Encyclopedia of Global Resources part 97 docx

5 kilometers thick, and it records the products of seafloor spreading. The top kilometer is composed of pillowed basalt. (Basalt is a dense black lava containing about50 percent byweight silicondioxide formed as a result of melting of the mantle.) A sequence of these basalts looks like a huge pile of black to green pillows. Pillows form when basalt lava erupts and is quenched underwater, perhaps 3 kilometers or more beneath the surface. These basalt flows are fed from a system ofvertical magmachannels known asa sheeted dyke complex (about 1 kilometer thick).The dykes are supplied magma from an underlying magma cham- ber, which upon cooling forms gabbro (about 3 kilometers thick).Gabbrois thebase ofthe crustal section and is underlain by mantle rocks called peridotite. Although there is wide agreement that ophiolites form by seafloor spreading, scientists do not agree on precisely where these form. Early ideas, that ophiolites formed at true mid-ocean ridges such as the East Pacific Rise or Mid-Atlantic Ridge, have been super- seded by the idea that they form at convergent mar- gins undergoing extension. A more recent idea, that ophiolites for the most part represent back-arc basin crust, has been challenged by the hypothesis that ophiolites form in forearc environments during the initiation of subduction zones. Ophiolites prove that processes of seafloor spreading and plate tectonics operated at the time the ophiolites formed. Therefore, the record of ophiolites can be interpreted as a record of when plate tectonics occurred on Earth. Ophiolites are common in rock sequences of the following time ages: 1,800 million years ago, 800 to 400 million years ago, and younger than 180 million years ago. Robert J. Stern See also: Earth’s crust; Lithosphere; Plate tectonics; Seafloor spreading. Organization for Economic Cooperation and Development Category: Organizations, agencies, and programs Date: Establishing treaty signed December 14, 1960; took effect September 30, 1961 Witha 2009 membership of thirty ofthe world’s indus - trialized countries, the Organization for Economic Cooperation and Development (OECD) is a forum for intergovernmental policy discussions and policy coor- dination as well as a “think tank” that researches and publishes information on a variety of worldwide economic, financial, and environmental problems and resource issues. Background The OECD was created asa successor tothe Organiza- tion for European Economic Cooperation (OEEC), which had been established in 1948. At that time, there were only two members, the United States and Canada, and the goal of the organization was to coordinate the use of Marshall Plan aid following World War II. Today, the goals of the organization are to as- sist member countries in helping their citizens reach better standards of living and to develop sustainable economic growth in member countries, while con- tributing to the development of the economies of nonmember countries. The OECD is also concerned with the free flow of international trade, human resources, scientific knowledge, and financial capital, while promoting development in industry and agriculture and protecting the environment. Headquartered in Paris, France, the OECD conducts extensive research and publishes on a broad range of economic issues. OECD has regional offices in Germany, Japan, Mexico, and the United States. It has worked with developing nations to help them en- ter the world free-market system. In 1994, Mexico became the first new member of the OECD in twenty years. In 2007, the organization opened discussions with Chile, Estonia, Israel, Russia, and Slovenia for possible membership. The OECD was also contemplating possible membership for five more countries: Brazil, China, India, Indonesia, and South Africa. These countries are referred to as “en- hanced engagement countries.” To promote and ad- minister relations with nonmember countries, the OECD created the Center for Cooperation with Non- Members (CCNM). Through CCNM, theOECD has a working relationship with more than seventy nonmember countries on all continents. The governance ofthe OECDis composedof three major bodies. The first governing body is the Council of Member Countries. Each country is represented by an ambassador who leads a delegation from the country. The council has decision-making power and hence is an overriding body. The second body is the Secretariat, managed by the secretary general, with a 888 • Organization for Economic Cooperation and Development Global Resources staff ofsome twenty-fivehundred employees.The Sec - retariat is organized into fifteen departments and di- rectorates. The third body is formed of committees, experts, and working groups. The OECD committee structure includes approximately two hundred committees and working groups. The committees and working groups are composed of experts from members and nonmember countries. The goal of these committees and working groups is to promote ideas, review scientific progress, and gather information in specific policy areas, such as