Range condition or health is normally expressed in relation to the range potential or climax successional state. The self-perpetuating climax state is assumed to be the end point in succession in achieving a potential natural community. The greater the deviation of a range ecosystem from the potential natural community, the poorer its range condition is considered to be.
Range condition is affected by many noxious weeds, forest in-growth, overgrazing by livestock and wildlife and land alienation for non-grazing purposes.
The Range Reference Areas Program was initiated in 1993 to quantify these threats to range health. The program goal is to establish representative ungrazed sites throughout the province to serve as benchmarks against which future rangeland conditions can be measured. These plots, analogous to the ministry’s growth and yield plots, will provide data on long-term forage production potential, species composition at different seral stages, rates of recovery on damaged rangelands and sustainable levels of forage use.
4.3.1 Range Productivity
[45]
Forage production on Crown range varies widely depending on the biogeoclimatic zone, site, range condition class, soil type, annual weather patterns and degree of canopy closure. On grasslands and low-elevation forests soil moisture is often limiting, and annual weather patterns significantly affect forage availability.
Relatively few data are available to describe forage productivity across all ecological conditions in B.C. A comprehensive range ecological classification system is not yet complete. Without such a system, systematic site-specific monitoring and inventorying of forage cannot be undertaken. The following information, derived from numerous site-specific research and technical publications produced over 30 years, does not characterize the full range of variability that likely occurs within and between biogeoclimatic zones. However, it indicates the variation that occurs and illustrates the complexity of factors affecting forage productivity in B.C.
Canopy closure is one of the most important determinants of forage production on forested range. The most productive sites for forage production are those without tree cover — the denser the canopy, the less forage tends to be produced. Range conditions also affect forage production. For example, one study reported average yields of about 110, 280, 450 and 620 kilograms of air-dry forage per hectare for lower grasslands in poor, fair, good and excellent range condition, respectively.46 Similar trends have been reported for the various range condition classes in mid and upper grasslands. Soil moisture and the interaction between soil moisture and canopy cover, also influence forage yield. At higher elevations effective moisture becomes less limiting, but density of forest canopy influences forage production profoundly. Production may be reduced by 60% in open stands, compared to stands with 80% crown closure.[47]
Weather also confounds the interpretation of research information about forage productivity on different sites and in different zones. Information from studies conducted years apart is difficult to compare because of year-to-year variation in growing season weather conditions and the sensitivity of forage production to moisture availability. In addition, species such as bluebunch wheatgrass can have considerable fall regrowth under favourable fall moisture and temperature conditions, leading to above average forage yield in some years.
In the southern Interior, forage production tends to be highest at mid-elevations in the Interior Douglas-fir zone. Grassland phases in the Interior Douglas-fir zone are some of the most productive grazing areas in the province (475 kilograms to 2700 kilograms of air-dry forage per hectare). Sites in the Bunchgrass zone, where only sporadic ponderosa pine and Douglas-fir occur, can also be very productive (250 kilograms to 1300 kilograms of air-dry forage per hectare).
Limited forage production data are available for the Montane Spruce and Engelmann Spruce–Subalpine Fir zones, especially under forest canopy. McLean and others suggest that a reasonable average for the Engelmann Spruce–Subalpine Fir zone in the Ashnola area west of Penticton is about 370 kilograms of air-dry forage per hectare. However, local pockets may have as much as 1800 kilograms of air-dry forage per hectare depending upon moisture availability and other site-specific factors.[48]
In the central and northern Interior, the most important biogeoclimatic zones for grazing are the Sub-Boreal Spruce and Sub-Boreal Pine–Spruce zones near Prince George and Smithers and the Boreal White and Black Spruce zone east of the Rocky Mountains in the Peace River region.
Few data are available documenting forage production potential throughout most of the Sub-Boreal Spruce zone. Forage production can range from 300 to 600 kilograms of air-dry forage per hectare under a canopy of spruce and pine, but can also exceed 3000 kilograms of air-dry forage per hectare on edaphic grassland sites.[49]
Generally, the Sub-Boreal Pine–Spruce zone has low capability for grazing and a short grazing season. Extensive wetlands throughout the area, however, are used for hay production and for grazing. On native sedge meadows forage production can range from 560 to 6000 kilograms of air-dry forage per hectare. Carrying capacity on some sites can be enhanced with proper water control, fertilization and seeding of certain grass species.
As much as 50% of the range resource in the Boreal White and Black Spruce zone in the Peace River area occurs in seral aspen communities. Forage yields vary depending on the site association and extent of canopy closure, but few data are available. Young trembling aspen stands tend to be less productive than mature stands, and forage production can vary from 400 to 1000 kilograms of air-dry forage per hectare.
