BIOMES OF THE EARTH - GRASSLANDS Part 9 docx

evaporation pan that is left standing in the open. Obviously the amount of water lost from the ground by evaporation cannot exceed the amount that falls as precipitation, but the potential evaporation can exceed the precipitation. It is pos- sible, therefore, for precipitation to increase but for the ground to become drier . If the average temperature rises by less than about 3.6°F (2°C), precipitation will increase more than the potential evaporation and so the ground will become more moist. This might allow some plant species to grow more vigorously at the expense of others, altering the balance of species in the natural grassland community, and it might encourage the growth of more trees. Where grassland has been converted to arable farmland, soil that is moister might increase crop yields, although crops could be damaged if some of the increased precipitation arrives in the form of violent hail- storms. If the average temperature rises by more than about 3.6°F (2°C), potential evaporation will increase faster than precipi- tation and the ground will become drier. This would be a more serious situation. Crops would need more irrigation to make good the shortfall, and in time natural grassland would become dominated by plants that tolerate drought while less tolerant plants would disappear. At present the evidence suggests that the rise in tempera- ture will be modest and grasslands will not suffer, although their composition may change. It is possible that forest might expand into moister areas of what is now grassland. If the rate of warming were to increase substantially, however, grasslands would be confined to the moister regions while other areas turned to semidesert or desert. Expansion of towns and roads Nowadays most Americans and Europeans live in cities. In the United States 79 percent of the population lives in urban areas. In the United Kingdom 89.5 percent of people are city dwellers, in France the proportion is 75.5 percent, and in Germany it is 87.7 percent. More Italians live in the country- side, but even in Italy 67.1 percent of the population is 214 GRASSLANDS THREATS TO GRASSLAND 215 urban. Russia is vast, but 73.3 percent of Russians live in cities. The move into the cities is fairly recent. Many city dwellers were born and raised in rural areas, and even more of them have parents or grandparents who lived in the countryside. Urban expansion is a process that accompanies the industri- alization of economies. Britain is one of the most highly urbanized countries in the world, but in about 1800 almost 75 percent of the population lived in villages and hamlets, and most of the towns outside London had fewer than 1,000 inhabitants. In 1851 approximately 25.5 percent of the pop- ulation lived in urban areas, but by 1931, only 80 years later, this proportion had risen to 76.7 percent. Industrialization and the associated urbanization occurred earlier in Britain than in most other countries, but even there many people still feel they have family links to the countryside. In other parts of the world the links are closer. People moved into the cities—and still do—in search of a better life. Employment opportunities were greater and wages were higher than those paid by farmers. Despite the overcrowding, poor sanitation, and appalling working condi- tions in the industrializing cities of the 19th and early 20th centuries, urban life promised better prospects of improved living standards. They offered hope—dreams of streets paved with gold. But as the unrealized dreams faded, the new city dwellers began to recall their former rural lives more fondly. Memories of clear blue skies, green fields, trees, rivers of clean water, and sweet-smelling air seemed very attractive amid the smoke and grime of the city streets. The long hours of hard labor in the cold, rain, and mud were forgotten, along with the hunger, grinding poverty, and insecurity that were the lot of most farmworkers. As a consequence, many modern city dwellers value the countryside highly. Some dream of moving there to live, and others content themselves with occasional visits, but even people who never leave the city find reassurance in the knowledge that the countryside exists and that they could visit it if an opportunity arose and they chose to do so. Many do visit the countryside, of course. When the railroads opened in the course of the 19th century one of their first tasks was to run excursions from the cities into the country- side, and the number of visitors increased still more rapidly when affordable mass-produced automobiles became avail- able. The countryside has come to be valued both as an amenity and as the historic background to the lives of our own fami- lies. Not surprisingly people guard it jealously and are strenu- ous in their opposition to any development that would diminish it. People object to the expansion of urban areas into the