Deforestation
Deforestation
Deforestation and biodiversity
Deforestation and the greenhouse effect
Deforestation refers to a longer-term conversion of forest to some other kind of ecosystem, such as agricultural or urbanized land. Sometimes, however, the term is used in reference to any situation in which forests are disturbed, for example by clear-cut harvesting, even if another forest subsequently regenerates on the site. Various human activities result in net losses of forest area and therefore contribute to deforestation. The most important causes of deforestation are the creation of new agricultural land and unsustainable harvesting of trees. In recent decades, deforestation has been proceeding most rapidly in underdeveloped countries of the tropics and subtropics.
The most important ecological consequences of deforestation are: the depletion of the economically important forest resource; losses of biodiversity through the clearing of tropical forests; and emissions of carbon dioxide with potential effects on global climate through an enhancement of Earth’s greenhouse effect. In some cases, indigenous cultures living in the original forest may be displaced by the destruction of their habitat.
Historical deforestation
Ever since the development of agriculture and settlements, humans have converted forest into agroeco-systems of various sort, or into urban land. There are numerous references in historical, religious, and anthropological literature to forests that became degraded and were then lost through overharvesting and conversion. For example, extensive forests existed in regions of the Middle East that are now almost entirely deforested. This can be evidenced by reference in the Bible to such places as the Forest of Hamath, the Wood of Ziph, and the Forest of Bethel, the modern locations of which are now desert. The cedars of Lebanon were renowned for their abundance, size, and quality for the construction of buildings and ships, but today they only survive in a few endangered groves of small trees. Much of the deforestation of the Middle East occurred thousands of years ago. However, even during the Crusades of the eleventh century through the thirteenth century, extensive pine forests stretched between Jerusalem (Israel) and Bethlehem (West Bank), and some parts of Lebanon had cedar-dominated forests into the nineteenth century. These are all now gone.
Similar patterns of deforestation have occurred in many regions of the world, including most of the Mediterranean area, much of Europe, south Asia, much of temperate North and South America, and, increasingly, many parts of the sub-tropical and tropical world.
Deforestation today
From earliest times to the present, the global extent of deforestation has been about 12%. This
loss included a 19% loss of closed forest in temperate and boreal latitudes, and a 5% loss of tropical and subtropical forests.
However, in recent decades the dynamics of deforestation have changed greatly. The forest cover in wealthier countries of higher latitudes has been relatively stable. In fact, regions of western Europe, the United States, and Canada have experienced an increase in their forest cover as large areas of poorer-quality agricultural land have been abandoned and then regenerated to forest. Although these temperate regions support large forest industries, post-harvest regeneration generally results in new forests, so that ecological conversions to agriculture and other non-forested ecosystems do not generally occur.
In contrast, the rate of deforestation in tropical regions of Latin America, Africa, and Asia have increased alarmingly in recent decades. This deforestation is driven by the rapid growth in size of the human population of these regions, with the attendant needs to create more agricultural land to provide additional food, and to harvest forest biomass as fuel. In addition, increasing globalization of the trading economy has caused large areas of tropical forest to be converted to agriculture to grow crops for an export market in wealthier countries, often to the detriment of local people.
According to the Food and Agriculture Organization (FAO) of the United Nations (UN), as of 2005, the world’s forested areas stand at just under 9.9 billion acres (4.0 billion hectares), or about 30% of total land area of Earth. This figure is based on a new definition associated with the term forest; that is, areas including at least 10% of canopy cover but those areas excluding stands of trees that are included with primary agricultural production. In 2000, the amount of the world’s total forest area stood at 9.6 billion acres (3.9 billion hectares). From 1990 to 2000, the world’s forests experienced an average net annual loss of 23.2 million acres (9.4 million hectares) per year. From 1990 to 2005, deforestation has occurred most rapidly in the following regions of the world: West Africa, Central America and Mexico, and Southeast Asia. Among nations, the most rapid rates of deforestation are: Costa Rica, Ecuador, El Salvador, Haiti, Ivory Coast, Jamaica, Malawi, Nepal, Nicaragua, Nigeria, and Sri Lanka.
Now into the 2000s, deforestation mainly comes from conversion of forested lands to agricultural lands. This accounts for about 32 million acres (13 million hectares) per year. However, increased amounts of forest re-plantings, natural expansions, and landscape restorations have reduced the total rate of deforestation.
Past estimates of global deforestation have been criticized as unreliable. These surveys of forest changes, compiled by FAO, have been considered to be problematic because of inconsistencies in the collection methodology. Problems included potentially biased information (frequently from agencies within the country itself), inconsistent definitions of land use, and data gathering techniques that changed from survey to survey. These issues are being addressed through the use of remote sensing techniques and a more consistent definition of what is considered a forest. Satellite imaging of the forests is now being used to produce consistent and verifiable information on a global scale. Scientists and policy-makers involved with the issue of deforestation rely on dependable and accurate data. This reliable information permits them to monitor changes and accurately determine the extent of the forest.
Loss of a renewable resource
Potentially, forests are a renewable natural resource that can be sustainably harvested to gain a number of economically important products, including lumber, pulp for the manufacture of paper, and fuel wood to produce energy. Forests also provide habitat for game species and, also, for the much greater diversity of animals that are not hunted for sport or food. In addition, forests sustain important ecological services related to clean air and water and the control of erosion.
Any loss of forest area detracts from these important benefits and represents the depletion of an important natural resource. Forest harvesting and management can be conducted in ways that encourage the regeneration of another forest after a period of recovery. However, this does not happen in the cases of agricultural conversion and some types of unsustainable forest harvesting. In such cases, the forest is mined (treated as a non-renewable-like resource) rather than treated as a renewable natural resource, and its area is diminished.
