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okanaganOkanagan Grasslands


Grassland Region

Area, ha

Ecoprovince

Okanagan

117,275

Southern Interior

Ecosections

Area, ha

Southern Okanagan Basin

Southern Okanagan Highland

Okanagan Range

Northern Okanagan Basin

Northern Okanagan Highland

33,290

12,570

19,635

39,905

9,375



The Grassland Landscape

The Okanagan grasslands region includes three major valley systems, the 240 kilometre long Okanagan valley and its tributaries, the steep-sided Similkameen river valley in the southwest and the Kettle valley in the southeast. In the hot and dry conditions of the South Okanagan wide-spaced bluebunch wheatgrass-big sage or Antelope-brush grasslands have a well-developed dry cryptogam layer. The influence of the Great Basin ecosystems is seen most in this part of the region, where the largest number of drought-adapted species occur in the province.

In the Similkameen valley most of the grasslands are found in the ponderosa pine and Interior Douglas-fir grasslands, with large areas in the Montane-Spruce zone and above. Unusual communities of bluebunch wheatgrass with Vasey’s sagebrush or threetip sagebrush occur in higher elevations of the Interior Douglas-fir and Montane-Spruce zones.

Kettle valley grasslands are found predominantly in the Ponderosa Pine and Interior Douglas-fir zones with a mixture of Idaho fescue, rough fescue, bluebunch wheatgrass and flowering plants.

North of Kelowna grasslands are found on the rolling benches and hills of the Interior Douglas-fir zone. Subalpine and alpine grasslands are found in the Hunters Range area north of the Shuswap River.

The underlying geology of the Okanagan grasslands region defines the major structure of the valleys and glaciation provided the final surfaces on which grasslands have developed. The ice sheet that covered the area 15,000 years ago was as much as 2150m thick. Ice retreated from the hillsides first, while it remained in the valley bottoms. Rivers flowed along the sides of Okanagan Lake, depositing moraine in long ridges that are particularly visible on the slopes north east of Kelowna.

As the ice melted in the valley, a large block remained at McIntyre Bluff north of Oliver, ponding back water in Glacial Lake Penticton to a height 100 metres above the present lake level. Rivers pouring into the lake deposited gravels and silts as terraces and fans that are now perched on the hillsides above the lake.

The silt cliffs that form the distinctive benches at Summerland and Penticton were deposited on the lake bottom and eroded as the lake level dropped. Post-glacial erosion deepened side valleys leaving a legacy of fans such as the large area between Skaha Lake and Okanagan Lake where Penticton stands today.

Terraces and fans left along the Similkameen River provide suitable conditions for bluebunch wheatgrass-big sage communities. The Kettle River valley was scoured by ice extending into the United States, with thick glacial lake deposits left as ice-damned lakes drained.

In the rainshadow of the Coast and Cascade Mountains, the Okanagan grasslands region is generally hot and dry in summer. Hot, dry air from the south in summer brings higher temperatures to the south Okanagan and almost desert conditions. Similarly the influence of Arctic air masses from the north in winter are felt more in the north and at higher elevations.

Precipitation increases from south to north with Oliver having 305 millimetres and Armstrong 488 millimetres. The Kettle valley also has more precipitation (420 millimetres) but less falls as snow than at many parts of the southern Okanagan. Okanagan Lake and the other lakes in the valley help to moderate temperatures throughout the year.

Historical Impacts

Okanagan region grasslands have been altered in a number of ways. Fire has always been present as a result of lightning strikes and aboriginal peoples are known to have set fires to improve grazing and plant food sources. Fires were also set by prospectors searching for mineral exposures and by early settlers.

Livestock grazing has impacted many areas of these dry grasslands, particularly along the old Brigade Trails from Kamloops to Washington State. 2-300 horses in each brigade used the routes, with many animals left out to fend for themselves along the way. The gold rush in the 1860s increased the need for beef and the gradual increase in permanent settlements created even more demand. By 1892, 20,000 head of cattle grazed the grasslands and dry forests between Oliver and Enderby.

