Plant communities consist of groups of plants that are adapted to similar combinations of climatic conditions and soils. Each different plant community by itself, or with other communities, provides a variety of habitats that are used by animals for food and shelter
Vegetation in British Columbia’s grasslands is very diverse due to the wide variations in climate, soils and topography throughout the province. Biogeoclimatic zones, defined as the broadest vegetation complexes that reflect the same regional climate, are used for range classification and management. The zones are generally named after one or two dominant plant species that are present over a wide range of conditions. Biogeoclimatic zones can be further broken down into subzones, which have less climatic variability and narrower geographic distribution than zones. Biogeoclimatic phases are areas within a zone that contain non-zonal ecosystems. In the Southern Interior, the most important zones in terms of area and forage production potential for livestock and wildlife are Bunchgrass, Ponderosa Pine, Interior Douglas-fir and Montane Spruce.
Different communities are present on north-facing slopes as compared with south-facing slopes and still others in swales as compared with knolls. Some plants are more sensitive than others to factors in the environment, such as grazing pressure. Overgrazing can change the plant species present and total forage production.
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Bunchgrass Zone
The Bunchgrass Zone is located in the hot, dry valley bottoms of southern BC. It is found in the Okanagan Valley south of Summerland, the Similkameen River Valley to Keremeos, the Thompson River Valley from Spences Bridge to Pritchard, the Nicola Valley, and the Middle Fraser and Lower Chilcotin River valleys from the Farwell Canyon to Big Bar. In BC, this biogeoclimatic zone usually occurs at lower elevations, 300 to 1000 meters. In BC, grasslands cover about 1.2 million hectares but only 300,000 hectares are classified as bunchgrass.
The climate of the Bunchgrass Zone is characterized by hot, dry summers and moderately cold winters often with little snowfall. Winter moisture is critical to plant growth because of heavy evaporation losses with spring and summer rains. The lowest elevation and hottest grasslands at 300 to 700 m are typically dominated by wide-spaced bluebunch wheatgrass with big sagebrush. Antelope-brush survives the slightly warmer winters in the southern areas. At elevations from 700 to 100 meters elevation in the dry warm bunchgrass, big sagebrush is absent and bunchgrass plants are closer spaced.
Bluebunch wheatgrass along with big sagebrush are the dominant species found throughout the zone, along with well-developed lichen crusts. Dominant grasses vary with site latitude, elevation and aspect, with porcupine grass being common at the north end of the zone, while Idaho and Rough fescue can dominate on north and east facing slopes in the south. As sites are modified by heavy grazing pressure, other plants become common include prairie sagewort, rabbit-brush, junegrass, Sandberg’s bluegrass, needle-and-thread grass and yarrow. Past grazing history has influenced the bunchgrass zone in BC and many hectares are dominated with weedy annual species from disturbance and prolonged misuse. Moisture and range condition cause wide fluctuations in forage production in the bunchgrass zone from 200 to 1000 kg/ha. Employing cattle grazing practices to ensure proper use and rests are critical in this zone.
Despite the arid climate, a variety of wetlands occur in the bunchgrass. They include cattail marshes, saline meadows, and riparian zones lined with shrubs. These wetlands are important sources of water for livestock as well as habitat for wildlife, supporting a high density and diversity of reptiles, birds, small mammals, and large ungulates.
The majority of the Bunchgrass Zone occurs on private land and is extensively used for cultivated crops or non-agricultural purposes. The remaining grasslands are critical to the livestock industry in BC because they provide spring, fall and winter range.
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Ponderosa Pine Zone
The Ponderosa Pine Zone is characterized by open, savannah-like stands of ponderosa pine with a well developed ground cover of grasses and forbs. This zone occupies 0.3% of the province or about 300,000 ha, and occurs at higher elevations than the Bunchgrass Zone and below the Douglas-fir Zone on the lower slopes and terraces of the driest, warmest valleys of the Southern Interior, typically between 300 to 900 m. This zone is the warmest and driest forest zone in the province.
The zone most frequently exists as a mixture of open forest and grassland. Plants found under the pine canopy are similar to those found in the Bunchgrass zone. Ponderosa pine is the dominant tree throughout the zone but Douglas-fir can also be found in the moist areas and gullies, as well as on drier sites in cooler northern areas. Few shrubs are present in the Ponderosa Pine Zone except for big sagebrush and rabbit-brush, and scattered plants of wild rose and Saskatoon in swales. Antelope-brush contributes to the understory in the southerly portions of the zone. Bluebunch wheatgrass, big sagebrush, and rough fescue or Idaho fescue dominate sites in good range condition. Fescues may replace bluebunch weheatgrass or become a co-dominant with it in the southern part of the zone. As in the Bunchgrass zone, grazing history has played a role in determining the composition of plants present. Under heavy grazing, less bluebunch wheatgrass and fescues are present, and more Sandberg’s bluegrass, needlegrass, cheatgrass and low-growing weeds.
