparently suitable, or at least not occupied. Additional habitat requirements, or other factors may exist that would explain why the extent of occurrence is much smaller than the extent of apparently suitable habitat.

Trends

Figure 4 shows the extent of biogeoclimatic units in which Phlox speciosa occurs. Within that area, suitable habitat is restricted to locations that meet the plant’s habitat requirements, outlined above, including a specific range of elevations (700-1100 m). The past and present extents of suitable habitat are unknown. There are fairly extensive areas of potential habitat that have not been surveyed, especially in areas lacking good road access and on Aboriginal lands.

The habitat availability for Phlox speciosa is clearly decreasing. The Okanagan Valley is considered one of the most endangered natural areas in Canada. There were significant habitat losses in the valley in the 20th century, and the losses are expected to continue. Very little of the valley has protected area status, and the area is heavily crossed by roads. In general, the habitats that support Phlox speciosa are subject to a variety of anthropogenic threats, including livestock grazing, range re-seeding, off-road recreation, agricultural cultivation and development, recreational property development, prescribed burning, forest encroachment, road and trail development, and alien plant species introductions (Royal British Columbia Museum 1995).

Recreational property development represents the most important trend in habitat loss. Within the current extent of occurrence, 41% of the area is privately owned land. The remainder of the extent of occurrence is within provincial crown land, but none of that crown land occurs within a protected area. Current private land uses in and around the extent of occurrence include rangeland, agricultural cultivation, hobby farms, golf course, residential properties, and recreational properties.

Habitat loss due to property development is illustrated by cases where Phlox speciosa occurs in yards directly adjacent to homes. In some cases, perhaps only a small area of habitat has been lost in others a larger loss may have occurred. At the time of writing, at least 32 ha of property were for sale and were marketed as undeveloped sites for the construction of homes and for keeping horses.

Figure 4. Extent of biogeoclimatic units within which Phlox speciosa occurs.

Figure 4.  Extent of biogeoclimatic units within which Phlox speciosa occurs

 

Habitat protection/ownership

The majority of the current extent of occurrence of Phlox speciosa, about 59%, occurs within provincial crown land. None of the provincial crown land within the extent of occurrence currently has protected area status.

The remainder of the extent of occurrence (41%) is privately owned land. The majority of the area of occupancy occurs on private land. The White Lake Ranch, which supports a portion of a population of Phlox speciosa, is on federal land owned by the National Research Council. The Ranch is being managed as a “biodiversity ranch” by the Nature Trust, in conjunction with the South Okanagan Similkameen Conservation Program. At the White Lake Ranch, conservation activities are being integrated with grazing and other sustainable resource uses to enhance biodiversity and other habitat values.

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