Grassland Ecosystems

The recolonisation of the land by plants and animals following melting of the glaciers that once covered most of North America (beginning about 15,000 years ago; see Earliest Beginnings) has not been a steady ecological progression, as climatic changes have been frequent and pronounced (Pitt and Hooper, 1994). Grasslands likely reached their maximum extent during a warm, dry period about 10,000 - 6,000 years ago. At that time, lowland grasslands may have merged with alpine meadows in very arid parts of the Columbia Basin, especially on south-facing slopes. Since then, the grassland/forest edge has retreated to lower elevations as the climate has become cooler and moister.

Grasslands currently occur in the southerly and eastern parts of the Columbia Basin as understory and openings in Ponderosa Pine and Interior Douglas-Fir biogeoclimatic zones, and to a lesser extent in the Montane Spruce and Englemann Spruce-Subalpine Fir zones. Although there are no defined Bunchgrass zones in the Basin, both the Interior Douglas-Fir and Ponderosa Pine zones have grassland phase variants in dry subzones of the Columbia Basin. These zones are the basis of our livestock (mainly cattle) industry, and are critical for grazing wildlife like elk and bighorn sheep. Much of the grassland and former grassland in the Columbia Basin, occurring in settled areas and valley bottoms, is private. The Ministry of Forests administers grazing licenses for forage and hay cutting on Crown land. The graph (above) shows the amount of grazing in the Nelson Forest Region, measured in Animal Unit Months (equivalent to the amount of forage a cow would consume in a month). Province-wide, and in the Columbia Basin, Crown land accounts for about 60% of livestock forage, and private land the other 40%.

Ponderosa pine (PP) and mid-elevation Interior Douglas-Fir (IDF) zones can be extremely productive for forage, and Englemann spruce-subalpine fir (ESSF) less so (graph at left). By contrast, the Interior Cedar-Hemlock (ICH) zone, widespread in the Columbia Basin, contains virtually no natural pasture land.

Threats

Threats to grasslands include forest encroachment, overgrazing by livestock, urban and agricultural development, and invasion by exotic weeds. Less than 1% of B.C. grasslands have any protection, although the Nature Trust of British Columbia has purchased grassland for conservation in the East Kootenay.

Overgrazing

Overgrazing of range lands reduces the highly nutritious native perennial bunchgrasses, and promotes less nutritious, weedy (often exotic) annual grasses and forbs (broad-leafed, herbaceous plants), and woody brush. Cattle also trample the ground, damaging a surface soil cover of lichens, bryophytes (mosses and their relatives) and cyanobacteria. This promotes germination of weed seeds and results in loss of soil moisture, further stressing native vegetation. Overgrazing by livestock (mainly horses, from mid-1800s, and, later, cattle) was serious in the early settlement period, and by 1900 had resulted in considerable damage to rangelands (Pitt and Hooper, 1994). Since the 1940s, with better management, grassland range conditions have generally improved in British Columbia, now providing 80% of livestock grazing.

Forest Encroachment

In the Nelson Forest Region, there has been a considerable loss of rangeland by forest encroachment, mainly in the Ponderosa Pine and Interior Douglas-Fir zones (Ministry of Forests, 1995). While difficult to quantify, Pitt and Hooper (1994) have estimated that 30% of the Chilcotin-Caribou grasslands have been lost to forest encroachment, and this estimate probably also applies to Kootenay grasslands. Provincial forest, environment and agriculture ministries and public interest groups have been experimenting with prescribed burns to reduce forest encroachment for some years, and are considering expanding this program considerably in the Rocky Mountain Trench area (see the Wildlife section for some examples).

Weed Invasion

Invasion by exotic weeds is one of the factors most clearly associated with ecological damage to rangelands. Harding (1994) listed 29 species of weed, mostly exotic, that cause economic losses to crops and range land in the Columbia Basin. Weed infestations occur mainly in agricultural areas, centres of human settlement and transportation corridors.

In the Columbia Basin, at least five species of beetles and insects have been introduced to control exotic weeds, mainly knapweeds, and another seven are in various stage of establishment and redistribution (Ministry of Forests, 1995). Introduction of non-native biological control agents is a double-edged sword. In most cases, thorough testing has ensured that the control agents attack only the target weed, and not native species. Cases are known, however, of alien control agents themselves damaging native ecosystems, and range managers know that exhaustive research and careful testing are needed to conduct a safe biological control program (Smith, 1994).

References

Harding, L.E., 1994. Introduced wildflowers and range and agricultural weeds in British Columbia. In L.E. Harding and E. McCullum (eds.), Biodiversity in British Columbia: our changing environment. Environment Canada.
Ministry of Forests, 1995. Forest, Range and Recreation Resource Analysis, 1994.
Pitt, M. and T.D. Hooper, 1994. Threats to biodiversity of grasslands in British Columbia. Chapter 20 in L. Harding and E. McCullum (eds.), Biodiversity in British Columbia: our changing environment. Environment Canada.
Smith, R., 1994. Effects of alien insects and microorganisms on the biodiversity of British Columbia's insect fauna. In L. Harding and E. McCullum (eds.), Biodiversity in British Columbia: our changing environment. Environment Canada.

Other Resources

Grasses of the Columbia Basin of British Columbia 2000 
ISBN 0-7726-4147-1
Download copy of book here