environment, economics, agriculture, trade, science, technology, employ- ment, education, taxation, and financial markets. The committees also develop guidelines and codes. The committee meetings are attended by approximately forty thousand people from member and nonmember countries. The OECD disseminates information about member countries’ economic indicators and the issues that their economies face. The OECD committees andworking groups focuson fiveareas: public governance, trade and liberalization, policy reform and development, managing new and evolving tech- nologies, and social protection. Impact on Resource Use A number of OECD committees work on natural resources, energy, environment, and sustainable development issues. The Industry and Energy Committee studies alternate sources of energy in order to lessen reliance on oil and encourage the development of multiple energy sources. Amongthe Agricultural Com- mittee’s concerns are fisheries issues, including conservation of stocks. During the Annual Meeting of Sustainable De- velopment Experts (AMSDE), a group of experts works on sustainability issues. The AMSDE encour- ages countries to mainstream sustainable development approaches andpolicies intotheir development strategies. It also oversees projects geared toward developing approaches for measuring sustainable development and methodologies for conducting sustainability assessments. The AMSDE also addresses the gender issueasit relates tosustainable development. Climate change is the most pressing environmental issue with which the OECD continues to work. A meeting held in May, 2009, among high-level repre- sentatives from all member countries and the five countries being considered for membership endorsed a major report to provide guidance forthe adaptation to climate change into development cooperation ac - tivities. In addition, the meeting delegates laid out a road map on how to create better working partner- ships between the environment and the development communities. One of the priorities of the OECD is to help member countries integrate their responses to climate change into their development strategies. The OECD also conducts analysis of the links between environmental, economic, and social issues in order to promote sustainable development in the members and nonmember countries. The OECD has a number of publications on this and related topics, including the impact of the environment on employ- ment, human health, and how government policies affect the environment. The OECD has extensive publications on the sub- ject of water resources and their sustainable management. One of the issues that some countries face is the poormanagement ofwaterresources thatsupport human consumption, ecosystem needs, and agriculture production. The OECD reports that to achieve the goal of cutting in half the number of people worldwide without access to safe water and sanitation services by 2015, countries need to develop better management of water supplies, put good governance structures in place, provide reliable financing, and involve the private sector. Since the inception of the organization, the work done by the OECD has been geared toward providing a framework and a forum in which member countries can compare their experiences, get answers to their problems, and coordinate their policies in the five major areas of the OECD’s activities. Over the years, the OECD has provided valuable information and data onsocial,environmental, agricultural,and financial issues, as well asmany other issues, about its member countries. Colleen M. Driscoll, updated by Lakhdar Boukerrou Web Site Organization for Economic Cooperation and Development http://www.oecd.org/home/ 0,2987,en_2649_201185_1_1_1_1_1,00.html See also: Developing countries; Energy economics; Energy politics; Fisheries; Greenhouse gases and global climate change; Lakes; United Nations Envi- ronment Programme; United Nations Framework Convention on Climate Change; Water pollution and water pollution control. Global Resources Organization for Economic Cooperation and Development • 889 Organization of Arab Petroleum Exporting Countries Category: Organizations, agencies, and programs Date: Established 1968 The Organization of Arab PetroleumExporting Coun- tries profoundly affected international economics and politics in 1973 when it curtailed oil shipments to countries supporting Israel. Background In 1968, Kuwait, Libya, and Saudi Arabia founded the Organizationof ArabPetroleum Exporting Coun- tries (OAPEC) to advance the political and economic interests of Arab oil-exporting states. Unlike the non- Arab members of the Organization of Petroleum Ex- porting Countries (OPEC), OAPEC founders shared a Mideast political agenda: the use of oil as a weapon in the Arab-Israeli conflict. Most of the Persian Gulf’s oil-exporting states eventually joined OAPEC. On October17,1973, OAPECministers responded to a U.S. decision to resupply Israel during the ongo- ing Yom Kippur War by agreeing to reduce oil shipments to countries supporting Israel. OAPEC’s action set petroleum-importing states bidding against one another for the oil upon which their