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Southern Thompson Upland

Grassland Region

Area, ha


Southern Thompson Upland


Southern Interior


Area, ha

Southern Thompson Upland


The Grassland Landscape

The Southern Thompson Upland is the rolling plateau area south of the Thompson River and bounded by the Fraser River valley in the west, the Okanagan valley in the east and the Similkameen River valley in the south. Almost 75% of the grasslands occur in the Interior Douglas-fir zone and 20% in the Bunchgrass zone. Over 85% of all the grasslands are found in the Nicola Valley with smaller areas around Princeton, at Tunkwa Lake and in the Mamit valley. Variations in the grassland species throughout the plateau reflect influences from the surrounding large valleys.

The Coast and Cascade Mountains provide a barrier from the weather systems that roll in from the Pacific, significantly reducing rainfall, particularly in the Similkameen valley. Grasslands have developed in the lower lying valleys and basins since the end of the last glaciation.

The largest area of grasslands is located in the Nicola Basin area east of Merritt and extending north towards Kamloops. This area matches the extent of the Glacial Lake Merritt that drained north towards the Thompson River. A smaller area of grasslands around Princeton covers another former glacial lake that occupied the Similkameen valley.

Historical Impacts

Most of the grasslands have been altered by prolonged, and sometimes heavy, livestock grazing.

They have been used for centuries by aboriginal peoples, who are known to have used fire to maintain food plants, and had horses by 1790. Only in the past 150 years has grazing been extensive and heavy, and especially in the lower elevation grasslands. Some areas of the Nicola valley were ploughed and seeded for crops, but many of those areas are slowly recovering their native species.

Research projects are giving grasslands managers a better understanding of grasslands species and their particular needs.

Unique features

southern1The valley that extends from Nicola Lake north to Campbell Creek contains a series of lakes of varying size, shape and character. The valley was deepened by vast quantities of meltwater from Glacial Lake Merritt that flowed north to the valley of the Thompson River through Campbell Creek. Shumway Lake and Trapp Lakes sit in winding, grass-draped valleys with low hills, while Napier Lake is in a deep, rock-lined canyon. High cliffs and talus slopes combined with the mix of grassland and forested areas create habitats for a wide range of species.

Shallow water, marshy areas and riparian woodlands provide habitat for a variety of migrating and resident bird species as well as many other wildlife species. A large variety and numbers of waterfowl can be seen in migration in spring and fall. The road along the valley provides many opportunities to view birds without disturbing them.

Plant Communities


BEC Zones with grasslands1

Major2 grassland BEC Subzones and Variants

Southern Thompson Basin

Bunchgrass Zone

Ponderosa Pine Zone

Interior Douglas-Fir Zone

Montana Spruce Zone

Englemann Spruce-Sub-Alpine Fir

BGxw1: Nicola Very Dry Warm Bunchgrass Variant

PPxh2: Thompson Very Dry Hot Ponderosa Pine Variant

IDFxh1: Okanagan Very Dry Hot Interior Douglas-fir Variant

IDFxh2: Thompson Very Dry Hot Interior Douglas-fir Variant

IDFdk1: Thompson Dry Cool Interior Douglas-fir Variant

Pavilion Ranges

Bunchgrass Zone

Ponderosa Pine Zone

Interior Douglas-Fir Zone

BGxh2: Nicola Very Dry Warm Bunchgrass Variant

BGxh3: Nicola Very Dry Warm Bunchgrass Variant

PPxh2: Thompson Very Dry Hot Ponderosa Pine Variant

IDFxh2: Thompson Very Dry Hot Interior Douglas-fir Variant

IDFdk1: Thompson Dry Cool Interior Douglas-fir Variant

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

2. Over 3,000 hectares

Nicola Very Dry Warm Bunchgrass Variant (BGxw1): 27,650 hectares

The grasslands of the lower elevations of the Nicola Basin are Middle Grasslands, similar to those in the Thompson-Pavilion region. Bluebunch wheatgrass is the dominant grass, with varying small amounts of needle and thread grass and junegrass. Flowering plants are also sparse and include large-fruited desert-parsley, mariposa lily, prairie sagewort, yarrow, lemonweed and arrow-leaved balsamroot.

Thompson Very Dry Hot Ponderosa Pine Variant (PPxh2): 4,235 hectares.

On the higher western slopes of the Nicola Basin and in patches in the Campbell Creek area, ponderosa pine savannah occurs where the summers are hotter and drier. Bluebunch wheatgrass is the dominant grass species between the widely-spaced trees, with common rabbit-brush, arrow-leaved balsamroot and a variety of other flowering plants.

Okanagan Very Dry Hot Interior Douglas-fir Variant (IDFxh1): 8,115 hectares.

The grasslands of the Princeton Basin are 100 metres higher than the Nicola Basin and are an extension of the Upper Grasslands of the Okanagan valley. Steppe, savannah, aspen copses and wetlands create a complex landscape where more or less ponderosa pine or Douglas-fir may be present. Bluebunch wheatgrass is the dominant grass species, but the presence of Idaho fescue distinguishes the basin from all surrounding plateau grasslands.

Thompson Very Dry Hot Interior Douglas-fir Variant (IDFxh2): 39,635 hectares.

This extension of the dry Upper Grasslands found in the Thompson-Pavilion region stretches above Douglas Lake from Knutsford to Merritt, and from Mamit Lake to the lower Nicola. Almost 30% of the grasslands in the whole region are found in this variant. Rough fescue and bluebunch wheatgrass are the principal grass species, with bluebunch wheatgrass dominating on the driest sites. Aspen groves have developed where there is more moisture.