Soil survey parties in the 1960s reported widespread overgrazing. These conditions allowed for the spread of non-native invasive species such as knapweeds into the grasslands. Agriculture in the form of orchards and vineyards, and urban development continue to intrude onto the grasslands of this region.

Grasslands in the Okanagan region are protected in parks and other conservation areas where livestock grazing is managed to reduce the impact on plant communities. Research projects, particularly in the South Okanagan, are giving grasslands managers a better understanding of grasslands species and their particular needs.

Unique Features

Saline Lakes

okanagan1Saline lakes form in depressions in the grassland landscape in the Bunchgrass and Interior Douglas-fir zones where there is no outlet for the collected water. Where the surrounding soils have high levels of soluble minerals, concentrations of salts can accumulate as the lakes fill with spring runoff.

During the hot, dry summers, when the rate of evaporation is higher than the rate at which water runs into the depression, the water level drops to expose the salts as rings around the edge. Salt-adapted plants grow around the edges in concentric rings. The yellowish alkali saltgrass has a fairly high tolerance for salt and but the dark red glasswort is not as tolerant and appears outside the saltgrass. Some particularly saline lakes teem with brine shrimp.

White Lake on the plateau west of Vaseux Lake and Spotted Lake west of Osoyoos are two special examples of the saline lakes found in many grasslands across the Okanagan grasslands region. White Lake usually dries out completely, exposing the white salt-encrusted basin; Spotted Lake has a cover of circles on the surface typical of a concentration of magnesium sulfate.

Plant Communities

Ecosections

BEC Zones with grasslands1

Major2 grassland BEC Subzones and Variants

Southern Okanagan Basin

Bunchgrass Zone

Ponderosa Pine Zone

Interior Douglas-Fir Zone

BGxh1: Okanagan Very Dry Hot Bunchgrass Variant

PPxh1: OkanaganVery Dry Hot Ponderosa Pine Variant

IDFxh1: Okanagan Very Dry Hot Interior Douglas-fir Variant

Southern Okanagan Highland

Ponderosa Pine Zone

Interior Douglas-Fir Zone

Interior Cedar-Hemlock Zone

PPdh1: Kettle Very Dry Hot Ponderosa Pine Variant

IDFdm1: Kettle Dry Mild Interior Douglas-fir Variant

IDFxh1: Okanagan Very Dry Hot Interior Douglas-fir Variant

Okanagan Range

Bunchgrass Zone

Ponderosa Pine Zone

Interior Douglas-Fir Zone

BGxh1: Okanagan Very Dry Hot Bunchgrass Variant

PPxh1: OkanaganVery Dry Hot Ponderosa Pine Variant

IDFxh1: Okanagan Very Dry Hot Interior Douglas-fir Variant

Northern Okanagan Basin

Montane Spruce Zone

Northern Okanagan Highlands

Engelmann Spruce-Sub-alpine Fir Zone

Alpine Tundra Zone

Bunchgrass Zone

Ponderosa Pine Zone

Interior Douglas-Fir Zone

Ponderosa Pine Zone
Interior Douglas-Fir Zone

Montane Spruce Zone

Engelmann Spruce-Sub-alpine Fir Zone

Interior Cedar-Hemlock Zone

BGxh1: Okanagan Very Dry Hot Bunchgrass Variant

PPxh1: Okanagan Very Dry Hot Ponderosa Pine Variant

IDFxh1: Okanagan Very Dry Hot Interior Douglas-fir Variant

PPxh1: Okanagan Very Dry Hot Ponderosa Pine Variant

IDFxh1: Okanagan Very Dry Hot Interior Douglas-fir Variant

IDFdm1: Kettle Dry Mild Interior Douglas-fir Variant

1. Click here to find out more about the Biogeoclimatic Ecosystems Classification(BEC) System

2. Over 3,000 hectares

Almost 50% of the grasslands of the Okanagan grasslands region occur in the Okanagan and Similkameen valleys in the lower elevation Bunchgrass and Ponderosa Pine zones. The Interior Douglas-fir zone in the North Okanagan Basin and the Kettle Valley portion of the North Okanagan Highlands account for most of the other grasslands.