economies depended. The price of oil soared, and OPEC was able to wrest control over the international petroleum market from the cartel of private oil compa- nies which had controlled it for much of the twentieth century. Impact on Resource Use It took the oil-importing countries nearly three years to adjust their economies to the resultant fourfold increase in the price of oil. The political fallout from OAPEC’s embargo was equally substantial. Japan and most European allies broke with the United States on Mideast policy in order to avoid having their oil shipments curtailed. Energy became a major policy issue everywhere in the developed industrial world. Joseph R. Rudolph, Jr. Web Site Organization of Arab Petroleum Exporting Countries http://www.oapecorg.org/ See also: Energy economics; Energy politics; Oil em - bargo and energy crises of 1973 and 1979; Oil industry; Organization of Petroleum Exporting Countries; Resources as a source of international conflict; Saudi Arabia. Organization of Petroleum Exporting Countries Category: Organizations, agencies, and programs Date: Established September 14, 1960 Largely ignored for twelve years, the Organization of Petroleum Exporting Countries achieved control over the international oil market in 1973. Since that time, its successes and failures in stabilizing the price of petroleum on the international market have had an impact on and have been affected by the health of the international economy, in general, and the pace of globalization, in particular. Background Venezuela, Iran, Iraq, Kuwait, and Saudi Arabia established OPEC in September, 1960, in order to attain as much control as possible over the international oil market. Subsequently, the United Arab Emirates, Qatar, Libya, Algeria, Indonesia, Angola, Nigeria, Gabon, and Ecuador have joined the organization; two of these countries, Indonesia and Gabon, have dropped out. Prior to 1973, OPEC was essentially a bureaucratic entity providing its members with oil market information. Between 1960 and 1973, however,the growing demand for imported oil from Western Europe and the United States gradually created a seller’s market. In October, 1973, a crisis ensued when OPEC declared an oil embargo against states friendly to Israel. OPEC exploited thesituation,taking overthe pricingofoil. Impact on Resource Use Because of petroleum’s importance as an energy source, stable and affordable petroleum prices were associated with economic recovery and sustained economic growth in the Western world for most of the second half of the twentieth century. Conversely, high energy pricesduring the1970’s andearly 1980’sled to a global recession and an opposition to globalization 890 • Organization of Arab Petroleum Exporting Countries Global Resources in parts of the developed world, which feared job losses because of outsourcing in economies already experiencing unacceptably high levels of unemploy- ment. During the thirty-five-year span between 1973 and 2008, three principal factors made creating and maintaining an affordable price forpetroleum on the world market difficult for OPEC: the organization’s internal composition; the presence of outside com- petitors inthe oil-export market;and theintermittent tightening of the oil market, often as a result of unforeseen political events. As an organization, OPEC is a confederate alli- ance, not a governing body for its members. Its suc- cess inmaintaining themarket pricethat itestablishes generally requires its members to voluntarily abide by the production quotas assigned to them. If they overproduce, a glut of oil can bring prices down. If they underproduce, the price of oil may increase. However, the price hike is likely to be followed by lower demand, and hence lower profits over a potentially long period. Establishing compliance between member states has often been difficult because of the diverse interests and situations of OPEC member states. OPEC’s effectivedecision-making periods have generally been those in which its members followed the guidelines of its Arabian Peninsula producers: principally Saudi Arabia, Kuwait, and the oil-exporting members ofthe United ArabEmirates. These are generally states with very deep reserves. Most have small populations, and hence, most have a generally low ability to absorb all of the capital earned by their exports. Moreover, those profits are often enormous compared to the earnings of other OPEC states because the cost of producing their oil is often less than one-tenth or one-fifteenth that of the more populous oil producers (for example, Nigeria and Venezuela) with expensive development needs. Thus, states like Saudi Arabia, where the cost of producing a barrel of oil in 2008 was only two dollars, have a long-term in- terest in maintaining the priceof oil at a level unlikely to induce their consumers to pursue alternative energy sources, because they are under no pressure to make significantprofits todayand havethe reserves to remain exporters for decades to come. They consti- tute OPEC’s price moderates. Meanwhile, OPEC’s members with high import bills andlarge populations, especiallyif theyare