Thompson Dry Cool Interior Douglas-fir Variant (IDFdk1): 48,280 hectares.

These grasslands continue the cooler, higher-elevation Upper Grasslands of the Thompson-Pavilion region, above Douglas Lake, around Tunkwa Lake, in the Mamit valley and continuing south to the Otter valley. The moister conditions found at these higher elevations provide a rich diversity of plants dominated by rough fescue and bluebunch wheatgrass. Aspen groves are extensive in some areas, and particularly in the southern valleys.

Other Grassland Communities

Small patches of grasslands are found in higher elevation variants throughout the Southern Thompson Upland region, usually associated with south-facing slopes. The largest areas are along the Coldstream River south of Merritt, in the Hayes Creek and Trout Creek valleys and in the northeast part of the plateau.

Aspen groves, lakes, ponds and wetlands are common features throughout the grasslands of the Southern Thompson Upland region. Aspen groves are locally quite extensive in gullies, at the toe of slopes and in depressions, especially in the higher elevation Interior Douglas-fir zone.

southern4Lakes range in size from the 25-kilometres of Nicola Lake to the artificially created one-kilometre Tunkwa Lake. Ponds and wetlands are especially common throughout the mid-high elevations and vary from bulrush-ringed to alkaline. They provide habitat for a particularly wide variety of waterfowl, especially in migration.

Rocks, cliffs and talus slopes provide further variety in grasslands plants, and important habitat for many wildlife species. They are widespread throughout the Southern Thompson Upland region at all elevations and contribute habitat elements important for the many raptor species that reside in or migrate through the area.

Key Plant Species

Trembling Aspen (Populus tremuloides)

  • A common feature on the grassland landscape where moisture collects
  • grows from suckers, creating large groups of the same clone that change colour at the same time in the fall
  • greenish-white bark contains chlorophyll and is torn off and eaten by moose in winter
  • rounded leaves with a pointed tip are bright green above, paler below
  • leaf stalk is flattened allowing the leaves to twirl or “tremble”
  • aspen groves are important habitat for grouse, hawks, owls and cavity-nesting birds.


More than 119 wildlife species, including 14 reptiles and amphibians, 79 birds, and 26 mammals are found in the Southern Thompson Upland region. Mule deer are the most common large mammal, using the grasslands in spring, summer and fall and moving to the protection of the open Douglas-fir and Ponderosa pine forests for the winter.

Many small mammal species are resident in the grasslands. The yellow-bellied marmot, muskrat, Western harvest mouse and meadow vole are the most common resident mammals in the Bunchgrass and Interior Douglas-fir zones. The pocket gopher is probably the most widespread small mammal in the Interior Douglas-fir zone, spending most of its life in underground burrows. The Thompson River is the northern limit of its extent .

The big brown bat and Yuma myotis are the two most common bat species found in elevations below 1070 metres and are often associated with water bodies. Both species roost in buildings and big brown bats may hibernate locally.

The variety and complexity of habitats in the region support over 160 species of birds. Black-billed magpie, vesper sparrow, meadowlark, American kestrel, red-tailed hawk and Northern harrier are common at lower elevations. The many lakes, ponds and wetlands from Campbell Creek south to Princeton and at higher elevations provide habitat for a wide variety of waterfowl, cavity nesters and songbirds. Species include American widgeon, Barrow’s goldeneye, mallard, ruddy duck, American coot red-shafted flicker, mountain bluebird, yellow warbler, red and yellow-headed blackbirds.

The many access roads in the region provide many opportunities to view waterfowl and a variety of raptors and songbirds from spring through fall.

Reptiles and amphibians are most numerous in lower elevations with common garter snake, wood frog and long-toed salamander most commonly found.

Check the list of wildlife viewing sites publications.

Species at Risk

Red and Blue listed grassland elements in the Southern Thompson Upland


Red List*

Blue List**

Vascular Plants

Plant Communities


Reptiles and Amphibians



Total Elements















*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.

There are many fewer red- and blue-listed species in Southern Thompson Upland than in any of the surrounding regions. Lack of research may explain some of the smaller numbers as many of these species have been found only once and others only a few times, although appropriate habitat may exist.

Some of the listed plant species have limited distribution in adjacent regions, such as Suksdorf’s lupine, freckled milk-vetch and threadstalked milk-vetch. All the others are found in other grassland regions.

Rubber boa and Great Basin spadefoot toad are the most common of the six listed reptiles and amphibians while the western rattlesnake is found only in the Princeton Basin. Listed bird species in the Southern Thompson Upland include American avocet, Brewer’s sparrow, bobolink, Lewis’s woodpecker, Western screech-owl. Two nests of the red-listed ferruginous hawk have been documented in the Aspen Grove and similar habitat exists elsewhere in the region.

The red-listed badger is not seen very often and introductions have been made to try to increase the population. Fringed myotis and spotted bat are two blue-listed bats that use the grasslands, cliffs and open forests for foraging, roosting and nesting.

A Species At Risk Profile

Silvery Sagebrush (Artemesia cana sp. cana)

Red-listed in BC.

southern5Silvery sage.

Little is known about this small member of the sagebrush family found only in the Merritt area. Conservation Data Centre mapping indicates it occurs near Logan Lake. It is found in the Interior Douglas-fir zone and possibly the Bunchgrass Zone. A mildly aromatic perennial from 0.4 to 1.5 metres tall, it has silvery, hairy branches and leaves. Some leaves may have two tiny lobed teeth as in big sage. Flower heads are held upright.

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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