This page contains archived content and is no longer updated. At the time of publication, it represented the best science available.
Causes of deforestation:Direct Causes
Humans have been deforesting the earth for thousands of years, primarily to clear land for crops or livestock. Although tropical forests are largely confined to developing countries, they do not only serve local or national needs; Economic globalization means that the needs and desires of the world's people affect them too. Direct causes of deforestation include agricultural expansion, deforestation (e.g. logging or harvesting wood for household fuel or charcoal), and infrastructure expansion such as road construction and urbanization. There is rarely a single direct cause of deforestation. Mostly several processes work simultaneously or sequentially to cause deforestation.
The direct primary cause of deforestation in the tropics is conversion to cropland and rangeland, mainly for subsistence, which consists of growing crops or raising livestock for daily needs. Conversion to agricultural land often results from several direct factors. For example, countries are building highways in remote areas to improve the transportation of goods overland. Road development itself causes a limited amount of deforestation. But roads also provide access to land that was previously inaccessible and often unclaimed. Logging, both legal and illegal, usually occurs after road improvements (and in some cases is the reason for road improvements). When loggers harvest an area's valuable wood, they move on. Roads and cleared areas become a magnet for settlers - farmers and ranchers whocut and burnthe rest of the forest for agricultural land or pasture, completing the chain of deforestation that began with the construction of roads. In other cases, forests that have been degraded by logging become vulnerable to fire and are eventually cleared by repeated accidental fires on neighboring farms or pastures.
- Effects on the climate
- causes of deforestation
- NASA Survey of Tropical Deforestation
- preserve tropical forests
While subsistence activities have so far dominated agriculturally driven deforestation in the tropics, large-scale commercial activities are playing an increasingly important role. In the Amazon, industrial livestock and soybean production are increasingly important drivers of deforestation for world markets, and in Indonesia, the conversion of tropical forests to commercial palm plantations to produce biofuels for export is a major driver of deforestation in Borneo and Sumatra.
In densely populated Central Africa, small patches of subsistence cover once-forested hillsides. (Photo ©2006Stefan Gara.)
Although poverty is often cited as aaunderlying cause of tropical deforestation, analyzes of several scientific studies show that this explanation is an oversimplification. Poverty drives people to migrate to the forest lines, where they cut down and burn forests to survive. But rarely is a single factor solely responsible for deforestation in the tropics.
State measures to promote economic development, such as Projects such as road and railroad upgrades have led to significant unintentional deforestation in the Amazon and Central America. Agricultural subsidies and tax breaks and logging concessions have also encouraged deforestation. Global economic factors such as a country's foreign debt, expanding global markets for tropical forest timber and pulp, or low domestic costs for land, labor and fuel can spur growth.
On the southern edge of the Amazon, in the Brazilian state of Mato Grosso, industrial producers of soya, sugar cane and corn are clearing huge areas of rainforest. (Photo ©2006 Guido van der Werf, VrijeUniversiteit, Amsterdam.)
Access to technology can increase or decrease deforestation. The availability of technologies that enable “industrial scale” agriculture can encourage rapid deforestation, while inefficient technologies in the timber industry increase collateral damage to surrounding forests and make subsequent deforestation more likely. Underlying factors are rarely isolated; Instead, multiple global and local factors are exerting synergistic influences on tropical deforestation in different geographic locations.
Tropical deforestation rates
Several international groups routinely produce estimates of deforestation in the tropics, most notably the Food and Agriculture Organization of the United Nations (FAO), which has produced an assessment of global forest resources every five to ten years since the late 1940s, the countries themselves, and since the ability The ability of countries to accurately estimate their forest resources varies with their financial, technological, and institutional resources, some countries' estimates are likely to be more accurate than others. Many countries use satellite imagery as the basis for their assessments, and some research teams used satellite data as the basis for global estimates of tropical deforestation in the 1980s and 1990s.
Some scientists and conservationists argue that the FAO provides an overly conservative estimate of deforestation rates, considering any area larger than one hectare (0.01 sq mi) and having at least 10% forest cover as reforested. This liberal definition of “forest” means that significant degradation can occur before the FAO classifies an area as deforested. On the other hand, some satellite studies indicate that deforestation rates are even lower than FAO reports suggest. In the most recent FAO Forest Assessment Report, published in 2005, the organization itself revised down deforestation rates for the 1990s, which were reported in 2001. Despite the revisions and discrepancies, the FAO assessment is the most comprehensive, by far the longest running, and the most widely used. Metric of global forest resources.
In addition to local factors, international trends are driving deforestation. The expansion of palm oil plantations in Indonesia and Malaysia is a response to high oil prices and, ironically, growing global demand for “green” biofuels. (Photo ©2006poorly drawn father)
All tropical forest sub-regions (color-coded) are represented in a list of the top 20 countries that cleared the most forests between 1990 and 2005. Brazil, the front runner, has cleared more than 42 million hectares, an area the size of California. (Graph by Robert Simmon, based on data provided by individual countries to the United Nations Foreign Agriculture OrganizationGlobal Forest Resource Assessment Report 2005.)
The FAO report does not compile statistics for tropical forest regions as a whole, but statistics at country and regional levels paint a bleak picture. The scale and impact of deforestation can be seen in different ways. One of them is given in absolute numbers: the total area of forest that has been cut down during a given period. According to this metric, the three most important rainforest areas, including South America, Africa and Southeast Asia, top the list. Brazil led the world in terms of total area deforested between 1990 and 2005. The country lost 42,330,000 hectares (163,436 sq mi) of forest, about the size of California. Rounding out the top 5 tropical countries with the largest total area of deforestation are Indonesia, Sudan, Myanmar and the Democratic Republic of the Congo.
While all major rainforest subregions (color-coded) are represented in a top 20 list of countries that cleared the highest percentage of their forests between 1990 and 2005, African countries (blue bars) dominate, starting with Comoros, a small island nation north of Madagascar. (Graph by Robert Simmon, based on data provided by individual countries to the United Nations Foreign Agriculture OrganizationGlobal Forest Resource Assessment Report 2005.)
Another way to look at deforestation is the percentage of a country's forest that has been cleared over time. On this metric, the island nation of Comoros (northern Madagascar) fared worse, clearing almost 60% of its forests between 1990 and 2005. Burundi, a landlocked country in Central Africa, took second place, clearing 47% of its forests. its woods. The other top 5 countries that cleared a large percentage of their forests were Togo in West Africa (44%); Honduras (37%); and Mauritania (36 percent). Thirteen other tropical countries or island regions cleared 20% or more of their forests between 1990 and 2005.
NASA Survey of Tropical Deforestation
Effects on the climate