politically ambitious and/or have thin reserves, normally push for the highest prices possible. As a practical matter, OPEC has generally had to accommodate the capital needs of these countries by allowing them to exceed their production quotas by approximately 5 percent even in times of abundant oil supply. None- theless, eventhis systemhas sometimesfailed tosatisfy its producer states, as in the case of Ecuador, which suspended its membership in OPEC from 1992-2007 because it felt its quotas were set too low and its dues were too high for the benefits it was receiving from OPEC membership. In tight energy markets like those that followed the disruption of Iranian and Iraqi exports in 1979 and the loss of Iraq’s export po- tential following the U.S. invasion of that country in 2003, the price “extremists” inside OPEC have often gained the upperhand, if only temporarily. Theresul- tant high energy prices have often led to recessionary conditions inthe oil-importing world,to adiminished demand for oil in the world market, and to falling profits for oil-exporting states. During such moments, OPEC has usually had difficulty reestablishing order in the petroleum market. OPEC contains some of the major oil-exporting states, and its members account for the vast majority of the world’s known petroleum reserves. It does not, however, have a monopoly on the global oil-export market. To the contrary, Mexico, Russia, and—in the past—Great Britain have constituted major export ri- vals, and they are joined by a variety of other, smaller non-OPEC exporting states like Norway and Oman. Some, like Mexico, have frequently attended OPEC meetings and have functioned within OPEC price guidelines. During times of declining demand, however, others have often sold their oil below OPEC’s official price, resulting in a price-cutting war for shrinking markets among OPEC states, gluts of oil on the world market, and a downward plunge in the price of oil that OPEC has had difficulty arresting. It was precisely this situation that caused OPEC to fail the first real test of its ability to control the oil market. During the second energy crisis in 1979, OPEC had bowed to the demands of its price extremists and allowed the price of a barrel of oil to rise to thirty-six dollars, trig- gering a global recession that drastically reduced the demand for oil at a moment when many producers needed revenue to pay their development bills. Un- der pressure from England’s primeminister Margaret Thatcher, who repeatedly offered tosell British North Sea oil at a price below the prices set by OPEC minis- ters scrambling to stabilize the market, Nigeria and other OPEC members also began selling below OPEC’s posted price in the hope of expanding their Global Resources Organization of Petroleum Exporting Countries • 891 individual shares of the market. In the resultant price war, the value of a barrel oil dropped dramatically, eventually to less than seven dollars per barrel, before order was restored. Finally, unforeseen political events, and sudden and equally unexpected economic downturns, have often made establishing and maintaining a stable price structure difficult for OPEC, even when its allo- cation process has enjoyed widespread support among OPEC member states. For example, in 1990, Iraq’s invasion of Kuwait, and the threatened loss of both Iraqi and Kuwaiti oil exports, created a specula- tor’s market and sharp rise in the cost of oil on the spot market to more than ten dollars per barrel above OPEC’s target price of approximately twenty dollars per barrel. To reestablish order in the market, not only did Saudi Arabia step up its production, but also OPEC had to free all of its members from their quota limits in order to fill the export gap and avoid another, potentially recession-inducing, run-up in the price of oil. Then, at the end of the 1990’s, an oppo- site challenge to OPEC’s ability to control the market materialized. At a time when many members were ex - ceeding their quotas by approximately 3 percent, an economic crisis in East Asia produced a sudden drop in anticipated demand and threatened to produce a glut ofoil on theworld marketand tocollapse OPEC’s target price, which was then approximately twenty- five dollars per barrel. Once again, Saudi action, not OPEC action, largely held the priceline. Saudi Arabia cut back its production sufficiently to offset the loss of demand from East Asia. In the early twenty-first century, the U.S. invasion of Iraq and the growing demand for oil from China and India provided a newtest of OPEC’s ability to prevent a recession-inducing price explosion. The test was particularly crucial because, at the time, the dif- ference between the world’s demand forimported oil and the amount of oil available for export was less than 1 million barrels of oil per day, and much of that available oil was located in politically volatile areas. By 2008, the price of oil had increased fivefold, another global recession was building, and OPEC’s ability to control themarket hadonce againbeen undoneby its 892 • Organization of Petroleum Exporting Countries Global Resources