BGxh1: Okanagan Very Dry Hot Bunchgrass Variant: 22,780 hectares

Some of the hottest and driest conditions in the province are found in the Southern Okanagan Basin from the valley bottom of the Okanagan and Similkameen at 250 metres to about 700 metres at Summerland. The area is the northern extension of similar grasslands that occur as far south as Oregon and has the most diverse array of grasslands species in the province.

okanagan2Antelope-brush and common rabbit-brush are the common shrub species on the driest sites while threetip sagebrush is widely distributed. Big sagebrush is found where there is more moisture, often accompanied by saskatoon, common chokecherry, Douglas maple and mock-orange. Ponderosa pine and Douglas-fir grow in moist sites.

Widely-spaced bluebunch wheatgrass is found on undisturbed sites with a healthy cryptogamic crust of lichens, mosses, algae and fungi. Prairie sagewort, junegrass, yarrow long-leaved phlox, prickly phlox, bitterroot and snow buckwheat are some common flowering plants of these sites. Idaho fescue and rough fescue dominate on cooler north- and east-facing slopes while giant wild rye is found in moist and saline sites at higher elevations.


PPxh1: OkanaganVery Dry Hot Ponderosa Pine Variant: 28,660 hectares

Open ponderosa pine grasslands are found between 335 and 940 metres above the bunchgrass variants as far north as Vernon in the Okanagan valley and to Keremeos in the Similkameen. Plant associations resemble those found further south in Washington and further north in BC.

Bluebunch wheatgrass, Idaho fescue and rough fescue are common grasses in these parkland areas of grasslands, open forest and shrubs. Some flowering plants also found include Sandberg’s bluegrass, junegrass, yarrow and arrow-leaved balsamroot. Antelope brush communities occur on the driest sites with red three-awn, bluebunch wheatgrass, snow buckwheat, common selaginella and arrow-leaved balsamroot.

The mountain pine beetle epidemic of 2005-07 has killed large numbers of the ponderosa pine trees in this variant and the impact this will have on the grasslands is not known.

PPdh1: Kettle Very Dry Hot Ponderosa Pine Variant: 5,150 hectares

Grasslands are more common than open forests in this variant as hot, dry summers and low snow cover in winter reduce the amount of moisture available for tree growth. They range from 450 to 950 metres on valley bottoms and south-facing slopes from Johnstone Creek to Boundary Falls and from July Creek to Christina Lake.

okanagan3In the least disturbed areas bluebunch wheatgrass, rough fescue and Idaho fescue cover most of the ground, with white silky lupine, arrow-leaved balsamroot, sticky geranium and lemonweed. Open ponderosa pine forests are most common on south-facing slopes with a mix of grasses and a variety of flowering plants including arrow-leaved balsamroot, sticky geranium, silky lupine and parsley-flowered buckwheat. Many sites have introduced species such as great mullein, yellow salsify and sulphur cinquefoil.
The impact of the mountain pine beetle on ponderosa pine trees in this variant and the subsequent impact on grasslands is unknown.

On upper slopes and rocky areas compact selaginella is the most common plant with bluebunch wheatgrass and occasionally common snowberry or saskatoon. Where soils are coarse in texture moisture does not remain for long and trees cannot thrive. Where these soils occur on mid-slopes, bluebunch bunch wheatgrass, with compact selaginella, thread-leaved phacelia, junegrass and introduced cheatgrass. A number of red-listed plant species are also found in these communities.
Noxious weeds are extensive in this variant and in places diffuse knapweed and cheatgrass can form nearly 50% of the cover. Other non-native species include Kentucky bluegrass, creeping bentgrass, field bindweed and common hound’s tongue.
okanagan4IDFxh1: Okanagan Very Dry Hot Interior Douglas-fir Variant: 44,335 hectares

The largest variant in the Okanagan grasslands region occurs in different forms. From the Canada/US border north to Enderby and along the Similkameen River valley to Princeton, open forests and grasslands are found between the Ponderosa Pine and Montane Spruce Zones.