Deforestation and biodiversity
At the present time, most of Earth’s deforestation involves the loss of tropical forests, which are extremely rich in species. Many of the species known to occur in tropical forests have local (or endemic) distributions, so they are vulnerable to extinction if their habitat is lost. In addition, tropical forests are thought to contain millions of additional species of plants, animals, and microorganisms as yet undiscovered by scientists.
Tropical deforestation is mostly caused by various sorts of conversions, especially to subsistence agriculture, and to market agriculture for the production of export commodities. Unsustainable logging and fuel wood harvesting also cause tropical deforestation. Less important causes of tropical deforestation include hydroelectric developments that flood large reservoirs and the production of charcoal as an industrial fuel. Because these extensive conversions cause the extinction of innumerable species, tropical deforestation is the major cause of the global biodiversity crisis.
Deforestation and the greenhouse effect
Mature forests contain large quantities of organic carbon, present in the living and dead biomass of plants, and in organic matter of the forest floor and soil. The quantity of carbon in mature forests is much larger than in younger, successional forests, or in any other type of ecosystem, including human agroecosystems. Therefore, whenever a mature forest is disturbed or cleared for any purpose, it is replaced by an ecosystem containing a much smaller quantity of carbon. The difference in carbon content of the ecosystem is balanced by an emission of carbon dioxide (CO2 ) to the atmosphere. This CO2 emission always occurs, but its rate can vary. The CO2 emission is relatively rapid, for example, if the biomass is burned, or much slower if resulting timber is used for many years and then disposed into an anaerobic landfill, where biological decomposition is very slow.
Prior to any substantial deforestation caused by human activities, Earth’s vegetation stored an estimated 990 billion tons (900 billion metric tons) of carbon, of which 90% occurred in forests. Mostly because of deforestation, only about 616 billion tons (560 billion metric tons) of carbon are presently stored in Earth’s vegetation, and that quantity is diminishing further with time. It has been estimated that between 1850 and 1980, CO2 emissions associated with deforestation were approximately equal to emissions associated with the combustion of fossil fuels. Although CO2 emissions from the use of fossil fuels has been predominant in recent decades, continuing
KEY TERMS
Conversion— A longer-term change in character of the ecosystem at some place, as when a natural forest is harvested and the land developed into an agroecosystem.
deforestation is an important source of releases of CO2 to the atmosphere.
The CO2 concentration in Earth’s atmosphere has increased from about 270 parts per million (ppm) prior to about 1850, to about 360 ppm in 1999, and it continues to increase. As of 2004, it stands at just over 377 ppm. Many atmospheric scientists hypothesize that these larger concentrations of atmospheric CO2 will cause an increasing intensity of an important process, known as the greenhouse effect, that interferes with the rate at which the Earth cools itself of absorbed solar radiation. If this theory proves to be correct, then a climatic warming could result, which would have enormous implications for agriculture, natural ecosystems, and human civilization.
Causes of deforestation
Any solution to the problem of deforestation must first address the social and economic reasons for the activity. While population growth and social unrest have been cited as causes, the most important reasons for deforestation are economic. The average annual income of many people in those countries most heavily impacted by deforestation is at extremely low levels. These people are forced to survive by any means necessary including subsistence agriculture and utilization of wood for cooking and heating (about two-thirds of tropical people use wood fuels as their major source of energy, particularly poorer people). They often follow new logging roads to the only available property, forestland. The search for valuable hardwoods, such as mahogany and teak, is the other major source of forest clearing. Cattle ranching, plantations, and mining also provide considerable economic incentive for the destruction of forests. The social and economic value of these activities is much greater for the people involved than any perceived environmental value of the forests.
The Earth Summits of 1992 and 2002 attempted to address the linkage of social issues, economics, and the environment, though little agreement among nations was achieved. Some conservation organizations have shown that the economic wealth of one country can be traded for the environmental riches of another. A plan known as a debt-for-nature swap is one possible method for addressing both economic and environmental issues associated with deforestation. Many countries in which deforestation is rampant are relatively poor and are often in debt to more developed nations. Under the plan, the debt is bought (at a significant discount) in exchange for a pledge by the country to protect some portion of its valuable biologic resources, or to fund the activities of local conservation organizations within its borders. Agreements of this type have been emplaced in Bolivia, Madagascar, Zambia and other countries.
As of 2006, forestation experts state that slash-and-burn activities (clearing forests for agricultural use) within tropical forests, such as in Brazil, are the largest cause for deforestation in the world. Many countries try to reduce the rate of poverty and homelessness by using slash-and-burn activities to quickly improve the state of their citizens. It is estimated that over 200 million people around the world use slash-and-burn activities. However, such activities are extremely short-term in nature, causing quick erosion and exhaustion of the soils.
See also Rainforest; Slash-and-burn agriculture.
Resources
BOOKS
Moran, Emilio F. and Elinor Ostrom, eds. Seeing the Forest and the Trees: Human-environment Interactions in Forest Ecosystems. Cambridge, MA: MIT Press, 2005.
Vajpevi, Dhirendra K. Deforestation, Environment, and Sustainable Development: A Comarative Analysis. Westport, CT: Praegar, 2001.
Wood, Charles H. and Roberto Porro, eds. Deforestation and Land Use in the Amazon. Gainesville: University of Florida Press, 2002.
PERIODICALS
Stokstad, Erik. “U.N. Report Suggests Slowed Forest Losses.” Science (March 23, 2001): 2294.
OTHER
National Aeronautic and Space Administration. “Better Monitoring of National and Global Deforestation Possible with Satellites.” May 30, 2001. <http://earthobservatory.nasa.gov/Newsroom/MediaAlerts/2001/200105304788.html> (accessed November 12, 2006).
Bill Freedman