OPEC delegates take an official photograph atthe organization’s 2000summit in Caracas,Venezuela.Venezuelan president Hugo Chávezis front-row center. (AP/Wide World Photos) price extremists exploiting economic and political conditions for their individual, short-term advantage. Once again, OPEC had to trim production quotas (in this case by 4 million barrels/day) in an effort to re- turn from a late-2008 low of thirty-five dollars per barrel to a target price of seventy-five dollars barrel. What has sustained OPEC as a major influence in the petroleum resources marketplace despite these obstacles to its effective functioning has been, on one hand, the combination of a repetitive economic cycle that oftenturns toOPEC’s favorand, onthe other,the failure of oil-importing states to break their oil habits. Low oil prices not only rekindle consumer demand but also usually bring a renewed complacency to the Western world. Corporations abandon alternative energy schemes because they are no longer commer- cially profitable. Governments back away from policies that would lower the use of oil (for example, by invoking very high taxes on all types of low kilometer- per-gallon vehicles) but would also be politically un- popular, especially in eras of cheap oil. Thus, the collapse of oil prices in the 1980’s was quickly followed by the abandonment of synthetic oil projects and gas-from-coal projects throughout the Western world. The concern with developing alternative energy sources inspired by Iraq’s invasion of Kuwait in 1990 quickly vanished after the liberation of Kuwait the following year and amid the decade of cheap imported oil of the 1990’s. Similarly, the drop in the cost of imported oil in 2008 immediately called into question the life expectancy of the energy-efficient and alternative-energy projects born when imported oil was $150 per barrel and gasoline was $1 per liter in the United States. In turn, the possible abandonment of these and other import-reducing projects quickly gave rise to projections that a new oil shock would soon reappear, once the global demand for oil began to grow significantly again. Joseph R. Rudolph, Jr. Further Reading Amuzegar, Jahangir. Managing the Oil Wealth: OPEC’s Windfalls and Pitfalls. New York: I. B. Tauris, 2001. Kohl, Wilfrid L., ed. After the Oil Price Collapse: OPEC, the United States, and the World Oil Market.Baltimore, Md.: Johns Hopkins University Press, 1991. Learsey, RaymondJ. Overa Barrel: BreakingOil’s Gripon Our Future. New York: Encounter Books, 2007. Yergin, Daniel. The Prize: The Epic Quest for Oil, Money, and Power. Newed.New York:The Free Press, 2008. Web Site Organization of Petroleum Exporting Countries http://www.opec.org/home See also: Energy politics;Oil and natural gas distribu- tion; Oil embargo and energy crises of 1973 and1979; Oil industry; Organization of Arab Petroleum Ex- porting Countries;Peak oil;Resources asa mediumof economic exchange; Resources as asource of international conflict; Saudi Arabia. Orthosilicate minerals Category: Mineral and other nonliving resources Orthosilicates are silicate minerals (minerals containing siliconand oxygen)in whichthe silicategroups are not linked to one another. Found worldwide, they are often used as abrasives, and some are used as gemstones. Definition Orthosilicates, also known as nesosilicates, are distin- guished from other silicates by the fact that their silicate groups (one silicon atom bonded to four oxygen atoms) are not linked to one another. The properties of the different orthosilicates are determined by the type of metal atoms that are bound to the silicate groups. Orthosilicates are usually hard minerals with a glassy luster in a variety of colors. Orthosilicates are found worldwide, usually within igneous and meta- morphic rocks. The most common orthosilicates are the olivines, which make up about 3 percent of the Earth’s crust by weight. Overview Because of their hardness, orthosilicates are often used asabrasives. Manyorthosilicatesare usedas gemstones because of their varied colors and glassy luster. Some orthosilicatesare usedto linethe interiorof furnaces. A few orthosilicates are used as sources for certain elements. Orthosilicates, unlike other silicates, have silicate groups that are not linked to neighboring silicate groups. These silicate groups may be bound to atoms of magnesium, iron, aluminum, oxygen, fluorine, manganese, calcium, chromium, zirconium, or tita - Global Resources Orthosilicate minerals • 893 nium. They may also be bound to hydroxyl groups (one oxygen atom bonded to one hydrogen atom). The most common orthosilicates are the olivines, which containmagnesium oriron. Olivinesaregreen, glassy minerals. Transparent olivines, known as peridots, are used as gemstones. Garnets are a group of orthosilicates with various chemical compositions, usually containing aluminum atoms in combination with other metallic atoms. In some garnets another metal takes the place of aluminum. Garnets are hard, glassy minerals ina variety ofcolors including red, yellow,green, and brown. Garnets are often usedas abrasives and gemstones. Orthosilicates