countryside, both because this reduces the area of country- side and because expansion that takes place on the edge of an existing city moves the countryside farther away from those living near the urban center. Roads provide access to the countryside, but to do so they remove ribbons of country- side. They are also visually intrusive and noisy, and vehicle exhausts from them pollute the air. Each year in the United States 1 million new homes and approximately 10,000 miles (16,000 km) of new roads are built in the 48 contiguous states and District of Columbia. Buildings and roads now cover 43,480 square miles (112,610 km 2 ). That is an area almost as large as the state of Ohio. It sounds immense, and the rate of expansion sounds alarming because of our high regard for the countryside across which these homes and roads are spreading. How can anyone doubt that urban expansion is gobbling up the countryside? Surely the scale of the problem is clear. At this rate it cannot be long before the few remaining patches of natural grassland vanish beneath the asphalt and concrete. Indeed the total urban area of the United States is large, but many of the new houses are built to replace old houses that have been demolished. Even if all of them were being built in open countryside, however, the United States is a big country and buildings and roads cover only a tiny proportion of it—no more than 1.4 percent. This makes the United States more highly urbanized than the world average, of 0.2 percent of the total land area, but less so than some coun- tries. In Britain buildings and roads cover 3.9 percent of the land. 216 GRASSLANDS THREATS TO GRASSLAND 217 This is not the way it appears to people traveling out from the cities. They see the road or rail track lined by buildings that extend far from the city center, with other groups of buildings in the distance, separated by fields and trees, giving them the impression that countryside survives only in pock- ets. It is not so, and the view from the air quickly dispels this false impression. Very little of the countryside has been sacri- ficed to urban development even in the most densely popu- lated and highly urbanized countries, and there is no reason to suppose the urban area will increase greatly in years to come. Buildings and roads are unlikely to spread across the world’s grasslands. Lessons from the Dust Bowl Grasslands grow in those parts of the world where the cli- mate is too dry to sustain forests but not so dry as to prevent all plant growth. In a climate of this type droughts are likely to occur at intervals, and the fact that the grassland plants survive shows they are adapted to periodic drought. The Great Plains of North America are no exception, and the drought that caused the Dust Bowl (see “The Dust Bowl” on pages 55–57) was not unique. It led to tragedy—for the land as well as for the families it ruined—because farmers had been lulled into a false sense of security by several years of good weather and because they failed to take measures that would have reduced the amount of soil erosion. Two lessons emerged from the Dust Bowl disaster. The first was that the native prairie grasses were able to survive pro- longed drought. The second was that soil erosion can be min- imized and that farmers needed to be educated in the tech- niques of soil conservation. Grassland ecologists in Nebraska, Iowa, and Kansas studied the effects of the drought as it developed. In the years prior to the drought, vegetation covered 85 percent of the surface on the short-grass prairie where no livestock grazed. As the drought progressed, the grasses began to die back and new growth failed to appear in the spring, until by 1940 plants covered only 20 percent of the surface. The composition of the grassland also changed. As some plants—other flowering herbs (forbs) as well as grasses—died back, others spread. Nevertheless, the ground was almost bare and its surface soil blew in the wind. When the drought ended with the return of the rain in the winter of 1941–42, grasses and forbs that had not been seen for several years began to emerge above ground. Their roots MANAGING THE GRASSLANDS CHAPTER 11 218 MANAGING THE GRASSLANDS 219 or underground stems had survived in a dormant state, need- ing only a generous soaking to stimulate them into produc- ing new shoots. Moreover even while dormant, those roots and underground stems (rhizomes) bound soil particles together. Soil blew from the natural prairie and produced dust storms, but much more soil blew from land where the native grasses had been removed. Soil scientists and ecologists recognized that certain parts of the short-grass prairie should not be cultivated because of the high risk of soil erosion during the inevitable periodic droughts. These areas were left as natural prairie or sown with native species where these had been removed. The need to improve farming practices was obvious, and in 1935 the Soil