BUNCHGRASS ECOSYSTEMS AND THE EARLY CATTLE INDUSTRY
The term "bunchgrass" refers to types of grasses that are characterized by their growth in tufts or bunches utilizing a single root system. As the stems of bunchgrasses grow up and outward from a narrow base, the stems form an "umbrella" protecting the base and root system from sun and evaporation. In the same manner, the stems act as a funnel to channel moisture into the centre and down into the root system. Because of these characteristics, bunchgrasses are particularly well adapted to the very dry conditions found in parts of the Thompson-Okanagan region. The main species of bunchgrasses in the region are described below.
Bluebunch wheat grass is an erect, bunch-forming, densely tufted perennial in the grass family with fibrous roots. It can grow up to one metre in height and cover up to half a square metre in surface. Its leaves are blue-green in colour, accounting for the name of the species. The individual spikelets are removed from each other and are found on alternating sides of the stem.
The species of bluebunch wheat grass found in British Columbia does not have awns on its spikelets, causing some to classify it as a sub-species (Agropyron spicatum var. inermev).
Bluebunch wheat grass was the predominant species of bunchgrass at the time of contact and can still be found in the driest moisture regimes and lowest elevations of the study area and up to the 3000 foot elevation depending on exposure and moisture conditions. It starts its growth early in the spring and is fully grown by late June.
Rough Fescue is an erect, densely tufted perennial bunchgrass the flowering stems of which can grow to a height of one metre and the bunches can cover up to .8 of a square metre of ground surface. Rough fescue is generally found at a higher elevation than bluebunch wheat grass and at altitudes lower than 2600 feet (near Kamloops) is confined to north- and east-facing slopes. The species also is more abundant in slightly damper moisture regimes than bluebunch wheat grass. Because of this, as altitude and moisture regime increases, rough fescue replaces bluebunch wheat grass as the dominant species
Needle-and-thread grass is another common large bunchgrass found in the Thompson-Okanagan. Its extremely long awns make it very distinctive, especially when it is in its mature stage with full flower and fruit. It greens up very early in the spring and, when green, it provides good forage for cattle.
Giant Wild Rye is a very tall bunchgrass which grows up to two metres in height. It is found along riverbanks, ravines, and moist slopes and is characterized by its distinctive greyish-blue tufts. Because of extreme size and coarseness, Giant Wild Rye is not utilized by cattle as for forage.
Idaho Fescue (also called bluebunch fescue or blue bunchgrass) is a smaller species and is not found north of 50 degrees latitude. The bunches, which are reddish at the bases, are more compact and the flowering stems up to a maximum of 60 centimetres high. Like Rough Fescue, Idaho Fescue is found more commonly on the more moist upland sites and is confined in the north- and east-facing slopes.
Because of the delicate nature of the bunchgrasses, an understanding of their growth characteristics is important for ranchers who intend to have cattle graze the bunchgrass ranges. By using the grasslands in the right season and to a safe degree, it is possible to maintain the abundant growth of the bunchgrass species. To do this effectively, the rancher must know the growth characteristics and requirements of each species. An understanding of the principles in grass growth is essential for effective range management. To illustrate the growth rate during the growing season, a "growth curve" is used. It shows that bunchgrasses develop slowly during the spring, followed by a period of rapid growth and then a tapering off of growth in early summer. The period of slow development in the spring may cover several weeks, depending on the weather. Because the temperature of the soil is too cold for root activity at this time, the food for plant growth comes from that which the plant has stored in the roots during the previous summer and fall. As the air and soil become warmer, more nutrients are absorbed from the soil and transported to the leaves where, in conjunction with the photosynthesis from sunlight, they are made into food for plant growth. As the leaf growth accelerates, the ability of the plant to produce more food increases and plant growth increases rapidly. Rapid growth continues until the plant begins to form seed stalks. It then tapers off, partially because of the increasing demand of seed stalks, flowers, and seed for food. At the same time, the onset of hot, dry weather also effects the rate of growth. Then growth slows down and the growth curve flattens out.
At the same time that top growth of the plant begins its rapid rise, the grass also begins to store up reserve plant food in the roots and crowns for the next year's use. But during the period of rapid growth and seed production, the storage of plant food slows down as all of the plant's resources go into production of seed stalks, flowers and seeds. Once this process is completed and the seeds have reached maturity, storage of nutrients increases again until growth stops. The adequate storage of food for future use is essential for plant survival, especially during times of drought, hard winters and insect damage.
Different species of bunchgrass have different growth habits, season of growth, forage yield, chemical composition, reaction to grazing, and other characteristics. For example, bluebunch wheat grass starts growth early in the spring and is therefore particularly susceptible to over grazing until the period of rapid growth begins. At this point the grass is no longer dependent on the limited supply of plant food stored in the roots and is able to extract raw materials for plant growth from the soil. Because bluebunch wheat grass has its lowest reserves of plant food when its tops are about seven inches (18 cm.) high, it should not be grazed to any significant extent before it surpasses this height. For bluebunch wheat grass and other bunchgrasses, it is best that at least half of the total season's growth be left to ensure adequate storage of nutrients for the future.
Grassland ranges in the Thompson-Okanagan are ready for grazing when the bluebunch wheat grass is about seven inches high. In the Kamloops area, this varies from about April 8 on lower ranges (1100 to 1700 feet) to about May 10 in the higher grasslands (2300 to 2800 feet). By the time bluebunch wheat grass is at this height, Rough Fescue is at the same height. Some top growth should be left at the end of the grazing period to ensure that the plant can continue to manufacture food for storage while moisture is still available in the soil. The continued grazing of bunchgrass too early in the season and grazing grass too closely during the growing season will result in the weakening of the plants and the eventual elimination of the bunchgrass species altogether.
Much of the above information is taken from: Mclean, A. & and Marchand, L. (1968). Grassland ranges in the Southern Interior of British Columbia. Canada Department of Agriculture Publication 1319.
Bunchgrass and beef