in which the silicate groups are bound only to aluminum atoms exist in three forms: andalusite (usually pink or red), sillimanite (usually white), and kyanite (usually light blue). All three vari- eties are often used to line the inside of furnaces because theyresisthigh temperatures. Kyanite’s unusual color has led to its use as a gemstone. Topaz isan orthosilicatecontaining aluminumand fluorine atoms along with hydroxyl groups. It is a very hard, glassy mineral which is used as a gemstone. To- paz may be colorless, resembling diamond, or may be yellow,blue, brown, orgreen. Redtopaz israre. Yellow topaz turns pink when subjected to heat, and some colors of topaz fade when exposed to light. Zircon, which contains zirconium, is a hard, brown, glassy mineral used as a gemstone or as a source of zirconium. Sphene, which contains calcium and titanium, is a moderately hard, brown, shiny mineral used as a source of titanium. Staurolite, which contains iron, aluminum,oxygen, and hydroxyl groups, is a hard,brown, glassymineral which often occurs asin- tersecting crystals that form natural crosses used as decorations. Rose Secrest See also: Abrasives; Garnet; Gems; Olivine; Silicates; Silicon. Overgrazing Category: Environment, conservation, and resource management Effects of overgrazing occur where there are more graz - ing animals than the land and vegetation can sup - port. Overgrazing has negatively affected many regions globally, including large portions of sub-Saharan Af- rica, the southwestern United States, and the Indian subcontinent in Asia. Areas that have been severely damaged by overgrazing may experience desertification, invasion by nonnative plant species, and an increase in endangered plant and animal species. Background Herbivores are animals that feed on plant material, and grazers are herbivores that feed primarily on grasses. Common examples are horses, cattle, ante- lope, andbison. Overgrazing occurswhen grazerpop- ulations exceed the carrying capacity of a specified area. Carrying capacityis thenumber of individualor- ganisms the resources of a given area can support without the area being damaged; carrying capacity varies from region to region. In overgrazing conditions, there are insufficient grasses and forbs to support the animal population in question. Depending on the grazer’s strategy, emigration or starvation will follow. Grasslands can handle normal grazing; only overgrazing adversely affects them. Overgrazing can result either from the presence of too many domestic grazers pastured in a specific area or the presence of too many wild herbivores on the rangeland. Thelatter canhappen when natural events, such as fire, or human developments, such asfarming or suburbanization, crowd wildlife into a more re- stricted range than the organisms had occupied under undisturbed conditions. In many regions of the world, species of wild herbivores that once experienced seasonal migrations over a wide geographic area have become confined to a much smaller range, resulting inmore stress onforage resources.As part of rangeland management, national parks and wildlife refuges must thin herds of grazers periodically to pre- serve the forage and ensure the long-term survival of the variousplantand animalspecies inanecosystem. Grasses’ Defenses Against Grazing Grasslands and grazers coevolved; thus, grasses can withstand grazing within the ecosystem’s carrying capacity. All plants have a site of new cell growth, called the meristem, where growth in height and girth occur. In most plants, the meristem is located at the top of the plant (the apical meristem). On grasses the meristem is located at the junction of the shoot and root, close to the ground. If a plant’s meristem is re - moved, the plant dies. If grasses had an apical meri - 894 • Overgrazing Global Resources stem, grazers—and lawn mowers—would kill grasses. Grasses survive mowing and grazing because they do not have an apical meristem. With a few exceptions, such as sheep, grazers do not disturb the meristem, and sheep do so only during overgrazing conditions. At proper levels ofgrazing, grazing actually stimulates grass to grow in height in an attempt to produce a flowering head for reproduction. Grazing also stimulates grass growth by removing older plant tissue at the top that is functioning at a lower photosynthetic rate. Grazers Mammalian grazers have high, crowned teeth with a great area for grinding to facilitate opening of plants’ cell walls in an attempt to release nutrients. The cell wall is composed of cellulose, which is very difficult for grazers to digest. Two major digestive-system grazing strategies have evolved. Ruminants, such as cows and sheep, evolved stomachs with four chambers to allow regurgitation inorder tochew food twice to maximize cellulose breakdown. In addition, intestinal bacteria digest the cellulose, releasing fatty acids that nourish the ruminants. Other grazers, such as rabbits and horses, house bacteria in the cecum, a pouch at the junction of the small and large intestines. These bacteria ferment the ingested plant material. The fer- mented productsof