Bunchgrass

The Bunchgrass (BG) zone occupies the driest and hottest regions of the southern interior of British Columbia (Lloyd et. al. 1990) and lies in valley bottoms in the Fraser, Similkameen, Nicola, Thompson, Chilcotin rivers and Okanagan valley. Upper elevations range from 700-1000m. The climate consists of dry, hot summers with a water deficit and cold winters. Mean annual precipitation ranges from 242 - 328mm and mean annual temperatures range from 5.8 – 9.2 C (Lloyd et. al 1990).

Lloyd et. al. (1990) recognizes two subzones that represent what is known as the lower and middle grasslands. The very dry, hot subzone (BGxh) occurs in the driest valley bottoms up to approximately 700 meters. The BGxh is also known as the lower grasslands. The very dry, warm subzone (BGxw) occurs above the BGxh up to approximately 1000 meters. This area is commonly called the upper grasslands. The Ponderosa Pine zone commonly occurs above the BG.

Soils are typically Chernozemic with thin humus forms, which are found on morainal, glaciofluvial, glaciolacustrine, colluvial and eolian parent materials.

Ecosystems

Due to an extensive water deficit in these ecosystems, grasslands predominate and forest cover are generally restricted to wet sites found near depressions and on lake and river shores. Sparse canopy cover of Douglas-fir and Ponderosa Pine occur on dry rocky outcrops and in open grasslands.

Grazing by cattle is common in this zone and has resulted in wide range of weedy, invasive species (Steen and Coupe 1997). Ecological knowledge of the climax vegetation on many grasslands is limited due to a lack of reference ecosystems for investigation. Overgrazed grasslands are commonly invaded by spotted and diffuse knapweed (Centaurea spp.) and Cheatgrass (Bromus tectorum).

The following plant information is summarized from the A Guide for Site Identification and Interpretation in the Kamloops Forest Region (Lloyd et. al. 1990). Typical zonal site series consist of several species including bluebunch wheatgrass (Pseudoroegneria spicata), Sandberg’s bluegrass (Poa sandbergii) and Cladonia spp. Lichens. Lower grasslands are represented by the occurrence of big sagebrush (Artemesia tridentata) and upper grasslands are typified by the occurrence of Junegrass (Koelaria macrantha) on zonal sites. Dry sites generally have sites series consisting of Antelope brush (Purshia tridentata), Needle-and-Thread grass (Hesperostipa comata), Bluebunch wheatgrass, prickly-pear cactus (Opuntia fragilis) and compact selaginella (Selaginella densa). Wetter grasslands are often found within a mosaic of dry sites and include rough fescue (Festuca campestris) and Giant wildrye (Leymus cinereus).

Forested sites in this zone generally occur in wetter depressions. Lloyd et. al. (1990) classifies site series in the lower grasslands as consisting of Ponderosa pine, Nootka rose (Rosa nootkana), Poison Ivy (Toxicodendron rydbergii), black cottonwood (Populus balsamifera), Snowberry (Symphoricarpos albus) and red-osier dogwood (Cornus sericea). In addition, upper forested grasslands are represented by site series consisting of Trembling aspen (Populus tremuloides), Snowberry and Kentucky bluegrass (Poa pratensis).

The most northern extent of the BG occurs in the Chilcotin region west of William’s Lake at the confluence of the Chilcotin and Fraser Rivers (Steen and Coupe 1997). Vegetation is similar in the Chilcotin with the exception that extensive invasion of non-native species is not as common as in southern British Columbia.

Due to the narrow geographic range this zone occupies and its unique climate, a large number of rare or endangered plants and animals occur here such as the badger and the western rattlesnake.

Resources

Cattle grazing, agriculture, recreation and human habitation are some of the most common uses of this zone. Abundant, productive soils allow for a variety of agriculture uses such as ranching, orchards, ginseng production and vineyards. Due to proximity to large water bodies such as Okanagan Lake, recreational water sports along with horseback riding, hunting, fishing, hiking and mountain biking are common. Lack of continuous forest cover in this zone limits forestry activities.

References

Lloyd, D., K. Angove, G. Hope, and C. Thompson. 1990. A guide to site identification and interpretation for the Kamloops Forest Region. B.C. Min. For., Res. Br., Victoria, B.C., Land Manage. Handb. No. 23. http://www.for.gov.bc.ca/hfd/pubs/docs/lmh/lmh23.htm

Meidinger, D. and Pojar, J. 1991. Ecosystems of British Columbia. British Columbia Ministry of Forests. 330 pp. http://www.for.gov.bc.ca/hfd/pubs/Docs/Srs/SRseries.htm

Steen, O.A., and R.A. Coupé. 1997. A field guide to forest site identification and interpretation for the Cariboo Forest Region. B.C. Min. For., Res. Br., Victoria, B.C., Land Manage. Handb. No. 39. http://www.for.gov.bc.ca/hfd/pubs/docs/lmh/lmh39.htm

Images © Ministry of Forests

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