Conservation Act established the Soil Con- servation Service (SCS) as a bureau of the U.S. Department of Agriculture (USDA). Hugh Hammond Bennett (1881–1960), one of the world’s leading authorities on soil conservation, was the first head of the SCS. The new service directed its help and advice beyond the Great Plains to farmers through- out the nation. Under Bennett’s direction SCS advisers promoted soil con- servation techniques that were traditional in Europe. Bernard Eduard Fernow (1851–1923), a German immigrant who went on to head the USDA Division of Forestry, had demonstrated them at the Cotton States International Exposition held at Atlanta, Georgia, in 1895. Fernow showed three large models that had been made according to his instructions to show the same farm under different conditions. The first model showed the erosion that followed when deforested land was farmed badly; the second showed the same land being reclaimed; and the third showed the land fully recovered and productive. Techniques to prevent soil erosion clearly exist- ed, and Fernow published photographs of his models in the 1895 edition of the Year Book of the United States Department of Agricultur e (now called the Yearbook of Agriculture). Experts also encouraged farmers to adopt dry farming methods (see the sidebar “Dr y farming” on page 224). The SCS divides the country into “soil conservation dis- tricts,” and in 1956 Congress designed the Great Plains Conservation Program to help farmers and ranchers devise and apply conservation measures to reduce the risk of ero- sion on their own land. Under the program landowners planted rows of trees and shrubs as windbreaks to shelter land from the wind. The program also improved the efficien- cy of irrigation systems and the reliability of water supplies to livestock. Many of the ponds built to conserve water also contain fish. Such measures as these have enhanced the beauty of the countryside, while increasing the productivity of the land. The drought that drove countless families from their farms generated dust clouds that filled the sky over vast areas, and created the Dust Bowl was a catastrophe of epic proportions. It demanded an effective response, and it received one. Droughts continue to occur at intervals—they are natural phenomena and inevitable—but even though they continue to generate dust storms, the damage can now be limited. Ranching on equatorial grasslands Cattle ranching is widespread on land that was formerly forested in tropical South America. Ranching accounts for an estimated 44 percent of all the deforestation that occurs in the whole of the South American tropical forest and for 70 percent of the deforestation in Brazil. Since the mid-1960s approximately 58,000 square miles (150,000 km 2 ) of Amazonian forest has been converted to grassland, mainly in southern Pará and northern Mato Grosso states. The ranchers are descended from Spanish and Portuguese settlers, and the first cattle ranch was established in 1692, on Marajó Island, near Belém, Brazil. Far from being a recent phenomenon, ranching is deeply rooted in Hispanic culture, and there have been cattle ranches in the South American Tropics for more than three centuries. Nor is it true that the conversion of tropical forest to cattle ranches is driven by the “hamburger connection”—the demand for cheap beef in the United States. International beef prices were high in the 1960s and early 1970s, and the United States was an important export market for South American beef during those years, but almost none of the beef was raised on deforested land. In 1982 the Amazon sup- 220 GRASSLANDS MANAGING THE GRASSLANDS 221 plied a mere 0.0007 percent of the beef consumed in the United States, and the Amazon region never produced more than five percent of Brazilian beef. The region has been a net importer of beef in most years. Most Brazilian beef is processed before export into such products as corned beef and sausages. Beef prices fell during the 1980s, and the U.S. market became more dependent on domestic production and imports from other North American Free Trade Agreement (NAFTA) members, with the result that U.S. beef imports from the whole of Latin America have declined greatly since then. Ranching expanded for several reasons. Land prices rose steadily for several decades in tropical Latin America, making land acquisition a sound investment, and when governments introduced settlement programs and designated particular forest areas as reserves for conservation, prices rose even faster. Buyers acquired their land from governments, and sev- eral governments made it a condition of ownership that the buyer occupy the land. This policy made deforestation a con- dition of land ownership. Since it was easier and cheaper to convert forest to ranch land than to plow it and grow crops, ranching became the simplest way to meet the requirement. Some governments paid subsidies for clearing forest and