In the Coldstream valley from Vernon to Lumby and on the east side of Okanagan Lake to Woods Lake it occurs as extensive open grasslands. Most of the variant in the Kettle valley has no trees or have small patches of aspen and Douglas-fir in moist draws and depressions. Near Bridesville Douglas-fir grasslands extend from the valley floor to merge with continuous forest.

Idaho fescue, rough fescue and bluebunch wheatgrass are the dominant grasses on least disturbed sites with silky lupine, arrow-leaved balsamroot, parsnip-flowered buckwheat and junegrass. Shrubs such as saskatoon, mock orange and common snowberry occupy moist areas and cooler slopes. Bluebunch wheatgrass, silky lupine and arrow-leaved balsamroot occur on drier sites.

Where grasslands have been heavily disturbed cheatgrass, dandelion, great mullein, compound fleabane and knapweeds are the dominant plants.

IDFdm1: Kettle Dry Mild Interior Douglas-fir Variant: 6,640 hectares

These grasslands are most extensive in the Kettle valley above the Ponderosa Pine grasslands and the warmer Interior Douglas-fir grasslands. They also occur east of Osoyoos from Anarchist Mountain to Bridesville and in the Granby River valley north of Grand Forks. In the Okanagan valley they extend along the east side between 560 and 1200 metres elevation from Osoyoos to Kelowna. Winters in these areas are relatively mild and snow free, summers are very hot, but frost can also occur in the growing season.

On sites in the best condition bluebunch wheatgrass is the dominant species with junegrass, yarrow and silky lupine. Big sagebrush may occur in places in the Okanagan and Idaho fescue occurs on moister sites.

Past grazing and cultivation in these grasslands have altered their composition with non-native plants and noxious weeds forming a large component of plant communities. Diffuse knapweed, cheatgrass, Kentucky bluegrass and quackgrass, common hound’s tongue, sulphur cinquefoil are only a few of the species found in various combinations, occasionally with bluebunch wheatgrass or Columbia bluegrass.

Other Grassland Communities

Small areas of grasslands occur in other BEC zones in the Okanagan grasslands region. Grasslands on Mount Kobau near Oliver and from Keremeos to Hedley in the Similkameen valley are in the Montane Spruce Zone from 1450 to 1650 metres in elevation. Red-listed in this zone, Vasey’s big sagebrush – Pinegrass communities occur on south-facing slopes with species characteristic of both forest and grassland, including pinegrass, Idaho fescue, silky lupine, western meadowrue and wild strawberry. On drier sites with moderately steep slopes Vasey’s sagebrush occurs in association with bluebunch wheatgrass and Idaho fescue. Common juniper may be found on some sites.

okanagan5Cottonwood forests are found on floodplains in the Okanagan grasslands region where common snowberry, Douglas maple and paper birch are part of a healthy shrub layer. Where prolonged flooding and strong currents occur dense stands of narrow-leaved willow and other shrubs develop. Only 15% of the original cottonwood stands remain on the channelized Okanagan River.

Aspen copses with a mix of shrubs are found in moist areas from the bunchgrass to the Montane Spruce Zone. Nootka rose, prickly rose, common snowberry and saskatoon are common shrubs, with tall Oregon-grape, Douglas maple and poison-ivy often found on dry sites such as talus slopes. Wetter sites have red-osier dogwood, water birch and Sitka alder. The amount and variety of flowering plants varies depending on the amount of moisture available.

Rocky outcrops, cliffs and talus slopes are common, especially at lower elevations in the Okanagan region. Occasional ponderosa pine or Douglas-fir trees find a foothold along with common rabbit-brush, big sagebrush and saskatoon. In the south Okanagan bluebunch wheatgrass and selaginella are common, but in the north of the valley kinnikinnick and pasture sage dominate. Dry talus slopes at the base of cliffs have a very sparse cover of vegetation. In the south Okanagan mock-orange, Antelope-brush and smooth sumac and in the north of the valley there are more shrub species that include chokecherry, Rocky Mountain juniper and shrubby penstemon.