thebacteria nourishthese grazers. Global Causes of Overgrazing Overgrazing by livestock has been caused by a variety of factors.In pastoral societies—inwhich wealth is tra- ditionally measured in terms of how many cattle, sheep, or other grazer individuals are owned—the rangeland is held in common; thus, the commons may become overgrazed. This happens because no single individual feels responsible for the land and in- stead worries only about increasing the size of his or her herd. Prior to industrialization many pastoral societies were nomadic andfollowed seasonalmigration patterns, which helped prevent overgrazing. How- ever, as world population has grown and the amount of common land available for grazing has shrunk, few truly nomadic societies remain. Estimates indicate that approximately 6 percent ofthe world’s population is pastoralist, but many formerly nomadic groups— such as the Tuareg in North Africa, Maasai of Kenya, and Tsaatan (also known as Dukha) of Mongolia— now reside in fixed settlements year-round. The in- ability to move their herds as they once did can result in overgrazing in the areas around their villages. Although overgrazing is often associated with pastoral nomads, overgrazing can and does occur where raising livestock is a purely commercial enterprise. The western United States, for example, experienced severe overgrazing on public lands in the nineteenth and early twentieth centuries when investors over- stocked the rangein hopes ofmaking a quick profit in the cattle industry. Similarly, private landowners occa- sionally attempt to raise more grazers thantheir pasturagecan support, but may not realize they have over- stocked untilthe land begins to show negative effects, such as erosion or desertification. Effects of Overgrazing Overgrazing can lead to a number of basic ecological problems. Over- grazed regions can experience desertification, for example. Many of the grasslands of the world occur in drier regions, such as the Ameri- can Southwest and northern Africa, where annual rainfall is not enough to support forests. Desertification is the intensification and expansion of deserts at the expense of neighbor - Global Resources Overgrazing • 895 On overgrazed land in Jonesborough, Tennessee, these goats struggle for survival. (AP/ Wide World Photos) ing grasslands. Whenovergrazing occurs along desert perimeters, the plant removal leads to decreased shading. This decreased shading increases the local air temperature. When the temperature increases, the air may no longer be able to cool down enough to release moisture in the form of dew. Dew is the primary source of precipitation in deserts, so without it, desert conditions intensify. Even a slight decrease in desert precipitation is serious. The result is hot and dry conditions, which lead to further plant loss and, potentially, to monocultures. The overgrazing of grasslands, combined with the existence ofnonnativespecies inan ecosystem,can result in the endangerment of species of native grasses and the creation of monocultures in regions where certain species have been removed. A monoculture is an ecosystemthat has lostdiversity; that is,one species becomes dominant and crowds out everything else. Because of the globalization of agriculture and trade, invasive nonnative species have become a problem in grasslands worldwide.For example,at onetime, cattle in the American Southwest fed exclusively on native grasses. Then nonnative grass species arrived in the New World via the guts of cows shipped from Europe. The nonnative grasses began to compete with the native grasses. European grass species have seeds with prickles and burs; southwestern native grasses do not, making them softer and more desirable to the cattle. Hence, European grasses experienced little, if any, grazing, while the much morepalatable southwestern native grasses experienced cattle grazing to the point of overgrazing. The result was drastic decline or loss of nativegrassland species. Animalsdependent on native grassland species must then emigrate or risk ex- tinction. For example, many ecologists conjecture that theCoachella Valley kit foxin California isthreat- ened because of the loss of grassland habitat upon which it is dependent. Solutions Desertification may be irreversible, but the elimina- tion of grazing along desert perimeters can at least help to prevent further desertification. One method to reestablish native grass species involves controlled- burn programs. Nonnative grassland species do not appear tobeas fire-resistant asnative grass speciesare. Therefore, controlled-burn programs have been used in some overgrazed grassland areas in an attempt to reestablish native grass species and eliminate nonna - tives. If successful, such programs will increase the biodiversity of the area and will improve the health of the ecosystem. Jessica O. Ellison, updated by Nancy Farm Männikkö Further Reading Barnes, Robert F.,et al.,eds.Forages, Volume One:An In- troduction to Grassland Agriculture. New York: Wiley- Blackwell, 2003. Brown, Lester R. “Eroding Soils and Shrinking Crop- land.” In Plan B: Rescuing a Planet