The Ponderosa Pine Zone is an important source of early spring and late-fall range for cattle in the Southern Interior Forest Region. In most years there is sufficient fall regrowth to provide supplemental forage. Ponds, which occur in depressions, provide water for livestock and wildlife in the spring, but often dry up during the summer.
These middle elevation grasslands have lesser big sagebrush and an increased dominance of bunchgrass than the Bunchgrass zone. Bluebunch wheatgrass is the primary forage plant on excellent condition range in both subzones and can account for 25 to 65% of the total forage production. Rough fescue and Idaho fescue are also important forage species in some areas. Forage production is influenced by soil type, range condition and tree canopy closure but can range from 480 to over 800 kg/ha.
The Ponderosa Pine Zone has relatively light snowfall and short winters, so it provides winter and spring forage for deer, big-horn sheep and Rocky Mountain Elk. The conifers also provide food and cover for many birds and small mammals. Rugged cliffs and talus slopes, which are common to the zone, can provide lambing grounds for bighorn sheep.
Interior Douglas-fir Zone
The Interior Douglas-fir Zone occupies most of the low- to mid-elevation terrain in the Southern Interior plateau, the Southern Rocky Mountain trench and portions of the lee side of the Coast Mountains. Topography varies from nearly level to rolling and steep slopes.
The zone occurs over a wide range of elevations from 350m in some valley bottoms to over 1450m where it often joins with the Montane Spruce Zone. Cool winters, warm dry summers and a fairly long growing season characterize the climate of the Interior Douglas-fir Zone. Both moisture deficits and deep frosts during the growing season can limit plant growth. The landscape of the Interior Douglas-fir Zone includes grasslands, savannahs with open canopies and grass understories, as well as closed forests with a ground cover consisting of a mix of shrubs, forbs and grasses.
Douglas-fir is the dominant tree species in the forested parts of this zone. Lodgepole pine commonly occurs at higher elevations where it forms even-aged stands after disturbance such as fire. Trembling aspen also occurs, especially on deep, rich soils. Generally the understory is well developed in Douglas-fir forests but few plants other than Saskatoon, birch leaved spirea, pinegrass, and feathermoss occur constantly across all subzones. Common shrubs and forbs include rose, willow, timber milk-vetch, creamy peavine and lupine.
The upper grasslands, as grassland phases in the Interior Douglas-fir Zone are commonly known, are important forage resources for livestock and wildlife. These grasslands occur due to a combination of soil, topographic conditions and fire. Grassland plant communities in the Interior Douglas-fir Zone share common species with the lower elevation grasslands in the Bunchgrass and Ponderosa Pine zones. In comparison with the lower grasslands however, they are characterized by the absence of big sagebrush and by having more forbs, taller grass growth, and denser plant cover. Under prolonged periods of heavy grazing, grasses can be replaced by forbs.
Bluebunch wheatgrass can be the sole dominant species on dry grassland sites throughout the zone, but with different moisture conditions it often co-dominates with rough fescue, Idaho fescue, or needlegrasses.
Many of these grasslands are like those found at lower elevations and contain plant communities altered by past grazing practices. Species composition on these sites generally contain less bluebunch and rough fescue, more Kentucky bluegrass and smaller bunchgrasses such as needle-and-thread, junegrass, and Columbia needlegrass.
The Interior Douglas-fir Zone is one of the most important zones for cattle and wildlife in BC. The open grasslands provide important range for livestock grazing in spring and fall months, as well as extensive grazing in semi-open forests and cut blocks in the summer. Pinegrass comprises 40 to 60% of the ground cover under the forest canopy and provides 50 to 65% of the available livestock forage. In open forest stands and grasslands, bluebunch wheatgrass, rough fescue or Idaho fescue can be the principal forage speices. Forage yields can range from 270 to 800 kg/ha in forest, and up to 1120 kg/ha in grasslands.
To learn more about ecological systems, click a link below.
Grazing Animals
Plant Responses to Grazing
Ecosystem Responses to Humans
Grassland Monitoring
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