GRAZING AND PLANTS
Grazing can have longterm negative impacts if these principles are not followed. Poor grazing management on more brittle areas initially leads to reduced plant vigour, followed by loss of valuable forage plants, loss of drought resistance and increased bare ground, soil erosion, disruptions in the water and mineral cycle and a longterm decline in range productivity.
Less brittle environments may not exhibit bare ground and significant soil erosion as a result of improper grazing. Instead, plant spacing may be closer. Other significant changes occur nevertheless, as in reduced productivity, undesirable species changes, and lowered diversity.
Advocates of livestock grazing suggest a special relationship between plants and grazing animals with grazing having the following beneficial effects:
removal of older tissue that is less efficient photosynthetically than younger tissue
increase in light intensity to lower, younger tissue
increase in stomatal resistance promoting water conservation
increase in forage production due to compensatory growth
recycling of nutrients available in urine and dung
faster breakdown of senescent forage by trampling
Researchers regard these claims as overly simplistic. In practice, plant response to grazing is complex and is related closely to genetics, environment, phenological stage as well as intensity and degree of grazing.
Grazing ceases to be beneficial when the plant is compromised. Uncontrolled grazing (grazing too early, too often, too severely, or at the wrong phenological stage) weakens plants.
Protection from grazing (total rest) often does not lead to the immediate benefits one would expect. A British Columbia study estimated that sites in the rough fescue and ponderosa pine zones would take 20 to 40 years to recover from fair to excellent condition under complete protection from grazing. It suggested grazing during the dormant period in order to improve range condition. In some cases fire may be required to return rangeland to its grass climax once shrubs have taken hold.
Plants are damaged least by grazing that occurs at maturity, or during dormancy. When grazing animals are forced to consume forage of low quality, however, their production declines. Animal performance is best when plant growth is at a maximum. Grazing management therefore involves maintaining an optimum balance between plant and animal requirements.
Refer to RANGE PLANTS, this chapter, for information on plant requirements and response to grazing. Also, refer to PLANT CHARACTERISTICS, Appendix 2, for individual species information.