Environmental Problems, Their Causes, and Sustainability 1

shrubs such as mesquite and prickly pear cactus. Finally,overgrazing can limit livestock production.We do not know the condition of much of theworld’s rangeland because of a lack of detailed surveys.However, limited data from surveys in variouscountries by the FAO indicate that overgrazing by livestockhas caused as much as a fifth of the world’srangeland to lose productivity, mostly by desertification(Figure 14-9).How Can Rangelands Be Managed MoreSustainably to Produce More Meat?Control and RestoreWe can sustain rangeland productivity by controllingthe number and distribution of livestock and byrestoring degraded rangeland.The most widely used method for more sustainablemanagement of rangeland is to control the number ofgrazing animals and the duration of their grazing in agiven area so the carrying capacity of the area is notexceeded. However, determining the carrying capacityof a range site is difficult and costly.Livestock tend to aggregate around natural watersources especially thin strips of lush vegetation alongstreams or rivers known as riparian zones (Figure 14-21,left) and ponds established to provide water for livestock.As a result, areas around such water sources tendto be overgrazed and other areas can be undergrazed.Studies indicate that 65–75% of the wildlife in thewestern United States depends totally on riparianhabitats. According to a 1999 study in the Journal of SoilUSDA, Natural Resources Conservation ServiceFigure 14-20 Rangeland: overgrazed (left) and lightly grazed (right).and Water Conservation, livestock grazing has damagedapproximately 80% of stream and riparian ecosystemsin the United States.To help prevent such damage, livestock can bemoved from one grazing area to another and riparianareas can be fenced off. Sometimes protected areas canrecover in a few years (Figure 14-21, right). Rancherscan also provide supplemental feed at selected sites andlocate water holes and tanks and salt blocks in strategicplaces.Bureau of Land ManagementBureau of Land ManagementFigure 14-21 Solutions: cattle on a riparian zone of a public rangeland along Arizona’s San Pedro River (left)in the mid-1980s just before this section of waterway was protected by banning domestic livestock grazing for15 years, eliminating sand and gravel operations and water pumping rights in nearby areas, and limiting accessby off-highway vehicles. The right photo shows the recovery of this riparian area at the same time of yearafter 10 years of protection.296 CHAPTER 14 Food and Soil Resources