Key Plant Species

okanagan6Antelope-brush (Purshia tridentata)

  • Widespread in the dry sagebrush grasslands of the South Okanagan
  • medium to tall deciduous shrub with stiff, woolly branches
  • small wedge-shaped leaves have three fine teeth at the tip and rolled edges
  • silvery-greenish and hairy on the upper surface, grey-woolly beneath
  • single yellow flowers with five petals cover the branches in spring
  • small pear-shaped black seeds are eaten by chipmunks, ground squirrels and deer mice
  • seed caches are a source of new seedlings
  • important browse for deer
  • conversion of antelope-brush grasslands to orchards and wineries has severely reduced the extent.



Wildlife

The Okanagan grasslands region has the highest diversity of wildlife in BC and many species use grasslands for some part of their needs. Several species are unique to the region and others are at or near the northern limit of their range. 

Insects in the grasslands are important for pollination, nutrient cycling and as food for other animals. Insect populations of the province have not been studied as much as the larger mammals, but many surveys and studies have been done in the south Okanagan and lower Similkameen. Many species are found nowhere else in BC, others nowhere else in Canada.

Rocky Mountain wood ticks are found throughout the lower elevation grasslands, but especially in rocky areas, from early March to late June.

The Okanagan grasslands region is home to almost 75% of all bird species in the province. Meadowlarks, vesper sparrows and common nighthawk are familiar ground-nesting birds of the open grasslands but many more species use the grasslands for at least part of their needs.

okanagan7Aspen groves are particularly rich food sources for a wide variety of species that also forage over the grasslands. Cavity nesters such as mountain bluebirds, swallows and woodpeckers, also raptors, songbirds and sparrows can all be found there. Marshes, ponds and wetlands with riparian vegetation provide further rich habitats for a variety of shorebirds, waterfowl, perching birds and raptors.

Both mule deer and white-tailed deer are widespread in the region and use the Bunchgrass and Ponderosa Pine zones in spring, fall and winter. Winter ranges include east slopes of Okanagan valley from Summerland to Penticton, the Ashnola valley and between Grand Forks and Christina Lake in the Kettle valley. Summers are spent in higher elevation forests, sometimes a long way from their winter home. Mountain goats use the lower slopes of the high cliffs between Keremeos and Hedley during the winter and small numbers are found on the steep rocky slopes on the west side of Okanagan Lake south of Summerland.

Small mammals include muskrat, bushy-tailed woodrat, bog lemmings, red squirrels, yellow-bellied marmots and Columbian ground squirrels. 11 species of bats are found in the grasslands and associated wetlands, cliffs, canyons and rocky outcrops. Okanagan Falls is the favoured place in the Okanagan valley for feeding bats on warm summer evenings.

Check the list of wildlife viewing sites publications.

Species at Risk

Red- and Blue-listed grassland elements in the Okanagan:

Element

Red List*

Blue List**

Vascular Plants

Plant Communities

Insects

Reptiles and Amphibians

Birds

Mammals

Total Elements

73

27

5

4

15

5

129

39

11

6

7

25

10

98

*Red list: List of ecological communities, and indigenous species and subspecies that are extirpated, endangered or threatened in British Columbia.

**Blue list: List of ecological communities, and indigenous species and subspecies of special concern (formerly vulnerable) in British Columbia.

The south Okanagan and lower Similkameen valley is Canada’s hot spot for red- and blue-listed species with over 30% (57 species) of the province’s listed species. Over 50% of the species are associated with grasslands, and more particularly with Antelope-brush plant communities. Only 10% of the Antelope-brush-Needle-and-thread grass community is left in the south Okanagan and it is ranked as one of the four most endangered ecosystems in Canada.