introducing livestock. These incentives have now ended in most countries. Ranchers also raise dairy cattle. The smaller stock farms generally specialize in dairying and the bigger ranches in beef production. Cleared forest was sown with pasture grasses and stocked with about one head of cattle on every two acres (1.5/ha), but after about five years there were some places where the pas- ture would support no more than one animal to every six acres (0.5/ha). Weeds had sprung up among the sown grass, sprouts were growing from tree stumps, and trampling by cattle had compacted the soil. Insect pests attacked the grasses, termites thrived, and birds and mammals continued to deposit weed seeds. Ranchers responded by sowing dif- ferent grass species and experimenting with different stock- ing densities. They found that if stocking is too sparse, the weeds will proliferate, and if it is too dense, the pasture will be overgrazed and the soil damaged by trampling—also en- couraging weeds. Ranchers and farmers control weeds main- ly by clearing them manually and by planting braquiarao, also called brizantão (Brachiaria brizantha), a pasture grass that grows vigorously and suppresses weeds. Herbicides are too costly to be used extensively . Demand for beef and dairy products is rising, and pastures must be improved if the demand is to be met with the least harm to the environment. This will require more research into the most suitable species of pasture grasses and the most efficient management techniques. Increasing the productivi- ty of existing farms and ranches will ease the pressure on the forest. There will be less need to clear the forest to provide more land, and landowners may find they have surplus land on which they can grow crops. This process will not remove the threat of deforestation, but it will reduce it. Farming tropical grasslands Tropical grasslands support large herds of grazing mammals such as buffalo, antelope, elephants, and gazelles. The Serengeti and Masai Mara are world famous for their herds of grazers and for the lions, cheetahs, hyenas, and dogs that pursue them (see “Protecting grassland species” on pages 201–204). Local people have hunted game animals through- out history, and in Africa they also graze domestic livestock— humped (zebu) cattle, sheep, and goats—on the savanna grassland. Savanna grasslands cover two-thirds of the land area of the African continent, and although the wildlife is protected in reserves such as the Serengeti and Masai Mara, grasslands outside the reserves are under threat. The human population is increasing, and some African countries encourage people to settle on the grasslands to relieve pressure on the much smaller areas of arable farmland. The people who live on the grassland and graze their livestock there depend on their domestic animals for food and income, and they rely on the natural vegetation for plant foods, fuel, and raw materials for building and for making household items such as furniture. 222 GRASSLANDS MANAGING THE GRASSLANDS 223 The average annual rainfall is 12–28 inches (300–700 mm), making the area too dry for conventional arable farming, and most people of the African savanna lead a pastoral life. Depending on local conditions, some live as nomads, mov- ing their livestock from one seasonal pasture to the next. Others live a more settled life, moving between winter and summer pastures. There are also ranches on the savanna, where the people have permanent homes and allow their cat- tle to range over a wide area. Some people grow a few crops as well as tending livestock. These ways of life are traditional, but as pressure on the grasslands has intensified, overgrazing has become a serious problem (see “Overgrazing and soil ero- sion” on pages 209–211). Savanna grasslands are so extensive and so many people depend on them that ways must be found to manage them more efficiently. At present grasslands are undervalued. The fate of tropical forests is a matter of great international con- cern, but grasslands are largely neglected. They belong to no one and are therefore vulnerable to the “tragedy of the com- mons.” A development program in the Darwin-Kakadu region of northern Australia is supporting farmers as they rapidly con- vert the grasslands to farmland. At the time the program began in 1979 buffalo were overgrazing and causing consid- erable damage. Agents removed more than 100,000 buffalo from the area between 1979 and 1990, but they were not eliminated entirely. A herd of domesticated buffalo was allowed to remain, but feral buffalo entering the farmed area from outside are removed whenever they are found. Most of the area comprises small-scale beef farms; there are larger properties to the south and west. Farmers have improved the pasture and the farms now produce cattle and buffalo. They also export hay, some of which is made into pelleted feed; increasing amounts of hay go to supply the needs of those raising recreational horses, a lucrative market. Northern Australian grasslands enjoy a moister climate than the African savanna, with rainfall averaging more than 33 inches (840 mm) a year, but it is possible to improve pas- ture and even to grow crops in regions with low rainfall. “Dry [...]