Grand coulee owl-clover (Orthocarpus barbatus) COSEWIC assessment and status report: chapter 7

Habitat

Habitat requirements

The British Columbia populations are found in the Bunchgrass Biogeoclimatic Zone of southern British Columbia. This area, particularly in the southern Okanagan Valley, has a cold, semi-arid steppe climate. Summers are hot and dry with mean July temperatures around 20°C. Precipitation is low with mean annual rainfall of about 300 mm. Growing seasons are relatively short with mean monthly temperatures falling below freezing from December to February in the valley bottoms.

Orthocarpus barbatusis restricted to extremely dry, big sagebrush (Artemisia tridentata) communities at lower elevations in the southern Okanagan Valley and the southern Similkameen Valley. The populations, at elevations of 370 to 930 m, receive little moisture after early summer, thus this species reaches senescence by mid-summer. The sites are often sandy to gravelly with open vegetation dominated by big sagebrush (Figure 4). Other frequent associates, with low cover values, include: Artemisia tripartita, Bromus tectorum, Ericameria nauseosus ssp. speciosa, Plantago patagonica, Hesperostipa comata, Poa bulbosa, P. pratensis, Phlox longifolia, Erigeron filifolius and Vulpia octoflora. Bromus tectorum, one of the most troublesome alien species in south-central British Columbia, is not as common in populations ofOrthocarpus barbatus as it is elsewhere in the region.


Figure 4. Orthocarpus barbatus habitat in the South Okanagan Grasslands Protected Area.

Orthocarpus barbatus habitat (see long description below).

Photo by Shyanne J. Smith.

Description of Figure 4

Artemisia tridentata and Ericameria nauseosus ssp. speciosa are the conspicuous shrubs on this slope. The herb, Orthocarpus barbatus are small straw-yellow plants scattered throughout the habitat but not readily seen in this photo. This is the highest quality site for O. barbatus in Canada.

Trends

The Bunchgrass Zone occupies less that one percent of the total area of British Columbia and is one of the most populated and developed areas in the British Columbia interior (Ministry of Forests 1998). In general, trends for natural habitats in the Okanagan Valley have shown a marked decline during recent years due to various land developments. Natural habitats have been appropriated for orchard, vineyard, golf course, housing and industrial developments. The South Okanagan is currently experiencing the fastest population increase in the province (Nature Trust 2004). According to Environment Canada (2003),the population of the Regional District of the Okanagan-Similkameen increased by 18% between 1991 and 2002, to almost 81,000 people. In addition, the town of Osoyoos has seen a population increase of over 22% between 1986 and 1996, making it the fastest growing municipality in the South Okanagan-Similkameen Regional District (Town of Osoyoos 2004).

Development in the Osoyoos area is currently occurring at a rapid pace on the east slopes of Mount Kruger, above downtown Osoyoos. Natural habitat has been destroyed by mineral exploration and golf course, housing, and industrial development. All of these, with the exception of mineral exploration, have destroyed potential Orthocarpus barbatus habitat as well as other potential rare species habitat (Figure 5).


Figure 5. Housing development near extant Orthocarpus barbatus populations on the slopes of Mt.Kruger

Housing development (see long description below).

Photo by Shyanne Smith 2003.

Description of Figure 5

Remnants of Artemisia tridentata and Purshia tridentata dominated habitat are visible above the houses. It is likely that this particular development, and the nearby 27-hole golf course, eliminated populations of O. barbatus.


Over-grazing by cattle, although a major threat in the past in both the southern Okanagan and southern Similkameen valleys, has recently become a lesser threat, since the range has deteriorated markedly and far fewer cattle now occupy the rangeland. This, however, has not resulted in fewer alien species. In recent years, a number of new alien species have appeared and found a place in over-grazed habitats. Crown lands on the eastern slopes of Mount Kruger are presently under grazing leases (J. Hobbs, pers. comm., 2004).

Protection/ownership

The westernmost population of O. barbatus in Canada is in the southern Similkameen River drainage and is located in the South Okanagan Grasslands Protected Area. This area receives protection under the Provincial Parks Act which does not allow such activities as logging and mining. The Grasslands Protected Area still has grazing leases in effect and there is little if any weed control. The population on the southeast slope of Mount Kruger, above the golf course (above the town of Osoyoos), is on privately owned land. The second population on the southeast slope of Mt. Kruger (above the racetrack) is on Crown Land. The easternmost site, near Veronica Lake, is located on privately owned rangeland.

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