Impact of livestock grazing on extensively managed grazing lands.

This chapter focuses on the environmental effects of livestock grazing on extensively managed grazing lands. Land resources in these regions used by livestock producers are predominantly rangeland with relatively small amounts of seeded, grassland pasture. Rangelands are uncultivated lands with native and often species-rich plant communities dominated by grasses, grass-like plants, forbs or shrubs. Grassland pasture is usually established on marginal farmland. Initially these pastures are composed of high-yielding forage species capable of responding to high levels of agronomic inputs. Because livestock production is the most common use of forage resources on rangelands and grassland pastures of the world, understanding the influence of livestock enterprises on grazing land is critical for the development of management strategies needed to optimize ecosystem functions. Grazing management strategies have been developed to maintain or improve the structure and function of plant communities known to provide sustainable forage resources for livestock grazing. Grazing management strategies affect many ecosystem components besides livestock and forage production. Grazing also influences plant community heterogeneity, soil chemical and physical properties and the distribution and cycling of nutrients within the plant-soil-water continuum.