... rhinoceroses and of the predators that pursue them the lions, cheetahs, hyenas, and hunting dogs With their wide skies and distant horizons the grasslands appeal to our love of freedom, of space, of travel They also remind us of the animals and grasses we depend on for food Grasslands can be cleared and plowed much more easily than forests, and although they are found in the interior of continents where... involve fertilization and is therefore asexual The progeny of apomixis are clones of their parent aquifer an underground body of permeable material (such as sand or gravel) lying above a layer of impermeable material 2 39 240 GRASSLANDS (such as rock or clay) that is capable of storing water and through which the GROUNDWATER flows asthenosphere the upper part of the MANTLE, in which the rocks are slightly... Illinois, 225 226 GRASSLANDS under the supervision of the eminent ecologists Victor Ernest Shelford (1877– 196 8) and Samuel Charles Kendeigh ( 190 4–86) There were further plantings at the Morton Arboretum, at Lisle, Illinois, in 196 3 Almost all the original North American prairie has disappeared, but the prairie plants have survived They grow along the sides of roads and railroads, and in graveyards The pioneers... on the fallow land, and from time to time these are plowed into the soil The plants gather moisture, and plowing buries their moist tissues before they have time to lose water by transpiration By the end of the fallow period the partly decomposed wild plants will have released sufficient moisture into the soil to sustain the next crop Dry farming is not unique to North America Farmers in many parts of. .. Robert Burns, the Scottish national poet 228 CONCLUSION He did not write, “My love is like a blade of grass.” Yet the apparent simplicity of grass is misleading It is a highly evolved, complex plant that belongs to a family (Poaceae) of some 9, 000 species that thrive everywhere from the equator to inside the Arctic Circle and from the edge of the desert to the edge of the ocean Among them the grasses... sown in the ground between the rows These crops grow through the rainy season and are harvested when they ripen The following year at the end of the dry season the farmer cuts the trees down to about three feet (1 m) above ground level The trimmed pieces themselves are useful; small, leafy twigs can be fed to livestock and the wood provides fuel In addition cutting the trees in this way makes them grow... around the leaf veins of C4 PLANTS, where carbon enters the light-independent stage of PHOTOSYNTHESIS bushveld a region of dry, savanna-type vegetation in southern Africa C3 plant a plant that uses a pathway of PHOTOSYNTHESIS in which the first product in the light-independent stage is 3phosphoglycerate, a compound with three carbon atoms in each molecule C4 plant a plant that uses a pathway of PHOTOSYNTHESIS... Coriolis effect the deflection due to the Earth s rotation experienced by bodies moving in relation to the Earth s surface; bodies are deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere corridor farming see ALLEY CROPPING coterie a group of prairie dogs living together cotyledon a seed leaf; the leaf that emerges from a germinating seed culm the stem of a grass... harbor many other flowering plants, and together the plants support a diverse population of animals Grasslands teem with life, including human life, for they support human populations and the livestock on which they depend The cereals that are our staple foods are grasses Bread, the “staff of life,” is made from the modern cultivated descendant of grasses that to this day grow wild in parts of Turkey... CONCLUSION What future for the grasslands? Grasslands are places of romance The Eurasian steppe that once stretched from the Danube to the Pacific is home to Mongolian nomads and Russian Cossacks The South American pampa is where the defiant gauchos used to ride; tribes of proud hunters once stalked the North American prairie, and cowboys rode the plains The African savanna is the land of antelope, gazelles, . (Poaceae) of some 9, 000 species that thrive everywhere from the equator to inside the Arctic Circle and from the edge of the desert to the edge of the ocean. Among them the grasses harbor many other. are sown in the ground between the rows. These crops grow through the rainy season and are harvested when they ripen. The following year at the end of the dry season the farmer cuts the trees down. program in the Darwin-Kakadu region of northern Australia is supporting farmers as they rapidly con- vert the grasslands to farmland. At the time the program began in 197 9 buffalo were overgrazing