Some plants, such as the red-listed short-flowered evening-primrose and Andean evening-primrose are restricted to the Southern Okanagan Basin, others are found only occasionally beyond that area, yet others have been found only in very specific locations. Threetip sagebrush is most abundant near the Canada/US border and occurs as far north as Summerland. Antelope-brush occurs as far north as Kaleden and east to southwest slopes of Anarchist Mountain with a few plants as far north as Westbank and as far west as Osprey lake north of Princeton.

Most of the 11 listed insect species are only found in the south Okanagan, with some not found elsewhere in Canada, including the Vivid dancer, Parawan tiger beetle, and ground mantid. The Mormon metalmark is found only in the south Okanagan and Similkameen while the Monarch ranges through the Okanagan valley as far as the Thompson region.

The red-listed night snake has only been found in one location but the rubber boa, western rattlesnake and racer are more readily seen in grasslands near wetlands and riparian areas, or their winter homes in talus slopes and rocky outcrops. The Great Basin spadefoot toad, painted turtle and tiger salamander are associated with ponds and shallow lake edges. The spadefoot toad overwinters by digging down deeply into the soft ground along pond edges. Tiger salamanders can live in the saline or alkaline conditions found in many ponds and wet areas of the Okanagan valley.

35 listed bird species are found in the south Okanagan and lower Similkameen but only 16 are found in the Kettle River valley. It is thought that the changes made in grassland communities by heavy grazing may account for the lower numbers in the Kettle valley. The red-listed sage thrasher nests at White Lake and Chopaka grasslands and ranges as far as the north Okanagan.

Brewer’s sparrow and yellow-breasted chat are found in sagebrush grasslands and riparian areas in the south Okanagan. The only known BC populations of the canyon wren are found in the cliffs and canyons between Osoyoos and Okanagan Falls. The blue-listed gray flycatcher, Lewis’s woodpecker and flammulated owl prefer the ponderosa pine zone.

The blue-listed California bighorn sheep depend on grasslands for a large part of their needs. In the Ashnola valley they move between lower elevation and sub-alpine or alpine grasslands. In the Okanagan valley they stay on the lower grasslands and open forest most of the year. Important wintering areas are used on the east side of the valley from Oliver to Penticton and at Shorts Creek on the northwest side of Okanagan Lake. In the south Okanagan bighorn sheep come in close contact with domestic livestock, agricultural activities and recreationists and have experienced die-offs. Residents have been involved in the recovery efforts for this herds.

The red-listed badger prefers the grasslands open forests in the Okanagan and Similkameen valleys. Numbers are low throughout the province. Blue-listed Nuttall’s cottontail is found in small numbers in sagebrush habitat in the south Okanagan and lower Similkameen.

Six listed bat species use grasslands and riparian areas for feeding and warm crevices in cliffs for resting and for rearing young. The western red bat is known only from Okanagan Falls in the Okanagan region.

A Species at Risk Profile: Pallid Bat

Red-listed in BC

Listed under the Federal Species at Risk Act (SARA)

The pallid bat is known in Canada only from Osoyoos to Okanagan Falls. Much more numerous further south in the US, pallid bat numbers in the Okanagan are not known, but the population is thought to be very small. These bats feed over open grasslands with scattered big sagebrush, rabbit-brush and Antelope-brush, and even along roadsides. They have separate daytime and night-time roosts in ponderosa pine trees, crevices and cliffs. It is not known if they hibernate in the Okanagan.

The pallid bats has dark grey wings and a light body with large tan coloured ears. Glands behind the nostril emit a skunk-like smell. Flying during the night, they hunt their prey by flying low over the grasslands and even spend time on the ground. Beetles and moths are their usual food in the Okanagan, which they may take back to their night roost to eat. Bats are themselves prey for owls, hawks and snakes as well as domestic cats.

Threats to bat populations include loss of habitat, and insects laden with pesticides used in fruit orchards.

For more information on species at risk in BC, visit our SAR page.

For definitions of technical terms, please see the GLOSSARY.

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