Under Stress and a Civilization in Trouble. New York: Norton, 2003. Collins, Scott L., and Linda L. Wallace, eds. Fire in North American Tallgrass Prairies. Norman: Univer- sity of Oklahoma Press, 1990. DeBano, Leonard F., Daniel G. Neary, and Peter F. Ffolliott. Fire’s Effects on Ecosystems. New York: J. Wiley, 1998. Gerrish, Jim. Management-Intensive Grazing: The Grass- roots of Grass Farming. Purvis, Miss.: Green Park Press, 2004. Gilles, Jere Lee, and Keith Jamtgaard. “Overgrazing in Pastoral Areas: The Commons Reconsidered.” Sociologica Ruralis 21 (2008): 129-141. Gordon, I. J., and H. H. T. Prins, eds. The Ecology of Browsing and Grazing. Berlin: Springer, 2008. Holechek, Jerry L., Rex D. Pieper, and Carlton H. Herbel. Range Management: Principles and Practices. 5th ed. New York: Prentice-Hall, 2004. Humphrey, L. R. The Evolving Science of Grassland Im- provement. New York: Cambridge University Press, 1997. Mysterud, Atle. “The Concept of Overgrazing and Its Role inManagement of Large Herbivores.” Wildlife Biology 12, no. 2 (2006): 129-141. Nation, Allan. Paddock Shift: Changing Views on Grass- land Farming.Jackson, Miss.:Green ParkPress,1997. Pollan, Michael. “Grass: Thirteen Ways of Looking at a Pasture.” In The Omnivore’s Dilemma: A Natural History of Four Meals. New York: Penguin Press, 2006. Stanley, Jim. “Overgrazing.”In Hill Country Landowner’s Guide. College Station: Texas A&M University Press, 2009. Vallentine, John F. Grazing Management. 2d ed. San Diego, Calif.: Academic Press, 2001. See also: Biodiversity; Bureau of Land Management, U.S.; Deep ecology; Ecozones and biogeographic realms; Fires; Land ethic; Sagebrush Rebellion; Spe - cies loss; Taylor Grazing Act. 896 • Overgrazing Global Resources Oxides Category: Mineral and other nonliving resources Oxygen is an abundant element that is also reactive; that is, it easily forms compounds—oxides—with other elements. Definition Oxides are combinations of oxygen and metals. Ox- ides are ores of a number of minerals and may them- selves be used as abrasives. Overview A simple oxide contains only one metal, whereas a multiple oxide contains two metals. Examples of simple oxides are tin oxides, manganese oxides, and iron oxides. When one tin atom is combined with two oxygen atoms, tin dioxide (SnO 2 ) is formed. Tin dioxide is also called cassiterite, which is derived from the Greek word for tin, kassiteros. Cassiterite can be found in high-temperature hydrothermal veins. When one manganese atom is combined with two oxygen atoms, manganese dioxide (MnO 2 , or pyrolusite) is formed. Pyrolusite can be found in bog, lake, or shallow ma- rine deposits. If two iron atoms are combined with three oxygen atoms, hematite (Fe 2 O 3 ) is formed. If three iron atoms are combined with four oxygen atoms, magne- tite (Fe 3 O 4 ) is formed. Examples of multiple oxides are magnesium-aluminum-oxide (spinel, MgAl 2 O 4 ), beryllium-aluminum-oxide (chrysoberyl, BeAl 2 O 4 ), and iron-titanium-oxide (ilmenite, FeTiO 3 ). Spinel can befound inbasic igneousrocks, theoriginal rocks of the Earth, formed directly from molten mineral matter billionsof yearsago. Chrysoberyl can befound in granite pegmatites, which are coarse-grained rocks formed after the bulk of the igneous rocks had been produced. Ilmenite can be found in both igneous rocks and pegmatite. When hydrogen is provided, hy- droxides such as MnO(OH) (manganite), Al(OH) 3 (gibbsite), and Mg(OH) 2 (brucite) may be formed. Global Resources Oxides • 897 Percentages of Oxides in Crustal Rocks Oxide Unmelted Peridotite in the Mantle Basalt Formed at Oceanic Ridges or Rises Andesite Formed at Subduction Zones Granitic Rock Along Continental Subduction Zones Continental Rift Basalt Shale Sandstone Near the Source Sandstone Far from the Source Limestone SiO 2 (silicon oxide) 45.0 49.0 59.0 65.0 50.0 58.0 67.0 95.0 5.0 TiO 2 (titanium oxide) 0.4 1.8 0.7 0.6 3.0 0.7 0.6 0.2 0.1 Al 2 O 3 (aluminum oxide) 8.7 15.0 17.0 16.0 14.0 16.0 14.0 1.0 0.8 Fe 2 O 3 (ferric iron oxide) 1.4 2.4 3.0 1.3 2.0 4.0 1.5 0.4 0.2 FeO (ferrous iron oxide) 7.5 8.0 3.3 3.0 11.0 2.5 3.5 0.2 0.3 MnO (manganese oxide) 0.15 0.15 0.13 0.1 0.2 0.1 0.1 — 0.05 MgO (magnesium oxide) 28.0 8.0 3.5 2.0 6.0 2.5 2.0 0.1 8.0 CaO (calcium oxide) 7.0 11.0 6.4 4.0 9.0 3.0 2.5 1.5 43.0 Na 2 O (sodium oxide) 0.8 2.6 3.7 3.5 2.8 1.0 2.9 0.1 0.05 K 2 O (potassium oxide) 0.04 0.2 1.9 2.3 1.0 3.5 2.0 0.2 0.3 Note: Compositions are given as weight percentages of the oxide in the entire rock. . most of the second half of the twentieth century. Conversely, high energy pricesduring the 1970 ’s andearly 1980’sled to a global recession and an opposition to globalization 890 • Organization of. Exporting Countries Global Resources in parts of the developed world, which feared job losses because of outsourcing in economies already experiencing unacceptably high levels of unemploy- ment absorb all of the capital earned by their exports. Moreover, those profits are often enormous compared to the earnings of other OPEC states because the cost of producing their oil is often less

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