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close this bookDiversity, Globalization, and the Ways of Nature (IDRC, 1995, 234 p.)
View the document(introduction...)
View the documentAcknowledgments
View the documentForeword
close this folder1. Introduction
View the documentGlobalization and the ways of nature
View the documentThe new globalization processes
close this folder2. Global trends and their effects on the environment
View the documentThe information revolution
View the documentDevelopment of global financial markets
View the documentDevelopment of more effective transportation networks
View the documentMovement of people
View the documentGlobalization and the unequal distribution of wealth
View the documentInternational migration
View the documentThe development of free markets
close this folder3. Planet-wide deterioration
View the document(introduction...)
View the documentOur sister planet
View the documentThe unusual, oxygenated planet
View the documentThe paradox of ozone
View the documentOceans can be degraded too
View the documentThe rivers are becoming muddy
View the documentOvershooting
close this folder4. Forests under attack
View the document(introduction...)
View the documentDeforestation in the 20th century
View the documentRain-forest environments
View the documentTemperate forests
close this folder5. Grasslands
View the documentSavannas
View the documentThe temperate grasslands
View the documentModifying grassland ecosystems
View the documentEnvironmental balance in grassland ecosystems
close this folder6. Aquatic ecosystems
View the documentExtractive exploitation
View the documentThe future of fish production
close this folder7. Managing planetary thirst
View the documentSome basic facts
View the documentWater supply and options
View the documentThe demand side of the issue
View the documentWater issues throughout the world
close this folder8. Protecting air quality
View the document(introduction...)
View the documentAir and its principal contaminants
View the documentProcesses of contamination in industrial and urban areas
View the documentCurrent and future trends
close this folder9. Clean energy for planetary survival
View the document(introduction...)
View the documentThe industrial revolution
View the documentThe use of hydroelectricity
View the documentThe age of petroleum
View the documentNuclear power
View the documentThe clean options
close this folder10. Africa in the 21st Century: Sunrise or sunset?
View the document(introduction...)
View the documentThe causes of poverty
View the documentHistorical causes of the current situation
View the documentWars are environmentally unfriendly
View the documentEvolution of environmental management in Africa
View the documentOld and new development models
close this folder11. Latin America and the Caribbean: A history of environmental degradation
View the document(introduction...)
View the documentIndigenous cultures
View the documentThe colonial period
View the documentExploitation of natural resources after independence
View the documentEffects of globalization on the environment
View the documentThe maquiladora phenomenon
close this folder12. The urban environmental challenge
View the documentThe development of modern cities
View the documentLarge cities in the Third World
View the documentThe megacities of today
close this folder13. Diversity and human survival
View the document(introduction...)
View the documentDocumenting diversity
View the documentResources for the future
View the documentDiversity of living systems
View the documentCauses and effects of the loss of natural diversity
View the documentDiversity and culture
View the documentRestoring what is lost
View the documentBiodiversity and research
close this folder14. Strategies for the future
View the document(introduction...)
View the documentDecentralize decision-making
View the documentPeople value their environment
View the documentProblems and responsibilities are global
View the documentBibliography

Savannas

Savannas are extensive tropical grassland areas that cover more than 10 million square kilometres of the Earth. The largest expanses are found in Africa (nearly 4 million square kilometres), South America, and, to a lesser degree, Asia and Australia. The dominant vegetation in savannas is usually grasses, intercalated with shrubs and trees. In some cases, shrubs and trees dominate, and savannas evolve into other ecosystems, such as:

· cerrado - a type of forest with a lower canopy and a bushier, grassier undergrowth (see Chapter 4);

· caatinga - a low-density, xerophytic ecosystem of bushes and shrubs with some trees characteristic of northeastern Brazil;

· chaco - a more xerophytic forest of low trees and bushes in extensive flatlands of Paraguay and northern Argentina; or

· sudan - herbaceous ecosystems with intercalated trees extending from the valley of the Nile to the Atlantic Ocean along the low tropical latitudes north of the equator.

The main characteristic of present-day savannas is their periodic (usually annual) water deficit. Both vegetation and fauna have adapted to it. Plants, for example, have developed deciduous aerial systems (leaves) and an annual cycle of growth.

Not all savannas are primary ecosystems (which evolve with little or no human intervention). Many, perhaps most, are secondary ecosystems (which result from human action). Frequently, shrubby, bushy, or forest areas have been and are being burned to make way for agriculture, raising cattle, or hunting. It is difficult to know to what extent today’s savannas are the result of a transformation of other preexisting ecosystems rather than naturally occurring. In Africa, the “savannization” process started very early. Setting forest fires is a common hunting strategy in many societies and Africa was the home of hunters for several hundred thousand years (if not millions).

It is likely that fragile, nongrassy ecosystems gave rise to savanna or even steppe environments perhaps as early as the mid-Pleistocene. Obviously, climate also changed during this geological epoch. During humid periods, savannization of deserts and encroachment of forests into savannas took place. However, the effects of geological changes during the last few hundred thousand years have been somewhat obscured by the impacts of continued human action.

After domestication of herbivorous animals and the spread of agriculture (starting about 10 thousand years ago, but intensifying during the last 3 thousand years), the processes of environmental savannization progressed further. Savannization of the Sudanese region is probably related to domestication of sorghum and millet and to the adaptation of previously domesticated animals to local environments - mainly cattle, goats, and sheep, but later also dromedaries in the Sahelian periphery. In the late 19th century and first half of the 20th century, after widespread European colonization, new commercial crops were introduced (such as peanuts), population growth accelerated, and new forested areas were cleared, transforming most of intertropical Africa into savannas. The remaining forests are retreating at a rapid rate.

In South America, the process of savannization is recent. When the Europeans arrived in the 16th century, there were few, if any, typical savannas. Most South American intertropical ecosystems are in subhumid climates with seasonal rains. Apparently during the humid subperiod of the mid-Quatemary, these areas were covered by trees or bushy vegetation (cerrado and chaco). In more arid areas, a less-dense, shrubby or bushy steppe vegetation developed (caatinga). Grasslands were restricted to temperate areas, particularly in the southern cone - the pampas and to the northern Ilanos.